Author name code: ofman ADS astronomy entries on 2022-09-14 author:"Ofman, Leon" ------------------------------------------------------------------------ Title: Observations of Ion-Scale Cyclotron Waves and Their Relationship with Non-thermal Ion Distributions in the Solar Wind Authors: Jian, Lan; Ofman, Leon; Wei, Hanying; Stevens, Michael; Alterman, Benjamin L.; Larson, Davin; Boardsen, Scott; Verniero, Jaye Bibcode: 2022cosp...44.1656J Altcode: Among contemporary heliospheric missions, Parker Solar Probe (PSP) and Wind spacecraft have been observing non-thermal distributions of solar wind ions from about 0.08 AU (about 17 solar radii) to 1 AU. There are sometimes secondary populations of protons and/or alpha particles as well as anisotropic ion distributions with respect to the interplanetary magnetic field (IMF). On the other hand, using the high-cadence magnetic field data from PSP and Wind missions, we have detected the near-circularly-polarized electromagnetic waves in the solar wind, in the frequency range near the local proton and alpha-particle cyclotron frequencies. They are preferentially observed when the IMF is radial. Based on our long-term (covering more than two years) surveys of these waves using PSP and Wind data, we investigate the relationship between the non-thermal solar wind ion distributions and the properties of these ion-scale waves. We also statistically study the radial variations of these solar wind ion parameters and wave properties (occurrence rate, wave frequency, wave power, etc.) in the inner heliosphere. Such an investigation using the solar wind plasma as a natural laboratory would deepen our general understanding of wave-particle interactions at ion kinetic scales. Title: Observations and Models of Proton and Alpha Particle Beams at PSP Perihelia with Implications for Solar Wind Heating Authors: Ofman, Leon; Jian, Lan; Larson, Davin; Boardsen, Scott; Verniero, Jaye Bibcode: 2022cosp...44.1087O Altcode: The Parker Solar Probe (PSP) Solar Wind Electrons Alphas & Protons (SWEAP)/Solar Probe Analyzers-Ions (SPAN-I) provide details of proton and alpha particle velocity distributions (VDFs), and associated kinetic wave activity detected with the FIELDS instrument. In particular the PSP observations at perihelia show that beam-core relative speed often exceeds the local Alfven speed, and that the ions temperatures are anisotropic with T$ _{\perp}/T_\parallel>1$. The origin of these ion beams and the implications for solar wind plasma kinetic heating are not well known. Recent hybrid modeling results show that large amplitude Alfven waves may drive the ion beams. Motivated by PSP observations we develop 2.5D and 3D hybrid-particle-in-cell (hybrid-PIC) models of proton and alpha particle super-Alfvenic beams in the solar wind plasma. We model for the first time the combined proton and alpha ion populations with beams and drifts, for a range of parameters relevant to PSP perihelia conditions. We find that beams and drifts drive nonlinearly coupled ion kinetic instabilities with associated ion-scale wave spectra in the inner-heliospheric solar wind. The results of the hybrid models provide the nonlinear evolution of the anisotropic core-beam ion VDFs, ion relative drifts, ion temperature anisotropies, and the wave k-spectra. We model the partition of the energies of the ions (thermal and kinetic), and waves (magnetic) due to the ion-kinetic instabilities. We conclude that the unstable ion beams can provide a mechanism for dissipating kinetic and waves energy resulting solar wind plasma heating. Title: Excitation and Damping of Slow Magnetosonic Waves in Flaring Hot Coronal Loops: Effects of Compressive Viscosity Authors: Ofman, Leon; Wang, Tongjiang Bibcode: 2022ApJ...926...64O Altcode: 2021arXiv211110696O Slow magnetosonic waves associated with flares were observed in coronal loops by Solar and Heliospheric Observatory/Solar Ultraviolet Measurements of Emitted Radiation, Solar Dynamics Observatory/Atmospheric Imaging Assembly in various EUV bandpasses, and other instruments. The excitation and damping of slow magnetosonic waves provides information on the magnetic, temperature, and density structure of the loops. Recently, it was found using 1.5D models that the thermal conduction is suppressed and compressive viscosity is enhanced in hot (T > 6 MK) flaring coronal loops. We model the excitation and dissipation of slow magnetosonic waves in hot coronal loops with realistic magnetic geometry, enhanced density, and temperature (compared to background corona) guided by EUV observations using a 3D magnetohydrodynamic (MHD) visco-resistive model. The effects of the compressive viscosity tensor component along the magnetic field are included with classical and enhanced viscosity coefficient values for the first time in a 3D MHD coronal loop model. The waves are excited by a velocity pulse at the footpoint of the loop at the coronal lower boundary. The modeling results demonstrate the excitation of the slow magnetosonic waves and nonlinear coupling to other wave modes, such as the kink and fast magnetosonic. We find significant leakage of the waves from the hot coronal loops with a small effect of viscous dissipation in cooler (6 MK) loops, and more significant effects of viscous dissipation in hotter (10.5 MK) coronal loops. Our results demonstrate that nonlinear 3D MHD models are required to fully account for the various wave couplings, damping, standing wave formation, and viscous dissipation in hot flaring coronal loops. Our viscous 3D MHD code provides a new tool for improved coronal seismology. Title: Modeling Ion Beams, Kinetic Instabilities, and Waves Observed by the Parker Solar Probe near Perihelia Authors: Ofman, Leon; Boardsen, Scott A.; Jian, Lan K.; Verniero, Jaye L.; Larson, Davin Bibcode: 2022ApJ...926..185O Altcode: 2021arXiv211202357O Recent in situ observations from the Parker Solar Probe (PSP) mission in the inner heliosphere near perihelia show evidence of ion beams, temperature anisotropies, and kinetic wave activity, which are likely associated with kinetic heating and acceleration processes of the solar wind. In particular, the proton beams were detected by PSP/Solar Probe Analyzers-Ion (SPAN-I) and related magnetic fluctuation spectra associated with ion-scale waves were observed by the FIELDS instrument. We present the ion velocity distribution functions (VDFs) from SPAN-I and the results of 2.5D and 3D hybrid-particle-in-cell models of proton and α particle super-Alfvénic beams that drive ion kinetic instabilities and waves in the inner heliospheric solar wind. We model the evolution of the ion VDFs with beams, and obtain the ion relative drifts speeds, and ion temperature anisotropies for solar wind conditions near PSP perihelia. We calculate the partition of energies between the particles (ions) along and perpendicular and parallel to the magnetic field, as well as the evolution of magnetic energy, and compare to observationally deduced values. We conclude that the ion beam driven kinetic instabilities in the solar wind plasma near perihelia are important components in the cascade of energy from fluid to kinetic scales, an important component in the solar wind plasma heating process. Title: Automated identification of transiting exoplanet candidates in NASA Transiting Exoplanets Survey Satellite (TESS) data with machine learning methods Authors: Ofman, Leon; Averbuch, Amir; Shliselberg, Adi; Benaun, Idan; Segev, David; Rissman, Aron Bibcode: 2022NewA...9101693O Altcode: 2021arXiv210210326O A novel artificial intelligence (AI) technique that uses machine learning (ML) methodologies combines several algorithms, which were developed by ThetaRay, Inc., is applied to NASA's Transiting Exoplanets Survey Satellite (TESS) dataset to identify exoplanetary candidates. The AI/ML ThetaRay system is trained initially with Kepler exoplanetary data and validated with confirmed exoplanets before its application to TESS data. Existing and new features of the data, based on various observational parameters, are constructed and used in the AI/ML analysis by employing semi-supervised and unsupervised machine learning techniques. By the application of ThetaRay system to 10,803 light curves of threshold crossing events (TCEs) produced by the TESS mission, obtained from the Mikulski Archive for Space Telescopes, the algorithm yields about 50 targets for further analysis, and we uncover three new exoplanetary candidates by further manual vetting. This study demonstrates for the first time the successful application of the particular combined multiple AI/ML-based methodologies to a large astrophysical dataset for rapid automated classification of TCEs. Title: Modeling the proton and particle beam and drift instabilities and the related ion-scale waves observed by the Parker Solar Probe in the solar wind Authors: Ofman, Leon; Jian, Lan; Boardsen, Scott; Verniero, Jaye; Larson, Davin Bibcode: 2021AGUFMSH11A..04O Altcode: Parker Solar Probe SPAN-I data near perihelia encounters (for example, E4-E8) find ion beams in protons and in alpha particle data, in addition to the proton-alpha drift velocity, and ion temperature anisotropies. The FIELDS instrument provides measurements of ion-scale waves with increased wave activity periods associated with enhanced ion beam magnitudes. It is well known from Vlasovs linear theory that ion velocity distributions (VDFs) with super-Alfvenic beams are subject to the ion-cyclotron instability and increase of ion temperature anisotropy with perpendicular and parallel (to the magnetic field) ion heating. Magnetosonic instability due to super-Alfvenic proton alpha drift can also contribute to the kinetic wave activity, produce anisotropic heating and ion scale waves. However, PSP data shows complex VDFs with multiple ion populations that require considering nonlinear interactions, growth, and nonlinear saturation of the ion instabilities. Motivated by the PSP observations we carry out 2.5D and 3D hybrid modeling of the expanding proton-alpha streaming solar wind plasma and study the excitation and relaxation of the ion kinetic instabilities, and their effects on ion-scale wave spectra. The models produce self-consistent proton and alpha particle VDFs, ion temperature anisotropies, and magnetic fluctuations spectra that can help understand the PSP ion and waves data and evaluate the impact of the ion kinetic instabilities on the heating of the SW plasma. Title: Are the properties of the ion cyclotron wave in the solar wind indicative for their sources? Authors: Wei, Hanying; Jian, Lan; Boardsen, Scott; Gershman, Daniel; Russell, Christopher; Ofman, Leon Bibcode: 2021AGUFMSH35C2068W Altcode: Electromagnetic waves near the ion cyclotron frequency have been frequently observed in the solar wind from a wide range of heliocentric distances. These waves could play important roles in energy transferring or mediating the temperature anisotropy between ion species. The recent studies of Parker Solar Probe data and the Magnetospheric Multiscale data suggest ion beams appear to be a major source for generating these circularly polarized and field-aligned propagating waves. STEREO and WIND observations, both far away from the Earth bow shock to exclude it from being the source, provide a large sample set to investigate the wave properties statistically. We use these observations to infer the properties of the source ions by assuming they are generated from ion beam or ion with temperature anisotropies. We suggest that super-Alfvenic relative drift of or unstable ion temperature anisotropy could be the possible source of these widely observed waves (from 0.1 to 1AU) in the heliosphere. Title: Radial Evolution of the Ion-Scale Cyclotron Waves from 0.1 to 1 AU Based on PSP, Wind, and STEREO Observations Authors: Jian, Lan; Boardsen, Scott; Wei, Hanying; Ofman, Leon; Stevens, Michael; Verniero, Jaye; Larson, Davin; Russell, Christopher Bibcode: 2021AGUFMSH45A2348J Altcode: Using the high-cadence magnetic field data from PSP (Parker Solar Probe), Wind, and STEREO (Solar Terrestrial Relations Observatory) missions, we have conducted long-term surveys of the circularly-polarized electromagnetic waves in the inner heliosphere and at 1 AU, in the frequency range near the local proton and alpha-particle cyclotron frequencies. Based on the large wave event lists from the three missions covering October 2018 March 2021, we investigate the radial evolution of the wave properties from 0.1 to 1 AU statistically, including the occurrence rate, wave frequency, wave power, etc. These waves are left-hand (LH) or right-hand (RH) polarized in the spacecraft frame, and they often propagate in the direction near the local magnetic field. We first select the events in which LH and RH waves occur closely in time or simultaneously, and then analyze their intrinsic frequencies in the plasma frame and how the wave parameters vary with plasma conditions such as the solar wind ion temperature anisotropy and relative drift. The implication of the radial evolution of the LH and RH waves on models of solar wind heating and acceleration is discussed. Title: Magnetohydrodynamic Waves in Open Coronal Structures Authors: Banerjee, D.; Krishna Prasad, S.; Pant, V.; McLaughlin, J. A.; Antolin, P.; Magyar, N.; Ofman, L.; Tian, H.; Van Doorsselaere, T.; De Moortel, I.; Wang, T. J. Bibcode: 2021SSRv..217...76B Altcode: 2020arXiv201208802B Modern observatories have revealed the ubiquitous presence of magnetohydrodynamic waves in the solar corona. The propagating waves (in contrast to the standing waves) are usually originated in the lower solar atmosphere which makes them particularly relevant to coronal heating. Furthermore, open coronal structures are believed to be the source regions of solar wind, therefore, the detection of MHD waves in these structures is also pertinent to the acceleration of solar wind. Besides, the advanced capabilities of the current generation telescopes have allowed us to extract important coronal properties through MHD seismology. The recent progress made in the detection, origin, and damping of both propagating slow magnetoacoustic waves and kink (Alfvénic) waves is presented in this review article especially in the context of open coronal structures. Where appropriate, we give an overview on associated theoretical modelling studies. A few of the important seismological applications of these waves are discussed. The possible role of Alfvénic waves in the acceleration of solar wind is also touched upon. Title: Large-scale EUV Waves and Their Implications for Global Coronal Seismology Authors: Liu, W.; Jin, M.; Wang, T.; Ofman, L.; Sun, X. Bibcode: 2021AAS...23832817L Altcode: Large-scale extreme ultraviolet (EUV) waves associated with coronal mass ejections (CMEs) and solar flares can provide novel diagnostics of the solar corona on global scales, an area yet to be fully exploited. We perform detailed analysis of various behaviors, such as reflection, refraction, and diffraction of several well-observed EUV waves, including those associated with the SOL2017-09-10 X8.2 flare and the SOL2011-02-15 X2 flare. We also performed data-constrained MHD simulations of these events using the University of Michigan Alfven Wave Solar Model (AWSoM). By comparing the observations and simulations, we benchmark diagnostics of the magnetic field strengths and thermal properties of the solar corona. This opens the door to the full applications to global coronal seismology using large-scale EUV waves. Title: Observations and 3D MHD Modeling of Small-scale Solar Prominence Oscillations Authors: Ofman, L.; Kucera, T.; DeVore, C. R. Bibcode: 2021AAS...23810607O Altcode: Small scale oscillations were recently observed in prominences with high resolution Hinode/SOT and IRIS SJI in unprecedented detail and identified as fast magnetosonic waves. The high-resolution observations provide evidence of flows of cool material, fluid instabilities such as Kelvin-Helmholtz and Rayleigh-Taylor, and the spectroscopic information provides evidence of Doppler shifts, heating, and cooling of the prominence material. Recently nonlinear fast magnetosonic waves were observed with periods in the range of 5-11 minutes and wavelengths in the plane of the sky (POS) of ~ 2000 km and flows, and the flows in narrow threads with POS speed ∼16-46 km/s. The nonlinear fast magnetosonic waves and flows were modeled using 2.5D MHD (Ofman & Kucera 2020). Here, we extend the study of the nonlinear fast magnetosonic waves using more realistic 3D MHD model. The model includes the 3D structure of the density and the magnetic field as well as mode coupling and demonstrate the propagating density compressions associated with the nonlinear fast magnetosonic waves, as well as the guided modes in the pillar. The 3D MHD modeling improve understanding of the POS effects in limb prominence oscillations observations. The results of the modeling are useful for coronal seismology of the prominence structure. Title: Oblique High Mach Number Heliospheric Shocks: The Role of α Particles Authors: Ofman, L.; Wilson, L. B.; Koval, A.; Szabo, A. Bibcode: 2021JGRA..12628962O Altcode: Spacecraft observations of heliospheric shocks often find oscillations in the magnetic field and density both, upstream and downstream. The downstream magnetic oscillations of oblique collisionless shocks were detected by Wind with 10.9 samples s-1 and DSCOVR spacecraft with high temporal resolution of 50 samples s-1. The density oscillations associated with the shocks are also evident in proton and α particle density by Wind (with much lower temporal resolution). Recently, we have investigated low Mach number low β oblique shock oscillations using satellite data and 2.5D hybrid modeling with electrons modeled as fluid and ions modeled as particles and found that α particles—an important component of heliospheric plasma—may affect considerably the downstream oscillations and the shock structure. The objective of the present study is to investigate the effects of α particles on high Mach number heliospheric shocks dynamics, oscillations, nonstationarity, and shock front rippling. We extend the study to high Mach number shocks (M > 3), investigate several α particle typical densities, and compare the results for the various shock parameters. We model the effects of α particles on the shock ramp, wake, and downstream oscillation structure and the kinetic properties of proton and α particle velocity distributions at various locations downstream of the shocks. Using the 2.5D hybrid model we found that the modeled high Mach number quasi perpendicular shock magnetic and density structures are significantly affected by α particles with typical solar wind relative abundances, suggesting that the observed high Mach number shocks are similarly affected by α particles. Title: Simulating the Solar Minimum Corona in UV Wavelengths with Forward Modeling II. Doppler Dimming and Microscopic Anisotropy Effect Authors: Zhao, Jie; Gibson, Sarah E.; Fineschi, Silvano; Susino, Roberto; Casini, Roberto; Cranmer, Steven R.; Ofman, Leon; Li, Hui Bibcode: 2021ApJ...912..141Z Altcode: In ultraviolet (UV) spectropolarimetric observations of the solar corona, the existence of a magnetic field, solar wind velocity, and temperature anisotropies modify the linear polarization associated with resonant scattering. Unlike previous empirical models or global models, which present blended results of the above physical effects, in this work, we forward-model expected signals in the H I Lyα line (121.6 nm) by adopting an analytic model that can be adjusted to test the roles of different effects separately. We find that the impact of all three effects is most evident in the rotation of the linear polarization direction. In particular, (1) for magnetic fields between ∼10 and ∼100 G, the Hanle effect modifies the linear polarization at low coronal heights, rotating the linear polarization direction clockwise (counterclockwise) when the angle between the magnetic field and the local vertical is greater (less) than the van Vleck angle, which is consistent with the result of Zhao et al.; (2) solar wind velocity, which increases with height, has a significant effect through the Doppler dimming effect at higher coronal heights, rotating the linear polarization direction in an opposite fashion to the Hanle effect; and (3) kinetic temperature anisotropies are most significant at lower heights in open nonradial magnetic field regions, producing tilt opposite to isotropic Doppler dimming. The fact that the three effects operate differently in distinct spatial regimes opens up the possibility for using linear polarization measurements in UV lines to diagnose these important physical characteristics of the solar corona. Title: Slow-Mode Magnetoacoustic Waves in Coronal Loops Authors: Wang, Tongjiang; Ofman, Leon; Yuan, Ding; Reale, Fabio; Kolotkov, Dmitrii Y.; Srivastava, Abhishek K. Bibcode: 2021SSRv..217...34W Altcode: 2021arXiv210211376W Rapidly decaying long-period oscillations often occur in hot coronal loops of active regions associated with small (or micro-) flares. This kind of wave activity was first discovered with the SOHO/SUMER spectrometer from Doppler velocity measurements of hot emission lines, thus also often called "SUMER" oscillations. They were mainly interpreted as global (or fundamental mode) standing slow magnetoacoustic waves. In addition, increasing evidence has suggested that the decaying harmonic type of pulsations detected in light curves of solar and stellar flares are likely caused by standing slow-mode waves. The study of slow magnetoacoustic waves in coronal loops has become a topic of particular interest in connection with coronal seismology. We review recent results from SDO/AIA and Hinode/XRT observations that have detected both standing and reflected intensity oscillations in hot flaring loops showing the physical properties (e.g., oscillation periods, decay times, and triggers) in accord with the SUMER oscillations. We also review recent advances in theory and numerical modeling of slow-mode waves focusing on the wave excitation and damping mechanisms. MHD simulations in 1D, 2D and 3D have been dedicated to understanding the physical conditions for the generation of a reflected propagating or a standing wave by impulsive heating. Various damping mechanisms and their analysis methods are summarized. Calculations based on linear theory suggest that the non-ideal MHD effects such as thermal conduction, compressive viscosity, and optically thin radiation may dominate in damping of slow-mode waves in coronal loops of different physical conditions. Finally, an overview is given of several important seismological applications such as determination of transport coefficients and heating function. Title: Rossby Waves in Astrophysics Authors: Zaqarashvili, T. V.; Albekioni, M.; Ballester, J. L.; Bekki, Y.; Biancofiore, L.; Birch, A. C.; Dikpati, M.; Gizon, L.; Gurgenashvili, E.; Heifetz, E.; Lanza, A. F.; McIntosh, S. W.; Ofman, L.; Oliver, R.; Proxauf, B.; Umurhan, O. M.; Yellin-Bergovoy, R. Bibcode: 2021SSRv..217...15Z Altcode: Rossby waves are a pervasive feature of the large-scale motions of the Earth's atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined. Title: The effects of the multi-ion kinetic instabilities on electromagnetic cyclotron wave spectra in the solar wind Authors: Ofman, Leon; Jian, Lan Bibcode: 2021cosp...43E.942O Altcode: Electromagnetic ion cyclotron (EMIC) waves were identified in the solar wind (SW) in the past using in-situ data from STEREO (Jian et al. 2009), Wind, and other spacecraft data. In-situ data in the inner heliosphere form Helios 1 & 2 show strong evidence of non-equilibrium (non-Maxwellian) ion velocity distribution functions (VDFs), differential alpha-proton streaming, ion temperature anisotropies, and various forms of magnetic fluctuation spectra with distinct ion kinetic scales effects. Parker Solar Probe perihelion measurements provide SW plasma data and are expected to provide VDFs of protons and alphas, with additional ion data expected from the Solar Orbiter. Motivated by these observations we carry out 2.5D and 3D hybrid modeling of the expanding proton-alpha streaming solar wind plasma and study the excitation and relaxation of the ion kinetic instabilities, and their effects on EMIC wave spectra. The models produce self-consistent ion VDFs, temperature anisotropies, and magnetic fluctuations spectra that can test and improve the predictions of linear Vlasov theory and compared to in-situ spacecraft measurements. The results help understanding the multi-ion SW plasma expansion and heating in the acceleration region close to the Sun. Title: Modeling the effects of α particles on collisionless oblique heliospheric shocks Authors: Ofman, Leon; Wilson, Lynn; Szabo, Adam; Koval, Andriy Bibcode: 2021APS..DPPBM0006O Altcode: The α particles in the solar wind are the second most abundant ion, and can carry significant energy, momentum and mass flux. We investigate the effects of α particles on the dynamics and the oscillations in high-Mach number (M >3) oblique heliospheric shocks. However, detailed in-situ observations of α particle properties in these shocks are rare, in particular at high cadence on-par with the magnetic field measurements. The downstream magnetic oscillations in oblique collisionless heliospheric shocks were detected by Wind with 10.9 samples/s and recently by DSCOVR spacecraft with high temporal resolution of 50 samples/s. The ions were also detected by Wind, albeit with lower temporal resolution then the magnetic oscillation. It is expected that Parker Solar Probe and Solar Orbiter will observe shocks in the inner heliosphere with detailed proton and α particle data with the expected increase of solar activity. Meanwhile, we report the results of 2.5D and 3D hybrid models of high Mach number shocks, where we investigate several α particle typical relative abundances, Mach numbers, and shock normal directions, and compare the results for the various shock parameters. In particular we model the effects of α particles on the shock ramp, wake, and downstream oscillations and study the kinetic properties of proton and α particle velocity distributions function (VDFs) downstream of the shocks. The modeling results demonstrate that with typical α particle solar wind abundances of 5% the dynamics and the oscillations of high-Mach number shocks is significantly affected, evident from comparison to proton only shock models. We discussed the implication of our modeling results to the interpretation of spacecraft observations.

LO acknowledges support by NASA Cooperative agreement NNG11PLA10A to CUA. Resources supporting this work were provided by the NASA High-End Computing(HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. Title: Comprehensive modeling of EMIC wave generation and their impact on different plasma populations using a kinetic convection diffusion model Authors: Kang, S. B.; Fok, M. C. H.; Glocer, A.; Ofman, L.; Denton, R. E.; Buzulukova, N. Bibcode: 2020AGUFMSM037..14K Altcode: Electromagnetic ion cyclotron (EMIC) waves play important roles in charged particle dynamics in the inner magnetosphere, heating both thermal ions and cold electrons and causing loss of both ring current ions and radiation belt electrons. EMIC waves are one of the key phenomena connecting ring current, cold plasma, and radiation belt populations through wave-particle interaction. Ring current ions with anisotropic pressure provides a free energy source to excite EMIC waves, whereas cold plasma population provides a reservoir taking energy from EMIC waves and medium for EMIC waves to be able to propagate. Therefore, modeling of EMIC waves (in particular their wave spectra and amplitudes) and their impact on different plasma populations are also very important in order to understand the dynamics between ring current, plasmasphere, and radiation belts. Hybrid or full particle codes can self-consistently calculate EMIC wave growth, wave amplitude, and their interaction with particle populations conserving all the basic physics, but it is difficult to simulate this on global scale because of their high computational cost. As a compromise, we use Comprehensive Inner Magnetosphere and Ionosphere (CIMI) model, which is a kinetic convection-diffusion model including ring current, plasmasphere, and radiation belt and parameterization of EMIC wave saturation amplitude, which estimates EMIC waves from a linear growth rate and plasma parameters such as densities and plasma pressure. We calculate event-specific linear growth rate and estimate global power spectral densities from the plasma parameters simultaneously calculated in CIMI. Furthermore, we calculate quasi-linear diffusion coefficients in momentum space and evaluate how EMIC waves heat or scatter ring current ions and radiation belt electrons. We also calculate the dependence of saturated EMIC wave amplitudes on various plasma parameters using the empirical formulas obtained from by 2.5D hybrid models. To validate, we compare RBSP observation to our simulation. This investigation represents a state-of-the-art comprehensive study of EMIC wave growth and their effects on ring current ions and radiation belt electrons. Title: Simulations of longitudinal oscillations in flaring coronal loops observed with SDO/AIA Authors: Wang, T.; Ofman, L.; Bradshaw, S. J. Bibcode: 2020AGUFMSH0430014W Altcode: Longitudinal intensity oscillations generated in flare-heated coronal loops were recently observed with SDO/AIA in 94 Å and 131 Å channels. These oscillations have been interpreted as standing or reflected propagating slow magnetoacoustic waves. They are mostly triggered by a circular-ribbon flare located at one footpoint of the loop, which may be associated with a fan-spine magnetic topology. The propagation, damping, and excitation mechanisms of such slow-mode waves in flaring loops are still poorly understood. Recent studies based on linear theory and 1D MHD simulations have demonstrated the determination of effective transport coefficients from observed oscillations by coronal seismology techniques (Wang et al 2015, 2018, 2019). Evidence for thermal conduction suppression and compressive viscosity enhancement has been found with this technique. The presence of anomalous transport processes in hot flaring plasma may help shed light on the wave excitation mechanism and long-standing puzzles such as long-duration EUV/X-ray flares. In this presentation, we report on the analyzed results for seven new oscillation events observed with SDO/AIA. By simulating the propagation of slow waves in a 2D and 3D MHD model of hot AR loop constrained by observations, we explore the effect of modified transport coefficients on the wave excitation and damping. We also study the effect of modified transport coefficients on the thermal evolution of a heated loop using a field-aligned HD model. Title: Oblique High Mach Number Heliospheric Shocks: the Role of Alpha Particles Authors: Ofman, L.; Koval, A.; Wilson, L. B., III; Szabo, A. Bibcode: 2020AGUFMSH0420012O Altcode: Spacecraft observations of heliospheric shocks often show oscillations in the magnetic field and density, both upstream and downstream. The magnetic oscillations of oblique collisionless shocks were detected by Wind and DSCOVR with high temporal resolution of up to 50 samples/s. The density oscillations associated with the shocks are also evident in density by Wind (with lower temporal resolution). Recently, we have investigated low Mach number low-beta oblique shock oscillations using satellite data and 2.5D hybrid modeling with electrons modeled as fluid and ions modeled as particles and found that alpha particles may affect considerably the downstream oscillations and the shock structure. Here, we extend the study to high Mach number shocks (M>3), investigate several alpha particle typical densities, and compare the results. Using the 2.5D hybrid model we found that high Mach number quasi-perpendicular shock magnetic and density structures are significantly affected by alpha particles typical densities, manifesting in effect on rippling, nonstationarity, and reformation of the shocks. Multiple point spacecraft observations are needed to properly account for these shock features. We investigate the effects of alpha particles relative abundance on the shock ramp, wake, and downstream oscillation structure as well as kinetic properties of proton and alpha particle velocity distributions. Title: Coronal Heating by MHD Waves Authors: Van Doorsselaere, Tom; Srivastava, Abhishek K.; Antolin, Patrick; Magyar, Norbert; Vasheghani Farahani, Soheil; Tian, Hui; Kolotkov, Dmitrii; Ofman, Leon; Guo, Mingzhe; Arregui, Iñigo; De Moortel, Ineke; Pascoe, David Bibcode: 2020SSRv..216..140V Altcode: 2020arXiv201201371V The heating of the solar chromosphere and corona to the observed high temperatures, imply the presence of ongoing heating that balances the strong radiative and thermal conduction losses expected in the solar atmosphere. It has been theorized for decades that the required heating mechanisms of the chromospheric and coronal parts of the active regions, quiet-Sun, and coronal holes are associated with the solar magnetic fields. However, the exact physical process that transport and dissipate the magnetic energy which ultimately leads to the solar plasma heating are not yet fully understood. The current understanding of coronal heating relies on two main mechanism: reconnection and MHD waves that may have various degrees of importance in different coronal regions. In this review we focus on recent advances in our understanding of MHD wave heating mechanisms. First, we focus on giving an overview of observational results, where we show that different wave modes have been discovered in the corona in the last decade, many of which are associated with a significant energy flux, either generated in situ or pumped from the lower solar atmosphere. Afterwards, we summarise the recent findings of numerical modelling of waves, motivated by the observational results. Despite the advances, only 3D MHD models with Alfvén wave heating in an unstructured corona can explain the observed coronal temperatures compatible with the quiet Sun, while 3D MHD wave heating models including cross-field density structuring are not yet able to account for the heating of coronal loops in active regions to their observed temperature. Title: Parker Solar Probe Proton Beams and Waves: Observations and Modeling Authors: Ofman, L.; Jian, L.; Boardsen, S. A. Bibcode: 2020AGUFMSH0490014O Altcode: Parker Solar Probe (PSP) observations with Solar Probe Analyzer for Ions (SPAN-I) detects the 3D velocity distribution function (VDF) of protons and a particles with evidence of super-Alfvénic beams. The data is supplemented with FIELDS instrument that shows evidence of accompanying ion-scale wave storms, such as reported in Verniero et al. (2020). We report new coordinated wave-particle investigations focusing on the periods with the extensive existence of proton beams near PSP perihelion. We use the observed plasma parameters of the proton beam events to setup 2.5D hybrid model (2 spatial dimensions with 3D velocity and magnetic field components). In the model the protons and alpha particles are modeled kinetically with Particle In Cell (PIC) method, while electrons are treated as fluid. We investigate the relaxation of the drift instability due to the proton beam events, the generation of non-thermal VDFs and temperature anisotropy of protons, the effects of alpha particles, and the associated spectrum of magnetic fluctuations. The modeling results are in good agreement with PSP observations, and allow investigating the onset and the kinetic evolution of proton beam events for a range of observationally motivated solar wind plasma parameters. Title: Fast Magnetosonic Waves and Flows in a Solar Prominence Foot: Observations and Modeling Authors: Ofman, Leon; Kucera, Therese A. Bibcode: 2020ApJ...899...99O Altcode: 2020arXiv200605885O We study recent observations of propagating fluctuations in a prominence foot with Hinode Solar Optical Telescope (SOT) high-resolution observations in Ca II and Hα emission, which we identify as nonlinear fast magnetosonic waves. Here we analyze further the observations of propagating waves and flows with Interface Region Imaging Spectrograph Mg II slit jaw images, in addition to Hinode/SOT Ca II images. We find that the waves have typical periods in the range of 5-11 minutes and wavelengths in the plane of the sky (POS) of about 2000 km, while the flows in narrow threads have a typical speed in the POS of ∼16-46 km s-1. We also detect apparent kink oscillations in the threads with flowing material, and apply coronal seismology to estimate the magnetic field strength in the range of 5-17 G. Using 2.5D MHD we model the combined effects of nonlinear waves and flows on the observed dynamics of the prominence material, and reproduce the propagating and refracting fast magnetosonic waves, as well as standing kink-mode waves in flowing material along the magnetic field. The modeling results are in good qualitative agreement with the observations of the various waves and flows in the prominence foot, further confirming coronal seismology analysis and improving the understanding of the fine-scale dynamics of the prominence material. Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10 Authors: Jin, M.; Liu, W.; Cheung, C. M. M.; Nitta, N.; DeRosa, M. L.; Manchester, W.; Ofman, L.; Downs, C.; Petrosian, V.; Omodei, N.; Moschou, S. P.; Sokolov, I. Bibcode: 2019AGUFMSH32A..01J Altcode: As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We assess several important observed and physical inputs (e.g., flux rope properties, polar magnetic field) in the model to better reproduce the multi-wavelength observations. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. By further combining with the white light and radio observations, we demonstrate the flux rope-corona interaction can greatly impact the early phase shock evolution (e.g., geometry and shock parameters) therefore plays a significant role for particle acceleration near the Sun in this event. By propagating the CMEs into the heliosphere and beyond the Earth and Mars orbits, we compare the model results with the in-situ measurements and demonstrate the importance of input polar magnetic field on the realistic CME modeling therefore space weather forecasting. Title: The effects of Alpha Particles on Oblique High Mach Number Heliospheric Shocks Authors: Ofman, L.; Wilson, L. B., III; Koval, A.; Szabo, A. Bibcode: 2019AGUFMSH23B3401O Altcode: Spacecraft observations of shocks often show oscillations in the magnetic field and density both, upstream and downstream. The magnetic oscillations of oblique collisionless shocks were detected by DSCOVR/MAG with high temporal resolution of 50 samples/s. The density oscillations associated with the shocks are seen by DSCOVR and Wind in protons and in α particle by Wind (with lower temporal resolution). Recently, we have investigated low Mach number low-β oblique shock oscillations using satellite data and 2.5D hybrid modeling with electrons modeled as fluid and ions modeled as particles. In particular we found that α particles may affect considerably the downstream oscillations and the shock structure. Here, we extend our previous study to high Mach number shocks (M>3) and investigate a range of plasma β values in the β<~1 range and compare the results to available observations of similar shocks. Using the 2.5D hybrid model we find that high Mach number shocks exhibit time-dependent corrugation (rippling) of the shock front. We investigate the effects of α particle abundances and other kinetic properties on the rippling and the non-stationarity of the oblique high Mach number shocks. We model the structure and the evolution of the proton and α particle velocity distributions in various locations in the downstream region of the shocks and discuss the observational implications. Title: Determination of transport coefficients from flare-induced slow magnetoacoustic waves by parametric study Authors: Wang, T.; Ofman, L.; Bradshaw, S. J. Bibcode: 2019AGUFMSH33D3408W Altcode: Recent studies of slow-mode waves in a flaring coronal loop observed by SDO/AIA have revealed the suppression of thermal conduction and significant enhancement of compressive viscosity in hot (~ 10 MK) plasma (Wang et al. 2015, 2018). The strong suppression of thermal conduction may provide an explanation for the slower-than-expected cooling of flare plasma in the decay phase, while the anomalously enhanced viscosity can explain the quick formation of standing slow magnetosonic waves seen in observations. In this study we aim at developing a new coronal seismology tool for determining the transport coefficients in flaring loop plasma based on a parametrical study of wave properties. For this purpose we are using a 1D nonlinear MHD loop model in combination with the linear theory. We find that the classical thermal conductivity is suppressed by a factor of about 3 derived from the observed phase shift between temperature and density perturbations, and the classical viscosity coefficient is enhanced by a factor of 10 from the observed decay time. Using the 1D loop model with these refined transport coefficients, we study the excitation of slow-mode waves by launching a flow pulse from one footpoint. The simulation can self-consistently produce the fundamental standing wave on a timescale in agreement with the observation. We extend the model to more realistic 2.5D MHD and study the effects of the seismology-determined transport coefficients on the wave excitation and damping times using simulations of a field-aligned hydrodynamic loop model with impulsive heating. We model the impulsive excitation of slow magnetosonic waves in a bipolar coronal active region (AR) using 2.5D MHD model that includes a hot and dense loop initially in hydrostatic equilibrium. We discuss the effect of the loop's transverse and longitudinal inhomogeneity on the resulting wave dynamics. Title: Determination of Transport Coefficients by Coronal Seismology of Flare-induced Slow-mode Waves: Numerical Parametric Study of a 1D Loop Model Authors: Wang, Tongjiang; Ofman, Leon Bibcode: 2019ApJ...886....2W Altcode: 2019arXiv190910910W Recent studies of a flaring loop oscillation event on 2013 December 28 observed by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory have revealed the suppression of thermal conduction and significant enhancement of compressive viscosity in hot (∼10 MK) plasma. In this study we aim at developing a new coronal seismology method for determining the transport coefficients based on a parametric study of wave properties using a 1D nonlinear magnetohydrodynamics (MHD) loop model in combination with the linear theory. The simulations suggest a two-step scheme: we first determine the effective thermal conduction coefficient from the observed phase shift between temperature and density perturbations as this physical parameter is insensitive to the unknown viscosity; then from the loop model with the obtained thermal conduction coefficient, we determine the effective viscosity coefficient from the observed decay time using the parametric modeling. With this new seismology technique we are able to quantify the suppression of thermal conductivity by a factor of about 3 and the enhancement of viscosity coefficient by a factor of 10 in the studied flaring loop. Using the loop model with these refined transport coefficients, we study the excitation of slow magnetoacoustic waves by launching a flow pulse from one footpoint. The simulation can self-consistently produce the fundamental standing wave on a timescale in agreement with the observation. Title: Hybrid Simulation of Solar-Wind-Like Turbulence Authors: Roberts, D. Aaron; Ofman, Leon Bibcode: 2019SoPh..294..153R Altcode: We present 2.5D hybrid simulations of the spectral and thermodynamic evolution of an initial state of magnetic field and plasma variables that in many ways represents solar wind fluctuations. In accordance with Helios near-Sun high-speed stream observations, we start with Alfvénic fluctuations along a mean magnetic field in which the fluctuations in the magnitude of the magnetic field are minimized. Since fluctuations in the radial flow speed are the dominant free energy in the observed fluctuations, we include a field-aligned v∥(k⊥) with an k−1 spectrum of velocity fluctuations to drive the turbulent evolution. The flow rapidly distorts the Alfvénic fluctuations, yielding spectra (determined by spacecraft-like cuts) transverse to the field that become comparable to the k∥ fluctuations, as in spacecraft observations. The initial near constancy of the magnetic field is lost during the evolution; we show this also takes place observationally. We find some evolution in the anisotropy of the thermal fluctuations, consistent with expectations based on Helios data. We present 2D spectra of the fluctuations, showing the evolution of the power spectrum and cross-helicity. Despite simplifying assumptions, many aspects of simulations and observations agree. The greatly faster evolution in the simulations is at least in part due to the small scales being simulated, but also to the non-equilibrium initial conditions and the relatively low overall Alfvénicity of the initial fluctuations. Title: Pitch Angle Scattering of Sub-MeV Relativistic Electrons by Electromagnetic Ion Cyclotron Waves Authors: Denton, R. E.; Ofman, L.; Shprits, Y. Y.; Bortnik, J.; Millan, R. M.; Rodger, C. J.; da Silva, C. L.; Rogers, B. N.; Hudson, M. K.; Liu, K.; Min, K.; Glocer, A.; Komar, C. Bibcode: 2019JGRA..124.5610D Altcode: Electromagnetic ion cyclotron (EMIC) waves have long been considered to be a significant loss mechanism for relativistic electrons. This has most often been attributed to resonant interactions with the highest amplitude waves. But recent observations have suggested that the dominant energy of electrons precipitated to the atmosphere may often be relatively low, less than 1 MeV, whereas the minimum resonant energy of the highest amplitude waves is often greater than 2 MeV. Here we use relativistic electron test particle simulations in the wavefields of a hybrid code simulation of EMIC waves in dipole geometry in order to show that significant pitch angle scattering can occur due to interaction with low-amplitude short-wavelength EMIC waves. In the case we examined, these waves are in the H band (at frequencies above the He+ gyrofrequency), even though the highest amplitude waves were in the He band frequency range (below the He+ gyrofrequency). We also present wave power distributions for 29 EMIC simulations in straight magnetic field line geometry that show that the high wave number portion of the spectrum is in every case mostly due to the H band waves. Though He band waves are often associated with relativistic electron precipitation, it is possible that the He band waves do not directly scatter the sub-megaelectron volts (sub-MeV) electrons, but that the presence of He band waves is associated with high plasma density which lowers the minimum resonant energy so that these electrons can more easily resonate with the H band waves. Title: On the Origin of Quasi-periodic Fast-mode Propagating Wave Trains (QFPs): A Statistical Survey Authors: Silver, Jay; Liu, Wei; Ofman, Leon Bibcode: 2019AAS...23421001S Altcode: The magnetized solar corona hosts a variety of waves that are physically important and can serve as useful diagnostic tools. One type of such coronal waves are Quasi-periodic Fast-mode Propagating wave trains (QFPs), which were first detected in extreme ultraviolet (EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). QFPs are not uncommon and are generally associated with some, but not all solar flares and/or coronal mass ejections (CMEs). To search for physical conditions that can contribute to QFP production, we carried out a systematic survey of QFPs from the full SDO mission. We found that about 1/5 of global EUV waves were associated with QFPs. We also conducted a comparative study of two active regions (ARs) visible between October and November 2014, AR12192 and AR12205, with very different levels of QFP activity. AR12205 produced less flares but more QFPs, which were all associated with blow-out, eruptive flares and global EUV waves. In contrast, AR12192 produced more (mostly confined) flares, but with virtually no QFPs and less CMEs. This suggests that blow-out eruptions could be a necessary, but not sufficient condition for QFP production and/or detectability. Title: The Global EUV Wave Associated with the SOL2017-09-10 X8.2 Flare: SDO/AIA Observations and Data-constrained MHD Simulations Authors: Liu, Wei; Jin, Meng; Ofman, Leon; DeRosa, Marc L. Bibcode: 2019AAS...23430701L Altcode: While large-scale extreme ultraviolet (EUV) waves associated with coronal mass ejections (CMEs) and solar flares are common, the EUV wave triggered by the X8 flare-CME eruption on 2017 September 10 was an extreme. This was, to the best of our knowledge, the first detection of an EUV wave traversing the full-Sun corona over the entire visible disk and off-limb circumference, manifesting a truly global nature. In addition to commonly observed reflections, it had strong transmissions in and out of both polar coronal holes, at elevated wave speeds of >2000 km/s within them. With an exceptionally large wave amplitude, it produced significant compressional heating to local coronal plasma. We present detailed analysis of SDO/AIA observations, global magnetic field extrapolations with the potential-field source surface (PFSS) model, and data-constrained MHD simulations of this event using the University of Michigan Alfven Wave Solar Model (AWSoM). By comparing the observations and simulations, we benchmark diagnostics of the magnetic field strengths and thermal properties of the solar corona on global scales. We discuss the future prospects of using such extreme EUV waves as probes for global coronal seismology, an area yet to be fully exploited. Title: Reconstructing Extreme Space Weather From Planet Hosting Stars Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander, D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz, M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.; Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage, K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy, N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen, A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.; Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.; Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.; Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian, A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.; Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville, V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.; Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.; Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.; Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova, S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T. Bibcode: 2019BAAS...51c.564A Altcode: 2019astro2020T.564A; 2019arXiv190306853A The goal of this white paper is to identify and describe promising key research goals to aid the theoretical characterization and observational detection of ionizing radiation from quiescent and flaring upper atmospheres of planet hosts as well as properties of stellar coronal mass ejections (CMEs) and stellar energetic particle (SEP) events. Title: Multi-fluid models and UV observations of coronal streamers Authors: Ofman, Leon; Abbo, Lucia; Giordano, Silvio Bibcode: 2019shin.confE.197O Altcode: The sources of the slow solar wind were long associated with coronal streamers through empirical connections from remote sensing and in-situ observations, and modeling. Near solar activity minimum the solar magnetic field is dominated by a tilted dipole and forms a streamer belt due to the outflow of the slow solar wind. Parker Solar Probe (PSP) will likely provide for the first time in-situ measurements in the stalks of streamers at perihelia. It has been found from Ulysses/SWICS observation that the signatures of the slow and fast solar wind could be identified by heavy ion abundances ratio. UV observations close to the Sun by the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO during the 1996 minimum activity has demonstrated that the streamer belt structure depends strongly on the observed emission lines, such as H I Ly alpha or O VI ions. Subsequent analysis and 2D multi-fluid modeling have shown that the variability of the heavy ion intensity in various parts of the streamers is associated with regions of slow solar wind outflow. We report the results of 3D multi-fluid models of coronal streamer belt and the associated emissivities of H I Ly alpha, O VI, and other heavy ions computed from the model results. We compare the results of the models with solar minimum observations and find good qualitative agreement. The 3D multi-fluid model allows computing the important line-of-sight integration effects on the observed streamer structure in the plane of the sky in the UV ion emission lines. The model shows the associations between the heavy ion properties in the cores and legs of streamers, and the slow solar wind outflow regions in realistic streamer belt structure, as well as in more realistic magnetic structure based on solar magnetogram boundary conditions. The results could be useful for understanding future PSP data. Title: Nonlinear Evolution of Ion Kinetic Instabilities in the Solar Wind Authors: Ofman, Leon Bibcode: 2019SoPh..294...51O Altcode: 2019arXiv190311343O In-situ observations of the solar wind (SW) plasma from 0.29 to 1 AU show that the protons and α particles are often non-Maxwellian, with evidence of kinetic instabilities, temperature anisotropies, differential ion streaming, and associated magnetic fluctuations spectra. The kinetic instabilities in the SW multi-ion plasma can lead to preferential heating of α particles and the dissipation of magnetic fluctuation energy, affecting the kinetic and global properties of the SW. Using for the first time a three-dimensional hybrid model, where ions are modeled as particles using the Particle-In-Cell (PIC) method and electrons are treated as fluid, we study the onset, nonlinear evolution and dissipation of ion kinetic instabilities. The Alfvén/ion cyclotron, and the ion drift instabilities are modeled in the region close to the Sun (∼10 Rs). Solar wind expansion is incorporated in the model. The model produces self-consistent non-Maxwellian velocity distribution functions (VDFs) of unstable ion populations, the associated temperature anisotropies, and wave spectra for several typical SW instability cases in the nonlinear growth and saturation stage of the instabilities. The 3D hybrid modeling of the multi-ion SW plasma could be used to study the SW acceleration region close to the Sun, which will be explored by the Parker Solar Probe mission. Title: Understanding the Role of α Particles in Oblique Heliospheric Shock Oscillations Authors: Ofman, L.; Koval, A.; Wilson, L. B.; Szabo, A. Bibcode: 2019JGRA..124.2393O Altcode: Recent observations by DSCOVR provide high temporal resolution (50 samples per second) magnetic vector field data that allows investigating the details of oblique heliospheric shock oscillations. It was found that some of these shocks exhibit magnetic oscillations, both downstream and upstream of the shock front. The DSCOVR/MAG magnetic field data are supplemented by an extensive database of low Mach number (M < 3) low-β (<1) shock data observed by Wind albeit with lower temporal resolution. Motivated by the observations, we use the 2.5D hybrid model of the oblique shocks with α particles in addition to kinetic protons and electron fluid. We model the properties of the oblique shocks for a number of typical parameters found in observations and study the effects of the shock parameters and the relative α particle abundances on the properties of the shock magnetic field, density, and velocity oscillations. We find the α particles "surf" on the shock front and produce a wake of density oscillations. We examine the details of the phase space of the ions as well as the ion velocity distribution functions in various parts of the shock and study their nonthermal properties. We determine the effects of the α particle kinetic properties and abundances on the structure and dynamics of the shock downstream oscillations for a range of parameters relevant to low Mach number low-β heliospheric shocks. Title: UV core dimming in coronal streamer belt and the projection effects Authors: Abbo, L.; Giordano, S.; Ofman, L. Bibcode: 2019A&A...623A..95A Altcode: During solar minimum activity, the coronal structure is dominated by a tilted streamer belt, associated with the sources of the slow solar wind. It is known that some UV coronal spectral observations show a quite evident core dimming in heavy ions emission in quiescent streamers. In this paper, our purpose is to investigate this phenomenon by comparing observed and simulated UV coronal ion spectral line intensities. First, we computed the emissivities and the intensities of HI Lyα and OVI spectral lines starting from the physical parameters of a time-dependent 3D three-fluid MHD model of the coronal streamer belt. The model is applied to a tilted dipole (10°) solar minimum magnetic structure. Next, we compared the results obtained from the model in the extended corona (from 1.5 to 4 R⊙) to the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO during the minimum of solar activity (1996). We investigate the line-of-sight integration and projection effects in the UV spectroscopic observations, disentangled by the 3D multifluid model. The results demonstrate that the core dimming in heavy ions is produced by the physical processes included in the model (i.e., combination of the effects of heavy ion gravitational settling, and energy exchange of the preferentially heated heavy ions through the interaction with electrons and protons) but it is visible only in some cases where the magnetic structure is simple, such as a (tilted) dipole.

Movie associated to Fig. 3 is available at https://www.aanda.org Title: Collisionless relaxation of the ion ring distribution in space plasma Authors: Ofman, L.; Moore, T. E.; Glocer, A. Bibcode: 2019P&SS..165...75O Altcode: Energetic processes often produce transversely-heated angular distributions of the magnetized core (lowest energy) plasma. This characteristic is found in solar wind ion pickup, resulting from cometary or interstellar gas ionization, in Earths' ionosphere, and with hot ions formed around the Space Transportation System during gas releases. We investigate the thermalization of O+ ion pickup using the 2.5D hybrid simulation method (with fluid electrons and kinetic ions) of the ion pickup (ring) distributions, formed in the auroral ionosphere, with a range of ring velocities and thermal to magnetic pressure ratios. We find that in the unstable collisonless regime the anisotropy of the non-thermal distribution produces the ion-cyclotron instability, and the nonlinear relaxation is accompanied by wave-particle scattering that results in an emitted power of EMIC waves. We conclude that ionospheric pickup thermalization is slow due to the small ring speed compared to the thermal and Alfvén speeds, while in the solar wind and other space plasmas regions with larger ion-ring velocity the collisionless relaxation and thermalization is rapid in terms of O+ ion gyro-period. Title: Observed and simulated coronal UV lines at solar minimum activity: The impact of the 3D tilted coronal streamer belt Authors: Abbo, L.; Giordano, S.; Ofman, L. Bibcode: 2019NCimC..42...24A Altcode: The aim of this study is to improve the knowledge of the slow solar wind origin. In particular, we compute the emissivities and the intensities of UV spectral lines starting from the physical parameters of a time-dependent 3D three-fluid MHD model of the tilted coronal streamer belt. The results obtained from the model are compared in the extended corona (at 1.5 and 1.9 R _{⊙} to the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO in the streamer belt during the minimum of solar activity (1996). The discussion is focused on the importance of the projection effects due to the integration along the line of sight in the coronal ultraviolet observations of streamer core dimming. Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10 Authors: Jin, Meng; Liu, Wei; Cheung, Mark; Nitta, Nariaki; Manchester, Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola Bibcode: 2018csc..confE..66J Altcode: As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We conduct detailed comparisons of the synthesized EUV images with SDO/AIA observations of global EUV waves. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. We also compare observed and simulated EUV intensities in multiple AIA channels to perform thermal seismology of the global corona. Furthermore, we track the 3D CME-driven shock surface in the simulation and derive the time-varying shock parameters together with the dynamic magnetic connectivity between the shock and the surface of the Sun, with which we discuss the role of CME-driven shocks in the long-duration Gamma-ray events. Title: A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10 X8.2+ Solar Flare-Coronal Mass Ejection Authors: Liu, Wei; Jin, Meng; Downs, Cooper; Ofman, Leon; Cheung, Mark C. M.; Nitta, Nariaki V. Bibcode: 2018csc..confE..40L Altcode: We report SDO/AIA observations of an extraordinary global extreme ultraviolet (EUV) wave triggered by the X8.2+ flare-CME eruption on 2017 September 10. This was one of the best EUV waves ever observed with modern instruments, yet it was likely the last one of such magnitudes of Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable characteristics include the following. (1) The wave was observed, for the first time, to traverse the full-Sun corona over the entire visible solar disk and off-limb circumference, manifesting a truly global nature, owing to its exceptionally large amplitude, e.g., with EUV enhancements by up to 300% at 1.1 Rsun from the eruption. (2) This leads to strong transmissions (in addition to commonly observed reflections) in and out of both polar coronal holes, which are usually devoid of EUV waves. It has elevated wave speeds >2000 km/s within them, consistent with the expected higher fast-mode magnetosonic wave speeds. The coronal holes essentially serve as new "radiation centers" for the waves being refracted out of them, which then travel toward the equator and collide head-on, causing additional EUV enhancements. (3) The wave produces significant compressional heating to local plasma upon its impact, indicated by long-lasting EUV intensity changes and differential emission measure increases at higher temperatures (e.g., log T=6.2) accompanied by decreases at lower temperatures (e.g., log T=6.0). These characteristics signify the potential of such EUV waves for novel magnetic and thermal diagnostics of the solar corona on global scales. Title: A Truly Global Extreme Ultraviolet Wave from the SOL2017-09-10 X8.2+ Solar Flare-Coronal Mass Ejection Authors: Liu, Wei; Jin, Meng; Downs, Cooper; Ofman, Leon; Cheung, Mark C. M.; Nitta, Nariaki V. Bibcode: 2018ApJ...864L..24L Altcode: 2018arXiv180709847L We report Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations of an extraordinary global extreme ultraviolet (EUV) wave triggered by the X8.2+ flare-CME eruption on 2017 September 10. This was one of the best EUV waves ever observed with modern instruments, yet it was likely the last one of such magnitudes of Solar Cycle 24 as the Sun heads toward the minimum. Its remarkable characteristics include the following. (1) The wave was observed, for the first time, to traverse the full-Sun corona over the entire visible solar disk and off-limb circumference, manifesting a truly global nature, owing to its exceptionally large amplitude, e.g., with EUV enhancements by up to 300% at 1.1 {R}⊙ from the eruption. (2) This leads to strong transmissions (in addition to commonly observed reflections) in and out of both polar coronal holes (CHs), which are usually devoid of EUV waves. It has elevated wave speeds >2000 {km} {{{s}}}-1 within the CHs, consistent with the expected higher fast-mode magnetosonic wave speeds. The CHs essentially serve as new “radiation centers” for the waves being refracted out of them, which then travel toward the equator and collide head-on, causing additional EUV enhancements. (3) The wave produces significant compressional heating to local plasma upon its impact, indicated by long-lasting EUV intensity changes and differential emission measure increases at higher temperatures (e.g., {log}T=6.2) accompanied by decreases at lower temperatures (e.g., {log}T=6.0). These characteristics signify the potential of such EUV waves for novel magnetic and thermal diagnostics of the solar corona on global scales. Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10 Authors: Jin, Meng; Liu, Wei; Cheung, Mark; Nitta, Nariaki; Manchester, Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola Bibcode: 2018shin.confE.207J Altcode: As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We conduct detailed comparisons of the synthesized EUV images with SDO/AIA observations of global EUV waves. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. We also compare observed and simulated EUV intensities in multiple AIA channels to perform thermal seismology of the global corona. Furthermore, we track the 3D CME-driven shock surface in the simulation and derive the time-varying shock parameters together with the dynamic magnetic connectivity between the shock and the surface of the Sun, with which we discuss the role of CME-driven shocks in the long-duration Gamma-ray events. Title: Modeling Flare-Generated Quasi-Periodic Propagating Fast Magnetosonic Waves Observed by SDO/AIA Authors: Ofman, Leon; Liu, Wei Bibcode: 2018cosp...42E2492O Altcode: Fast-propagating (phase speeds of ∼1000 km/s) quasi-periodic, fast-mode wave (QFPs) accompanying many solar flares have been discovered by SDO/AIA (Liu et al. 2011). They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs), driven by flare-pulsations duration of impulsive phase. The fast magnetosonic waves provide information on the magnetic, density, and temperature structure through coronal seismology. While all previously reported QFP waves originate from a single localized flaring source, we report the first AIA observation and 3D MHD modeling of counter-QFPs originating from two 'sympathetic' flares. The waves are excited at the two sources associated with flare locations and connected by magnetic loops, by time-depended forcing, constrained by the spatial (localized) and quasi-periodic temporal evolution of the flare pulsations. With the aid of 3D MHD modeling we investigate the excitation, propagation, nonlinearity, and interaction of the counter-propagating waves for a range of key parameters, such as the properties of the flaring sources and the background magnetic topology. In addition to QFPs, we find evidence of associated waves, such as trapped fast (kink) modes in coronal loops, and slow mode waves propagating along the AR loops. Our model results are in qualitative agreement with the AIA-observed counter propagating waves providing the first direct evidence of counter-propagating fast magnetosonic waves that carry significant energy flux in low-corona magnetic structures. Title: The Best and Last of Solar Cycle 24 - The Global EUV Wave from the X8 Flare-CME Eruption on 2017-Sept-10: SDO/AIA Observations and Data-constrained Simulations Authors: Liu, Wei; Ofman, Leon; Nitta, Nariaki; Cheung, Mark; Downs, Cooper; Jin, Meng Bibcode: 2018cosp...42E2051L Altcode: Global extreme ultraviolet (EUV) waves are commonly associated with coronal mass ejections (CMEs) and flares. One particular EUV wave that was triggered by the X8 flare-CME eruption on 2017 September 10 was extraordinary - one of the best EUV waves ever observed with modern instruments (e.g., SDO/AIA and GOES/SUVI), yet likely the last one of such magnitudes in Cycle 24 as the Sun heads toward the solar minimum. We present here detailed analysis of SDO/AIA observations of this event and comparison with high-fidelity, data-constrained MHD simulations using the University of Michigan Alfven Wave Solar Model (AWSoM). Observational highlights include: (1) The EUV wave traverses almost the entire visible solar disk and circumference, manifesting its truly global nature. This vast range is mainly due to the exceptionally large wave amplitude, with EUV intensity changes by up to a factor of 3 (as opposed to, e.g., 30% for moderate events). (2) The large wave amplitude also leads to the novel detection of strong transmission components (in addition to commonly observed reflections) into and through both polar coronal holes, at elevated apparent wave speeds up to 2600 km/s. (3) The wave also produces significant heating, indicated by long-lasting EUV intensity changes. As such, this EUV wave offers unique magnetic and thermal diagnostics of the global, CME-spawning corona. Our MHD simulations have largely reproduced the observed features. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the host active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations. This suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions, whose source-region magnetic fields cannot be directly observed, and thus offer useful implications for space-weather predictions. Title: Motions in Prominence Barbs Observed on the Solar Limb Authors: Kucera, T. A.; Ofman, L.; Tarbell, T. D. Bibcode: 2018ApJ...859..121K Altcode: We analyze and discuss an example of prominence barbs observed on the limb on 2016 January 7 by the Hinode/Solar Optical Telescope in Ca II and Hα, the Interface Region Imaging Spectrograph, with slit jaw images and Mg II spectral data, and the Solar Dynamics Observatory’s Atmospheric Imaging Assembly. In the recent literature there has been a debate concerning whether these features, sometimes referred to as “tornadoes,” are rotating. Our data analysis provides no evidence for systematic rotation in the barbs. We do find line-of-sight motions in the barbs that vary with location and time. We also discuss observations of features moving along the barbs. These moving features are elongated parallel to the solar limb and tend to come in clusters of features moving along the same or similar paths in the plane of the sky during a period of 10 minutes to an hour, moving toward or away from the limb. The motion may have a component along the line of sight as well. The spectral data indicate that the features are Doppler shifted. We discuss possible explanations for these features. Title: Effect of Transport Coefficients on Excitation of Flare-induced Standing Slow-mode Waves in Coronal Loops Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.; Davila, Joseph M. Bibcode: 2018ApJ...860..107W Altcode: 2018arXiv180503282W Standing slow-mode waves have been recently observed in flaring loops by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. By means of the coronal seismology technique, transport coefficients in hot (∼10 MK) plasma were determined by Wang et al., revealing that thermal conductivity is nearly suppressed and compressive viscosity is enhanced by more than an order of magnitude. In this study, we use 1D nonlinear MHD simulations to validate the predicted results from the linear theory and investigate the standing slow-mode wave excitation mechanism. We first explore the wave trigger based on the magnetic field extrapolation and flare emission features. Using a flow pulse driven at one footpoint, we simulate the wave excitation in two types of loop models: Model 1 with the classical transport coefficients and Model 2 with the seismology-determined transport coefficients. We find that Model 2 can form the standing wave pattern (within about one period) from initial propagating disturbances much faster than Model 1, in better agreement with the observations. Simulations of the harmonic waves and the Fourier decomposition analysis show that the scaling law between damping time (τ) and wave period (P) follows τ ∝ P 2 in Model 2, while τ ∝ P in Model 1. This indicates that the largely enhanced viscosity efficiently increases the dissipation of higher harmonic components, favoring the quick formation of the fundamental standing mode. Our study suggests that observational constraints on the transport coefficients are important in understanding both the wave excitation and damping mechanisms. Title: Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling Authors: Ofman, Leon; Liu, Wei Bibcode: 2018ApJ...860...54O Altcode: 2018arXiv180500365O Since their discovery by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) in the extreme ultraviolet, rapid (phase speeds of ∼1000 km s-1), quasi-periodic, fast-mode propagating (QFP) wave trains have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology (CS). The reported waves usually originate from a single localized source associated with the flare. Here we report the first detection of counter-propagating QFPs associated with two neighboring flares on 2013 May 22, apparently connected by large-scale, trans-equatorial coronal loops. We present the first results of a 3D MHD model of counter-propagating QFPs in an idealized bipolar AR. We investigate the excitation, propagation, nonlinearity, and interaction of the counter-propagating waves for a range of key model parameters, such as the properties of the sources and the background magnetic structure. In addition to QFPs, we also find evidence of trapped fast- (kink) and slow-mode waves associated with the event. We apply CS to determine the magnetic field strength in an oscillating loop during the event. Our model results are in qualitative agreement with the AIA-observed counter-propagating waves and used to identify the various MHD wave modes associated with the observed event, providing insights into their linear and nonlinear interactions. Our observations provide the first direct evidence of counter-propagating fast magnetosonic waves that can potentially lead to turbulent cascade and carry significant energy flux for coronal heating in low-corona magnetic structures. Title: Understanding the Role of Alpha Particles in Oblique Heliospheric Shock Oscillations Authors: Ofman, Leon; Koval, Andriy; Wilson, Lynn B., III; Szabo, Adam Bibcode: 2018tess.conf22302O Altcode: Recent observations by DSCOVR provide high temporal resolution (50Hz) magnetic vector field data that allows investigating the details of oblique heliospheric shock oscillations. It was found that the shocks exhibits oscillations, both, downstream and upstream of the shock front. The DSCOVR/MAG magnetic field data is supplemented by extensive database of low-Mach number (M<3) low-β (β<1) shock data observed by WIND (Wilson et al. 2017) albeit with lower temporal resolution. Motivated by the observations we develop 1D and 2D hybrid models of the oblique shocks with alpha particles in addition to kinetic protons and electron fluid. We model the properties of the oblique shocks for a range of parameters found in observations and study the effects of the shock parameters, such as the Mach number, electron and ion beta, oblique angle, and the relative alpha abundances on the properties of the shock oscillations. We find that the alphas surf on the shock front and produce a wake. We examine the detail of the phase space of the ions as well as the ion velocity distribution functions in various parts of the shock and study their non-thermal properties. We determine the effects of the alpha kinetic properties, and abundances on the structure and dynamics of the shock oscillations for a range of parameters relevant to low Mach number low-beta shocks. The results help quantify the relation between the alpha particle physical parameters and the magnetic properties of oblique shocks in the heliosphere. Title: Motions in Prominence Barbs Observed on the Solar Limb Authors: Kucera, Therese Ann; Ofman, Leon; Tarbell, Theodore D. Bibcode: 2018tess.conf21059K Altcode: We analyze and discuss an example of prominence barbs observed on the Title: Excitation and Damping of Standing Slow-Mode Waves in Flaring Coronal Loops Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.; Davila, Joseph M. Bibcode: 2018tess.conf22204W Altcode: We analyze and model a flare-induced longitudinal oscillation event detected by SDO/AIA. The magnetic field extrapolation and flare emission features suggest that the wave event is generated by slipping and null-point-type reconnections in a closed fan-spine magnetic topology, and the large spine loop appears to be heated impulsively to the flare temperature before the wave disturbances travel along it. By means of the seismology technique, we determined the transport coefficients in hot (about 10 MK) plasma, and found that thermal conductivity is nearly suppressed and compressive viscosity is enhanced by more than an order of magnitude from the observed wave properties. Using a flow pulse injected at the loop's footpoint constrained by the observation, we simulate the excitation of slow-mode waves in two types of 1D loop models. We find that the models with the seismology-determined transport coefficients can excite the standing waves quickly as observed, while the models with the classical transport coefficients excites basically the reflecting propagating waves. Simulations of harmonic waves and the Fourier decomposition analysis reveal a scaling between damping time and wave period as Td ~ P in the former type of models, while Td ~ P2 in the latter type. This suggests that anomalously large viscosity can efficiently enhance the dissipation of higher harmonic components, favoring quick setup of the fundamental standing mode. Our study indicates that observational constraints on the transport coefficients are crucial in understanding both the wave excitation and damping mechanisms. Title: Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10 Authors: Jin, Meng; Liu, Wei; Cheung, Chun Ming Mark; Nitta, Nariaki; Manchester, Ward; Ofman, Leon; Downs, Cooper; Petrosian, Vahe; Omodei, Nicola Bibcode: 2018tess.conf31905J Altcode: As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We conduct detailed comparisons of the synthesized EUV images with SDO/AIA observations of global EUV waves. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. We also compare observed and simulated EUV intensities in multiple AIA channels to perform thermal seismology of the global corona. Furthermore, we track the 3D CME-driven shock surface in the simulation and derive the time-varying shock parameters together with the dynamic magnetic connectivity between the shock and the surface of the Sun, with which we discuss the role of CME-driven shocks in the long-duration Gamma-ray events. Title: Kelvin-Helmholtz instability in a twisting solar polar coronal hole jet observed by SDO/AIA Authors: Zhelyazkov, I.; Zaqarashvili, T. V.; Ofman, L.; Chandra, R. Bibcode: 2018AdSpR..61..628Z Altcode: 2017arXiv170603703Z We investigate the conditions under which the fluting (m = 2), m = 3 , and m = 12 magnetohydrodynamic (MHD) modes in a uniformly twisted flux tube moving along its axis become unstable in order to model the Kelvin-Helmholtz (KH) instability in a twisting solar coronal hole jet near the northern pole of the Sun. We employed the dispersion relations of MHD modes derived from the linearized MHD equations. We assumed real wavenumbers and complex angular wave frequencies, namely complex wave phse velocities. The dispersion relations were solved numerically at fixed input parameters (taken from observational data) and varying degrees of torsion of the internal magnetic field. It is shown that the stability of the modes depends upon five parameters: the density contrast between the flux tube and its environment, the ratio of the external and internal axial magnetic fields, the twist of the magnetic field lines inside the tube, the ratio of transverse and axial jet's velocities, and the value of the Alfvén Mach number (the ratio of the tube axial velocity to Alfvén speed inside the flux tube). Using a twisting jet of 2010 August 21 by SDO/AIA and other observations of coronal jets we set the parameters of our theoretical model and have obtained that in a twisted magnetic flux tube of radius of 9.8 Mm, at a density contrast of 0.474 and fixed Alfvén Mach number of ≅ 0.76 , for the three MHD modes there exist instability windows whose width crucially depends upon the internal magnetic field twist. It is found that for the considered modes an azimuthal magnetic field of 1.3 - 1.4 G (computed at the tube boundary) makes the width of the instability windows equal to zero, that is, it suppress the KH instability onset. On the other hand, the times for developing KH instability of the m = 12 MHD mode at instability wavelengths between 15 and 12 Mm turn out to be in the range of 1.9 - 4.7 min that is in agreement with the growth rates estimated from the temporal evolution of the observed unstable jet's blobs in their initial stage. Title: Excitation of flare-induced waves in coronal loops and the effects of radiative cooling Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang Bibcode: 2018AdSpR..61..645P Altcode: 2017arXiv170604219P EUV imaging observations from several space missions (SOHO/EIT, TRACE, and SDO/AIA) have revealed a presence of propagating intensity disturbances in solar coronal loops. These disturbances are typically interpreted as slow magnetoacoustic waves. However, recent spectroscopic observations with Hinode/EIS of active region loops revealed that the propagating intensity disturbances are associated with intermittent plasma upflows (or jets) at the footpoints which are presumably generated by magnetic reconnection. For this reason, whether these disturbances are waves or periodic flows is still being studied. This study is aimed at understanding the physical properties of observed disturbances by investigating the excitation of waves by hot plasma injections from below and the evolution of flows and wave propagation along the loop. We expand our previous studies based on isothermal 3D MHD models of an active region to a more realistic model that includes full energy equation accounting for the effects of radiative losses. Computations are initialized with an equilibrium state of a model active region using potential (dipole) magnetic field, gravitationally stratified density and temperature obtained from the polytropic equation of state. We model an impulsive injection of hot plasma into the steady plasma outflow along the loops of different temperatures, warm (∼1 MK) and hot (∼6 MK). The simulations show that hot jets launched at the coronal base excite slow magnetoacoustic waves that propagate to high altitudes along the loops, while the injected hot flows decelerate rapidly with heights. Our results support that propagating disturbances observed in EUV are mainly the wave features. We also find that the effect of radiative cooling on the damping of slow-mode waves in 1-6 MK coronal loops is small, in agreement with the previous conclusion based on 1D MHD models. Title: Energy release from a stream of infalling prominence debris on 2011 September 7-8 Authors: Inglis, A. R.; Gilbert, H. R.; Ofman, L. Bibcode: 2017AGUFMSH43A2805I Altcode: In recent years high-resolution and high-cadence EUV imaging has revealed a new phenomenon, impacting prominence debris, where prominence material from failed or partial eruptions can impact the lower atmosphere and release energy. We present a clear example of this phenomenon occurring on 2011 September 7-8. The initial eruption of prominence material was associated with an X1.8-class flare from AR11283, occurring at 22:30 UT on 2011 September 7, resulting in a semi-continuous stream of this material returning to the solar surface between 00:20 - 00:40 UT on 2011 September 8. A substantial area remote from the original active region experienced brightening in multiple EUV channels observed by SDO/AIA. Using the differential emission measure, we estimated the energetic properties of this event. We found that the radiated energy of the impacted plasma was of order 10^27 ergs, while the upper limit on the thermal energy peaked at 10^28 ergs. Based on these estimates we were able to determine the mass content of the debris to be in the range 2x10^14 < m < 2x10^15 g. Given typical promimence masses, the likely debris mass is towards the lower end of this range. This clear example of a prominence debris event shows that significant energy release takes place during these events, and that such impacts may be used as a novel diagnostic tool for investigating prominence material properties. Title: Three-dimensional hybrid modeling of ion kinetic instabilities in space plasma Authors: Ofman, L. Bibcode: 2017AGUFMSH33A2759O Altcode: Ion kinetic instabilities in space plasma are believed to play an imprortant role in energy transport, heating, dissipation of turbulence, as well as in generating of spectrum of magnetic fluctuations in the kinetic frequency range. The velocity distribution functions (VDFs) of unstable ion populations are generally non-Maxwellian and provide the free energy source that drives the waves. The VDFs were measured in-situ by satellites such as Helios, WIND, and would be obtained in the future Parkers' Solar Probe close to the Sun. In particular, temperature anisotropy provides a measure of VDF non-equilibroum structure, that together with parallel-beta determine the threshold of kinetic instabilities, such as mirror, ion-cyclotron, and firehose. Drifting population of alphas with respect to protons lead to the magnetosonic instability. So far, these isntabilities were studied primaraly using 1.5D or 2.5D particle-in-cell (PIC) or hybrid models (where electrons are modeled as a fluid), i.e., in 1 or 2 spatial dimensions with 3 components of velocity and magnetic field. I will present the results of recent full 3D hybrid models that studies these instabilities for heliospheric conditions and compare to previous modeling results. I will discuss the agreement and the differences between the 3D and more approximate models of the VDFs, the magnetic fluctuations spectra, and the temporal evolution of the anisotropy for typical instabilities relevant for space plasma. I will duscuss the use of the modeled VDFs for diagnostic of the physical processes that lead to space plasma energization from the observed VDFs in the heliospheric and magnetospheric plasma. Title: Energy Release in the Solar Atmosphere from a Stream of Infalling Prominence Debris Authors: Inglis, A. R.; Gilbert, H. R.; Ofman, L. Bibcode: 2017ApJ...847L..17I Altcode: 2017arXiv170801555I Recent high-resolution and high-cadence extreme-ultraviolet (EUV) imaging has revealed a new phenomenon, impacting prominence debris, where prominence material from failed or partial eruptions can impact the lower atmosphere, releasing energy. We report a clear example of energy release and EUV brightening due to infalling prominence debris that occurred on 2011 September 7-8. The initial eruption of material was associated with an X1.8-class flare from AR 11283, occurring at 22:30 UT on 2011 September 7. Subsequently, a semicontinuous stream of this material returned to the solar surface with a velocity v > 150 km s-1, impacting a region remote from the original active region between 00:20 and 00:40 UT on 2011 September 8. Using the Solar Dynamics Observatory/Atmospheric Imaging Assembly, the differential emission measure of the plasma was estimated throughout this brightening event. We found that the radiated energy of the impacted plasma was {L}{rad}∼ {10}27 erg, while the thermal energy peaked at ∼1028 erg. From this we were able to determine the mass content of the debris to be in the range 2× {10}14< m< 2× {10}15 g. Given typical prominence masses, the likely debris mass is toward the lower end of this range. This clear example of a prominence debris event shows that significant energy release takes place during these events and that such impacts may be used as a novel diagnostic tool for investigating prominence material properties. Title: Effects of transport coefficients on excitation of flare-induced standing slow-mode waves Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph Bibcode: 2017SPD....48.0202W Altcode: The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA, and interpreted as the slow-mode standing waves. By means of the seismology technique we have, for the first time, determined the transport coefficients in the hot (>9 MK) flare plasma, and found that thermal conductivity is suppressed by at least 3 times and viscosity coefficient is enhanced by a factor of 15 as the upper limit (Wang et al. 2015, ApJL, 811, L13). In this presentation, we first discuss possible causes for conduction suppression and viscosity enhancements. Then we use the nonlinear MHD simulations to validate the seismology method that is based on linear analytical analysis, and demonstrate the inversion scheme for determining transport coefficients using numerical parametric study. Finally, we show how the seismologically-determined transport coefficients are crucial for understanding the excitation of the observed standing slow-mode waves in coronal loops and the heating of the loop plasma by a footpoint flare. Title: Realistic Modeling of Fast MHD Wave Trains in Coronal Active Regions Authors: Ofman, Leon; Sun, Xudong Bibcode: 2017SPD....4840503O Altcode: Motivated by recent SDO/AIA observations we have developed realistic modeling of quasi-periodic, fast-mode propagating MHD wave trains (QFPs) using 3D MHD model initiated with potential magnetic field extrapolated from the solar coronal boundary. Localized quasi-periodic pulsations associated with C-class flares that drive the waves (as deduced from observations) are modeled with transverse periodic displacement of magnetic field at the lower coronal boundary. The modeled propagating speed and the form of the wave expansions matches the observed fast MHD waves speed >1000 km/s and topology. We study the parametric dependence of the amplitude, propagation, and damping of the waves for a range of key model parameters, such as the background temperature, density, and the location of the flaring site within the active region. We investigate the interaction of multiple QFP wave trains excited by adjacent flaring sources. We use the model results to synthesize EUV intensities in multiple AIA channels and obtain the model parameters that best reproduce the properties of observed QFPs, such as the recent DEM analysis. We discuss the implications of our modeling results for the seismological application of QFPs for the diagnostic of the active region field, flare pulsations, end estimate the energy flux carried by the waves. Title: Fast-mode Coronal EUV Wave Trains Associated with Solar Flares and CMEs Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Karlicky, Marian; Chen, Bin Bibcode: 2017SPD....48.0401L Altcode: As a new observational phenomenon, Quasi-periodic, Fast Propagating EUV wave trains (QFPs) are fast-mode magnetosonic waves closely related to quasi-periodic pulsations commonly detected in solar flares (traditionally with non-imaging observations). They can provide critical clues to flare energy release and serve as new tools for coronal seismology. We report recent advances in observing and modeling QFPs, including evidence of heating and cooling cycles revealed with differential emission measure (DEM) analysis that are consistent with alternating compression and rarefaction expected for magnetosonic waves. Through a statistical survey, we found a preferential association of QFPs with eruptive flares (with CMEs) rather than confined flares (without CMEs). We also identified some correlation with quasi-periodic radio bursts observed at JVLA and Ondrejov observatories. We will discuss the implications of these results and the potential roles of QFPs in coronal heating and energy transport. Title: Dissipation of kinetic instabilities in proton-alpha solar wind plasma Authors: Ofman, Leon; Roberts, D. A.; Vinas, A. -F. Bibcode: 2017shin.confE.114O Altcode: Collisionless dissipation of kinetic instabilities plays an important role in shaping the properties of the solar wind plasma, as evident from WIND, Helios, ACE, and other satellite data. We present the results of 2.5D and 3D hybrid modeling or the proton-alpha solar wind plasma (with fluid electrons) and study parametrically the dissipation of magnetosonic drift and temperature anisotropy driven instabilities. We demonstrate the role of the background solar wind density and velocity inhomogeneities on the collisionless anisotropic heating and cooling of the plasma ion components. We find that the anisotropic plasma heating and the associated non-Maxwellian velocity distribution functions (VDFs) are affected by the background inhomogenities. We demonstrate the generation and evolution of the parallel and obliquely propagating kinetic wave spectra by the instabilities, and the associated dispersion relations. We discuss the relation of our modeling results to the kinetic dissipation processes observed in the solar wind. Title: The effects of inhomogeneous proton-α drifts on the heating of the solar wind Authors: Ofman, L.; Viñas, A. F.; Roberts, D. A. Bibcode: 2017JGRA..122.5839O Altcode: Previous modeling studies have demonstrated that waves and super-Alfvénic drift can lead to perpendicular preferential heating of the α particles with respect to protons. Using 2.5-D hybrid model of the solar wind α-proton plasma, we study the effects of inhomogeneous (across the magnetic field) background streaming focusing on the fast solar wind. We explore the effects of an initial relative, inhomogeneous ion drift on the perpendicular ion heating and cooling and consider the effects of solar wind expansion. We study the spectrum of the magnetic fluctuations in the inhomogeneous background solar wind and demonstrate the generation of oblique waves and their effects on enhanced resonant anisotropic ion heating. The model reproduces the typical ion temperature anisotropy values seen in observations. Using our model, we find that inhomogeneous super-Alfvénic ion drift in the plasma generates significant power of oblique waves in the solar wind plasma, in addition to enhanced heating compared to the nondrifting populations. We demonstrate the effects of various inhomogeneity profiles and regions of the drift on the ion anisotropic heating in super-Alfvénic and near-Alfvénic drifts. We find that the cooling effect due to the solar wind expansion is not significant when super-Alfvénic drifts are considered. Title: Growth and nonlinear saturation of electromagnetic ion cyclotron waves in multi-ion species magnetospheric plasma Authors: Ofman, L.; Denton, R. E.; Bortnik, J.; An, X.; Glocer, A.; Komar, C. Bibcode: 2017JGRA..122.6469O Altcode: The growth and saturation of electromagnetic ion cyclotron (EMIC) waves is essential to the magnetospheric dynamics. Determining and isolating the effects of multiple ion parameters such as temperatures, anisotropies, and relative abundances is important for quantifying these processes in the magnetospheric plasma. In order to study these process, we utilize a 2.5-D hybrid model (where ions are modeled with the particle-in-cell (PIC) method, and electrons are modeled as background neutralizing fluid) to study the nonlinear electromagnetic wave-particle interactions of hot H+, cold H+, cold He+, and cold or hot O+ ions for a broad range of typical magnetospheric parameters. The excitation of EMIC waves is driven by the temperature anisotropy of hot H+ in our model. As a result, we quantify the parametric dependence of the linear growth, the nonlinear saturation level of perpendicular magnetic fluctuations, and the temporal evolution of the ion temperature anisotropies. We establish the relation between key plasma parameters and the saturated EMIC wave power, using either power law fits or a nonlinear regression method. We construct the dispersion relation of the waves using the results of the model and investigate the energy content in the various branches of the dispersion (k∥-ω space), showing that the different modes can generate wave power in different regions of k space. We find that large O+ concentration reduces the growth and saturated amplitude of the waves; but the waves are less sensitive to the temperature of the O+ in the temperature range relevant to the magnetosphere. Title: Hα Doppler shifts in a tornado in the solar corona Authors: Schmieder, B.; Mein, P.; Mein, N.; Levens, P. J.; Labrosse, N.; Ofman, L. Bibcode: 2017A&A...597A.109S Altcode: 2016arXiv161202232S Context. High resolution movies in 193 Å from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamic Observatory (SDO) show apparent rotation in the leg of a prominence observed during a coordinated campaign. Such structures are commonly referred to as tornadoes. Time-distance intensity diagrams of the AIA data show the existence of oscillations suggesting that the structure is rotating.
Aims: The aim of this paper is to understand if the cool plasma at chromospheric temperatures inside the tornado is rotating around its central axis.
Methods: The tornado was also observed in Hα with a cadence of 30 s by the MSDP spectrograph, operating at the Solar Tower in Meudon. The MSDP provides sequences of simultaneous spectra in a 2D field of view from which a cube of Doppler velocity maps is retrieved.
Results: The Hα Doppler maps show a pattern with alternatively blueshifted and redshifted areas of 5 to 10'' wide. Over time the blueshifted areas become redshifted and vice versa, with a quasi-periodicity of 40 to 60 min. Weaker amplitude oscillations with periods of 4 to 6 min are superimposed onto these large period oscillations.
Conclusions: The Doppler pattern observed in Hα cannot be interpreted as rotation of the cool plasma inside the tornado. The Hα velocity observations give strong constraints on the possible interpretations of the AIA tornado. Title: Inference of magnetic field in the coronal streamer invoking kink wave motions generated by multiple EUV waves Authors: Srivastava, A. K.; Singh, Talwinder; Ofman, Leon; Dwivedi, Bhola N. Bibcode: 2016MNRAS.463.1409S Altcode: 2016arXiv160600337S; 2016MNRAS.tmp.1136S We analyse the observations from Solar TErrestrial RElations Observatory (STEREO) of an oscillating coronal streamer. STEREO-B Extreme Ultraviolet Imaging (EUVI) temporal data on 2012 March 7 show an evolution of two consecutive EUV waves that interact with footpoint of a coronal streamer clearly evident in the co-spatial and co-temporal STEREO-B/COR-1 observations. The waves are observed in the STEREO-B/EUVI too, and its apparent energy exchange with coronal streamer generates kink oscillations. We apply the methodology of magnetohydrodynamic (MHD) seismology of the observed waves and determine the magnetic field profile of the coronal streamer. In particular, we estimate the phase velocities of the kink wave perturbations by tracking them at different heights. We also estimate electron densities inside and outside the streamer using spherically symmetric inversion of polarized brightness images in STEREO-B/COR-1. We detect two large-scale kink wave oscillations that diagnose exponentially decaying radial profiles of magnetic field in streamer up to 3 solar radii. Within the limit of observational and systematic uncertainties, we find that magnetic field of streamer varies slowly at various heights, although its nature always remains exponentially decaying with height. It is seen that during evolution of second kink motion in streamer, it increases in brightness (thus mass density), and also in areal extent slightly, which may be associated with decreased photospheric magnetic flux at footpoint of streamer. As a result, magnetic field profile produced by second kink wave is reduced within streamer compared to the one diagnosed by the first one. Title: Observations and Modeling of Plasma Waves in the Solar Atmosphere Authors: Liu, W.; Ofman, L.; Downs, C. Bibcode: 2016AGUFMSH14B..01L Altcode: The solar atmosphere, especially the extended corona, provides rich observations of magnetohydrodynamic (MHD) waves and plasma waves in general. Such waves can be used as seismological tools to probe the physical conditions of the medium in which they travel, such as the coronal magnetic field and plasma parameters. Recent high-resolution imaging and spectroscopic observations in extreme ultraviolet (EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and in UV by the Interface Region Imaging Spectrograph (IRIS) have opened a new chapter in understanding these waves and in utilizing them for coronal seismology. We will review such new observations of two intimately related phenomena - global EUV waves (so-called "EIT waves") associated with coronal mass ejections (CMEs) and quasi-periodic, fast-mode magnetosonic wave trains associated with flares. We will focus on the generation and propagation of global EUV waves and their interaction with coronal structures, as well as the correlation of AIA-detected fast-mode wave trains with flare pulsations seen from radio to hard X-ray wavelengths. We will also present recent MHD modeling efforts in reproducing these waves using realistic, observationally-driven simulations. We will discuss the roles of such waves in energy transport within the solar atmosphere and in their associated CME/flare eruptions. Title: Fundamental Physics of the Slow Solar Wind - What do we Know? Authors: Ofman, L.; Abbo, L.; Antiochos, S. K.; Hansteen, V. H.; Harra, L.; Ko, Y. K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.; von Steiger, R.; Wang, Y. M. Bibcode: 2016AGUFMSH42A..01O Altcode: Fundamental physical properties of the slow solar wind (SSW), such as density, temperature, outflow speed, heavy ion abundances and charges states were obtained from in-situ measurements at 1AU in the past from WIND, ACE, and other spacecraft. Plasma and magnetic field measurement are available as close as 0.3 AU from Helios data, Spektr-R, and MESSENGER spacecraft. Remote sensing spectroscopic measurements are available in the corona and below from SOHO/UVCS, Hinode, and other missions. One of the major objectives of the Solar Orbiter and Solar Probe Plus missions is to study the sources of the SSW close to the Sun. The present state of understanding of the physics of the SSW is based on the combination of the existing observations, theoretical and numerical 3D MHD and multi-fluid models, that connect between the SSW sources in the corona and the heliosphere. Recently, hybrid models that combine fluid electrons and kinetic ions of the expanding solar wind were developed, and provide further insights of the local SSW plasma heating processes that related to turbulent magnetic fluctuations spectra and kinetic ion instabilities observed in the SSW plasma. These models produce the velocity distribution functions (VDFs) of the protons and heavier ions as well as the ion anisotropic temperatures. I will discuss the results of the above observations and models, and review the current status of our understanding of the fundamental physics of the SSW. I will review the open questions, and discuss how they could be addressed with near future observations and models. Title: Growth and Nonlinear Saturation of Electromagnetic Ion Cyclotron Waves In Multi-Ion Species Magnetospheric Plasma: 2.5D Hybrid Modeling Authors: Ofman, L.; Denton, R. E.; Bortnik, J.; Glocer, A.; Roman, N. M. Bibcode: 2016AGUFMSM31A2458O Altcode: We investigate the collisionless interactions of a multiple ion species magnetospheric plasma and study the parametric dependence of electromagnetic ion cyclotron (EMIC) wave growth and saturation. We utilize a 2.5D hybrid model (where ions are treated as particles using the PIC method, and electrons are modeled as a background neutralizing fluid) to study the nonlinear electromagnetic wave-particle interactions of cold H+, hot H+, He+, and O+ ions for a broad range of typical magnetospheric parameters. The excitation of EMIC waves is driven primarily by the temperature anisotropy of hot H+. We vary (independently) the initial parallel beta, temperature anisotropy, and concentrations of the hot H+ component, He+, and O+ ions in five sweeps of these parameters. The effects of O+ density and temperature are considered in two additional parameters sweeps. We investigate the parametric dependence of the initial brief linear growth, the nonlinear saturation level of perpendicular magnetic fluctuations, and the temporal evolution of the ion temperature anisotropies. We construct the dispersion relation of the waves using the results of the model at several times during the evolution at the initial growth stage and at the nonlinear saturated state and investigate the energy content in the various branches of the dispersion (in k||-ω space). We determine the distribution of energy in the left-hand polarized ion-resonant and the right-hand modes. The results are compared and contrasted with the predictions of linear Vlasov theory. We discuss the implications of our results for the physics of the inner magnetosphere and radiation belts. Title: Power law "thermalization" of ion pickup and ionospheric outflows Authors: Moore, T. E.; Ofman, L.; Glocer, A.; Gershman, D. J.; Khazanov, G. V.; Paterson, W. R. Bibcode: 2016AGUFMSM51F2564M Altcode: One observed feature of ionospheric outflows is that the active ion heating processes produce power law tails of the core plasma velocity distribution, as well as transverse or conic peaks in the angular distributions. This characteristic is shared with hot ion distributions produced by ion pickup in the solar wind, resulting from cometary or interstellar gas ionization, and with hot ions observed around the Space Transportation System during gas releases. We revisit relevant observations and consider the hypothesis that the ion pickup thermalization process tends to produce power law (𝛋) energy distributions, using a simulation of the instability of a simple pickup (ring) distribution. Simulation results are derived for cases representative of both solar wind pickup, where ion velocities exceed the local Alfvén speed, and ionospheric pickup, where the local Alfvén speed exceeds ion velocities. The sub-Alfvenic pickup ring distribution appears to have a slow growth rate (per ion gyro period), that is, the instability evolves more slowly in the latter case than in the former. Implications for ionospheric outflow are discussed. Title: Slow Solar Wind: Observations and Modeling Authors: Abbo, L.; Ofman, L.; Antiochos, S. K.; Hansteen, V. H.; Harra, L.; Ko, Y. -K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.; von Steiger, R.; Wang, Y. -M. Bibcode: 2016SSRv..201...55A Altcode: 2016SSRv..tmp...34A While it is certain that the fast solar wind originates from coronal holes, where and how the slow solar wind (SSW) is formed remains an outstanding question in solar physics even in the post-SOHO era. The quest for the SSW origin forms a major objective for the planned future missions such as the Solar Orbiter and Solar Probe Plus. Nonetheless, results from spacecraft data, combined with theoretical modeling, have helped to investigate many aspects of the SSW. Fundamental physical properties of the coronal plasma have been derived from spectroscopic and imaging remote-sensing data and in situ data, and these results have provided crucial insights for a deeper understanding of the origin and acceleration of the SSW. Advanced models of the SSW in coronal streamers and other structures have been developed using 3D MHD and multi-fluid equations. Title: Dynamic Mapping of Prominence Activity Authors: Thompson, Barbara J.; Gilbert, Holly R.; Kirk, Michael S.; Mays, M. Leila.; Ofman, Leon; Uritsky, Vadim; Wyper, Peter; Hovis-Afflerbach, Beryl Bibcode: 2016usc..confE..82T Altcode: We present the results of a prominence mapping effort designed to extract the dynamics of erupting prominences. The material from partially erupting prominences can fall back to the sun, tracing out the topology of the mid- and post-eruptive corona. One question involving the range of observed behavior is the role of magnetic field topology and evolution in determining the motion of the erupting prominence material. A variable-g ballistic approximation is applied to study the motion of the material, using the deviations from constant angular momentum as a means of quantifying the local Lorentz (and other) forces on each piece of material. Variations in dynamic behavior can be traced back to changes in the local magnetic field and the formation of instabilities such as Rayleigh-Taylor. We discuss the use of the prominence trajectories as a means of diagnosing eruptive topologies. Title: Flare-associated Fast-mode Coronal Wave Trains Detected by SDO/AIA: Recent Observational Advances Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Cheung, Mark; De Pontieu, Bart Bibcode: 2016usc..confE.107L Altcode: Quasi-periodic Fast Propagating wave trains (QFPs) are new observational phenomena discovered by SDO/AIA in extreme ultraviolet (EUV). They were interpreted as fast-mode magnetosonic waves using MHD modeling, and also found to be closely related to quasi-periodic pulsations in solar flare emission ranging from radio to X-ray wavelengths. The significance of QFPs lies in their diagnostic potential (and possibly in flare energy transport), because they can provide critical clues to flare energy release and serve as new tools for coronal seismology. In this presentation, we report recent advances in observing QFPs. In particular, using differential emission measure (DEM) inversion, we found clear evidence of heating and cooling cycles that are consistent with alternating compression and rarefaction expected for magnetosonic wave pulses. We also found that different local magnetic and plasma environments can lead to two distinct types of QFPs located in different spatial domains with respect to their accompanying coronal mass ejections (CMEs). More interestingly, from a statistical survey of over 100 QFP events, we found a preferential association with eruptive flares rather than confined flares. We will discuss the implications of these results and the potential roles of QFPs in coronal heating, energy transport, and solar eruptions. Title: Determination of transport coefficients from flare-excited standing slow-mode waves observed by SDO/AIA Authors: Wang; Tongjiang; Ofman, Leon; Davila, Joseph M. Bibcode: 2016usc..confE..36W Altcode: The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 Angstrom bandpasses. These oscillations show similar physical properties (such as period, decay time, and trigger) as the Doppler shift oscillations previously detected by the SOHO/SUMER spectrometer in flare lines formed above 6 MK, which were mostly interpreted as the slow-mode standing waves. By applying the coronal seismology method we have, for the first time, found quantitative evidence of thermal conduction suppression in a hot (>9 MK) flare-heated loop with SDO/AIA (Wang et al. 2015, ApJL, 811, L13). This result has significant implications in two aspects. The first aspect is that the conduction suppression suggests the need of greatly enhanced compressive viscosity to interpret the observed strong wave damping. The second aspect is that the conduction suppression provides a reasonable mechanism for explaining the long-duration events where the hot plasma detected in X-rays or EUV in many flares cools much slower than expected from the classical Spitzer conductive cooling. In this presentation, we first review the observational results of the event, and then discuss possible causes for conduction suppression and viscosity enhancements. In addition, we will use the nonlinear MHD simulations to validate the seismology method that is based on linear analytical analysis, and demonstrate the inversion scheme for determining transport coefficients using numerical parametric study. Finally, as an application of our analysis, we will demonstrate how the observationally-constrained transport coefficients are crucial in providing a self-consistent explanation for the rapid excitation of standing slow-mode waves in a coronal loop by a footpoint flare. Title: Coronal and Flare Diagnostic with SDO/AIA-discovered Fast MHD Wave Trains in Active Regions Authors: Ofman, Leon; Liu, Wei Bibcode: 2016usc..confE.106O Altcode: Recently, SDO/AIA discovered quasi-periodic, fast-mode propagating MHD wave trains (QFPs) that propagate at high speeds of more than 1000 km/s. The waves provide a new diagnostic tool for coronal seismology that includes information on the flare energy release and the magnetic structure of the active regions. Many events are now available in a statistical study. However, for improved accuracy of coronal seismology, 3D MHD modeling is required and simple wave-mode analysis may be insufficient. We present new results of observationally constrained models of QFPs using our recently upgraded radiative, thermally conductive, visco-resistive 3D MHD code. The waves are excited by time-depended boundary conditions constrained by the spatial (localized) and quasi-periodic temporal evolution of a C-class flare typically associated with QFPs, and produce observable density and temperature fluctuations. We investigate parametrically the excitation, propagation, and damping of the waves for a range of key model parameters, such as the background temperature, density, magnetic field structure, and the location of the flaring site within the active region. We synthesize EUV intensities in multiple AIA channels and then obtain the model parameters that best reproduce the properties of observed QFPs, such as the recent DEM analysis. We discuss the implications of our modeling results for the seismological application of QFPs for the diagnostic of the active region field and flare pulsations. Title: Dynamic Mapping of Prominence Activity Authors: Thompson, Barbara J.; Uritsky, Vadim; Ofman, Leon Bibcode: 2016shin.confE.141T Altcode: We present the results of a prominence mapping effort designed to extract the dynamics of both erupting and quiescent prominences. The material from partially erupting prominences can fall back to the sun, tracing out the topology of the post-eruptive corona. A variable-g ballistic approximation is applied to study the motion of the material, using the deviations from constant angular momentum as a means of quantifying the local Lorentz (and other) forces on each piece of material. Variations in dynamic behavior can be traced back to changes in the local magnetic field and the formation of instabilities such as Rayleigh-Taylor. Title: Brightenings Caused by Falling Filament Material on 2011 September 7 Authors: Gilbert, Holly; Inglis, Andrew; Mays, M. Leila; Ofman, Leon; Provornikova, Elena Bibcode: 2016shin.confE.138G Altcode: Solar filaments exhibit a range of eruptive-like dynamic activity from the full, or partial, eruption of the filament mass and surrounding magnetic structure, as a CME, to a fully confined dynamic evolution or "failed" eruption. On 2011 September 7, a partial eruption of a filament was observed by SDO and STEREO, generating a substantial stream of returning filament material that exhibited a strong interaction with the solar surface. Similarly to the recently studied 2011 June 7 event, the impact sites show clear evidence of brightening in the observed EUV wavelengths due to energy release by the impact. We explore two plausible physical mechanisms that would cause such brightening: heating of the plasma due to the kinetic energy of the impacting material - compression of the plasma, or reconnection between the magnetic field of the low-laying loops with the field carried by the impacting material, or combination thereof. By analyzing the emission of the brightenings in several SDO/AIA wavelengths, and comparing the kinetic energy of the impacting material to the radiative energy we provide clues for the dominant mechanism of energy release involved in the observed brightenings. We compare this event to another in which we performed the same analysis (2011 June 7) where we determined that compression was the dominant mechanism. Title: Motions in Prominence Barbs as observed by Hinode/SOT and IRIS Authors: Kucera, Therese A.; Ofman, Leon; Tarbell, Theodore D. Bibcode: 2016SPD....47.0316K Altcode: We discuss observations of prominence barb dynamics as observed by Hinode/SOT and IRIS. Prominence barbs extend outwards to the side of the main prominence spine and downwards towards the chromosphere. Their properties, including the structure of their magnetic field and the nature of the motions observed in them are a subject of current debate. We use a combination of high cadence, high resolution imaging, H-alpha Doppler, and Mg II line profile data to analyze and understand waves and flows in barbs and discuss their ramifications in terms of a model of the barb magnetic field as collection of dipped field lines. Title: Fast-mode Coronal Wave Trains Detected by SDO/AIA: Recent Observational Progress Authors: Liu, Wei; Downs, Cooper; Ofman, Leon Bibcode: 2016SPD....4730802L Altcode: Quasi-periodic Fast Propagating wave trains (QFPs) are a new observational phenomenon discovered by SDO/AIA in extreme ultraviolet (EUV). They are fast-mode magnetosonic waves, closely related to quasi-periodic pulsations in solar flare emission ranging from radio to X-ray wavelengths. The significance of QFPs lies in their diagnostic potential, because they can provide critical clues to flare energy release and serve as new tools for coronal seismology. In this presentation, we report recent advances in observing QFPs. In particular, using differential emission measure (DEM) inversion, we found clear evidence of heating and cooling cycles that are consistent with alternating compression and rarefaction expected for magnetosonic wave pulses. We also found that different local magnetic and plasma environments can lead to two distinct types of QFPs located in different spatial domains with respect to their accompanying coronal mass ejections (CMEs). Moreover, recent IRIS observations of QFP source regions revealed sawtooth-like flare ribbon motions, indicative of pulsed magnetic reconnection, that are correlated with QFP excitation. More interestingly, from a statistical survey of over 100 QFP events, we found a preferential association with eruptive flares rather than confined flares. We will discuss the implications of these results and the potential roles of QFPs in coronal heating, energy transport, and solar eruptions. Title: Realistic Modeling of SDO/AIA-discovered Coronal Fast MHD Wave Trains in Active Regions Authors: Ofman, Leon; Liu, Wei Bibcode: 2016SPD....47.0621O Altcode: High-resolution EUV observations by space telescopes have provided plenty of evidence for coronal MHD waves in active regions. In particular, SDO/AIA discovered quasi-periodic, fast-mode propagating MHD wave trains (QFPs), which can propagate at speeds of ~1000 km/s perpendicular to the magnetic field. Such waves can provide information on the energy release of their associated flares and the magnetized plasma structure of the active regions. Before we can use these waves as tools for coronal seismology, 3D MHD modeling is required for disentangling observational ambiguities and improving the diagnostic accuracy. We present new results of observationally contained models of QFPs using our recently upgraded radiative, thermally conductive, visco-resistive 3D MHD code. The waves are excited by time-depended boundary conditions constrained by the spatial (localized) and quasi-periodic temporal evolution of a C-class flare typically associated with QFPs. We investigate the excitation, propagation, and damping of the waves for a range of key model parameters, such as the background temperature, density, magnetic field structure, and the location of the flaring site within the active region. We synthesize EUV intensities in multiple AIA channels and then obtain the model parameters that best reproduce the properties of observed QFPs. We discuss the implications of our model results for the seismological application of QFPs and for understanding the dynamics of their associated flares. Title: Coronal Seismology of Flare-Excited Standing Slow-Mode Waves Observed by SDO/AIA Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M. Bibcode: 2016SPD....47.0632W Altcode: Flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 Å bandpasses. Based on the interpretation in terms of a slow-mode wave, quantitative evidence of thermal conduction suppression in hot (>9 MK) loops has been obtained for the first time from measurements of the polytropic index and phase shift between the temperature and density perturbations (Wang et al. 2015, ApJL, 811, L13). This result has significant implications in two aspects. One is that the thermal conduction suppression suggests the need of greatly enhanced compressive viscosity to interpret the observed strong wave damping. The other is that the conduction suppression provides a reasonable mechanism for explaining the long-duration events where the thermal plasma is sustained well beyond the duration of impulsive hard X-ray bursts in many flares, for a time much longer than expected by the classical Spitzer conductive cooling. In this study, we model the observed standing slow-mode wave in Wang et al. (2015) using a 1D nonlinear MHD code. With the seismology-derived transport coefficients for thermal conduction and compressive viscosity, we successfully simulate the oscillation period and damping time of the observed waves. Based on the parametric study of the effect of thermal conduction suppression and viscosity enhancement on the observables, we discuss the inversion scheme for determining the energy transport coefficients by coronal seismology. Title: Quasi-periodic fast-mode magnetosonic wave trains within coronal waveguides associated with flares and CMEs Authors: Liu, Wei; Ofman, Leon; Broder, Brittany; Karlický, Marian; Downs, Cooper Bibcode: 2016AIPC.1720d0010L Altcode: 2015arXiv151207930L Quasi-periodic, fast-mode, propagating wave trains (QFPs) are a new observational phenomenon recently discovered in the solar corona by the Solar Dynamics Observatory with extreme ultraviolet (EUV) imaging observations. They originate from flares and propagate at speeds up to ∼2000 km s-1 within funnel-shaped waveguides in the wakes of coronal mass ejections (CMEs). QFPs can carry suffcient energy fluxes required for coronal heating during their occurr ences. They can provide new diagnostics for the solar corona and their associated flares. We present recent observations of QFPs focusing on their spatio-temporal properties, temperature dependence, and statistical correlation with flares and CMEs. Of particular interest is the 2010-Aug-01 C3.2 flare with correlated QFPs and drifting zebra and fiber radio bursts, which might be different manifestations of the same fast-mode wave trains. We also discuss the potential roles of QFPs in accelerating and/or modulating the solar wind. Title: MHD Waves in the Solar Wind Authors: Ofman, L. Bibcode: 2016GMS...216..241O Altcode: This chapter focuses on reviewing several observational aspects of magnetohydrodynamic (MHD) waves in the solar wind, in particular on Alfvén waves, Alfvénic turbulent spectrum, and their role in heating and accelerating the solar wind. It also reviews computational models that incorporate Alfvén waves as the driving source of the wind in the lower corona (coronal holes) and in the inner heliosphere, with emphasis on multi-dimensional models. Evidence for MHD waves in the solar wind is obtained from interplanetary scintillation (IPS) observations using Earth-based radio telescope observations of distant (galactic) radio sources. The solar wind electron density variability in the line of sight affects the received radio signal. The propagating fluctuations and their correlations are used to estimate the solar wind velocity and the wave amplitude in the parallel and the perpendicular directions in line of sight. Title: Evidence of thermal conduction suppression in hot coronal loops: supplementary results Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova, Elena; Davila, Joseph M. Bibcode: 2016IAUS..320..202W Altcode: 2015arXiv151002750W Slow magnetoacoustic waves were first detected in hot (>6 MK) flare loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in Fe xix and Fe xxi lines. Recently, such longitudinal waves have been found by SDO/AIA in the 94 and 131 Å channels. Wang et al. (2015) reported the first AIA event revealing signatures in agreement with a fundamental standing slow-mode wave, and found quantitative evidence for thermal conduction suppression from the temperature and density perturbations in the hot loop plasma of >~ 9 MK. The present study extends the work of Wang et al. (2015) by using an alternative approach. We determine the polytropic index directly based on the polytropic assumption instead of invoking the linear approximation. The same results are obtained as in the linear approximation, indicating that the nonlinearity effect is negligible. We find that the flare loop cools slower (by a factor of 2-4) than expected from the classical Spitzer conductive cooling, approximately consistent with the result of conduction suppression obtained from the wave analysis. The modified Spitzer cooling timescales based on the nonlocal conduction approximation are consistent with the observed, suggesting that nonlocal conduction may account for the observed conduction suppression in this event. In addition, the conduction suppression mechanism predicts that larger flares may tend to be hotter than expected by the EM-T relation derived by Shibata & Yokoyama (2002). Title: Flare-associated Fast-mode Coronal Wave Trains Discovered by SDO/AIA: Physical Properties and Implications Authors: Liu, W.; Ofman, L.; Downs, C.; Cheung, C. M. M.; Broder, B.; De Pontieu, B. Bibcode: 2015AGUFMSH54B..02L Altcode: Quasi-periodic Fast Propagating wave trains (QFPs) are a new observational phenomenon discovered in extreme ultraviolet (EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). They are fast-mode magnetosonic waves, closely related to quasi-periodic pulsations in solar flare emission ranging from radio to X-ray wavelengths. The significance of QFPs lies in their diagnostic potential, because they can provide critical clues to flare energy release and serve as new tools for coronal seismology. In this presentation, we report recent advances in observing and modeling QFPs. For example, using differential emission measure (DEM) inversion, we found clear evidence of heating and cooling cycles that are consistent with alternating compression and rarefaction expected for magnetosonic wave pulses. Moreover, recent IRIS observations of QFP source regions revealed sawtooth-like flare ribbon motions, indicative of pulsed magnetic reconnection, that are correlated with QFP excitation. More interestingly, from a survey of over 100 QFP events, we found a preferential association with eruptive flares rather than confined flares. We will discuss the implications of these results and the potential roles of QFPs in coronal heating, energy transport, and solar eruptions. Title: Fast Wave Trains Associated with Solar Eruptions: Insights from 3D Thermodynamic MHD Simulations Authors: Downs, C.; Liu, W.; Torok, T.; Linker, J.; Mikic, Z.; Ofman, L. Bibcode: 2015AGUFMSH22A..06D Altcode: EUV imaging observations during the SDO/AIA era have provided new insights into a variety of wave phenomena occurring in the low solar corona. One example is the observation of quasi-periodic, fast-propagating wave trains that are associated with solar eruptions, including flares and CMEs. While there has been considerable progress in understanding such waves from both an observational and theoretical perspective, it remains a challenge to pin down their physical origin. In this work, we detail our results from a case-study 3D thermodynamic MHD simulation of a coronal mass ejection where quasi-periodic wave trains are generated during the simulated eruption. We find a direct correlation between the onset of non-steady reconnection in the flare current sheet and the generation of quasi-periodic wave train signatures when patchy, collimated downflows interact with the flare arcade. Via forward modeling of SDO/AIA observables, we explore how the appearance of the wave trains is affected by line-of-sight integration and the multi-thermal nature of the coronal medium. We also examine how the wave trains themselves are channeled by natural waveguides formed in 3D by the non-uniform background magnetic field. While the physical association of the reconnection dynamics to the generation of quasi-periodic wave trains appears to be a compelling result, unanswered questions posed from recent observations as well as future prospects will be discussed. Title: Transition From Turbulence to Dissipation in the Solar Wind Plasma: Results From Hybrid Simulations Authors: Ofman, L.; Roberts, D. A. Bibcode: 2015AGUFMSH11E2419O Altcode: Spacecraft observations such as WIND, and ACE show ample evidence of turbulent spectra of magnetic and velocity fluctuations, and kinetic dissipation in the solar wind plasma at ~1AU. Helios and MESSENGER confirm these properties close to the Sun at ~0.3AU, and future Solar Probe+ mission will provide information on turbulent spectra closer to the Sun in the outer corona. The transition between turbulence and dissipation occurs at scales that have clear dependence on heliocentric distance, as expected from solar wind expansion. We perform 2.5 hybrid modeling studies (where ions are described as particles, and electrons as background fluid) of the evolution of the turbulent spectra of fluctuations in electron-proton-He++ solar wind plasma at 1AU and closer to the Sun by varying the model plasma parameters. We investigate the dependence of the turbulence cascade and the transition to kinetic dissipation on the plasma parameters. We consider the effects of the solar wind expansion on the evolution of the turbulence and on the ion heating. We find important differences between the magnetic fluctuations spectrum, and the velocity fluctuations parallel and perpendicular to the field affected by ion-cyclotron, and mirror instabilities, as well as proton and alpha density fluctuations due to coupling to magnetosonic instability. We investigate the effects of the alpha-proton drift, and an injected spectrum on the turbulent magnetic fluctuations on the evolution of the solar wind plasma and the ion heating. Title: Slow Solar Wind: Observable Characteristics for Constraining Modelling Authors: Ofman, L.; Abbo, L.; Antiochos, S. K.; Hansteen, V. H.; Harra, L.; Ko, Y. K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.; von Steiger, R.; Wang, Y. M. Bibcode: 2015AGUFMSH11F..03O Altcode: The Slow Solar Wind (SSW) origin is an open issue in the post SOHO era and forms a major objective for planned future missions such as the Solar Orbiter and Solar Probe Plus.Results from spacecraft data, combined with theoretical modeling, have helped to investigate many aspects of the SSW. Fundamental physical properties of the coronal plasma have been derived from spectroscopic and imaging remote-sensing data and in-situ data, and these results have provided crucial insights for a deeper understanding of the origin and acceleration of the SSW.Advances models of the SSW in coronal streamers and other structures have been developed using 3D MHD and multi-fluid equations.Nevertheless, there are still debated questions such as:What are the source regions of SSW? What are their contributions to the SSW?Which is the role of the magnetic topology in corona for the origin, acceleration and energy deposition of SSW?Which are the possible acceleration and heating mechanisms for the SSW?The aim of this study is to present the insights on the SSW origin and formationarisen during the discussions at the International Space Science Institute (ISSI) by the Team entitled ''Slowsolar wind sources and acceleration mechanisms in the corona'' held in Bern (Switzerland) in March2014--2015. The attached figure will be presented to summarize the different hypotheses of the SSW formation. Title: Deriving Kinematic Properties of Non-Radial, Asymmetric and Deflecting CMEs: Methods and Implications Authors: Thompson, B. J.; Liewer, P. C.; Mays, M. L.; Richardson, I. G.; Kwon, R.; Ofman, L.; Makela, P. A.; Ireland, J.; Hess, P.; Waldron, Z. Bibcode: 2015AGUFMSH33B2467T Altcode: An improved understanding of the kinematic properties of CMEs and CME-associated phenomena has several impacts: 1) a less ambiguous method of mapping propagating structures into their inner coronal manifestations, 2) a clearer view of the relationship between the "main" CME and CME-associated brightenings, and 3) an improved identification of the heliospheric sources of shocks, Type II bursts, and SEPs. However, there are several challenges in characterizing the kinematic properties of CMEs. Most rapidly-evolving eruptions are accompanied by changes in the surrounding corona. The larger the impact on the surrounding corona, the more difficult it is to separate the "main" CME from the CME-associated brightenings. Complicating the issue is the range of observed propagation properties: super-radial expansion, asymmetric expansion, non-radial propagation, and alterations in the direction of propagation. These properties can be a function of both the internal magnetic structure of the CME and the structure of the corona through which the CME is propagating. While the relative contribution of internal/external factors can be difficult to assess, it is of fundamental importance because it not only reveals the nature of CMEs but also CME-associated phenomena such as EUV waves, Type II radio bursts, shocks, and SEPs. Most halo CMEs are a combination of both the "main" CME and the CME-associated brightenings, but new diagnostic methods such as time convolution mapping can help separate the CME mass from the impacted corona. Additionally, while most CME-fitting methods assume symmetry about the radial direction, adaptive methods allow us to study highly asymmetric CME expansion and take into account the fundamentally different natures of the CME and the shocked/deflected corona. Several methods will be examined, and each has their respective strengths and weaknesses; for example, the difference between the direction of a highly non-radial CME and a sun-centered model's orientation can exceed 45 degrees, which impacts our ability to correctly assess changes in propagation direction and the causes of these changes. We examine the assumptions inherent in these methods and how they may produce artifacts that can influence conclusions about CME kinematics. Title: Coronal seismology of flare-excited longitudinal slow magnetoacoustic waves in hot coronal loops Authors: Wang, T.; Ofman, L.; Sun, X.; Provornikova, E. A.; Davila, J. M. Bibcode: 2015AGUFMSH13B2435W Altcode: The flare-excited longitudinal intensity oscillations in hot flaring loops have been recently detected by SDO/AIA in 94 and 131 bandpasses. These oscillations show similar physical properties (such as period, decay time, and trigger) as those slow-mode standing waves previously detected by the SOHO/SUMER spectrometer in Doppler shift of flare lines formed above 6 MK. The multi-wavelength AIA observations with high spatio-temporal resolution and wide temperature coverage enable us to measure both thermal and wave properties of the oscillating hot plasma with unprecedented accuracy. These new measurements can be used to diagnose the complicated energy transport processes in flare plasma by a technique called coronal seismology based on the combination of observations and MHD wave theory. From a detailed case study we have found evidence for thermal conduction suppression in hot loops by measuring the polytropic index and analyzing the phase relationship between the temperature and density wave signals. This result is not only crucial for better understanding the wave dissipation mechanism but also provides an alternative mechanism to explain the puzzles of long-duration events and X-ray loop-top sources which show much slower cooling than expected by the classical Spitzer conductive cooling. This finding may also shed a light on the coronal heating problem because weak thermal conductivity implies slower cooling of hot plasma in nanoflares, so increasing the average coronal temperature for the same heating rate. We will discuss the effects of thermal conduction suppression on the wave damping and loop cooling based on MHD simulations. Title: Nonlinear MHD Waves in a Prominence Foot Authors: Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B. Bibcode: 2015ApJ...813..124O Altcode: 2015arXiv150907911O We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ∼ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5-11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5-14 G. For the typical prominence density the corresponding fast magnetosonic speed is ∼20 km s-1, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure. Title: Stability of Rotating Magnetized Jets in the Solar Atmosphere. I. Kelvin-Helmholtz Instability Authors: Zaqarashvili, Teimuraz V.; Zhelyazkov, Ivan; Ofman, Leon Bibcode: 2015ApJ...813..123Z Altcode: 2015arXiv151001108Z Observations show various jets in the solar atmosphere with significant rotational motions, which may undergo instabilities leading to heat ambient plasma. We study the Kelvin-Helmholtz instability (KHI) of twisted and rotating jets caused by the velocity jumps near the jet surface. We derive a dispersion equation with appropriate boundary conditions for total pressure (including centrifugal force of tube rotation), which governs the dynamics of incompressible jets. Then, we obtain analytical instability criteria of KHI in various cases, which were verified by numerical solutions to the dispersion equation. We find that twisted and rotating jets are unstable to KHI when the kinetic energy of rotation is more than the magnetic energy of the twist. Our analysis shows that the azimuthal magnetic field of 1-5 G can stabilize observed rotations in spicule/macrospicules and X-ray/extreme-ultraviolet (EUV) jets. On the other hand, nontwisted jets are always unstable to KHI. In this case, the instability growth time is several seconds for spicule/macrospicules and a few minutes (or less) for EUV/X-ray jets. We also find that standing kink and torsional Alfvén waves are always unstable near the antinodes, owing to the jump of azimuthal velocity at the surface, while the propagating waves are generally stable. Kelvin-Helmholtz (KH) vortices may lead to enhanced turbulence development and heating of surrounding plasma therefore, rotating jets may provide energy for chromospheric and coronal heating. Title: Three-dimensional MHD modeling of vertical kink oscillations in an active region plasma curtain Authors: Ofman, L.; Parisi, M.; Srivastava, A. K. Bibcode: 2015A&A...582A..75O Altcode: 2015arXiv150505427O Context. Observations on 2011 August 9 of an X 6.9-class flare in active region (AR) 11263 by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), were followed by a rare detection of vertical kink oscillations in a large-scale coronal active region plasma curtain in extreme UV coronal lines with periods in the range 8.8-14.9 min.
Aims: Our aim is to study the generation and propagation of the magnetohydrodynamic (MHD) oscillations in the plasma curtain taking the realistic 3D magnetic and the density structure of the curtain into account. We also aim to test and improve coronal seismology for a more accurate determination of the magnetic field than with the standard method.
Methods: We use the observed morphological and dynamical conditions, as well as plasma properties of the coronal curtain, to initialize a 3D MHD model of the observed vertical and transverse oscillations. To accomplish this, we implemented the impulsively excited velocity pulse mimicking the flare-generated nonlinear fast magnetosonic propagating disturbance interacting obliquely with the curtain. The model is simplified by utilizing an initial dipole magnetic field, isothermal energy equation, and gravitationally stratified density guided by observational parameters.
Results: Using the 3D MHD model, we are able to reproduce the details of the vertical oscillations and study the process of their excitation by a nonlinear fast magnetosonic pulse, propagation, and damping, finding agreement with the observations.
Conclusions: We estimate the accuracy of simplified slab-based coronal seismology by comparing the determined magnetic field strength to actual values from the 3D MHD modeling results, and demonstrate the importance of taking more realistic magnetic geometry and density for improving coronal seismology into account.

A movie associated to Fig. 1 is available in electronic form at http://www.aanda.org Title: Evidence of Thermal Conduction Suppression in a Solar Flaring Loop by Coronal Seismology of Slow-mode Waves Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova, Elena; Davila, Joseph M. Bibcode: 2015ApJ...811L..13W Altcode: 2015arXiv150900920W Analysis of a longitudinal wave event observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory is presented. A time sequence of 131 Å images reveals that a C-class flare occurred at one footpoint of a large loop and triggered an intensity disturbance (enhancement) propagating along it. The spatial features and temporal evolution suggest that a fundamental standing slow-mode wave could be set up quickly after meeting of two initial disturbances from the opposite footpoints. The oscillations have a period of ∼12 minutes and a decay time of ∼9 minutes. The measured phase speed of 500 ± 50 km s-1 matches the sound speed in the heated loop of ∼10 MK, confirming that the observed waves are of slow mode. We derive the time-dependent temperature and electron density wave signals from six AIA extreme-ultraviolet channels, and find that they are nearly in phase. The measured polytropic index from the temperature and density perturbations is 1.64 ± 0.08 close to the adiabatic index of 5/3 for an ideal monatomic gas. The interpretation based on a 1D linear MHD model suggests that the thermal conductivity is suppressed by at least a factor of 3 in the hot flare loop at 9 MK and above. The viscosity coefficient is determined by coronal seismology from the observed wave when only considering the compressive viscosity dissipation. We find that to interpret the rapid wave damping, the classical compressive viscosity coefficient needs to be enhanced by a factor of 15 as the upper limit. Title: Evidence of thermal conduction depression in hot coronal loops Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Provornikova, Elena; Davila, Joseph Bibcode: 2015IAUGA..2257766W Altcode: Slow magnetoacoustic waves were first detected in hot (>6 MK) flare loops by the SOHO/SUMER spectrometer as Doppler shift oscillations in Fe XIX and Fe XXI lines. These oscillations are identified as standing slow-mode waves because the estimated phase speeds are close to the sound speed in the loop and some cases show a quarter period phase shift between velocity and intensity oscillations. The observed very rapid excitation and damping of standing slow mode waves have been studied by many authors using theories and numerical simulations, however, the exact mechanisms remain not well understood. Recently, flare-induced longitudinal intensity oscillations in hot post-flare loops have been detected by SDO/AIA. These oscillations have the similar physical properties as SUMER loop oscillations, and have been interpreted as the slow-mode waves. The multi-wavelength AIA observations with high spatio-temporal resolution and wide temperature coverage allow us to explore the wave excitation and damping mechanisms with an unprecedented detail to develope new coronal seismology. In this paper, we present accurate measurements of the effective adiabatic index (γeff) in the hot plasma from the electron temperature and density wave signals of a flare-induced longitudinal wave event using SDO/AIA data. Our results strikingly and clearly reveal that thermal conduction is highly depressed in hot (∼10 MK) post-flare loops and suggest that the compressive viscosity is the dominant wave damping mechanism which allows determination of the viscosity coefficient from the observables by coronal seismology. This new finding challenges our current understanding of thermal energy transport in solar and stellar flares, and may provide an alternative explanation of long-duration events and enhance our understand of coronal heating mechanism. We will discuss our results based on non-ideal MHD theory and simulations. We will also discuss the flare trigger mechanism based on magnetic topology derived from SDO/HMI vector magnetic fields using nonlinear force-free field extrapolations and discuss the wave excitation mechanism based on 3D MHD modeling of the active region. Title: Relative drifts and temperature anisotropies of protons and α particles in the expanding solar wind: 2.5D hybrid simulations Authors: Maneva, Y. G.; Ofman, L.; Viñas, A. Bibcode: 2015A&A...578A..85M Altcode: 2014arXiv1410.3358M Context. We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and α particles in the collisionless turbulent low- tildeβ solar wind plasma.
Aims: We study the generation of differential streaming by wave-particle interactions and absorption of turbulent wave spectra. Next we focus on the role of the relative drifts for the turbulent heating and acceleration of ions in the collisionless fast solar wind streams.
Methods: The energy source is given by an initial broad-band spectrum of parallel propagating Alfvén-cyclotron waves, which co-exists with the plasma and is self-consistently coupled to the perpendicular ion bulk velocities. We include the effect of a gradual solar wind expansion, which cools and decelerates the minor ions. We here consider for the first time the combined effect of self-consistently initialized dispersive turbulent Alfvénic spectra with differentially streaming protons and α particles in the expanding solar wind outflows within a 2.5D hybrid simulation study.
Results: For differential streaming of Vαp < 0.5VA, the selected initial wave spectrum accelerates the minor ions in the non-expanding wind. At Vαp = 0.5VA the relative drift speed remains nearly steady. For ions that stream below this threshold value, the waves act to increase the magnitude of the relative drift speed. Ions that stream faster than the threshold value become subject to a nonlinear streaming instability, and as the system evolves, their bulk velocities decrease. We find that the solar wind expansion strongly affects the relative drift speed and significantly slows down both ion species for all values of the relative drift speeds considered in this study. The initial nonresonant wave spectra interact with the particles, resulting in preferential and anisotropic heating for the minor ions with a prominent increase of their perpendicular temperature, which overcomes the effect of the double-adiabatic cooling that is due to the solar wind expansion. Finally, the initial parallel spectra undergo a micro-turbulent nonlinear cascade during which oblique waves are generated, whose intensity depends on the value of the relative drift speed. Title: Turbulent photospheric drivers of multiscale solar corona Authors: Uritsky, Vadim M.; Ofman, Leon; Davila, Joseph M. Bibcode: 2015TESS....121305U Altcode: We investigate the collective dynamics of transient photospheric and coronal events detected using high-resolution solar magnetograms and coronal emission images. We focus on statistical, ensemble-averaged properties of the interacting solar regions [Uritsky et al., 2011, 2013, 2014; Uritsky and Davila, 2012], as opposed to case-oriented methodologies recruited in some previous studies. The behavior of solar events is studied in the three-dimensional space-time enabling accurate representation of the event evolution. By applying advanced data analysis methods including feature tracking algorithms, multiscale correlation analysis and scaling analysis techniques, we identify leading physical scenarios of the photosphere - corona coupling in quiet and active solar regions, and strive to identify new statistical precursors of coronal eruptions. We also discuss the possibility of modeling multiscale photosphere - corona interactions using idealized three-dimensional MHD models. The obtained results shed a new light on the origin of multiscale dissipation in the solar corona by enabling quantitative validation of several popular statistical physical scenarios, such as e.g. intermittent turbulence, self-organized criticality, and topological complexity. Title: Ion Heating in Inhomogeneous Expanding Solar Wind Plasma: The Role of Parallel and Oblique Ion-cyclotron Waves Authors: Ozak, N.; Ofman, L.; Viñas, A. -F. Bibcode: 2015ApJ...799...77O Altcode: 2014arXiv1407.4622O Remote sensing observations of coronal holes show that heavy ions are hotter than protons and their temperature is anisotropic. In-situ observations of fast solar wind streams provide direct evidence for turbulent Alfvén wave spectrum, left-hand polarized ion-cyclotron waves, and He++ - proton drift in the solar wind plasma, which can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Furthermore, the solar wind is expected to be inhomogeneous on decreasing scales approaching the Sun. We study the heating of solar wind ions in inhomogeneous plasma with a 2.5D hybrid code. We include the expansion of the solar wind in an inhomogeneous plasma background, combined with the effects of a turbulent wave spectrum of Alfvénic fluctuations and initial ion-proton drifts. We study the influence of these effects on the perpendicular ion heating and cooling and on the spectrum of the magnetic fluctuations in the inhomogeneous background wind. We find that inhomogeneities in the plasma lead to enhanced heating compared to the homogenous solar wind, and the generation of significant power of oblique waves in the solar wind plasma. The cooling effect due to the expansion is not significant for super-Alfvénic drifts, and is diminished further when we include an inhomogeneous background density. We reproduce the ion temperature anisotropy seen in observations and previous models, which is present regardless of the perpendicular cooling due to solar wind expansion. We conclude that small scale inhomogeneities in the inner heliosphere can significantly affect resonant wave ion heating. Title: Spectroscopic Diagnosis of Propagating disturbances in coronal loops: Waves or flows? Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M. Bibcode: 2015arXiv150104082W Altcode: The analysis of multiwavelength properties of propagating disturbances (PDs) using Hinode/EIS observations is presented. Quasi-periodic PDs were mostly interpreted as slow magnetoacoustic waves in early studies, but recently suggested to be intermittent upflows of the order of 50-150 km/s based on the Red-Blue (RB) asymmetry analysis of spectral line profiles. Using the forward models, velocities of the secondary component derived from the RB analysis are found significantly overestimated due to the saturation effect when its offset velocities are smaller than the Gaussian width. We developed a different method to examine spectral features of the PDs. This method is assuming that the excessive emission of the PD profile against the background (taken as that prior to the PD) is caused by a hypothetic upflow. The derived LOS velocities of the flow are on the order of 10-30 km/s from the warm (1-1.5 MK) coronal lines, much smaller than those inferred from the RB analysis. This result does not support the flow interpretation but favors of the early wave interpretation. Title: Role of Parallel and Oblique Ion-Cyclotron Waves in Heating Ions in an Inhomogeneous Expanding Solar Wind Plasma Authors: Ofman, L.; Ozak, N. O.; Vinas, A. F. Bibcode: 2014AGUFMSH33A4147O Altcode: In-situ observations of fast solar wind streams at distances of 0.29 AU and beyond by Helios and recently by MESSENGER, and at ~1 AU by STEREO, ACE, and Wind spacecraft provide direct evidence for the presence of turbulent Alfvén wave spectrum and of left-hand polarized ion-cyclotron waves as well as He++ - proton drift in the solar wind plasma. The waves and the super-Alfvénic drift can produce temperature anisotropies by resonant absorption and perpendicular heating of the ions. Measurements indicate that proton velocity distributions are generally non-Maxwellian with evidence for beams, while remote sensing observations of coronal holes have shown that heavy ions are hotter than protons with a temperature anisotropy greater than one (Ti,perp> Ti,||). In addition to the anisotropy, it is expected that the solar wind will be inhomogeneous on decreasing scales approaching the Sun. Here we use a 2.5 D hybrid code and extend previous work to study the heating of solar wind ions (H+, He+) in an inhomogeneous plasma background. We explore the effects of an initial ion drift and of a turbulent wave spectrum on the perpendicular ion heating and cooling and on the spectrum of the magnetic fluctuations in the inhomogeneous background solar wind. Using the 2D hybrid model we find that inhomogeneities in the plasma generate significant power of oblique waves in the solar wind plasma, in addition to enhanced heating compared to the homogenous solar wind case. We find that the cooling effect due to the solar wind expansion is only significant when sub-Alfvénic drifts are explored. On the other hand, the cooling is not significant in the presence of a super-Alfvénic drift, and it is even less significant when we include an inhomogeneous background density. We are able to reproduce the ion temperature anisotropy seen in observations and previous models and find that small-scale inhomogeneities in the inner heliosphere can have a significant impact on resonant wave ion heating. Title: Modeling the heating and the acceleration of the fast solar wind ion Authors: Ofman, L.; Vinas, A. F. Bibcode: 2014AGUFMSH33A4119O Altcode: The solar wind is the major component of solar activity and is the variable background state for the propagating solar disturbances that affect the heliosphere and interact with planetary magnetospheres. However, the physical mechanisms of solar wind acceleration and heating are not fully understood. During periods of solar maxima streamers dominate the solar corona and the slow solar wind streams are ubiquitous in the heliosphere. The ion composition and the charge states of the solar wind streams measured in situ and are used to determine their coronal origin. The physical properties of the multi-ion solar wind plasma and turbulent wave spectra are modeled with multifluid models, while the kinetic processes that lead to solar wind ion heating by resonant waves and instabilities are modeled with 2.5 hybrid models that include the kinetic ion wave-particle interactions and ion-cyclotron wave heating processes. We will show recent results of multi-fluid and hybrid models constrained by remote sensing and in situ observations of the solar wind and discuss how this modeling approach improves understanding of the heating and acceleration processes of the solar wind. Title: Coronal Extreme Ultraviolet (EUV) Waves and Their Seismological Applications Authors: Liu, W.; Ofman, L. Bibcode: 2014AGUFMSH23C..01L Altcode: Magnetohydrodynamic (MHD) waves can be used as seismological tools to probe the physical conditions of the solar corona, including its magnetic field and plasma parameters. Recent high cadence and full-disk imaging observations in extreme ultraviolet (EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) have opened a new chapter in understanding these waves and utilizing them for coronal seismology. We will review such new observations, focusing on two intimately related phenomena - global EUV waves (so-called "EIT waves") associated with coronal mass ejections (CMEs) and quasi-periodic, fast-mode magnetosonic wave trains associated with flares: (1) The generation and propagation of global EUV waves and their interaction with coronal structures, e.g., reflection and refraction, can provide diagnostics for the global corona in which they propagate, such as mapping the spatial distribution of the wave phase speed and thus the magnetic field strength. (2) AIA-detected fast-mode wave trains are closely correlated with flare pulsations seen from radio to hard X-rays and propagate at typically 500-2000 km/s along funnel-shaped waveguides often located within CME bubbles. They can provide diagnostics for flare energy release mechanisms and the local corona around the flaring active region. We will discuss the roles of such waves in energy transport within the solar atmosphere and in their associated CME/flare eruptions. Title: Brightenings Associated with Falling Filament Material Authors: Gilbert, H. R.; Inglis, A. R.; Mays, M. L.; Ofman, L.; Provornikova, E.; Thompson, B. J.; Young, C. A. Bibcode: 2014AGUFMSH13B4101G Altcode: Solar filaments exhibit a range of eruptive-like dynamic activity, including in some cases the confined or 'failed' ejection of prominence material from the solar atmosphere. In rare cases material that fails to erupt exhibits a strong interaction with the lower corona as the material returns to the solar surface, observed as substantial broadband brightening of EUV emission. We investigate a selection of recent partial prominence eruptions in order to understand the apparent rarity of the brightening phenomenon. Using combined data from SDO/AIA and STEREO, we explore the energetics and kinematics of these events, assessing the likely conditions of both the corona and the prominence material that are required in order to explain these EUV brightenings. We further demonstrate the potential of this phenomenon as diagnostic tool for both prominence material conditions and the coronal magnetic field. Title: SDO/AIA Observation and Modeling of Flare-excited Slow Waves in Hot Coronal Loops Authors: Wang, T.; Ofman, L.; Provornikova, E.; Sun, X.; Davila, J. M. Bibcode: 2014AGUFMSH13A4074W Altcode: The flare-excited standing slow waves were first detected by SOHO/SUMER as Doppler shift oscillations in hot (>6 MK) coronal loops. It has been suggested that they are excited by small or micro- flares at one loop's footpoint. However, the detailed excitation mechanism remains unclear. In this study, we report an oscillation event observed by SDO/AIA in the 131 channel. The intensity disturbances excited by a C-class flare propagated back and forth along a hot loop for about two period with a strong damping. From the measured oscillation period and loop length, we estimate the wave phase speed to be about 410 km/s. Using a regularized DEM analysis we determine the loop temperature and electron density evolution and find that the loop plasma is heated to a temperature of 8-12 MK with a mean about 9 MK. These measurements support the interpretation as slow magnetoacousic waves. Magnetic field extrapolation suggests that the flare is triggered by slipping and null-point-type reconnections in a fan-spine magnetic topology, and the injected (or impulsively evaporated) hot plasmas flowing along the large spine field lines form the oscillating hot loops. To understand why the propagating waves but not the standing waves as observed previously are excited in this event, we preform simulations using a 3D MHD model based on the observed magnetic configuration including full energy equation. Our simulations indicate that the nature of loop temperature structure is critical for the excitation of whether propagating or standing waves in a hot loop. Our result demonstrates that the slow waves may be used for heating diagnostics of coronal loops with coronal seismology. We also discuss the application of coronal seismology for estimating the average magnetic field strength in the hot loop based on the observed slow waves. Title: Advances in Observing Various Coronal EUV Waves in the SDO Era and Their Seismological Applications (Invited Review) Authors: Liu, Wei; Ofman, Leon Bibcode: 2014SoPh..289.3233L Altcode: 2014SoPh..tmp...67L; 2014arXiv1404.0670L Global extreme-ultraviolet (EUV) waves are spectacular traveling disturbances in the solar corona associated with energetic eruptions such as coronal mass ejections (CMEs) and flares. Over the past 15 years, observations from three generations of space-borne EUV telescopes have shaped our understanding of this phenomenon and at the same time led to controversy about its physical nature. Since its launch in 2010, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has observed more than 210 global EUV waves in exquisite detail, thanks to its high spatio-temporal resolution and full-disk, wide-temperature coverage. A combination of statistical analysis of this large sample, more than 30 detailed case studies, and data-driven MHD modeling, has been leading their physical interpretations to a convergence, favoring a bimodal composition of an outer, fast-mode magnetosonic wave component and an inner, non-wave CME component. Adding to this multifaceted picture, AIA has also discovered new EUV wave and wave-like phenomena associated with various eruptions, including quasi-periodic fast propagating (QFP) wave trains, magnetic Kelvin-Helmholtz instabilities (KHI) in the corona and associated nonlinear waves, and a variety of mini-EUV waves. Seismological applications using such waves are now being actively pursued, especially for the global corona. We review such advances in EUV wave research focusing on recent SDO/AIA observations, their seismological applications, related data-analysis techniques, and numerical and analytical models. Title: Brightenings Caused by Falling Filament Material on 2011 September 7 Authors: Gilbert, Holly; Inglis, Andrew; Mays, Leila; Ofman, Leon; Provornikova, Elena Bibcode: 2014AAS...22432313G Altcode: Solar filaments exhibit a range of eruptive-like dynamic activity from the full, or partial, eruption of the filament mass and surrounding magnetic structure, as a CME, to a fully confined dynamic evolution or ‘failed’ eruption. On 2011 September 7, a partial eruption of a filament was observed by SDO and STEREO, generating a substantial stream of returning filament material that exhibited a strong interaction with the solar surface. Similarly to the recently studied 2011 June 7 event, the impact sites show clear evidence of brightening in the observed EUV wavelengths due to energy release by the impact. We explore two plausible physical mechanisms that would cause such brightening: heating of the plasma due to the kinetic energy of the impacting material - compression of the plasma, or reconnection between the magnetic field of the low-laying loops with the field carried by the impacting material, or combination thereof. By analyzing the emission of the brightenings in several SDO/AIA wavelengths, and comparing the kinetic energy of the impacting material to the radiative energy we provide clues for the dominant mechanism of energy release involved in the observed brightenings. We compare this event to another in which we performed the same analysis (2011 June 7) where we determined that compression was the dominant mechanism. Title: Two-dimensional hybrid models of H+-He++ expanding solar wind plasma heating Authors: Ofman, L.; Viñas, A. F.; Maneva, Y. Bibcode: 2014JGRA..119.4223O Altcode: Preferential heating and acceleration of the solar wind He++ ions compared to protons in fast solar wind streams have been known for decades, thanks to in situ spacecraft measurements at 0.29-5 AU. Turbulent magnetic field fluctuations with approximate power law spectra have been observed as well. However, the exact causes of these processes are still not known due to the lack of detailed information on the magnetic field fluctuations and ion velocity distributions in the acceleration region of the solar wind. Here the collisionless heating processes in expanding solar wind plasma are investigated using 2-D hybrid modeling with parameters appropriate to the heliocentric distance of 10 RS. In this study the ion dynamics is described kinetically, while electrons are treated as a background massless fluid in an expanding solar wind model. The source of free energy for the heating is introduced through an initial nonequilibrium state of the plasma with large He++ ion temperature anisotropy or with super-Alfvénic relative ion drift. We also employ an externally imposed spectrum of magnetic fluctuations in the frequency range below the proton gyroresonant frequency to heat the He++ ions. We investigate the effects of solar wind radial expansion by modeling several values of the expansion rate in a parametric study. We find that the preferential ion heating is attained in both nonexpanding and expanding solar wind models. Thus, the expansion has little effect on the preferential He++ ion heating by the processes considered here. Moreover, the expansion leads to faster evolution of the magnetosonic drift instability, reducing the drift velocity to lower values sooner, and the corresponding generation of the magnetic fluctuations that heat the ions, compared to the nonexpanding case. This is due to the reduction of the perpendicular particle velocities in the expanding (inflated) frame. For cases with little proton perpendicular heating, the solar wind expansion leads to the reduction of the proton temperature anisotropy to values less than one in the low-βp∥ solar wind acceleration region consistent with some observed values. However, this effect must be offset by perpendicular proton heating—likely by the same process that heats the He++ ions to be consistent with the full range of observed proton perpendicular temperature values. Title: Modeling the multi-ion structure of the solar corona Authors: Ofman, Leon; Provornikova, Elena; Wang, Tongjiang Bibcode: 2014AAS...22440805O Altcode: The solar corona is typically observed in EUV by SDO/AIA and other instruments using the heavy ion emission lines such as Fe IX, Fe XII, and other ion emission lines. However, the relative (to protons) abundance of the emitting ions is very low and the collisional coupling between the Fe ions and electrons decreases rapidly with height in the low corona, while gravitational settling may become significant in quiescent long-lived magnetic structures, such as streamers. Thus, the structure of the weakly collisional solar corona imaged in Fe IX (and other heavy ions) may differ significantly from the structure of the main electron-proton constituents of the corona. The electron structure is observed by white light coronagraphs, and during solar eclipses in the low corona. I present the results of multi-fluid modeling of coronal streamers and other magnetic structures that demonstrate the effects of weak coupling between the heavy ions and the coronal electron-proton components, and show that the multi-ion coronal structure must be taken into account in interpretation of EUV observations. Title: Height-dependent Refraction of A Global EUV Wave and Its Associated Sympathetic Eruptions Authors: Liu, Wei; Ofman, Leon; Downs, Cooper; Schrijver, Karel Bibcode: 2014AAS...22421814L Altcode: The height dependence of global extreme-ultraviolet (EUV) waves in the solar corona, especially of their wave-like behaviors such as transmission and reflection, is critical to understanding their physical nature. Prior observations of such behaviors, when detected on the solar disk, were compromised because height-dependent information is lost due to the line-of-sight projection from a top-down view. We report a global EUV wave on the limb observed by SDO/AIA from a side-view that evidently shows height-dependent transmission and refraction. As the wave travels through an active region, the orientation of the low-corona wave front changes from a forward inclination toward the solar surface to a backward inclination. This indicates that the EUV wave speed is lower at higher altitudes, which is expected because of the rapid drop with height of the Alfven and fast-mode speeds in active regions, as predicted by MHD models. When traveling into the active region, the EUV wave speed in the low corona increases from ~600 km/s to ~900 km/s. In addition, in the neighborhood of the active region, sympathetic eruptions of local coronal structures take place sequentially upon the wave impact and may appear as wave reflection. Understanding propagation behaviors of global EUV waves brings us one step closer to fully utilizing them for seismological diagnostics of the global corona, such as mapping the spatial distribution of the Alfven speed and magnetic field strength. Title: SDO/AIA observations and model of standing waves in hot coronal loops excited by a flare Authors: Wang, Tongjiang; Ofman, Leon; Provornikova, Elena; Davila, Joseph M. Bibcode: 2014AAS...22432354W Altcode: The strongly damped Doppler shift oscillations in hot coronal loops were first observed by SOHO/SUMER in flare lines formed at plasma temperature more than 6 MK. They were mainly interpreted as the standing slow magnetosonic waves excited by impulsive energy release at the loop’s footpoint based on the measured properties and on MHD modeling results. Longitudinal waves with similar properties have been recently observed by SDO/AIA in active region loops. In this study, we report a new event that exhibited the flare-excited intensity disturbances propagating back and forth in a hot coronal loop imaged by AIA in 131 bandpass. We measure the physical parameters of the wave and loop plasma, determine the loop geometry, and explore the triggering mechanism. We identify the wave modes (propagating or standing waves) based on these measurements and on 3D MHD modeling. A loop model is constructed with enhanced density in a hydrostatic equilibrium following potential or force-free magnetic field lines extrapolated from the photospheric magnetic field data observed by SDO/HMI. We also discuss the applications of coronal seismology to this event. Title: Waves and jets in coronal loops: the effects of radiative cooling Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang Bibcode: 2014AAS...22432348P Altcode: Observations with Hinode/EIS of coronal loops in solar active regions revealed that propagating disturbances of EUV intensity are associated with plasma upflows or jets at loops footpoints. To investigate the excitation and evolution of waves due to plasma jets, we expand recent studies with more realistic 3D MHD model that includes full energy equation with empirical heating and radiative cooling terms. We perform 3D MHD simulations of loops by applying different flow drivers at the loops footpoints, a single upflow pulse and a broadband excitation of small amplitude (subsonic) velocity pulses. Parameters of the pulses are chosen according to the observed properties. We initialize the computations with an equilibrium state of a model active region using potential (dipole) magnetic field, gravitationally stratified density and temperature obtained from polytropic equation of state of the background coronal plasma. We study the initiation and the dynamics of plasma flows, excitation and damping of waves, and flow-wave interactions in the loops for various forms of heating. We investigate the effects of radiation losses on the damping of MHD waves on the jets in coronal loops. Title: 3D MHD modeling of waves excited by hot plasma jets in active regions loops Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang Bibcode: 2014shin.confE.158P Altcode: EUV imaging and spectroscopic observations from several space missions (SOHO, TRACE, Hinode/EIS, SDO/AIA) have revealed a presence of propagating disturbances in solar coronal loops interpreted as MHD waves. Recent observations with Hinode/EIS of active region loops showed that propagating disturbances of EUV intensity are associated with plasma upflows (or jets) at loops footpoints. In our study we aim to investigate the excitation and evolution of waves in the loops due to hot plasma jets at their footpoints. We expand previous isothermal studies with more realistic 3D MHD model of active region that includes full energy equation accounting for effects of radiative losses. Computations are initialized with an equilibrium state of a model active region using potential (dipole) magnetic field, gravitationally stratified density and temperature obtained from polytropic equation of state of the background coronal plasma. We model two scenarios of wave excitation in both warm ( 1 MK) and hot ( 6 MK) loops: impulsive injection of hot plasma into the steady plasma outflow and repetitive small-scale hot plasma jets. Parameters of the jets are chosen according to the observed properties. We study the initiation and the dynamics of plasma flows, excitation and damping of waves, and flow-wave interactions in the loops. We investigate the effects of radiation losses on the damping of MHD waves on the jets in coronal loops. Title: Modeling quasi-perpendicular shock front ion dynamics and magnetic evolution Authors: Ofman, Leon; Gedalin, Michael; Provornikova, Elena Bibcode: 2014shin.confE..14O Altcode: Collisionless shocks result from CMEs propagating in the heliosphere, and in regions of interaction between the solar wind and solar system bodies. The shocks are responsible for energetic processes and particle acceleration in the heliosphere. The magnetized shocks efficiently convert the energy of the directed ion flow into gyration energy of particles behind the shock front. Downstream ions play the key role in the postshock dynamics, including development of instabilities and eventual thermalization of the plasma. We use 2D hybrid model to study the magnetic evolution and the dynamics of ions in a quasi-perpendicular shock. The 2D hybrid modeling approach allows full kinetic nonlinear description of the proton and other ion motions, wave-particle interactions for parallel propagating and oblique waves, and velocity distribution functions (VDFs) in the magnetized plasma of the shocks, while the electrons are treated as background neutralizing fluid. The magnetic and VDFs structure of the shock can be directly compared to in-situ spacecraft measurements. The boundary conditions appropriate for shocks are non-periodic and finite difference solver is implemented for the fields. We investigate a broad range of shock parameters such as the Mach number and find the conditions where laminar, as well as corrugated shock-fronts are produced. The structure of the shock fronts affects the energy transfer between the shock and the particle populations, as well as the diagnostic of spacecraft measurements. Title: Quasi-periodic Fast-mode Magnetosonic Wave Trains Detected by SDO/AIA and Their Correlation with Quasi-period Flare Pulsations Authors: Liu, Wei; Ofman, Leon; Fleishman, Gregory; Downs, Cooper Bibcode: 2014shin.confE.157L Altcode: Quasi-periodic fast propagating wave trains (QFPs; Liu et al. 2011, 2012) are a new phenomenon recently discovered in extreme ultraviolet (EUV) by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). They are fast-mode magnetosonic waves, closely related to quasi-periodic pulsations of solar flares observed from radio to hard X-rays. QFPs usually originate from a flare and propagate at typically 500-2000 km/s within a funnel-shaped waveguide located inside a CME bubble. QFPs can potentially be used for coronal seismological diagnostics and provide critical clues to flare energy release and particle acceleration processes. We will present recent observational and numerical results of QFPs and compare them with quasi-periodic flare pulsations. Title: Nonlinear MHD waves in a Prominence Foot: Observations and Models Authors: Ofman, Leon; Schmieder, Brigitte; Kucera, Therese; Knizhnik, Kalman Bibcode: 2014cosp...40E2338O Altcode: Recent high-resolution observations with Hinode/SOT in Ca II emission of a prominence on October 12, 2012 show highly dynamic small-scale motions in the prominence material. Observations in Hα and of Doppler shifts show similar propagating fluctuations. However the optically thick nature of the emission lines inhibits unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (dI/I~ dn/n). The waves are evident as significant density fluctuations (dn/n~O(1)) with weak height dependence, and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations on the order of 5 minutes, and wavelengths ~<2000 km. Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field is measured with THEMIS and is found to be 5-14 G. For the typical prominence density the corresponding fast magnetosonic speed is ~20 km/s in qualitative agreement with the propagation speed of the detected wave. We use 2D and 3D MHD numerical models to reproduce the nonlinear magnetosonic waves with the typical parameters of the prominence guided by observations. We investigate the parameter range of the model that fits the observed properties of the waves in order confirm the identification of the wave nature of these observations. Title: Three-dimensional MHD modeling of flare-induced waves in coronal loops: thermal effects Authors: Provornikova, Elena; Ofman, Leon; Wang, Tongjiang Bibcode: 2014cosp...40E2635P Altcode: EUV imaging and spectroscopic observations from several space missions (SOHO, TRACE, Hinode/EIS, SDO/AIA) have revealed the presence of MHD waves in solar coronal loops. Past analysis of SOHO/SUMER data suggested that slow magnetosonic waves in hot coronal loops are excited by flares at the loop`s footpoint. Recent Hinode/EIS observed propagating disturbances in active region loops were interpreted as flows as well as waves most likely generated by plasma outflows or jets. In order to understand dynamics of plasma in coronal loops due to flares or jets at the lower corona boundary, we perform full 3D MHD modeling of an active region and consider different mechanisms of wave excitation. We assume an initial equilibrium of the model active region with dipole magnetic field structure, gravitationally stratified density and temperature obtained from polytropic equation of state of the background coronal plasma. We extend previous isothermal studies by including full energy equation with empirical heating and radiative losses terms in the model. We study waves in both, short and long loops, and consider two excitation mechanisms in the model: impulsive plasma injection into the steady plasma upflow along the magnetic field lines, and impulsive heating at the footpoint of the loop. We show initiation and evolution of flows, excitation and damping of waves and flow-wave interaction in the loops. We compare our new results with previous models and observations. Title: Measuring Temperature-dependent Propagating Disturbances in Coronal Fan Loops Using Multiple SDO/AIA Channels and the Surfing Transform Technique Authors: Uritsky, Vadim M.; Davila, Joseph M.; Viall, Nicholeen M.; Ofman, Leon Bibcode: 2013ApJ...778...26U Altcode: 2013arXiv1308.6195U A set of co-aligned high-resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling a quantitative description of subvisual coronal motions with low signal-to-noise ratios of the order of 0.1%. The technique operates with a set of one-dimensional "surfing" signals extracted from position-time plots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency-velocity space that exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square-root dependence predicted for slow mode magneto-acoustic waves which seem to be the dominating wave mode in the loop structures studied. This result extends recent observations by Kiddie et al. to a more general class of fan loop system not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels. Title: Global Coronal Seismology in the Extended Solar Corona through Fast Magnetosonic Waves Observed by STEREO SECCHI COR1 Authors: Kwon, Ryun-Young; Kramar, Maxim; Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Chae, Jongchul; Zhang, Jie Bibcode: 2013ApJ...776...55K Altcode: We present global coronal seismology for the first time, which allows us to determine inhomogeneous magnetic field strength in the extended corona. From the measurements of the propagation speed of a fast magnetosonic wave associated with a coronal mass ejection (CME) and the coronal background density distribution derived from the polarized radiances observed by the STEREO SECCHI COR1, we determined the magnetic field strengths along the trajectories of the wave at different heliocentric distances. We found that the results have an uncertainty less than 40%, and are consistent with values determined with a potential field model and reported in previous works. The characteristics of the coronal medium we found are that (1) the density, magnetic field strength, and plasma β are lower in the coronal hole region than in streamers; (2) the magnetic field strength decreases slowly with height but the electron density decreases rapidly so that the local fast magnetosonic speed increases while plasma β falls off with height; and (3) the variations of the local fast magnetosonic speed and plasma β are dominated by variations in the electron density rather than the magnetic field strength. These results imply that Moreton and EIT waves are downward-reflected fast magnetosonic waves from the upper solar corona, rather than freely propagating fast magnetosonic waves in a certain atmospheric layer. In addition, the azimuthal components of CMEs and the driven waves may play an important role in various manifestations of shocks, such as type II radio bursts and solar energetic particle events. Title: Rippled quasi-perpendicular collisionless shocks: Local and global normals Authors: Ofman, L.; Gedalin, M. Bibcode: 2013JGRA..118.5999O Altcode: Proper determination of the shock normal is necessary for reliable determination of observed heliospheric shock parameters and comparison of observations with theory. The existing methods work sufficiently well for low and moderate Mach numbers one-dimensional stationary shocks. Higher-Mach-number shocks are no longer planar at the scales of the ion convective gyroradius or smaller. In rippled shock fronts, the local shock normal may differ substantially from the global normal. The former is determined by the local direction of the fastest variation of the magnetic field, while the latter is determined by the far upstream and far downstream plasma conditions. Here we use 2-D hybrid modeling of quasi-perpendicular collisionless shocks with moderate and high Mach numbers to quantify the difference between the directions of the two normals. We find that the angle between the local normal and the global normal may be as large as 40° within the front of a rippled heliospheric shock. The coplanarity method of the shock normal determination is sensitive to the choice of the region for the magnetic field averaging. We also find that the usage of the sliding averaging region in the close vicinity of the shock transition provides satisfactory estimates of the global normal. Title: Energy Release from Impacting Prominence Material Following the 2011 June 7 Eruption Authors: Gilbert, H. R.; Inglis, A. R.; Mays, M. L.; Ofman, L.; Thompson, B. J.; Young, C. A. Bibcode: 2013ApJ...776L..12G Altcode: 2013arXiv1309.1769G Solar filaments exhibit a range of eruptive-like dynamic activity, ranging from the full or partial eruption of the filament mass and surrounding magnetic structure as a coronal mass ejection to a fully confined or failed eruption. On 2011 June 7, a dramatic partial eruption of a filament was observed by multiple instruments on board the Solar Dynamics Observatory (SDO) and Solar-Terrestrial Relations Observatory. One of the interesting aspects of this event is the response of the solar atmosphere as non-escaping material falls inward under the influence of gravity. The impact sites show clear evidence of brightening in the observed extreme ultraviolet wavelengths due to energy release. Two plausible physical mechanisms for explaining the brightening are considered: heating of the plasma due to the kinetic energy of impacting material compressing the plasma, or reconnection between the magnetic field of low-lying loops and the field carried by the impacting material. By analyzing the emission of the brightenings in several SDO/Atmospheric Imaging Assembly wavelengths, and comparing the kinetic energy of the impacting material (7.6 × 1026-5.8 × 1027 erg) to the radiative energy (≈1.9 × 1025-2.5 × 1026 erg), we find the dominant mechanism of energy release involved in the observed brightening is plasma compression. Title: Three-dimensional Magnetohydrodynamic Modeling of Propagating Disturbances in Fan-like Coronal Loops Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M. Bibcode: 2013ApJ...775L..23W Altcode: 2013arXiv1308.0282W Quasi-periodic propagating intensity disturbances (PDs) have been observed in large coronal loops in EUV images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. Motivated by the scenario that the coronal upflows could be the cumulative result of numerous individual flow pulses generated by sporadic heating events (nanoflares) at the loop base, we construct a velocity driver with repetitive tiny pulses, whose energy frequency distribution follows the flare power-law scaling. We then perform three-dimensional MHD modeling of an idealized bipolar active region by applying this broadband velocity driver at the footpoints of large coronal loops which appear open in the computational domain. Our model successfully reproduces the PDs with similar features as the observed, and shows that any upflow pulses inevitably excite slow magnetosonic wave disturbances propagating along the loop. We find that the generated PDs are dominated by the wave signature as their propagation speeds are consistent with the wave speed in the presence of flows, and the injected flows rapidly decelerate with height. Our simulation results suggest that the observed PDs and associated persistent upflows may be produced by small-scale impulsive heating events (nanoflares) at the loop base in the corona, and that the flows and waves may both contribute to the PDs at lower heights. Title: Fast Magnetosonic Waves and Global Coronal Seismology in the Extended Solar Corona Authors: Kwon, Ryun Young; Zhang, J.; Kramar, M.; Wang, T.; Ofman, L.; Davila, J. M. Bibcode: 2013SPD....4410303K Altcode: We present global coronal seismology, for the first time, that allows us to determine inhomogeneous magnetic field strengths in a wide range of the extended solar corona. We use observations of propagating disturbance associated with a coronal mass ejection observed on 2011 August 4 by the COR1 inner coronagraphs on board the STEREO spacecraft. We establish that the disturbance is in fact a fast magnetosonic wave as the upper coronal counterpart of the EIT wave observed by STEREO EUVI and travels across magnetic field lines with inhomogeneous speeds, passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. We derive magnetic field strengths along the azimuthal trajectories of the fronts at heliocentric distances 2.0, 2.5, and 3.0 Rs, using the varying speeds and electron densities. The derived magnetic field strengths are consistent with values determined with a potential field source surface model and reported in previous works. The ranges of the magnetic field strengths at these heliocentric distances are 0.44 ± 0.29, 0.23 ± 0.15, and 0.26 ± 0.14 G, respectively. The uncertainty in determining magnetic field strengths is about 40 %. This work demonstrates that observations of fast magnetosonic waves by white-light coronagraphs can provide us with a unique way to diagnose magnetic field strength of an inhomogeneous medium in a wide spatial range of the extended solar corona. Title: Quasi-periodic Fast-mode Magnetosonic Wave Trains Inside and Outside CME Bubbles Detected by SDO/AIA Authors: Liu, Wei; Ofman, L.; Downs, C.; Title, A. M. Bibcode: 2013SPD....44...50L Altcode: Quasi-periodic fast-mode magnetosonic wave trains both inside and outside expanding CME bubbles have recently been discovered by SDO/AIA (Liu et al. 2011, 2012; Shen & Liu 2012). In general, a wave train inside a CME bubble originates from a flare site and propagates along a funnel of coronal loops at typically 1000-2000 km/s (Ofman et al. 2011). A wave train outside a CME usually originates from a CME flank and propagates in the low corona along the solar surface following the leading front of a global EUV wave at typically 500-1000 km/s. The former is primarily seen in the cooler 171 Angstrom channel with a characteristic temperature of 0.8 MK, while the latter is pronounced in the hotter 193 and 211 Angstrom channels of typically 1.6-2.0 MK. What is the relationship between the two types of wave trains? Why do they appear differently in location and wavelength (temperature)? To answer these questions, we report here for the first time the evidence that the wave train beyond the CME bubble is the continuation of the same wave train along the funnel within the CME. The continuous deceleration of the waves is consistent with the expected decrease of the local fast-mode speed with distance from the active region (e.g., Ofman et al. 2011; Downs et al. 2012). There is an abrupt change of the wave speed at the topological interface where the expanding CME flank is located, indicative of contrasting magnetic and plasma conditions, which can give rise to different (fast-mode) speeds and wavelength (temperature) dependent appearances of these wave trains.Abstract (2,250 Maximum Characters): Quasi-periodic fast-mode magnetosonic wave trains both inside and outside expanding CME bubbles have recently been discovered by SDO/AIA (Liu et al. 2011, 2012; Shen & Liu 2012). In general, a wave train inside a CME bubble originates from a flare site and propagates along a funnel of coronal loops at typically 1000-2000 km/s (Ofman et al. 2011). A wave train outside a CME usually originates from a CME flank and propagates in the low corona along the solar surface following the leading front of a global EUV wave at typically 500-1000 km/s. The former is primarily seen in the cooler 171 Angstrom channel with a characteristic temperature of 0.8 MK, while the latter is pronounced in the hotter 193 and 211 Angstrom channels of typically 1.6-2.0 MK. What is the relationship between the two types of wave trains? Why do they appear differently in location and wavelength (temperature)? To answer these questions, we report here for the first time the evidence that the wave train beyond the CME bubble is the continuation of the same wave train along the funnel within the CME. The continuous deceleration of the waves is consistent with the expected decrease of the local fast-mode speed with distance from the active region (e.g., Ofman et al. 2011; Downs et al. 2012). There is an abrupt change of the wave speed at the topological interface where the expanding CME flank is located, indicative of contrasting magnetic and plasma conditions, which can give rise to different (fast-mode) speeds and wavelength (temperature) dependent appearances of these wave trains. Title: Modeling coronal loop oscillations in realistic magnetic and density structures Authors: Ofman, Leon; Wang, T.; Malanushenko, A.; Davila, J. M. Bibcode: 2013SPD....4410404O Altcode: Recently, ubiquitous coronal loop oscillations were detected in active region loops by SDO/AIA. Hinode/EIS observations indicate that quasi-periodic flows are present at footpoints of loops in active regions, and related propagating disturbances (PD's) were detected in open and closed loop structures. Recent 3D MHD models in idealized (bipolar) active regions (Ofman et al. 2012; Wang et al. 2013, this meeting) have demonstrated that the flows can produce slow magnetosonic waves in loops, as well as transverse oscillations. We extend the idealized studies by considering more realistic magnetic field structures modeled by including photospheric magnetic field extrapolated to the corona as boundary and initial conditions for the 3D MHD modeling. We use potential and nonlinear magnetic field extrapolations combined with gravitationally stratified density and introduce flows at the corona-transition region boundary in our 3D MHD model. We apply coronal seismology to the resulting loop oscillations and compare to oscillation events detected by SDO/AIA. We aim to improve the accuracy of coronal seismology by modeling coronal loop oscillations in realistic magnetic geometry and density structures. Title: Three-Dimensional MHD Modeling of Propagating Disturbances in Fanlike AR Coronal Loops Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M. Bibcode: 2013SPD....44...36W Altcode: Quasi-periodic propagating intensity disturbances (PDs) have been observed in cool (about 1 MK) coronal loops in EUV images over a decade. They are widely accepted to be slow magnetosonic waves since their propagation velocity is close to the coronal sound speed. However, recent spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. Motivated by the scenario that the observed persistent upflows could be cumulative result of numerous individual flow pulses generated by sporadic heating events (nanoflares) at the loop base, we constructed a broadband velocity driver with repetative tiny pulses, whose energy frequency distribution follows the flare power-law scaling distribution. We then performed 3D MHD modeling of an idealized bipolar active region by applying this broadband velocity driver at the footpoints of coronal loops which appear open in the computational domain. Our model successfully reproduced the propagating disturbances with similar features as the observed. We find, based on our simulations, that upflow pulses unavoidably excites a slow magnetosonic wave fronts propagating along the loop with the phase speed which is much larger than the local flow speed as the flow velocity decreases with height. Our modeling results support that the observed PDs are mainly the signature of waves above the footpoints of the loops, and suggest that the observed PDs and associated persistent upflows may be driven by the same mechanism such as impulsive heating at the loop base. Title: Slow mode waves and quasi-periodic upflows in the multi-temperature solar corona as seen by the SDO Authors: Uritsky, Vadim; Davila, J. M.; Viall, N.; Ofman, L. Bibcode: 2013SPD....4410405U Altcode: We report results the analysis of coronal fan loops in a non-flaring solar active region exhibiting temperature-dependent propagating optical disturbances. A 6-hour set of high resolution coronal observations provided by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) has been used for characterizing apparent propagating patterns at multiple coronal temperatures (131A, 171A, 193A and 211A). A new data analysis methodology has been developed enabling an identification of subvisual motions with low signal-to-noise ratios not previously examined in this context. The technique involves spatiotemporal tracking of fan loop filaments containing propagating disturbances, construction of position - time plots for different temperature channels, obtaining the waveforms of the propagating optical features, and evaluation of Fourier spectral power of the waveforms as a function of phase speed and frequency. Using this methodology, we identified the parameters of propagating optical disturbances in different magnetic geometries, and classified these events as waves and/or plasma jets. We explored coronal conditions favoring wave-like and jet-like traveling plasma density enhancements in fan loops and the mechanisms of their generation, damping and interaction. The results obtained are compared with the behavior of a resistive MHD model exhibiting both types of propagating disturbances. Title: Brightenings Caused by Falling Filament Material in the 2011 June 7 Event Authors: Gilbert, Holly; Inglis, A.; Ofman, L.; Mays, L. M.; Thompson, B. J.; Young, A. Bibcode: 2013SPD....44...30G Altcode: Solar filaments exhibit a range of eruptive-like dynamic activity from the full, or partial, eruption of the filament mass and surrounding magnetic structure, as a CME, to a fully confined dynamic evolution or ‘failed’ eruption. On 2011 June 7, a dramatic partial eruption of a filament was observed by multiple instruments and SDO and STEREO. One of the interesting aspects of this partial eruption was the response of the surface as non-erupting material fell back under the influence of gravity. The impact sites show clear evidence of brightening in the observed EUV wavelengths due to energy release by the impact. There are two plausible physical mechanisms of the brightening: heating of the plasma due to the kinetic energy of the impacting material - compression of the plasma, or reconnection between the magnetic field of the low-laying loops with the field carried by the impacting material, or combination thereof. By analyzing the emission of the brightenings in several SDO/AIA wavelength, and comparing the kinetic energy of the impacting material (with true velocity determined from triangulation of the two STEREO spacecraft) to the radiative energy we provide clues for the dominant mechanism of energy release involved in the observed brightenings. Title: The effect of broad-band Alfvén-cyclotron waves spectra on the preferential heating and differential acceleration of He++ ions in the solar wind Authors: Maneva, Y. G.; Ofman, L.; Viñas, A. F. Bibcode: 2013AIPC.1539...34M Altcode: In anticipation of results from inner heliospheric missions such as the Solar Orbiter and the Solar Probe we present the results from 1.5D hybrid simulations to study the role of magnetic fluctuations for the heating and differential acceleration of He++ ions in the solar wind. We consider the effects of nonlinear Alfvén-cyclotron waves at different frequency regimes. Monochromatic nonlinear Alfvén-alpha-cyclotron waves are known to preferentially heat and accelerate He++ ions in collisionless low beta plasma. In this study we demonstrate that these effects are preserved when higherfrequency monochromatic and broad-band spectra of Alfvén-proton-cyclotron waves are considered. Comparison between several nonlinear monochromatic waves shows that the ion temperatures, anisotropies and relative drift are quantitatively affected by the shift in frequency. Including a broad-band wave-spectrum results in a significant reduction of both the parallel and the perpendicular temperature components for the He++ ions, whereas the proton heating is barely influenced, with the parallel proton temperature only slightly enhanced. The differential streaming is strongly affected by the available wave power in the resonant daughter ion-acoustic waves. Therefore for the same initial wave energy, the relative drift is significantly reduced in the case of initial wave-spectra in comparison to the simulations with monochromatic waves. Title: Global Coronal Seismology in the Extended Solar Corona through Fast Magnetosonic Waves Observed by STEREO SECCHI COR1 Authors: Kwon, Ryun Young; Zhang, Jie; Kramar, Maxim; Wang, Tongjiang; Ofman, Leon; Davila, Joseph M. Bibcode: 2013shin.confE..75K Altcode: We present global coronal seismology, for the first time, that allows us to determine inhomogeneous magnetic field strengths in a wide range of the extended solar corona. We use observations of a fast magnetosonic wave associated with a coronal mass ejection observed on 2011 August 4 by the COR1 inner coronagraphs on board the STEREO spacecraft. In order to estimate inhomogeneous magnetic field strength, we choose the azimuthal trajectories of the wave front at heliocentric distances 2.0, 2.5, and 3.0 solar radii and determine the speeds of the wave front and electron densities using polarized brightness images along the trajectories. The magnetic field strengths are derived with an uncertainty less than 40 % and consistent with values determined with a potential field source surface model and reported in previous works. The characteristics of the coronal medium revealed with our global coronal seismology are that: (1) density, magnetic field strength, plasma beta are lower in the coronal hole than in the streamers, (2) magnetic field strength decreases slowly with height but electron density decreases rapidly so that local fast magnetosonic speed increases while plasma beta falls off with height, and (3) the variations of local fast magnetosonic speed and plasma beta are in accordance with the electron density rather than magnetic field strength. These characteristics of the coronal medium imply that Moreton and EIT waves are downward shock fronts of fast magnetosonic waves refracted from the upper solar corona, rather than freely propagating fast magnetosonic waves in a certain solar atmospheric layer. In addition, the azimuthal components of CMEs may play an important role in various manifestations of shocks, such as type II radio bursts and solar energetic particle events. Title: Turbulent heating and acceleration of He++ ions by spectra of Alfvén-cyclotron waves in the expanding solar wind: 1.5-D hybrid simulations Authors: Maneva, Y. G.; ViñAs, A. F.; Ofman, L. Bibcode: 2013JGRA..118.2842M Altcode: Both remote sensing and in situ measurements show that the fast solar wind plasma significantly deviates from thermal equilibrium and is strongly permeated by turbulent electromagnetic waves, which regulate the ion temperature anisotropies and relative drifts. Thus, the ion kinetics is governed by heating and cooling related to absorption and emission of ion-acoustic and ion-cyclotron waves, as well as nonresonant pitch angle scattering and diffusion in phase space. Additionally, the solar wind properties are affected by its nonadiabatic expansion as the wind travels away from the Sun. In this study we present results from 1.5-D hybrid simulations to investigate the effects of a nonlinear turbulent spectrum of Alfvén-cyclotron waves and the solar wind expansion on the anisotropic heating and differential acceleration of protons and He++ ions. We compare the different heating and acceleration by turbulent Alfvén-cyclotron wave spectra and by pure monochromatic waves. For the waves and the wave spectra used in our model, we find that the He++ ions are preferentially heated and by the end of the simulations acquire much more than mass-proportional temperature ratios, Tα/Tp>mα/mp. The differential acceleration between the two species strongly depends on the initial wave amplitude and the related spectral index and is often suppressed by the solar wind expansion. We also find that the expansion leads to perpendicular cooling for both species, and depending on the initial wave spectra, it can either heat or cool the ions in parallel direction. Despite the cooling effect of the expansion in perpendicular direction, the wave-particle interactions provide an additional heating source, and the perpendicular temperature components remain higher than the adiabatic predictions. Title: Brightenings Caused by Falling Filament Material in the 2011 June 7 Event Authors: Gilbert, Holly; Inglis, Andrew; Mays, Leila; Ofman, Leon; Thompson, Barbara; Young, Alex Bibcode: 2013shin.confE..74G Altcode: Solar filaments exhibit a range of eruptive-like dynamic activity, ranging from the full or partial eruption of the filament mass and surrounding magnetic structure as a coronal mass ejection (CME), to a fully confined dynamic evolution or 'failed' eruption. On 2011 June 7, a dramatic partial eruption of a filament was observed by multiple instruments on SDO and STEREO. One of the interesting aspects of this partial eruption is the response of the solar atmosphere as non-escaping material falls inward under the influence of gravity. The impact sites show clear evidence of brightening in the observed EUV wavelengths due to energy release. Two plausible physical mechanisms explaining the brightening are considered: heating of the plasma due to the kinetic energy of impacting material compressing the plasma, or reconnection between the magnetic field of the low-lying loops and the field carried by the impacting material. By analyzing the emission of the brightenings in several SDO/AIA wavelengths, and comparing the kinetic energy of the impacting material ((2.12-60.4) - 10^26 ergs) to the radiative energy ( 10^25 ergs) we find the dominant mechanism of energy release involved in the observed brightening is plasma compression. Title: Two-dimensional hybrid simulations of quasi-perpendicular collisionless shock dynamics: Gyrating downstream ion distributions Authors: Ofman, L.; Gedalin, M. Bibcode: 2013JGRA..118.1828O Altcode: collisionless shocks undergo structural changes with the increase of the Mach number. These changes are related to the increasing role of the reflected ions, which have a highly nongyrotropic distribution. Eventually, it is expected that the shock front becomes nonstationary. At low and moderate Mach numbers, the fraction of reflected ions is small, yet recent observations show the existence of a well-pronounced structure of the postshock magnetic field in the close vicinity of the transition layer. Large amplitude oscillations were earlier interpreted as waves generated by the shock front or passing through the shock in the downstream direction. Here we show, using two-dimensional hybrid simulations of quasi-perpendicular shocks, that the gyration of the directly transmitted ions downstream of the ramp produces the spatial pressure variations, which are accompanied with the observed magnetic oscillations due to the momentum conservation. In a wide range of the upstream ion temperatures, the low and moderate-Mach-number shocks remain stationary and one-dimensional, so that the magnetic and electric field depend only on the coordinate along the shock normal. The downstream ion distributions gradually gyrotropize due to the collisionless mixing of gyrophases. Nonstationary effects in these shocks do not affect noticeably the ion dynamics. However, we find that with the increase of the Mach number, shocks form rippled fronts in the low-β and moderate-β regimes. Title: Stochastic Coupling of Solar Photosphere and Corona Authors: Uritsky, Vadim M.; Davila, Joseph M.; Ofman, Leon; Coyner, Aaron J. Bibcode: 2013ApJ...769...62U Altcode: 2012arXiv1212.5610U The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvénic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor. Title: Observations and models of the slow solar wind in coronal streamers during solar minimum Authors: Ofman, L. Bibcode: 2013AGUSMSH31B..05O Altcode: A quiescent dipolar streamer belt often dominated the coronal streamer structures during past solar minima. Past UV observations with SOHO/UVCS show that the intensity of heavy ion emission lines (such as O VI and Mg X) is dimmer at the cores than at the streamer edges. Three-fluid 2.5D models indicated that the observed emission variability is the signature of slow solar wind outflow regions, where Coulomb coupling between the electron, protons, and heavy ions leads to enhanced emission of heavy ions at the edges of streamers. Recently, Ofman et al (2011, 2012) have modeled in detail the three-fluid interactions and the emission in a quiescent streamer due to Ly α, O 5+, and Mg 9+ ions at solar minimum, and used the model results to synthesize the corresponding line emissions. They found that the model results are in good agreement with observations, provided that the heavy ions experience preferential heating compared to protons. Similar results were found to hold for He++ ions in quiescent streamers. Recently, the 2.5D three-fluid model was extended to full 3D, allowing modeling the ion abundance variations in tilted dipole streamer belt, and eventually in solar maximum streamers. I will discuss the implication of heavy ion emission structure in streamers and the corresponding three-fluid models on the understanding of the slow solar wind sources. Title: Global oscillations and small scale dynamics of a filament Authors: Tian, Hui; Ofman, Leon; Wang, Tongjiang Bibcode: 2013enss.confE.104T Altcode: Using AIA data, we observed global oscillatory motions along the axis of a filament with detailed small scale dynamics. The global oscillation lasted for more than two days before the eruption of the filament. Both magnetic tension and gravity are likely to be involved in the global oscillation, as predicted by theoretical models. A closer look of the detailed dynamics within the filament suggests that torsional motions around the prominence axis are also present. Torsional motions around the two legs of the filament resemble the so-called "solar tornadoes" observed at limb by AIA. Variable counter-streaming flows in the prominence body were detected as well before the filament eruption. The HMI magnetic field data and multi-line diagnostics are used to investigate possible mechanisms responsible for the different types of oscillations and flows before the eventual eruption of the filament. Title: Vertical kink oscillations of coronal loops triggered by recurrent jets Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M. Bibcode: 2013enss.confE..99W Altcode: Transverse coronal loop oscillations were first observed by TRACE in EUV images, and have been interpreted as global standing kink modes. These loop oscillations are thought to be excited by a blast wave in the form of a shock or a fast-mode wave produced by a flare or CME. In this presentation, we report simultaneous imaging and spectroscopic observations with SDO/AIA and Hinode/EIS of a vertical loop oscillations triggered by recurrent jets at the footpoints. These oscillations start with a fast disturbance traveling along the loop with the propagating speed more than 500 km/s, much faster than the apparent EUV jets. The vertical loop oscillations are associated with quasi-periodic outwardly propagating features with the speeds 30-300 km/s, suggestive of loop expansions. In addition, we perform 3D MHD modeling of a typical such event to understand the excitation of kink oscillations by impulsive flows. Title: Recent Advances in Observations of Coronal EUV Waves Authors: Liu, Wei; Ofman, Leon; Aschwanden, Markus J.; Nitta, Nariaki; Zhao, Junwei; Title, Alan M. Bibcode: 2013enss.confE..67L Altcode: MHD waves can be used as seismological tools to decipher otherwise elusive physical parameters of the solar corona, such as the magnetic field strength and plasma density. Recent high cadence, high resolution, full-disk imaging observations from SDO/AIA have opened a new chapter in understanding these waves. Various types of EUV waves associated with flares/CMEs have been discovered or observed in unprecedented detail. In this talk, we will review such new observations, focusing on the following topics and their interrelationships: (1) quasi-periodic fast waves traveling along coronal funnels within CME bubbles at speeds up to 2000 km/s, associated with flare pulsations at similar frequencies; (2) quasi-periodic wave trains within broad, diffuse pulses of global EUV waves (so-called "EIT waves") running ahead of CME fronts; (3) interactions of global EUV waves with local coronal structures on their paths, such as flux-rope coronal cavities and their embedded filaments (kink oscillations) and coronal holes or active regions (deflections). We will discuss the implications of these observations on coronal seismology, on their roles in transporting energy through different parts of the solar atmosphere, and on understanding their associated eruptive flares/CMEs. Title: STEREO Observations of Fast Magnetosonic Waves in the Extended Solar Corona Associated with EIT/EUV Waves Authors: Kwon, Ryun-Young; Ofman, Leon; Olmedo, Oscar; Kramar, Maxim; Davila, Joseph M.; Thompson, Barbara J.; Cho, Kyung-Suk Bibcode: 2013ApJ...766...55K Altcode: We report white-light observations of a fast magnetosonic wave associated with a coronal mass ejection observed by STEREO/SECCHI/COR1 inner coronagraphs on 2011 August 4. The wave front is observed in the form of density compression passing through various coronal regions such as quiet/active corona, coronal holes, and streamers. Together with measured electron densities determined with STEREO COR1 and Extreme UltraViolet Imager (EUVI) data, we use our kinematic measurements of the wave front to calculate coronal magnetic fields and find that the measured speeds are consistent with characteristic fast magnetosonic speeds in the corona. In addition, the wave front turns out to be the upper coronal counterpart of the EIT wave observed by STEREO EUVI traveling against the solar coronal disk; moreover, stationary fronts of the EIT wave are found to be located at the footpoints of deflected streamers and boundaries of coronal holes, after the wave front in the upper solar corona passes through open magnetic field lines in the streamers. Our findings suggest that the observed EIT wave should be in fact a fast magnetosonic shock/wave traveling in the inhomogeneous solar corona, as part of the fast magnetosonic wave propagating in the extended solar corona. Title: New frontiers in wave studies and coronal seismology Authors: Ofman, Leon Bibcode: 2013enss.confE..72O Altcode: The launch of the SDO and the unprecedented high resolution, high cadence observations with AIA provide new details on wave activity in the solar corona. These observations, supplemented by spectroscopic data from Hinode/EIS, theory, and numerical modeling open new frontiers in wave studies and in coronal seismology - the use of waves for the determination of the physical parameters (such as the magnetic field and density) in the corona. The idealized theoretical wave studies were recently expanded by sophisticated there-dimensional MHD models that include additional phenomena, such as more realistic coronal loop magnetic and density structure, broad band waves, and quasi-periodic flows, enabling further expansion of coronal seismology as a tool for coronal plasma diagnostics. I will review the recent progress in observational and theoretical studied of waves and the development of coronal seismology. Title: Coronal and Solar Wind Ion heating by dispersive Alfven waves - 2.5D hybrid simulations Authors: Maneva, Y.; Ofman, L.; Vinas, A. Bibcode: 2013enss.confE..65M Altcode: We perform 2.5D hybrid simulations to model the preferential heating and differential acceleration of minor ions as observed by remote sensing in coronal holes and measured in situ in the fast solar wind at various heliospheric distances. We consider a low-beta plasma consisting of fluid electrons, particle-in-cell protons and He++ ions and different spectra of parallel propagating Alfven-cyclotron waves as initial energy source for the ion heating and acceleration. For fixed low wave-numbers the generated wave spectrum generally shifts towards higher frequencies in multi-species plasma. This effect is further enhanced when differential streaming is present due to the expected preferential acceleration of heavy ions in coronal holes. We use the results from the cold plasma linear theory to initialize the nonlinear 2.5D hybrid simulations and compare the resulting ion heating, temperature anisotropies and differential streaming when the initial wave spectra belongs to the alpha-cyclotron and the proton-cyclotron dispersion branches, with and without initial relative drifts, and study the nonlinear 2D effects, extending our previous 1D hybrid studies. Finally, we investigate the effect of a gradual solar wind expansion, consider its influence on the wave-particle interactions and discuss its implications for non-adiabatic perpendicular cooling for both ion species. Title: Observations and Models of Slow Solar Wind with Mg9 + Ions in Quiescent Streamers Authors: Ofman, L.; Abbo, L.; Giordano, S. Bibcode: 2013ApJ...762...18O Altcode: 2012arXiv1211.1524O Quiescent streamers are characterized by a peculiar UV signature as pointed out by the results from the observations of the Ultraviolet and Coronograph Spectrometer (UVCS) on board SOHO: the intensity of heavy-ion emission lines (such as O VI) shows dimmer core relative to the edges. Previous models show that the structure of the heavy-ion streamer emission relates to the acceleration regions of the slow solar wind at streamer legs and to gravitational settling processes in the streamer core. Observations of Mg9 + ion EUV emission in coronal streamers at solar minimum were first reported by the UVCS instrument. The Mg X 625 Å emission is an order of magnitude smaller than the O VI 1032 Å emission, requiring longer exposures to obtain statistically significant results. Here, Mg X coronal observations are analyzed and compared, for the first time, with the solar minimum streamer structure in hydrogen and O VI emissions. We employ the 2.5D three-fluid model, developed previously to study the properties of O5 + ions in streamers, and calculate for the first time the density, temperature, and outflow structure of Mg9 + ions in the solar minimum streamer. The Mg9 + ions are heated by an empirical radial heating function constrained by observations of the kinetic ion temperature obtained from Mg X emission line profiles. The detailed structure of Mg9 + density, temperature, and outflow speed is determined by the Coulomb momentum and energy exchange as well as electromagnetic interactions with electrons and protons in the three-fluid model of the streamer. The results of the model are in good qualitative agreement with observations, and provide insights on the possible link between the magnetic structure of the streamer, slow solar wind sources, and relative abundances of heavy ions. Title: Ion heating and acceleration by Alfvén-cyclotron and kinetic Alfvén waves - 2.5D hybrid simulations Authors: Maneva, Y. G.; Ofman, L.; Vinas, A. Bibcode: 2012AGUFMSH51B2251M Altcode: We perform 2.5D hybrid simulations to investigate the anisotropic preferential heating and differential acceleration of heavy ions in the collisionless fast solar wind. We consider low plasma β conditions in the extended solar corona to study the turbulent ion heating and differential acceleration of He++ ions by initial wave-spectra of parallel finite amplitude Alfvén-cyclotron waves and investigate their anisotropic cascade and energy transfer towards perpendicular wave numbers. We investigate the generation of oblique modes and compare the differential streaming, the ion heating and acceleration rates, when the initial wave-spectra consists of kinetic Alfvén waves and when initially parallel, and oblique Alfvén-cyclotron wave are considered. The results are applied to better understanding the anisotropic turbulent cascade in the solar wind, the origin of ion differential streaming and the regulation of ion temperature anisotropies via plasma micro-instabilities and wave-particle interactions. Title: Two-dimensional hybrid models of ion dynamics in collisionless quasi-perpendicular shocks Authors: Gedalin, M.; Ofman, L. Bibcode: 2012AGUFMSH32B..06G Altcode: Spacecraft observations show that collisionless shocks are ubiquitous in the heliosphere from CME shock fronts to the heliospheric termination shock with broad range of Mach numbers. Evidently, quasi-perpendicular collisionless shocks undergo structural changes with the increase of the Mach number. These changes are related to the increasing role of the reflected ions, which have a highly non-gyrotropic distribution. Eventually, it is expected that the shock front becomes non-stationary and rippled. At low and moderate Mach numbers the fraction of reflected ions is small, yet recent observations show existence of a well-pronounced structure of the post-shock magnetic field in the close vicinity of the transition layer. Here we show, using 2D hybrid simulations, that the gyration of the directly transmitted ions downstream of the ramp produces spatial pressure variations, accompanied with the observed magnetic oscillations due to the momentum conservation. In a wide range of the upstream ion temperatures the low and moderate Mach number shocks remain stationary and one-dimensional (on smaller scale than the variation of the global magnetic field), so that the magnetic and electric field depend only on the coordinate along the shock normal. The downstream ion distributions gradually gyrotropize due to the collisionless mixing of gyrophases of the ion velocity distributions. Non-stationary effects in these shocks do not affect noticeably the ion dynamics. However, we find that with the increase of the Mach number rippled fronts are formed in the low-beta and moderate-beta regimes. Title: Three-fluid model of the slow solar wind with Mg9+ ions in quiescent steamers and comparison to observations Authors: Ofman, L.; Abbo, L.; Giordano, S. Bibcode: 2012AGUFMSH53A2256O Altcode: Quiescent streamers are characterized by a peculiar UV signature as pointed out by the results from the observations of the Ultraviolet and Coronograph Spectrometer (UVCS) on board SOHO: the intensity of heavy ion emission lines (such as OVI and Mg X) show dimmer core relative to the edges. Previous models have shown that the structure of the heavy ion streamer emission relates to the acceleration regions of the slow solar wind in open field regions and to gravitational settling processes in the streamers close field core. The UVCS instrument first produced observations of Mg X 625 A emission in coronal streamers at solar minimum, which is an order of magnitude smaller than the O VI 1032A emission, requiring longer exposures for statistically significant results. We analyze and compare coronal Mg X observations for the first time with the solar minimum streamer structure in hydrogen and O VI emissions. We employ the 2.5D three-fluid model, developed previously to study the properties of O VI emission streamers, and calculate for the first time the density, temperature, and outflow structure of preferentially heated Mg 9+ ions in the solar minimum streamer. The structure of empirically heated Mg9+ ion density, temperature, and outflow speed in the streamer are determined by the Coulomb momentum and energy exchange as well as electromagnetic interactions with electrons and protons in the three-fluid model. The results of the model are in good qualitative agreement with observations, and provide insights on the possible link between the magnetic structure of the streamer, slow solar wind sources, and relative abundance variation of heavy ions. Title: Erratum: "SDO/AIA Observation of Kelvin-Helmholtz Instability in the Solar Corona" (2011, ApJ, 734, L11) Authors: Ofman, L.; Thompson, B. J. Bibcode: 2012ApJ...760L..19O Altcode: No abstract at ADS Title: Persistent Doppler Shift Oscillations Observed with Hinode/EIS in the Solar Corona: Spectroscopic Signatures of Alfvénic Waves and Recurring Upflows Authors: Tian, Hui; McIntosh, Scott W.; Wang, Tongjiang; Ofman, Leon; De Pontieu, Bart; Innes, Davina E.; Peter, Hardi Bibcode: 2012ApJ...759..144T Altcode: 2012arXiv1209.5286T Using data obtained by the EUV Imaging Spectrometer on board Hinode, we have performed a survey of obvious and persistent (without significant damping) Doppler shift oscillations in the corona. We have found mainly two types of oscillations from February to April in 2007. One type is found at loop footpoint regions, with a dominant period around 10 minutes. They are characterized by coherent behavior of all line parameters (line intensity, Doppler shift, line width, and profile asymmetry), and apparent blueshift and blueward asymmetry throughout almost the entire duration. Such oscillations are likely to be signatures of quasi-periodic upflows (small-scale jets, or coronal counterpart of type-II spicules), which may play an important role in the supply of mass and energy to the hot corona. The other type of oscillation is usually associated with the upper part of loops. They are most clearly seen in the Doppler shift of coronal lines with formation temperatures between one and two million degrees. The global wavelets of these oscillations usually peak sharply around a period in the range of three to six minutes. No obvious profile asymmetry is found and the variation of the line width is typically very small. The intensity variation is often less than 2%. These oscillations are more likely to be signatures of kink/Alfvén waves rather than flows. In a few cases, there seems to be a π/2 phase shift between the intensity and Doppler shift oscillations, which may suggest the presence of slow-mode standing waves according to wave theories. However, we demonstrate that such a phase shift could also be produced by loops moving into and out of a spatial pixel as a result of Alfvénic oscillations. In this scenario, the intensity oscillations associated with Alfvénic waves are caused by loop displacement rather than density change. These coronal waves may be used to investigate properties of the coronal plasma and magnetic field. Title: Hybrid simulation of the shock wave formation behind the Moon Authors: Israelevich, P.; Ofman, L. Bibcode: 2012epsc.conf...39I Altcode: 2012espc.conf...39I A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Wellknown effects as electric charging of the cavity affecting the plasma flow and counter streaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. Simulations with lower electron temperatures (Te~20eV) show weakened shock formation behind the moon at much greater distances. The shock disappears for typical solar wind conditions (Ti ~ Te) Therefore, in order to observe the trailing shock, a satellite should have a trajectory passing very close to the wake axis during the period of hot solar wind streams. We expect the shock to be produced at periods of high electron temperature solar wind streams (Ti<<Te~100eV). The appearance of the standing shock wave is expected at the distance of ~ 7RM downstream of the Moon. Title: Hybrid simulation of the shock wave trailing the Moon Authors: Israelevich, P.; Ofman, L. Bibcode: 2012JGRA..117.8223I Altcode: 2012JGRA..11708223I A standing shock wave behind the Moon was predicted by Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Well-known effects as electric charging of the cavity affecting the plasma flow and counterstreaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. We expect the shock to be produced at periods of high electron temperature solar wind streams (Ti ≪ Te ∼ 100 eV). The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of the magnetic barrier. The appearance of the standing shock wave is expected at the distance of ∼7RM downstream of the Moon. Title: Slow Magnetosonic Waves and Fast Flows in Active Region Loops Authors: Ofman, L.; Wang, T. J.; Davila, J. M. Bibcode: 2012ApJ...754..111O Altcode: 2012arXiv1205.5732O Recent extreme ultraviolet spectroscopic observations indicate that slow magnetosonic waves are present in active region (AR) loops. Some of the spectral data were also interpreted as evidence of fast (~100-300 km s-1) quasi-periodic flows. We have performed three-dimensional magnetohydrodynamic (3D MHD) modeling of a bipolar AR that contains impulsively generated waves and flows in coronal loops. The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with an upflow-driven steadily or periodically in localized regions at the footpoints of magnetic loops. The resulting flows along the magnetic field lines of the AR produce higher density loops compared to the surrounding plasma by injection of material into the flux tubes and the establishment of siphon flow. We find that the impulsive onset of flows with subsonic speeds result in the excitation of damped slow magnetosonic waves that propagate along the loops and coupled nonlinearly driven fast-mode waves. The phase speed of the slow magnetosonic waves is close to the coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock-like wave trains are produced. When the upflows are driven periodically, undamped oscillations are produced with periods determined by the periodicity of the upflows. Based on the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and persistent upflows may be produced by the same impulsive events at the bases of ARs. Title: Quasi-periodic Fast-mode Wave Trains within a Global EUV Wave and Sequential Transverse Oscillations Detected by SDO/AIA Authors: Liu, Wei; Ofman, Leon; Nitta, Nariaki V.; Aschwanden, Markus J.; Schrijver, Carolus J.; Title, Alan M.; Tarbell, Theodore D. Bibcode: 2012ApJ...753...52L Altcode: 2012arXiv1204.5470L We present the first unambiguous detection of quasi-periodic wave trains within the broad pulse of a global EUV wave (so-called EIT wave) occurring on the limb. These wave trains, running ahead of the lateral coronal mass ejection (CME) front of 2-4 times slower, coherently travel to distances >~ R ⊙/2 along the solar surface, with initial velocities up to 1400 km s-1 decelerating to ~650 km s-1. The rapid expansion of the CME initiated at an elevated height of 110 Mm produces a strong downward and lateral compression, which may play an important role in driving the primary EUV wave and shaping its front forwardly inclined toward the solar surface. The wave trains have a dominant 2 minute periodicity that matches the X-ray flare pulsations, suggesting a causal connection. The arrival of the leading EUV wave front at increasing distances produces an uninterrupted chain sequence of deflections and/or transverse (likely fast kink mode) oscillations of local structures, including a flux-rope coronal cavity and its embedded filament with delayed onsets consistent with the wave travel time at an elevated (by ~50%) velocity within it. This suggests that the EUV wave penetrates through a topological separatrix surface into the cavity, unexpected from CME-caused magnetic reconfiguration. These observations, when taken together, provide compelling evidence of the fast-mode MHD wave nature of the primary (outer) fast component of a global EUV wave, running ahead of the secondary (inner) slow component of CME-caused restructuring. Title: Ion heating by dissipation of nonlinear Alfven-cyclotron waves Authors: Maneva, Yana G.; Ofman, L.; Vinas, A. Bibcode: 2012shin.confE.196M Altcode: We present the results from hybrid simulations to investigate the ion heating and acceleration by dissipation of large-amplitude Alfven-cyclotron waves. We compare the resulting heating and acceleration by a monochromatic wave and a broad band wave spectra and find that for the same total wave energy input the broad band leads to similar heating but to a lower rate for the ion differential acceleration. We investigate the influence of solar wind expansion and show that its effect on the ion kinetics highly depends on the initial wave spectra and the relative drifts. In general the slow expansion considered in the model leads to perpendicular cooling and changes the energy input required for heating of the corona and acceleration of the solar wind. Title: Growing Transverse Oscillations of a Multistranded Loop Observed by SDO/AIA Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Su, Yang Bibcode: 2012ApJ...751L..27W Altcode: 2012arXiv1204.1376W The first evidence of transverse oscillations of a multistranded loop with growing amplitudes and internal coupling observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory is presented. The loop oscillation event occurred on 2011 March 8, triggered by a coronal mass ejection (CME). The multiwavelength analysis reveals the presence of multithermal strands in the oscillating loop, whose dynamic behaviors are temperature-dependent, showing differences in their oscillation amplitudes, phases, and emission evolution. The physical parameters of growing oscillations of two strands in 171 Å are measured and the three-dimensional loop geometry is determined using STEREO-A/EUVI data. These strands have very similar frequencies, and between two 193 Å strands a quarter-period phase delay sets up. These features suggest the coupling between kink oscillations of neighboring strands and the interpretation by the collective kink mode as predicted by some models. However, the temperature dependence of the multistranded loop oscillations was not studied previously and needs further investigation. The transverse loop oscillations are associated with intensity and loop width variations. We suggest that the amplitude-growing kink oscillations may be a result of continuous non-periodic driving by magnetic deformation of the CME, which deposits energy into the loop system at a rate faster than its loss. Title: Slow-Mode Oscillations of Hot Loops Excited at Flaring Footpoints Authors: Wang, T.; Liu, W.; Ofman, L.; Davila, J. Bibcode: 2012ASPC..456..127W Altcode: 2017arXiv170605427W The analysis of a hot loop oscillation event using SOHO/SUMER, GOES SXI, and RHESSI observations is presented. Damped Doppler shift oscillations were detected in the Fe xix line by SUMER, and interpreted as a fundamental standing slow mode. The evolution of soft X-ray emission from GOES/SXI and hard X-ray sources from RHESSI suggests that the oscillations of a large loop are triggered by a small flare, which may be produced by interaction (local reconnection) of this large loop with a small loop at its footpoint. This study provides clear evidence supporting our early conjecture that the slow-mode standing waves in hot coronal loops are excited by impulsive heating (small or microflares) at the loop's footpoint. Title: Propagating Intensity Disturbances in Fan-like Coronal Loops: Flows or Waves? Authors: Wang, T.; Ofman, L.; Davila, J. M. Bibcode: 2012ASPC..455..227W Altcode: 2011arXiv1101.6017W Quasi-periodic intensity disturbances propagating upward along the coronal structure have been extensively studied using EUV imaging observations from SOHO/EIT and TRACE. They were interpreted as either slow mode magnetoacoustic waves or intermittent upflows. In this study we aim at demonstrating that time series of spectroscopic observations are critical to solve this puzzle. Propagating intensity and Doppler shift disturbances in fanlike coronal loops are analyzed in multiple wavelengths using sit-and-stare observations from Hinode/EIS. We find that the disturbances did not cause the blue-wing asymmetry of spectral profiles in the warm (∼1.5 MK) coronal lines. The estimated small line-of-sight velocities also did not support the intermittent upflow interpretation. In the hot (∼2 MK) coronal lines the disturbances did cause the blue-wing asymmetry, but the double fits revealed that a high-velocity minor component is steady and persistent, while the propagating intensity and Doppler shift disturbances are mainly due to variations of the core component, therefore, supporting the slow wave interpretation. However, the cause for blueward line asymmetries remains unclear. Title: SDO/AIA Detection of Quasi-periodic Wave Trains Within Global EUV ("EIT") Waves and Their Coronal Seismology Implications Authors: Liu, Wei; Ofman, L.; Aschwanden, M. J.; Nitta, N.; Schrijver, C. J.; Title, A. M.; Tarbell, T. D. Bibcode: 2012AAS...22051501L Altcode: The nature of global EUV waves (so-called "EIT waves") has long been under debate because of instrumental limitations and projection effects when viewed on the solar disk. We present here high cadence SDO/AIA observations of global EUV waves occurring on the limb. We report newly discovered quasi-periodic wave trains located in the low corona within a broad, diffuse pulse of the global EUV wave ahead of the lateral CME front/flank. These waves coherently travel to large distances on the order of 1 solar radii with initial velocities up to 1400 km/s. They have dominant 1-3 minute periodicities that often match the X-ray pulsations of the accompanying flare, suggestive of a causal connection. In addition, recently discovered quasi-periodic fast propagating (QFP) waves of 1000-2000 km/s (Liu, Title, Zhao et al. 2011 ApJL) are found in the funnel of coronal loops rooted at the flare kernel. These waves are spatially confined within the CME bubble and rapidly disappear while approaching the CME front, suggestive of strong damping and/or dispersion. These observations provide new evidence of the fast-mode wave nature of the primary, fast component of a global EUV wave, running ahead of a secondary, slow component of CME-caused restructuring of the coronal magnetic field. We suggest that the two types of quasi-periodic waves are both integral parts of global coronal dynamics manifested as a CME/flare eruption, and they have important implications for global and local coronal seismology. Title: Stereo Observations Of Fast Magnetosonic Waves In The Extended Corona Authors: Kwon, Ryun Young; Davila, J. M.; Ofman, L. Bibcode: 2012AAS...22052106K Altcode: Here, we present fast magnetosonic waves propagating across solar radial magnetic fields. STEREO COR1 and EUVI observations showed coronal disturbances associated with flares/CMEs and they propagate in the low solar corona in the form of EIT waves and in the high solar corona (above 1.5 Rs) in the form of density compressions along radial magnetic field lines above EIT wave fronts. It turns out that the coronal disturbances pass through streamers which contain a magnetic separatrix. The wave energy appears to be trapped by the streamers and this leads to stationary fronts at the footpoints of the streamers. Our results suggest that the coronal disturbances associated with flares/CMEs are fast magnetosonic waves propagating with local fast magnetosonic speeds and passing through magnetic separatrices. Moreover, we conclude that EIT waves are ‘real’ fast magnetosonic waves. The speeds of the coronal disturbances are 475 ± 14, 926 ± 19, 1217 ± 24, 1734 ± 48, and 1928 ± 42 km/s at 1.0, 1.6, 2.0, 2.5, and 3.0 Rs, respectively. Using coronal seismology, we estimated magnetic field strengths corresponding to these speeds at the heights and they are 1.81 ± 0.06, 0.98 ± 0.02, 0.70 ± 0.01, 0.55 ± 0.02, and 0.39 ± 0.01 G, respectively. Title: Growing Transverse Oscillations of a Multistranded Loop Observed by SDO/AIA Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M.; Su, Y. Bibcode: 2012AAS...22020717W Altcode: The flare-excited transverse loop oscillations previously observed by TRACE have been mainly interpreted as the global fast kink modes. These oscillations typically have a rapid decay, and their damping mechanism has been a major topic of theoretical studies. In this presentation, we report an unusual case of transverse loop oscillations with growing amplitudes observed by SDO/AIA for the first time. This oscillation event was triggered by a flare associated with a CME above the limb. The multiwavelength analysis reveals that the loop consists of multithermal strands and their dynamical behaviors are temperature-dependent. These strands have very similar oscillation frequencies and appear to oscillate in-phase or in a quarter-period phase delay. These features suggest the coupling between kink oscillations of neighboring strands and the interpretation by the collective kink mode as predicted by some models. The transverse loop oscillations are also associated with intensity and loop width variations. We determine the trigger of the oscillation and measure the 3-D loop geometry using STEREO/EUVI-A data. The possible mechanisms that can excite the growing kink oscillations will be discussed. Title: Impulsively Driven Waves And Flows In Coronal Active Regions Authors: Ofman, Leon; Wang, T.; Davila, J. M.; Liu, W. Bibcode: 2012AAS...22032204O Altcode: Recent SDO/AIA and Hinode EIS observations indicate that both (super) fast and slow magnetosonic waves are present in active region (AR) magnetic structures. Evidence for fast (100-300 km/s) impulsive flows is found in spectroscopic and imaging observations of AR loops. The super-fast waves were observed in magnetic funnels of ARs. The observations suggest that waves and flow are produced by impulsive events, such as (micro) flares. We have performed three-dimensional magnetohydrodynamic (3D MHD) simulations of impulsively generated flows and waves in coronal loops of a model bi-polar active region (AR). The model AR is initiated with a dipole magnetic field and gravitationally stratified density, with impulsively driven flow at the coronal base of the AR in localized magnetic field structures. We model the excitation of the flows in hot (6MK) and cold (1MK) active region plasma, and find slow and fast magnetosonic waves produced by these events. We also find that high-density (compared to surrounding corona) loops are produced as a result of the upflows. We investigate the parametric dependence between the properties of the impulsive flows and the waves. The results of the 3D MHD modeling study supports the conjecture that slow magnetosonic waves are often produced by impulsive upflows along the magnetic field, and fast magnetosonic waves can result from impulsive transverse field line perturbations associated with reconnection events. The waves and flows can be used for diagnostic of AR structure and dynamics. Title: Spectroscopic Diagnosis of Propagating Disturbances in Coronal Loops: Waves or flows? Authors: Wang, T.; Ofman, L.; Davila, J. M. Bibcode: 2012ASPC..456...91W Altcode: The analysis of multiwavelength properties of propagating disturbances (PDs) using Hinode/EIS observations is presented. Quasi-periodic PDs were mostly interpreted as slow magnetoacoustic waves in early studies, but recently suggested to be intermittent upflows of the order of 50-150 km s-1 based on the Red-Blue (RB) asymmetry analysis of spectral line profiles. Using the forward models, velocities of the secondary component derived from the RB analysis are found significantly overestimated due to the saturation effect when its offset velocities are smaller than the Gaussian width. We developed a different method to examine spectral features of the PDs. This method is assuming that the excessive emission of the PD profile against the background (taken as that prior to the PD) is caused by a hypothetic upflow. The derived LOS velocities of the flow are on the order of 10-30 km s-1 from the warm (1-1.5 MK) coronal lines, much smaller than those inferred from the RB analysis. This result does not support the flow interpretation but favors of the early wave interpretation. Title: Hybrid simulation of the shock wave trailing the Moon Authors: Israelevich, P.; Ofman, L. Bibcode: 2012EGUGA..14.2121I Altcode: Standing shock wave behind the Moon was predicted be Michel (1967) but never observed nor simulated. We use 1D hybrid code in order to simulate the collapse of the plasma-free cavity behind the Moon and for the first time to model the formation of this shock. Starting immediately downstream of the obstacle we consider the evolution of plasma expansion into the cavity in the frame of reference moving along with the solar wind. Well-known effects as electric charging of the cavity affecting the plasma flow and counter streaming ion beams in the wake are reproduced. Near the apex of the inner Mach cone where the plasma flows from the opposite sides of the obstacle meet, a shock wave arises. The shock is produced by the interaction of oppositely directed proton beams in the plane containing solar wind velocity and interplanetary magnetic field vectors. In the direction across the magnetic field and the solar wind velocity, the shock results from the interaction of the plasma flow with the region of the enhanced magnetic field inside the cavity that plays the role of magnetic barrier. The appearance of the standing shock wave is expected at the distance of ~ 7RM downstream of the Moon. Title: Growing and coupled transverse oscillations of a multistranded loop observed by SDO/AIA Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph M.; Su, Yang Bibcode: 2012decs.confE..51W Altcode: We report the first evidence of transverse oscillations of a multistranded loop with growing amplitudes and internal coupling observed by SDO/AIA. The loop oscillations were triggered by a flare-CME event occurring in an active region visible at the limb. The multiwavelength analysis reveals the temperature dependence of multiple strands, which show differences in their oscillation amplitudes, phases and emission evolution. The physical parameters of growing transverse oscillations in 171A band are measured and the 3-D loop geometry is determined using STEREO/EUVI-A data. The strands have very similar oscillation frequencies and appear to oscillate in-phase or in a quarter-period phase delay. The observed oscillation properties of the loop strands agree with theoretically expected coupling between neighboring strands of a loop that undergoes a global kink mode oscillation. The transverse loop oscillations are also associated with intensity and loop width variations. We discuss the possible mechanisms that can excite the kink oscillations with growing amplitudes, and their associations with intensity and loop width variations. Title: Modeling waves, flows, and instabilities produced by impulsive events in coronal active regions Authors: Ofman, L.; Liu, W.; Wang, T. J.; Davila, J. M.; Thompson, B. J. Bibcode: 2012decs.confE..73O Altcode: Recent high-resolution observations by SDO/AIA combined with spectral data from Hinode provide insights into the properties of MHD waves, flows, and instabilities in coronal active region plasma and their connection with impulsive energy release. Shear flow driven instabilities, such as the Kelvin-Helmholtz (KH) instability were only recently detected in detail in the corona. I will present recent results of 3D MHD models of slow and fast magnetosonic waves in active regions excited by jets and quasi-periodic flows driven by micro-flares at loops' footpoints. I will discuss models of super-fast magnetosonic waves detected recently by SDO/AIA. I will also discuss models of global (EIT) waves, and KH instabilities driven by CMEs. The relations between waves, flows, instabilities, and impulsive events such as flares and CMEs are becoming apparent thanks to the combination of observational data analysis and the 3D MHD modeling. Understanding these relations is useful for coronal seismology and for tracing the flow of energy from the transition region to the corona. Title: SDO/AIA Observations of Various Coronal EUV Waves Associated with Flares/CMEs and Their Coronal Seismology Implications Authors: Liu, Wei; Ofman, Leon; Aschwanden, Markus J.; Nitta, Nariaki; Zhao, Junwei; Title, Alan M. Bibcode: 2012decs.confE..87L Altcode: MHD waves can be used as diagnostic tools of coronal seismology to decipher otherwise elusive critical physical parameters of the solar corona, such as the magnetic field strength and plasma density. They are analogous to acoustic waves used in helioseismology, but with complexities arising from the magnetic field and nonlinearity. Recent high cadence, high resolution, full-disk imaging observations from SDO/AIA have opened a new chapter in understanding these waves. Various types of EUV waves associated with flares/CMEs have been discovered or observed in unprecedented detail. In this presentation, we will review such new AIA observations, focusing on the following topics and their interrelationships: (1) quasi-periodic fast waves traveling along coronal funnels within CME bubbles at speeds up to 2000 km/s, associated with flare pulsations at similar frequencies; (2) quasi-periodic wave trains within broad, diffuse pulses of global EUV waves (so-called EIT waves) running ahead of CME fronts; (3) interactions of global EUV waves with local coronal structures on their paths, such as flux-rope coronal cavities and their embedded filaments (kink oscillations) and coronal holes/active regions (deflections). We will discuss the implications of these observations on coronal seismology, on their roles in transporting energy through different parts of the solar atmosphere, and on understanding their associated eruptive flares/CMEs. Title: SDO/AIA Observations of Quasi-periodic Fast (~1000 km/s) Propagating (QFP) Waves as Evidence of Fast-mode Magnetosonic Waves in the Low Corona: Statistics and Implications Authors: Liu, W.; Ofman, L.; Title, A. M.; Zhao, J.; Aschwanden, M. J. Bibcode: 2011AGUFMSH33A2043L Altcode: Recent EUV imaging observations from SDO/AIA led to the discovery of quasi-periodic fast (~2000 km/s) propagating (QFP) waves in active regions (Liu et al. 2011). They were interpreted as fast-mode magnetosonic waves and reproduced in 3D MHD simulations (Ofman et al. 2011). Since then, we have extended our study to a sample of more than a dozen such waves observed during the SDO mission (2010/04-now). We will present the statistical properties of these waves including: (1) Their projected speeds measured in the plane of the sky are about 400-2200 km/s, which, as the lower limits of their true speeds in 3D space, fall in the expected range of coronal Alfven or fast-mode speeds. (2) They usually originate near flare kernels, often in the wake of a coronal mass ejection, and propagate in narrow funnels of coronal loops that serve as waveguides. (3) These waves are launched repeatedly with quasi-periodicities in the 30-200 seconds range, often lasting for more than one hour; some frequencies coincide with those of the quasi-periodic pulsations (QPPs) in the accompanying flare, suggestive a common excitation mechanism. We obtained the k-omega diagrams and dispersion relations of these waves using Fourier analysis. We estimate their energy fluxes and discuss their contribution to coronal heating as well as their diagnostic potential for coronal seismology. Title: Three-Dimensional MHD Models of Waves and Flows in Coronal Active Region Loops Authors: Ofman, L.; Wang, T.; Davila, J. M. Bibcode: 2011AGUFMSH34B..02O Altcode: Recent observations show that slow magnetosonic waves are present in active region loops, and are often associated with subsonic up-flows of coronal material. In order to study the relation between up-flows and waves we develop a 3D MHD model of an idealized bi-polar active region with flows in coronal loops. The model is initiated with a dipole magnetic field and gravitationally stratified isothermal atmosphere. To model the effects of flares, coronal material is injected in small-scale regions at the base of the model active region. The up-flows have sub-sonic speeds of ∼100 km/s and are steady or periodic, producing higher density loops by filling magnetic flux-tubes with injected material. We find that the up-flows produce fast and slow magnetosonic waves that propagate in the coronal loops. We perform a parametric study of up-flow magnitude and periodicity, and the relation with the resulting waves. As expected, we find that the up-flow speed decreases with loop height due to the diverge of the flux tubes, while the slow magnetosonic speed is independent of height. When the amplitude of the driving pulses is increased above the sound speed, we find that slow shocks are produced in the loops. Using the results of the 3D MHD model we show that observed slow magnetosonic waves in active region loops can be driven by impulsive flare-produced up-flows at the transition region/corona interface of active regions. Title: Propagating low-frequency waves in coronal streamers observed by STEREO COR1 Authors: Kwon, R.; Davila, J. M.; Ofman, L. Bibcode: 2011AGUFMSH43C1981K Altcode: Compressional and transverse propagating waves high above the solar surface may play an important role in heating and accelerating the solar wind. Waves with periods of about an hour were detected in streamers in the past using SOHO/LASCO observations. STEREO COR1 provides us with the coronagraph (~4 solar radius) with high temporal resolution (5 min time cadence) so that it allows us to study low frequency waves systematically and address line-of-sight ambiguity. We present a method to detect the periodic oscillations along coronal streamers observed by STEREO COR1 and to determine the wavelength, period and phase speed with wavelet analysis. Further, we discuss physical implications of our results and the possible origin of the waves we found. Title: Hybrid Modeling of Solar Wind Ion Heating Authors: Maneva, Y. G.; Ofman, L.; Vinas, A. - Bibcode: 2011AGUFMSH53B2038M Altcode: Hybrid simulations are performed to describe the anisotropic and preferential heating of protons and minor ions in a hot multi-species solar wind plasma. The electrons are considered as a massless fluid to ensure that the total charge and current are conserved, whereas the ions are treated fully kinetically. The energy source is a spectrum of Alfvén-cyclotron waves. The minor ions are differentially accelerated depending the wave spectra, the values of their plasma β and their relative number densities. We discuss the effects of the heating by Alfvén-cyclotron wave spectra on the ions and compare them with the ion heating by pure monochromatic large-amplitude Alfvén-cyclotron waves. We consider the effects of solar wind expansion and compare the results for various forms of Alfvénic wave spectra on the ion heating and acceleration in expanding solar wind plasma. The heating by Alfvén-cyclotron waves in both homogeneous and inhomogeneous plasma is considered in 2.5D study. We find that inhomogeneity leads to preferential heating of minor and heavy ions, whereas their differential acceleration is strongly dependent on the input wave spectra considered. Title: Modeling Super-fast Magnetosonic Waves Observed by SDO in Active Region Funnels Authors: Ofman, L.; Liu, W.; Title, A.; Aschwanden, M. Bibcode: 2011ApJ...740L..33O Altcode: Recently, quasi-periodic, rapidly propagating waves have been observed in extreme ultraviolet by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) instrument in about 10 flare/coronal mass ejection (CME) events thus far. A typical example is the 2010 August 1 C3.2 flare/CME event that exhibited arc-shaped wave trains propagating in an active region (AR) magnetic funnel with ~5% intensity variations at speeds in the range of 1000-2000 km s-1. The fast temporal cadence and high sensitivity of AIA enabled the detection of these waves. We identify them as fast magnetosonic waves driven quasi-periodically at the base of the flaring region and develop a three-dimensional MHD model of the event. For the initial state we utilize the dipole magnetic field to model the AR and include gravitationally stratified density at coronal temperature. At the coronal base of the AR, we excite the fast magnetosonic wave by periodic velocity pulsations in the photospheric plane confined to a funnel of magnetic field lines. The excited fast magnetosonic waves have similar amplitude, wavelength, and propagation speeds as the observed wave trains. Based on the simulation results, we discuss the possible excitation mechanism of the waves, their dynamical properties, and the use of the observations for coronal MHD seismology. Title: Coronal Seismology in the SDO Era: AIA Observations of Various Coronal Waves Associated with CMEs/Flares Authors: Liu, Wei; Ofman, Leon; Aschwanden, Markus J.; Nitta, Nariaki; Zhao, Junwei; Title, Alan M. Bibcode: 2011sdmi.confE..49L Altcode: MHD waves, as critical diagnostic tools of coronal seismology, can be used to decipher otherwise elusive physical parameters of the solar corona, such as the magnetic field strength and plasma density. They are analogous to acoustic waves used in helioseismology. Recent high cadence, high resolution, full-disk imaging observations from SDO/AIA have opened a new chapter in understanding these waves. Various types of waves associated with flares and/or CMEs have been discovered. In this presentation, we will review such new AIA observations, focusing on the following topics: (1) fine structures in CME-related global EUV waves (so-called EIT waves), including a diffuse pulse superimposed with multiple sharp fronts or "ripples" (Liu et al. 2010, ApJL); (2) quasi-periodic fast waves traveling in coronal funnels at speeds up to 2000 km/s and associated with flares pulsating at similar frequencies (Liu et al. 2011, ApJL); (3) interaction of global EUV waves with local coronal structures on their paths, such as flux-rope coronal cavities (triggered kink oscillations, Liu et al. in preparation) and coronal holes/active regions (deflection). We will discuss the implications of these observations on coronal seismology and on understanding their associated flares and CMEs. We also anticipate to exchange ideas with helioseismologists at this workshop, in a hope to bring together coronal seismology and helioseismology techniques to advance our understanding of solar oscillations from the interior to the upper atmosphere. Title: Slow Magnetoacoustic Wave Oscillation of an Expanding Coronal Loop Authors: Schmidt, J. M.; Ofman, L. Bibcode: 2011ApJ...739...75S Altcode: We simulated an expanding loop or slow coronal mass ejection (CME) in the solar corona dimensioned with size parameters taken from real coronal expanding loops observed with the STEREO spacecraft. We find that the loop expands to Sun's size within about one hour, consistent with slow CME observations. At the top of the loop, plasma is being blown off the loop, enabled with the reconnection between the loop's flux rope magnetic field and the radial magnetic field of the Sun, thus yielding feeding material for the formation of the slow solar wind. This mechanism is in accordance with the observed blob formation of the slow solar wind. We find wave packets traveling with local sound speed downward toward the footpoints of the loop, already seen in coronal seismology observations and simulations of stationary coronal loops. Here, we generalize these results for an expanding medium. We also find a reflection of the wave packets, identified as slow magnetoacoustic waves, at the footpoints of the loop. This confirms the formation of standing waves within the coronal loop. In particular, the reflected waves can partly escape the loop top and contribute to the heating of the solar wind. The present study improves our understanding on how loop material can emerge to form blobs, major ingredients of slow CMEs, and how the release of the wave energy stored in slow magnetoacoustic waves, and transported away from the Sun within expanding loops, contributes to the acceleration and formation of the slow solar wind. Title: Hybrid simulation of ion-acoustic waves excitation by non-linear Alfvén wave Authors: Israelevich, P. L.; Ofman, L. Bibcode: 2011AdSpR..48...25I Altcode: The results of one dimensional hybrid simulation of standing Alfvén wave in low beta plasma are presented. Plasma is accelerated from the anti-nodes toward the nodes of the standing waves with finite amplitude under the action of the variable magnetic field pressure. As a result, a sharp maximum of the number density (and electron pressure) arises near the nodes of the standing wave. The plasma flow is spatially modulated with half wavelength of the driving Alfvén wave. Standing ion-acoustic waves produced by spatial modulation of the flow are observed in hybrid simulation. The effective parallel electric field E∗=E+{1}/{ne}∇pe appears due to both electron pressure gradient near the nodes and electron pressure variations in the acoustic waves. Title: Direct Imaging of Quasi-periodic Fast Propagating Waves of ~2000 km s-1 in the Low Solar Corona by the Solar Dynamics Observatory Atmospheric Imaging Assembly Authors: Liu, Wei; Title, Alan M.; Zhao, Junwei; Ofman, Leon; Schrijver, Carolus J.; Aschwanden, Markus J.; De Pontieu, Bart; Tarbell, Theodore D. Bibcode: 2011ApJ...736L..13L Altcode: 2011arXiv1106.3150L Quasi-periodic propagating fast mode magnetosonic waves in the solar corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory. In the 2010 August 1 C3.2 flare/coronal mass ejection event, we find arc-shaped wave trains of 1%-5% intensity variations (lifetime ~200 s) that emanate near the flare kernel and propagate outward up to ~400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 ± 130 km s-1. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-ω diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k-ω ridge shows a broad frequency distribution with power peaks at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of (0.1-2.6) × 107 erg cm-2 s-1 estimated at the coronal base is comparable to the steady-state heating requirement of active region loops. Title: Multi-fluid Model of a Streamer at Solar Minimum and Comparison with Observations Authors: Ofman, Leon; Abbo, Lucia; Giordano, Silvio Bibcode: 2011ApJ...734...30O Altcode: We present the results of a time-dependent 2.5-dimensional three-fluid magnetohydrodynamic model of the coronal streamer belt, which is compared with the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO during the past minimum of solar activity (Carrington Rotation 1913). Our previous three-fluid streamer model has been improved by considering the solar magnetic field configuration relevant for solar minimum conditions, and preferential heating for O5 + ions. The model was run until a fully self-consistent streamer solution was obtained in the quasi-steady state. The plasma parameters from the multi-fluid model were used to compute the expected UV observables from H I Lyα 1216 Å and O VI 1032 Å spectral lines, and the results were compared in detail with the UVCS measurements. A good agreement between the model and the data was found. The results of the study provide insight into the acceleration and heating of the multi-ion slow solar wind. Title: SDO/AIA Observation of Kelvin-Helmholtz Instability in the Solar Corona Authors: Ofman, L.; Thompson, B. J. Bibcode: 2011ApJ...734L..11O Altcode: 2011arXiv1101.4249O We present observations of the formation, propagation, and decay of vortex-shaped features in coronal images from the Solar Dynamics Observatory associated with an eruption starting at about 2:30 UT on 2010 April 8. The series of vortices were formed along the interface between an erupting (dimming) region and the surrounding corona. They ranged in size from several to 10 arcsec and traveled along the interface at 6-14 km s-1. The features were clearly visible in six out of the seven different EUV wave bands of the Atmospheric Imaging Assembly. Based on the structure, formation, propagation, and decay of these features, we identified the event as the first observation of the Kelvin-Helmholtz instability (KHI) in the corona in EUV. The interpretation is supported by linear analysis and by a nonlinear 2.5-dimensional magnetohydrodynamic model of KHI. We conclude that the instability is driven by the velocity shear between the erupting and closed magnetic field of the coronal mass ejection. The shear-flow-driven instability can play an important role in energy transfer processes in coronal plasma. Title: SDO/AIA Observations of a Global EUV Disturbance Traveling into a Coronal Cavity and Its Subsequent Oscillations: New Evidence of Fast Mode MHD Waves Authors: Liu, Wei; Aschwanden, M. J.; Ofman, L.; Nitta, N. V.; Tarbell, T. D. Bibcode: 2011SPD....42.0906L Altcode: 2011BAAS..43S.0906L We report new SDO/AIA observations of a global EUV disturbance that propagates at 600 km/s and sweeps through a coronal cavity, instigating its bodily transverse oscillations. The high temporal resolution and large FOV of AIA allow us to clearly see, for the first time, the timing coincidence between the onsets of the oscillations and the arrival of the disturbance at increasing distances covering 300 Mm in the neighborhood of the cavity. There is a time delay of the oscillations from the near side to the far side of the cavity, which is consistent with the travel time of the global perturbation. In addition, we find a fine structure consisting of evenly spaced pulses of periods 100-120 s within the global disturbance. In contrast, the CME loop expansion falls behind the global disturbance at a smaller velocity of 200 km/s. These observations suggests that this global disturbance is a real fast mode MHD wave that continues propagating into the cavity, rather than an apparent wave caused by CME expulsion that is not expected to penetrate through a topological separatrix, including the flux rope cavity boundary here. The cavity and its hosted prominence have oscillation amplitudes of 20 km/s and periods of 20-30 minutes. Such unusually long periods, compared with a few minutes commonly observed in coronal loops, likely reflect kink mode oscillations of the long cavity flux rope of a large length (a fraction of the solar radius). Title: Evidence For Forced Kink-mode Loop Oscillations Observed By Sdo/aia Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M.; Su, Y. Bibcode: 2011SPD....42.2113W Altcode: 2011BAAS..43S.2113W Transverse loop oscillations were first discovered by TRACE in EUV wavelength and interpreted as global fast kink modes. These oscillations are impulsively excited by flares or filament eruptions and often show a strong damping within few oscillation periods. The oscillations and the damping mechanism have been intensively studied in observation and theory, leading to great advance in coronal seismology. However, measurements of the damping rate remains difficult, often limited by the short length of the detectable oscillation sequence in one single filter. SDO/AIA with multiple wavebands of unprecedentedly high sensitivity and wide temperature coverage provides a good opportunity in improving the accuracy of these measurements. Here we present an example of long-lasting oscillation events observed using SDO/AIA. In this event, kink oscillations of a slowly evolving coronal loop seen in 171, 193 and 211 A bands are excited by several flow ejections. The oscillations last over one and a half hours with periods of 3-4 min and no evident decay. In particular, the amplitudes of the oscillations show increase during the period of a large flow ejection with speeds of 200-300 km/s which lasts for about a half hour, and then falls down at speeds of 60-70 km/s measured in 304 A band. We interpret the growing oscillations as driven fast magnetosonic waves by impacting flows. We perform preliminary 3D MHD study of the event using an idealized bipolar active region model. Title: 3D Structure and the Evolution of EUV Bright Points Observed by STEREO/SECCHI/EUVI: Evidence for Coronal Magnetic Reconnection Driven by Emerging Magnetic Flux? Authors: Kwon, Ryun Young; Davila, J. M.; Ofman, L. Bibcode: 2011SPD....42.1808K Altcode: 2011BAAS..43S.1808K The 3D structure of EUV bright points and its physical relation with the underlying magnetic flux concentrations are unveiled here observationally for the first time. The heights of EUV bright points have been measured within their lifetimes by 3D reconstruction method developed by Kwon, Chae, & Zhang (2010) using data sets taken from STEREO/SECCHI/EUVI. We found three distinct changes in the heights which were decreasing, increasing, and constant. In general, EUV bright points are multi-temperature loop system whose hot loops (T 106.2K) with an average height of 8.9Mm are overlying cooler loops (T < 106.0K) with an average height of 6.7Mm. This loop system has cool legs which have the peak temperature of T 104.9K and an average height of 5.2Mm. The heights were found to have remarkable correlations with lengths and distances of two opposite magnetic flux concentrations, indicating that the 3D structures of bright points were determined by the geometry of associated photospheric magnetic fluxes. Accordingly, the three types of bright points we found were associated with three distinct types of their underlying magnetic fragments: converging, diverging, and shearing. In all cases, both flux emergences and flux cancellations were observed during the lifetimes of the bright points. The flux emergences were dominant in the initial phase and the flux cancellations were significant after the intensities reached their maxima. Our results suggest that EUV bright points may be the flaring loop systems (Masuda et al. 1994) formed by coroanl magnetic reconnection and the flux emergence appears to be important to driving the coronal magnetic reconnection. Title: Pulsed Flows Along a Cusp Structure Observed with SDO/AIA Authors: Thompson, Barbara; Démoulin, P.; Mandrini, C.; Mays, M.; Ofman, L.; Van Driel-Gesztelyi, L.; Viall, N. Bibcode: 2011SPD....42.2117T Altcode: 2011BAAS..43S.2117T We present observations of a cusp-shaped structure that formed after a flare and coronal mass ejection on 14 February 2011. Throughout the evolution of the cusp structure, blob features up to a few Mm in size were observed flowing along the legs and stalk of the cusp at projected speeds ranging from 50 to 150 km/sec. Around two dozen blob features, on order of 1 - 3 minutes apart, were tracked in multiple AIA EUV wavelengths. The blobs flowed outward (away from the Sun) along the cusp stalk, and most of the observed speeds were either constant or decelerating. We attempt to reconstruct the 3-D magnetic field of the evolving structure, discuss the possible drivers of the flows (including pulsed reconnection and tearing mode instability), and compare the observations to studies of pulsed reconnection and blob flows in the solar wind and the Earth's magnetosphere. Title: Direct Imaging by SDO/AIA of Quasi-periodic Propagating Fast Mode Magnetosonic Waves of 2000 km/s in the Solar Corona Authors: Liu, Wei; Title, A. M.; Zhao, J.; Ofman, L.; Schrijver, C. J.; Aschwanden, M. J.; De Pontieu, B.; Tarbell, T. D. Bibcode: 2011SPD....42.2114L Altcode: 2011BAAS..43S.2114L Quasi-periodic, propagating fast mode magnetosonic waves in the corona were difficult to observe in the past due to relatively low instrument cadences. We report here unprecedented evidence of such waves directly imaged in EUV by the new SDO/AIA instrument. In the 2010 August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1-5% intensity variations emanating near the flare kernel and propagating outward along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2350 +/- 210 km/s. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-omega diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin, giving an equal phase and group velocity of 1630 +/- 760 km/s averaged over the event. This k-omega ridge shows a broad frequency distribution with prominent power at four non-harmonic frequencies, 5.5, 14.5, 25.1, and 37.9 mHz, among which the 14.5 mHz (period: 69 s) signal is the strongest. The signal at 5.5 mHz (period: 181 s, same as chromospheric 3-minute oscillations) temporally coincides with flare pulsations, suggesting a common origin of possibly quasi-periodic magnetic reconnection. The instantaneous wave energy flux of (0.1-2.6)e7 ergs/cm2/s estimated at the coronal base is comparable to the steady-state heating requirement of active region loops. Title: Modeling Waves And Flows In Active Region Loops Authors: Ofman, Leon; Wang, T.; Davila, J. M. Bibcode: 2011SPD....42.1815O Altcode: 2011BAAS..43S.1815O Recent Hinode/EIS observations indicated that slow magnetosonic waves are present in active region loops. Some of the spectral data were also interpreted as evidence of quasi-periodic flows. We perform three dimensional MHD model of an active region with waves and flows in coronal loops. The model is initiated with a dipole magnetic field and gravitationally stratified density, and velocity pulses are driven periodically in localized regions at the footpoints of magnetic loops. The resulting flows produce higher density loops compared to the surrounding plasma by injecting material along the field. We find that the excitation of periodic flows with subsonic speeds result in the excitation of slow magnetosonic waves that propagate along the loops. The phase speed of the waves is 100 km/s, close to coronal sound speed. When the amplitude of the driving pulses is increased we find that slow shock trains are produced. Using the results of the 3D MHD model we suggest that the observed slow magnetosonic waves and quasi periodic-flows are driven by the same quasi-periodic impulsive events at the bases of active regions. Title: Modeling Fast Magnetosonic Waves Observed by SDO in Active region Funnels Authors: Ofman, Leon; Liu, W.; Title, A.; Aschwanden, M. Bibcode: 2011SPD....42.2104O Altcode: 2011BAAS..43S.2104O Recently, quasi-periodic, propagating waves have been observed in EUV by the SDO/AIA instrument in about 10 flare/CME events thus far. A typical example is the waves associated with the 2010 August 1 C3.2 flare/CME that exhibited arc-shaped wave trains propagating in an active region magnetic funnel with 5% intensity variations at speeds in the range of 1000-2000 km/s. The fast temporal cadence and high sensitivity of AIA enabled the detection of these waves. We identify them as fast magnetosonic waves driven quasi-periodically at the base of the flaring region, and develop a three-dimensional MHD model of the event. For the initial state we utilize the dipole magnetic field to model the active region, and include gravitationally stratified density at coronal temperature. At the coronal base of the active region we excite the fast magnetosonic wave by periodic velocity pulsations in the photospheric plane confined to the funnel of magnetic field line. The excited fast magnetosonic waves have similar amplitude, wavelength and propagation speeds as the observed wave trains. Based on the simulation results, we discuss the possible excitation mechanism of the waves, their dynamical properties, and the use of the event for coronal MHD seismology. Title: Slow-Mode Oscillations of Hot Coronal Loops Excited at Flaring Footpoints Authors: Wang, Tongjiang; Liu, W.; Ofman, L.; Davila, J. M. Bibcode: 2011SPD....42.2214W Altcode: 2011BAAS..43S.2214W A large number of strongly damped oscillations in hot coronal loops have been observed by SOHO/SUMER in the past decade in Doppler shifts of flaring (>6 MK) lines (Fe XIX and Fe XXI). These oscillations with periods on the order of 10-30 min were interpreted as fundamental standing slow modes. They often manifest features such as recurrence and association with a flow (100-300 km/s) pulse preceding to the oscillation, which suggests that they are likely driven by microflares at the footpoints. With coordinated RHESSI observations, we have found a dozen such events supporting this conjecture. A typical event is presetned here. By analyzing RHESSI hard X-ray and GOES/SXI soft X-ray emissions as well as SUMER Doppler shifts, we identify the flare that triggers the loop oscillations. From RHESSI spectra, we measure physical parameters such as temperature, emission measure, and thermal/non-thermal energy contents as functions of time. We discuss the wave excitation mechanism based on these observations. Our results provide important observational constraints that can be used for improving theoretical models of magnetosonic wave excitation, and for coronal seismology. Title: The Role of Active Region Loop Geometry. II. Symmetry Breaking in Three-dimensional Active Region: Why are Vertical Kink Oscillations Observed so Rarely? Authors: Selwa, M.; Solanki, S. K.; Ofman, L. Bibcode: 2011ApJ...728...87S Altcode: We present numerical results of simulations of kink oscillations of coronal loops in an idealized active region (AR) that is initialized as a potential dipole magnetic configuration with gravitationally stratified density. We consider loops, with density higher than the surrounding plasma, embedded into the dipolar AR. We study the excitation of kink oscillations of such loops by velocity pulses at different positions, of a given duration and amplitude. The position of the pulse varies in the parametric studies. For a central (symmetric) loop within the AR, we find that the amplitude of vertical kink oscillations is significantly amplified in comparison to horizontal kink oscillations for exciters located centrally (symmetrically) below the loop. For pulses initiated further from such a symmetric loop a combination of vertical and horizontal oscillations is excited. The scenario changes significantly when we study an inclined loop (non-symmetric within a dipole field). In this case, we do not see vertical kink oscillations of any significant amplitude being excited, while horizontal ones can be easily detected. These results indicate that the reason why vertical kink oscillations are observed so rarely is that their excitation requires a set of conditions to occur simultaneously: the exciting pulse must be located roughly below the loop apex and the loop itself must be located symmetrically within the group of loops. The new findings of the present study show the importance of not only the position of the pulse, but mainly of the location of the loop within the set of field lines having the same magnetic connectivity. We find that the slow propagating wave is excited in all the studied loops and its excitation does not depend either on the geometry of the loop or the pulse. We discuss TRACE observations of coronal loop oscillations in view of our findings and find that our results can be used for identifying the polarization of the kink mode based on the location of the loop within the set of field lines of the same connectivity and the position of the flare. Title: Probing the Thermodynamics and Kinematics of Solar Coronal Streamers Authors: Airapetian, V.; Ofman, L.; Sittler, E. C.; Kramar, M. Bibcode: 2011ApJ...728...67A Altcode: We present the results of a resistive magnetohydrodynamic (MHD) model of an equatorially confined streamer belt using observational constraints for the heating and acceleration of the solar wind. To initiate the 2.5 dimensional MHD calculations, we used the Potential Field Source Surface model of the coronal magnetic field configuration with the boundary conditions at the photosphere specified by the National Solar Observatory/GONG magnetogram data. Calculations were performed for the fully thermal conductive model with observationally constrained heat flux, q eff, and the effective temperature, T eff, derived from the semi-empirical steady-state two-dimensional model of the solar corona. We compared the results of the model to a polytropic solution (polytropic index γ = 1.05), and demonstrate that our MHD model is in better agreement with reconstructed density and observed flow velocity than the polytropic model for the coronal streamer structure observed during 2008 February 1-13 by the COR1 coronagraph on board the STEREO spacecraft. Title: The Role of Active Region Loop Geometry. I. How Can it Affect Coronal Seismology? Authors: Selwa, M.; Ofman, L.; Solanki, S. K. Bibcode: 2011ApJ...726...42S Altcode: We present numerical results of coronal loop oscillation excitation using a three-dimensional (3D) MHD model of an idealized active region (AR) field. The AR is initialized as a potential dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. We study different ways of excitation of vertical kink oscillations of this loop by velocity: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. We vary the geometry of the loop in the 3D MHD model and find that it affects both the period of oscillations and the synthetic observations (difference images) that we get from oscillations. Due to the overestimated effective length of the loop in the case of loops which have maximum separation between their legs above the footpoints (>50% of observed loops), the magnetic field obtained from coronal seismology can also be overestimated. The 3D MHD model shows how the accuracy of magnetic field strength determined from coronal seismology can be improved. We study the damping mechanism of the oscillations and find that vertical kink waves in 3D stratified geometry are damped mainly due to wave leakage in the horizontal direction. Title: SDO/AIA Observation of Kelvin-Helmholtz Instability in the Solar Corona associated with CME Authors: Ofman, L.; Thompson, B. J. Bibcode: 2010AGUFMSH14A..02O Altcode: We present observations of the formation, propagation and decay of vortex-shaped features in coronal images from the Solar Dynamics Observatory (SDO) associated with Coronal Mass Ejection (CME) at about 2:34UT on Apr 8, 2010. The series of vortices are seen at 3:20UT to 3:37UT formed along the interface between erupting (dimming) region and the surrounding corona and ranged in size from several to ten arcseconds, traveling along the interface at approximately 5 km/sec. The features are clearly visible in five out of the six different EUV wavebands of the Atmospheric Imaging Assembly (AIA). Based on the structure, formation, propagation and decay of these features, we conclude that these are the first observations of the Kelvin-Helmholtz (KH) instability in the corona. The KH instability is likely driven by the velocity shear between the erupting and closed magnetic field regions. We compare the dynamics and structure of SDO/AIA observation to an MHD model of KH instability in the nonlinear stage in magnetized plasma, and find good agreement. Title: Winds from Luminous Late-type Stars. II. Broadband Frequency Distribution of Alfvén Waves Authors: Airapetian, V.; Carpenter, K. G.; Ofman, L. Bibcode: 2010ApJ...723.1210A Altcode: 2010arXiv1008.3955A We present the numerical simulations of winds from evolved giant stars using a fully nonlinear, time-dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully nonlinear MHD wind simulations to include a broadband frequency spectrum of Alfvén waves that drive winds from red giant stars. We calculated four Alfvén wind models that cover the whole range of the Alfvén wave frequency spectrum to characterize the role of freely propagated and reflected Alfvén waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate that, unlike linear Alfvén wave-driven wind models, a stellar wind model based on plasma acceleration due to broadband nonlinear Alfvén waves can consistently reproduce the wide range of observed radial velocity profiles of the winds, their terminal velocities, and the observed mass-loss rates. Comparison of the calculated mass-loss rates with the empirically determined mass-loss rate for α Tau suggests an anisotropic and time-dependent nature of stellar winds from evolved giants. Title: Web-Based Data Processing System for Automated Detection of Oscillations with Applications to the Solar Atmosphere Authors: Sych, R. A.; Nakariakov, V. M.; Anfinogentov, S. A.; Ofman, L. Bibcode: 2010SoPh..266..349S Altcode: 2010SoPh..tmp..154S; 2010arXiv1005.3591S A web-based, interactive system for the remote processing of imaging data sets (i.e., EUV, X-ray, and microwave) and the automated interactive detection of wave and oscillatory phenomena in the solar atmosphere is presented. The system targets localized, but spatially resolved, phenomena such as kink, sausage, and longitudinal propagating and standing waves. The system implements the methods of Periodmapping for pre-analysis, and Pixelized Wavelet Filtering for detailed analysis of the imaging data cubes. The system is implemented on the dedicated data-processing server http://pwf.iszf.irk.ru, which is situated at the Institute of Solar-Terrestrial Physics, Irkutsk, Russia. Input data in the .sav, .fits, or .txt formats can be submitted via the local and/or global network (the Internet). The output data can be in the png, jpeg, and binary formats, on the user's request. The output data are periodmaps; narrowband amplitude, power, phase and correlation maps of the wave's sources at significant harmonics and in the chosen spectral intervals, and mpeg movies of their evolution. The system was tested by the analysis of the EUV and microwave emission from the active region NOAA 10756 on 4 May 2005 observed with TRACE and the Nobeyama Radioheliograph. The similarity of the spatial localization of three-minute propagating waves, near the footpoint of locally open magnetic-field lines determined by the potential-field extrapolation, in both the transition region and the corona was established. In the transition region the growth of the three-minute amplitude was found to be accompanied by the decrease in the line-of-sight angle to the wave-propagation direction. Title: Wave Modeling of the Solar Wind Authors: Ofman, Leon Bibcode: 2010LRSP....7....4O Altcode: The acceleration and heating of the solar wind have been studied for decades using satellite observations and models. However, the exact mechanism that leads to solar wind heating and acceleration is poorly understood. In order to improve the understanding of the physical mechanisms that are involved in these processes a combination of modeling and observational analysis is required. Recent models constrained by satellite observations show that wave heating in the low-frequency (MHD), and high-frequency (ion-cyclotron) range may provide the necessary momentum and heat input to coronal plasma and produce the solar wind. This review is focused on the results of several recent solar modeling studies that include waves explicitly in the MHD and the kinetic regime. The current status of the understanding of the solar wind acceleration and heating by waves is reviewed. Title: Modeling the Slow Solar Wind during the Solar Minimum Authors: Ofman, L.; Kramar, M. Bibcode: 2010ASPC..428..321O Altcode: 2010arXiv1004.4847O During the solar minimum, STEREO observations show that the three-dimensional structure of the solar corona can be described well by a tilted bipolar magnetic configuration. The slow solar wind is modeled using a three-fluid model that includes heavy ions such as He II and O VI. The model is initialized with a dipole magnetic field and spherically symmetric density. The resulting steady state, non-potential, and non-uniform streamer configuration calculated with this model is compared to STEREO observations of the streamer density structure. SOHO/UVCS observations are used to compare the O VI emission to model results. We discuss the unique properties of the solar wind produced in this configuration. Title: Three-dimensional MHD Model Of Active Region Loop Oscillations With Background Flow Authors: Ofman, Leon; Schmidt, J.; Wang, T. Bibcode: 2010AAS...21630204O Altcode: Recent observations by Hinode satellite show that oscillating coronal loops with periods of several minutes contain cool flowing material at 100 km/s. The flow may affects significantly the oscillations and the damping of the wave energy. We model the oscillating loops with background flow in 3D MHD model of a bi-polar active region, that includes the effects of loop curvature and chromospheric boundary conditions. The oscillations are excited impulsively by a velocity pulse. We study the effects of flow magnitude, and loop parameters on the excitation and damping of the oscillations. The results of the parametric study have implication for coronal seismology, and for wave heating of active region coronal loops. Title: Three-dimensional MHD Modeling Of Waves In Active Regions: Comparison To Observations Authors: Schmidt, Joachim; Ofman, L. Bibcode: 2010AAS...21640717S Altcode: 2010BAAS...41..862S We present the results of 3D MHD models of waves in active regions generated by a CME. We study the propagation and reflection of the waves in the solar corona and compare to recent STEREO observations. We also investigate the excitation of oscillations in individual coronal loops in realistic active region magnetic field initialized with extrapolated WSO magnetogram data. We compare the results of the model to EUV observations and demonstrate the development and application of coronal seismology. Title: What Do High-resolution EIT Waves Tell Us About CMEs? Authors: Thompson, Barbara; Biesecker, D. A.; Nitta, N.; Ofman, L.; West, M. J. Bibcode: 2010AAS...21640229T Altcode: Although many studies have demonstrated that some coronal waves are not generated by coronal mass ejections, we have learned a great deal about the ability of coronal mass ejections to drive large-scale coronal waves, also called "EIT waves." We present new results based on EIT wave amplitude, timing, speed, and direction of propagation, with respect to their correlation with CME-related dimmings, speeds, locations and widths. Furthermore, we demonstrate the ability to correlate different aspects of EIT waves with some of the observed structure of CMEs observed in coronagraph data. Finally, we expand on the discussion of the types of wave modes that can be generated by a coronal mass ejection, and how these observations can serve as a diagnostic of the type of impulse a CME can deliver to the surrounding corona. These diagnostics are obtained by examining the motion of individual field lines, requiring high-resolution observations like those provided by TRACE and SDO/AIA. Title: The Role of Active Region Topology in Excitation, Trapping, and Damping of Coronal Loop Oscillations Authors: Selwa, M.; Ofman, L. Bibcode: 2010ApJ...714..170S Altcode: We investigate the role of magnetic field topology in dense coronal loop oscillation by the means of three-dimensional magnetohydrodynamic numerical simulations of two models of idealized active regions (ARs). The first AR model is initialized as a straight cylinder surrounded by the field lines of the same length and orientation. The second model consists of a potential dipole magnetic configuration and contains a loop with a higher density than its surroundings. Dipole field lines have position-dependent length and orientation in contrary to straight ones. We study different ways of excitation of transverse loop oscillations by an external pulse and a nearly eigenmode excitation implemented inside the loop. We find that perturbation acting directly on a single loop excites oscillations both in cylindrical and dipole loops. However, the leakage of the wave energy is larger in a curved loop compared to a straight loop. External excitation of the whole AR is efficient in the excitation of oscillation in the straight field configuration, but results in less efficient excitation in the case of dipole field. We show that excitation of collective motion of straight field lines having the same wave periods and planes of the oscillations requires much less energy than excitation of dipole field lines having position-dependent orientation and wave periods and being excited individually, not having a collective mode of oscillation. We conclude that coherent motion of straight field lines is one of the factors that decrease the energy leakage from an oscillating loop, while individual motions of dipole field lines require more energy from the source to produce the loop oscillations, and also lead to higher damping rate compared to the straight field case. We discuss Transition Region and Coronal Explorer (TRACE) observations of coronal loop oscillations in view of our theoretical findings. We show several examples of time signatures of transversal loop oscillations observed by TRACE that agree with numerical simulations of externally excited oscillations. Title: Acceleration and Heating of Solar Wind Ions by Nonlinear Waves Authors: Ofman, L. Bibcode: 2010aogs...21....1O Altcode: Recent advances in observations and modeling provide better understanding of the possible role of waves in the acceleration and heating of the solar wind. Ulysses, ACE, Helios, SOHO, TRACE, and other satellite observations found ample evidence for waves in the corona and in the solar wind. Numerical models show that nonlinear interaction between MHD waves and the plasma can provide the necessary momentum and heat input to produce the fast solar wind in coronal holes. It was also found that the heating of solar wind protons and heavy ions is more significant than of electrons. Temperature anisotropy suggests that ion-cyclotron wave heating is taking place in heavy ions. In this review article, several recent observations and numerical models of nonlinear wave driven wind are discussed. Title: Propagating Intensity Disturbances In Coronal Loops: Waves Or Flows? Authors: Wang, Tongjiang; Ofman, L.; Davila, J. M. Bibcode: 2010AAS...21640715W Altcode: 2010BAAS...41..862W Quasi-periodic propagating intensity disturbances were found by SOHO/EIT and TRACE imaging observations in fanlike coronal loops 10 year ago. The 3 min and 5 min oscillations have been interpreted as propagating slow magnetoacoustic waves which originate from the photospheric p-mode oscillations due to the wave leakage. However, some cases show oscillations with periodicities of more than 10 min, which are hard to explain by wave leakage, and so were argued in some studies that they may be periodic flows. In this presentation, we report the first observation of multiple-periodic (12 and 25 min) propagating disturbances along a fan-like coronal structure simultaneously detected in both intensity and Doppler shift in the Fe XII line with EIS onboard Hinode. We measured Doppler shift amplitude of 1-2 km/s, relative intensity amplitude of (3-5)% and the apparent propagation speed of 100-120 km/s. The amplitude relationship between intensity and Doppler shift oscillations provides convincing evidence that these propagating features are a manifestation of slow magnetoacoustic waves but not flows. The feature of symmetric line profiles also confirms that the measured small Doppler-shift amplitudes are not due to the line wing enhancement caused by high-speed flows. A new application of coronal seismology is provided based on these observations, with which we determine the inclination angle of the magnetic field and the temperature of a coronal loop. We will also show the result of multi-temperature line analysis to explore the temperature-dependent behavior of this phenomenon. Title: Hybrid model of inhomogeneous solar wind plasma heating by Alfvén wave spectrum: Parametric studies Authors: Ofman, L. Bibcode: 2010JGRA..115.4108O Altcode: 2010JGRA..11504108O Observations of the solar wind plasma at 0.3 AU and beyond show that a turbulent spectrum of magnetic fluctuations is present. Remote sensing observations of the corona indicate that heavy ions are hotter than protons and their temperature is anisotropic (T$\perp$/T$\parallel$ $\gg$ 1). We study the heating and the acceleration of multi-ion plasma in the solar wind by a turbulent spectrum of Alfvénic fluctuations using a 2-D hybrid numerical model. In the hybrid model the protons and heavy ions are treated kinetically as particles, while the electrons are included as neutralizing background fluid. This is the first two-dimensional hybrid parametric study of the solar wind plasma that includes an input turbulent wave spectrum guided by observation with inhomogeneous background density. We also investigate the effects of He++ ion beams in the inhomogeneous background plasma density on the heating of the solar wind plasma. The 2-D hybrid model treats parallel and oblique waves, together with cross-field inhomogeneity, self-consistently. We investigate the parametric dependence of the perpendicular heating, and the temperature anisotropy in the H+-He++ solar wind plasma. It was found that the scaling of the magnetic fluctuations power spectrum steepens in the higher-density regions, and the heating is channeled to these regions from the surrounding lower-density plasma due to wave refraction. The model parameters are applicable to the expected solar wind conditions at about 10 solar radii. Title: Global Simulation of an Extreme Ultraviolet Imaging Telescope Wave Authors: Schmidt, J. M.; Ofman, L. Bibcode: 2010ApJ...713.1008S Altcode: We use the observation of an Extreme Ultraviolet Imaging Telescope (EIT) wave in the lower solar corona, seen with the two Solar Terrestrial Relations Observatory (STEREO) spacecraft in extreme ultraviolet light on 2007 May 19, to model the same event with a three-dimensional (3D) time-depending magnetohydrodynamic (MHD) code that includes solar coronal magnetic fields derived with Wilcox Solar Observatory magnetogram data, and a solar wind outflow accelerated with empirical heating functions. The model includes a coronal mass ejection (CME) of Gibson and Low flux rope type above the reconstructed active region with parameters adapted from observations to excite the EIT wave. We trace the EIT wave running as circular velocity enhancement around the launching site of the CME in the direction tangential to the sphere produced by the wave front, and compute the phase velocities of the wave front. We find that the phase velocities are in good agreement with theoretical values for a fast magnetosonic wave, derived with the physical parameters of the model, and with observed phase speeds of an incident EIT wave reflected by a coronal hole and running at about the same location. We also produce in our 3D MHD model the observed reflection of the EIT wave at the coronal hole boundary, triggered by the magnetic pressure difference between the wave front hitting the hole and the boundary magnetic fields of the coronal hole, and the response of the coronal hole, which leads to the generation of secondary reflected EIT waves radiating away in different directions than the incident EIT wave. This is the first 3D MHD model of an EIT wave triggered by a CME that includes realistic solar magnetic field, with results comparing favorably to STEREO Extreme Ultraviolet Imager observations. Title: Streamers study at solar minimum: combination of UV observations and numerical modeling Authors: Abbo, Lucia; Ofman, Leon; Giordano, Silvio Bibcode: 2010AIPC.1216..387A Altcode: The present study concerns a comparison between the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO during the minimum of solar activity (1996) and the results of a time-dependent 2.5 D three-fluid MHD model of coronal streamer belt. The aim of the study is to improve the knowledge of the slow solar wind acceleration mechanism and the origin of its variability. Title: Excitation of vertical kink waves in a solar coronal arcade loop by a periodic driver Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Ofman, L. Bibcode: 2010A&A...512A..76S Altcode:
Aims: We study an oscillatory driver as a possible excitation mechanism of vertical kink loop oscillations in the ideal MHD regime.
Methods: We consider a solar coronal magnetic arcade with a dense photospheric layer. The two-dimensional numerical model that we implement includes the effects of nonlinearity and line curvature on the excitation and attenuation of fast magnetosonic kink waves. We investigate the effects of a driven sinusoidal pressure pulse and compare it with the impulsive excitation by a pressure pulse that impacts the overlying loop.
Results: Our numerical simulations reveal wave signatures that are reminiscent of vertical loop oscillations seen in TRACE observational data.
Conclusions: We conclude that attenuation of vertical kink oscillations can be reduced to the value observed by adopting an oscillatory instead of an impulsive excitation. An oscillatory driver also naturally explains why only a small subset of all loops is excited to oscillate transversally in an active region. Title: 2.5d Mhd Simulations Of Winds From Red Giants Stars: Broadband Alfvén Waves Authors: Airapetian, Vladimir; Carpenter, K.; Ofman, L. Bibcode: 2010AAS...21542703A Altcode: 2010BAAS...42..342A We present the numerical simulations of winds from evolved giant stars using a fully non-linear, time dependent, 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully non-linear MHD wind simulations to the parameter space that describes winds from red giant stars. In the current version of this Alfvén wave driven model, a wind is driven by randomly generated low-frequency non-linear Alfvén waves in a broadband frequency range at the base of the wind. We simulate freely propagated and partially reflected Alfvén waves in the gravitationally stratified atmosphere of a late-type giant star, in a self-consistent manner, until a steady-state wind is formed. Our simulations demonstrate that, unlike linear Alfven wave-driven wind models, a stellar wind model based on plasma acceleration due to low frequency broad-band non-linear Alfvén waves, can consistently reproduce the observed radial velocity profiles of the winds, their terminal velocities, the turbulent broadening of UV lines emitted from those winds and the observed mass loss rates. We find that conversion of non-linear transverse Alfvén waves into longitudinal magnetosonic waves plays the major role in depositing momentum and energy into the stellar wind. The fitting of mass-loss rates from α Tau with the predicted rate suggests a highly anisotropic stellar wind in this evolved giant. The model also predicts a variation of the wind mass-loss rates on time scales of 1 month. Title: Propagating intensity disturbances in coronal loops: Waves or flows? Authors: Wang, Tongjiang; Ofman, Leon; Davila, Joseph Bibcode: 2010cosp...38.2924W Altcode: 2010cosp.meet.2924W Quasi-periodic propagating intensity disturbances were found by SOHO/EIT and TRACE imaging observations in fanlike coronal loops 10 year ago. The 3 min and 5 min oscillations have been interpreted as propagating slow magnetoacoustic waves which originate from the photospheric p-mode oscillations due to the wave leakage. However, some cases show oscil-lations with periodicities of more than 10 min, which are hard to explain by wave leakage, and so were argued in some studies that they may be periodic flows. In this presentation, we report the first observation of multiple-periodic (12 and 25 min) propagating disturbances along a fan-like coronal structure simultaneously detected in both intensity and Doppler shift in the Fe xii line with EIS onboard Hinode. We measured Doppler shift amplitude of 1-2 km/s, relative intensity amplitude of (3-5)% and the apparent propagation speed of 100-120 km/s. The amplitude relationship between intensity and Doppler shift oscillations provides convinc-ing evidence that these propagating features are a manifestation of slow magnetoacoustic waves but not flows. The feature of symmetric line profiles also confirms that the measured small Doppler-shift amplitudes are not due to the line wing enhancement caused by high-speed flows. A new application of coronal seismology is provided based on these observations, with which we determine the inclination angle of the magnetic field and the temperature of a coronal loop. We will also show the result of multi-temperature spectral line analysis to explore the temperature-dependent behavior of this phenomenon. Title: Ion-acoustic Waves Excitation by a standing Alfvén wave Authors: Israelevich, Peter; Ofman, Leon Bibcode: 2010cosp...38.2039I Altcode: 2010cosp.meet.2039I The results of hybrid simulation of standing Alfvén wave in low beta plasma are presented. Plasma is accelerated from the anti-nodes toward the nodes of the standing waves with finite amplitude under the action of the magnetic field pressure. As a result, a sharp maximum of the number density (and electron pressure) arises near the nodes. The plasma flow is modulated by the doubled frequency of the driving Alfvén wave thus giving rise to ion-acoustic waves. The effective parallel electric field appears due to both electron pressure gradient near the nodes and electron pressure variations in the acoustic waves. Landau damping limits the amplitude of the exited ion-acoustic waves. In the 1D case, Landau damping can be avoided only if Te is much larger than Ti, since the electric current is perpendicular to the background magnetic field. However, if ion-acoustic waves are excited by alternating field-aligned current (i.e. by oblique Alfvén wave), the ion-acoustic instability occurs for strong currents with carriers velocity larger than cs, and the excitation becomes more effective. This process may account for the observations of parallel electric field in the auroral ionosphere. Title: Comparison of observations and multi-fluid models of streamers at solar minimum Authors: Ofman, Leon; Abbo, Lucia; Giordano, Silvio; Kramar, Maxim Bibcode: 2010cosp...38.2940O Altcode: 2010cosp.meet.2940O We present the results comparison between the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrom-eter (UVCS) on-board SOHO and STEREO during the past minima of solar activity (CR1913; and CR2066) and the results of a time-dependent 2.5D three-fluid MHD model of the coronal streamer belt. The previous three-fluid (e, p, and O5+ or He++ ) streamer model has been improved by considering real solar magnetic field obtained by Wilcox Solar Observatory as boundary condition, and PFSS model as initial state of the magnetic configuration. This is the first study that incorporates real magnetic field in the three-fluid model. The model was run until fully self consistent streamer was formed in the quasi-steady state. The electron density reconstructed from STEREO Cor1 observations was compared to the results of the three-fluid model to validate the model. The plasma parameters from the multi-fluid model were used to compute the expected UV observables from HI Ly-α and OVI 1032 spectral lines and the results were compared in details with the UVCS measurements. Title: Hinode/EIS Observations of Propagating Slow Magnetoacoustic Waves in a Coronal Loop Authors: Wang, T. J.; Ofman, L.; Davila, J. M. Bibcode: 2009ASPC..415...28W Altcode: We present the first Hinode/EIS observations of 5 min quasi-periodic oscillations detected in the transition region and corona at the footpoint of a coronal loop. The oscillations are characterized by a series of wave packets with nearly constant period, typically persisting for 4--6 cycles. There is an in-phase relation between Doppler shift and intensity oscillations, indicating upwardly propagating slow magnetoacoustic waves in the loop. We find that the oscillations detected in the five coronal lines are highly correlated, and the amplitude decreases with increasing temperature. These oscillations may be caused by the leakage of the photospheric p-modes through the chromosphere and transition region into the corona, which has been suggested as the source for intensity oscillations previously observed by TRACE. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithread structure near the footpoint. Title: Two-dimensional Hybrid model of Collisionless Relaxation of Ion Distributions downstream of Quasi-perpendicular Shocks Authors: Ofman, L.; Gedalin, M. Bibcode: 2009AGUFMSH42A..05O Altcode: Recent STEREO observations reveal that large scale downstream magnetic oscillations are quite typical for quasi-perpendicular low-Mach number shock. It has been shown recently, both in theory and 1D hybrid simulations, that these oscillations are, most plausibly, related to the collisionless relaxation of the downstream gyrating ion distributions. A number of observed shocks exhibit clear deviations from one-dimensionality. We extend our previous analysis to two-spatial dimensions by using 2D hybrid code, which allows studying the inhomogeneity along the shock front. We investigate in detail the formation of gyrating distributions in this 2D geometry and further relaxation of these distributions accompanying with generation of magnetic oscillations. Title: Global simulation of an EIT wave Authors: Schmidt, J. M.; Ofman, L. Bibcode: 2009AGUFMSH41B1658S Altcode: We use the observation of an EIT wave in the lower solar corona, seen with the two STEREO s/c in extreme ultraviolet light on 19 May 2007, to model the same event with a three-dimensional (3D) time-depending magneto hydrodynamic (MHD) code that includes solar coronal magnetic fields derived with Wilcox Solar Observatory magnetogram data, a solar wind outflow accelerated with empirical heating functions. The model includes a coronal mass ejection (CME) of Gibson and Low flux rope type above the reconstructed active region with parameters adapted from observations to excite the EIT wave. We trace the EIT wave running as circular velocity enhancement around the launching site of the CME in the direction tangential to the sphere produced by the wavefront, and compute the phase velocities of the wavefront. We find that the phase velocities are in good agreement with theoretical values for a fast magnetosonic wave, derived with the physical parameters of the model, and with observed phase speeds of an EIT wave reflected by a coronal hole and running at about the same location. We also produce in our 3D MHD model the observed reflection of the EIT wave at the coronal hole boundary, triggered by the magnetic pressure difference between the wave front hitting the hole and the boundary magnetic fields of the coronal hole, and the response of the coronal hole, which leads to the generation of secondary reflected EIT waves radiating away in different direction than the incident EIT wave. Title: Dynamics of Coronal Streamers: 2.5D MHD simulations with semi-empirical heating and momentum terms Authors: Airapetian, V.; Ofman, L.; Sittler, E. C.; Kramar, M. Bibcode: 2009AGUFMSH41B1657A Altcode: We present the results of fully non-linear resistive magnetohydrodynamic (MHD) simulations of an equatorially confined streamer belt using observational constrains in a two-fluid 2.5D MHD modeling in spherical geometry . Specifically, we used the PFSS model of the initial coronal magnetic field configuration with the boundary conditions at the photosphere specified by the NSO/GONG magnetogram data. Calculations were performed for the fully thermally conductive case with the two-component (electrons and protons) heat flux, qeff , and the effective temperature, Teff, derived from the semi-empirical steady-state model (SG model). Our simulations were performed between the coronal base at 1.02 to 5 solar radii. We show that our MHD simulations are more realistic than polytropic models, and capable of reproducing basic thermodynamic and kinematic properties of the coronal streamer structure observed in July 3-17, 2007 by COR1 STEREO. Title: Progress, Challenges, and Perspectives of the 3D MHD Numerical Modeling of Oscillations in the Solar Corona Authors: Ofman, Leon Bibcode: 2009SSRv..149..153O Altcode: Recent high temporal and spatial resolution satellite observations of the solar corona provide ample evidence of oscillations in coronal structures. The observed waves and oscillations can be used as a diagnostic tool of the poorly known coronal parameters, such as magnetic field, density, and temperature. The emerging field of coronal seismology relies on the interpretation of the various coronal oscillations in terms of theoretically known wave modes, and the comparison of observed and theoretical wave mode properties for the determination of the coronal parameters. However, due to complexity of coronal structures the various modes are coupled, and the application of linear theory of idealized structures to coronal loops and active regions limits the usefulness of such methods. Improved coronal seismology can be achieved by the development of full 3D MHD dynamical model of relevant coronal structures and the oscillation phenomena. In addition to improved accuracy compared to linear analysis, 3D MHD models allow the diagnostic method to include nonlinearity, compressibility, and dissipation. The current progress made with 3D MHD models of waves in the corona is reviewed, and the challenges facing further development of this method are discussed in the perspective of future improvement that will be driven by new high resolution and high cadence satellite data, such as received from Hinode and STEREO, and expected from SDO. Title: Collisionless relaxation of ion distributions downstream of laminar quasi-perpendicular shocks Authors: Ofman, L.; Balikhin, M.; Russell, C. T.; Gedalin, M. Bibcode: 2009JGRA..114.9106O Altcode: 2009JGRA..11409106O Directed flow of incident ions provides the free energy which is redistributed in a shock among heated ions and electrons, accelerated particles, and magnetic compression. In low Mach number laminar shock the main channel of conversion is into downstream gyrating ions. Just behind the shock transition the ion distribution is substantially nongyrotropic, which results in spatially periodic variations of the ion pressure and, consequently, in time stationary downstream oscillations of the magnetic field. In the absence of significant level of nonstationarity, gyrotropization is due to the gyrophase mixing and slow. Theoretical analysis of the phenomenon and supporting hybrid simulations are presented. It is shown that these oscillations are more likely to be observed at low Mach number low β shocks, while at higher Mach numbers or higher β they may be obscured by waves crossing the shocks. Title: Hinode/EIS observations of propagating low-frequency slow magnetoacoustic waves in fan-like coronal loops Authors: Wang, T. J.; Ofman, L.; Davila, J. M.; Mariska, J. T. Bibcode: 2009A&A...503L..25W Altcode: 2009arXiv0908.0310W Aims: We report the first observation of multiple-periodic propagating disturbances along a fan-like coronal structure simultaneously detected in both intensity and Doppler shift in the Fe xii 195 Å line with the EUV Imaging Spectrometer (EIS) onboard Hinode. A new application of coronal seismology is provided based on this observation.
Methods: We analyzed the EIS sit-and-stare mode observation of oscillations using the running difference and wavelet techniques.
Results: Two harmonics with periods of 12 and 25 min are detected. We measured the Doppler shift amplitude of 1-2 km s-1, the relative intensity amplitude of 3%-5% and the apparent propagation speed of 100-120 km s-1.
Conclusions: The amplitude relationship between intensity and Doppler shift oscillations provides convincing evidence that these propagating features are a manifestation of slow magnetoacoustic waves. Detection lengths (over which the waves are visible) of the 25 min wave are about 70-90 Mm, much longer than those of the 5 min wave previously detected by TRACE. This difference may be explained by the dependence of damping length on the wave period for thermal conduction. Based on a linear wave theory, we derive an inclination of the magnetic field to the line-of-sight about 59 ± 8°, a true propagation speed of 128 ± 25 km s-1 and a temperature of 0.7 ± 0.3 MK near the loop's footpoint from our measurements.

Appendix is only available in electronic form at http://www.aanda.org Title: Analysis of Active Region and Quiet Sun Spectra from SERTS-99 Observations Authors: Coyner, Aaron J.; Davila, J. M.; Brosius, J. W.; Ofman, L. Bibcode: 2009SPD....40.1216C Altcode: The Solar EUV Research Telescope and Spectrograph is a rocket-based instrument that uses high resolution extreme ultraviolet spectra to investigate features in the solar corona and transition region. The 1999 flight occurred on 24 June 1999 and obtained spectra from both active regions and quiet sun regions on the solar disk covering a spectral bandpass 300-355 angstroms We report here the calibrated intensities and measured linewidths determined from the spatially-averaged spectra of both active regions and quiet sun regions respectively. In addition, we determine a distribution of non-thermal velocity components from the measured linewidths of the identified lines. This distribution provides a quantitative constraint on the available energy of non-thermal origin in the observed regions which is available for coronal heating. Title: Propagating Slow Magnetoacoustic Waves in Coronal Loops Observed by Hinode/EIS Authors: Wang, T. J.; Ofman, L.; Davila, J. M. Bibcode: 2009ApJ...696.1448W Altcode: 2009arXiv0902.4480W We present the first Hinode/EUV Imaging Spectrometer observations of 5 minute quasi-periodic oscillations detected in a transition-region line (He II) and five coronal lines (Fe X, Fe XII, Fe XIII, Fe XIV, and Fe XV) at the footpoint of a coronal loop. The oscillations exist throughout the whole observation, characterized by a series of wave packets with nearly constant period, typically persisting for 4-6 cycles with a lifetime of 20-30 minutes. There is an approximate in-phase relation between Doppler shift and intensity oscillations. This provides evidence for slow magnetoacoustic waves propagating upward from the transition region into the corona. We find that the oscillations detected in the five coronal lines are highly correlated, and the amplitude decreases with increasing temperature. The amplitude of Doppler shift oscillations decrease by a factor of about 3, while that of relative intensity decreases by a factor of about 4 from Fe X to Fe XV. These oscillations may be caused by the leakage of the photospheric p-modes through the chromosphere and transition region into the corona, which has been suggested as the source for intensity oscillations previously observed by Transition Region and Coronal Explorer. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithread structure near the footpoint. Thus, this property may have potential value for coronal seismology in diagnostic of temperature structure in a coronal loop. Title: Propagating Slow Magnetoacoustic Waves in Coronal Loops Observed by Hinode/EIS Authors: Wang, Tongjiang; Ofman, L.; Davila, J. Bibcode: 2009SPD....40.3003W Altcode: We present two cases of propagating slow magnetoacoustic waves in coronal loops observed by Hinode/EIS. In the first case, the 5-min waves were detected in a transition-region line (He II) and five coronal lines (Fe X - Fe XV) at a plage region. We find that the oscillations detected in coronal lines are highly correlated, and the amplitude decreases with increasing temperature. These waves may be caused by the leakage of the p-modes through the chromosphere and transition region into the corona. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithermal fine structure near the footpoint. In the second case, outwardly propagating (on the order of 100 km/s) quasi-periodic disturbances along a fan-like coronal structure were for the first time detected simultaneously in intensity and Doppler shift. The measured amplitudes for the oscillations are consistent with the interpretation in terms of slow magnetoacoustic waves rather than high-speed outflows. The waves contain multiple harmonics of the periods of 12 min and 25 min. Their origin is not clear. The damping length of these low-frequency waves is distinctly longer than that of 5 min waves previously detected by TRACE in the similar structure. A new application of coronal seismology is given based on this observation, with which the true sound speed and temperature near the loop's footpoint are estimated. The work of LO and TJW was supported by NRL grant N00173-06-1-G033. LO was also supported by NASA grant NNG06GI55G. Title: Probing Thermodynamic and Kinematic Properties of a Coronal Streamer Event Formed During the Solar Minimum Authors: Airapetian, Vladimir; Ofman, L.; Sitter, E., Jr.; Kramar, M. Bibcode: 2009SPD....40.1409A Altcode: We present the results of semi-empirical time-dependent fully non-linear magnetohydrodynamic (MHD) simulations of an equatorially confined streamer belt using observational constrains in a two-fluid 2.5D MHD modeling. Specifically, we reproduced the COR1 STEREO observations of an equatorially confined streamer obtained in July 3-17, 2007. For this streamer event we used the PFSS model of the initial coronal magnetic field configuration with the boundary conditions at the photosphere specified by the NSO/GONG magnetogram data. Calculations were performed for nearly isothermal polytropic flow and for the fully thermally conductive case with the two-component (electrons and protons) heat flux, qeff, and the effective temperature, Teff , derived from a semi-empirical state-state model (SG model). We show that our realistic MHD simulations are capable of reproducing basic thermodynamic and kinematic properties of the observed coronal streamer structure at distances between 1.5 to 4 solar radii. Title: Constraints On Coronal Non-thermal Velocities From SERTS 1991-1997 Observations Authors: Coyner, Aaron J.; Davila, J. M.; Ofman, L. Bibcode: 2009SPD....40.1302C Altcode: The determination of non-thermal velocities from spectral line observations provide insight into the availability of additional energy sources within the observed regions of the corona. These non-thermal velocities can be attributed to waves, electron beams, turbulent motions among other potential sources. Observationally constraining these velocities directly limits the available energy for heating within the observed coronal regions. We present the determination of non-thermal velocity distributions from the 397 identified lines from the SERTS 1991-1997 flights covering the spectral range 171-355 angstroms along with the distributions for the 253 lines identified in active regions, the 102 lines from quiet sun regions, and 42 lines from off limb observations respectively. We find that for all four the velocity distributions peak at non-thermal velocities between 23-30 km/s independent of activity level suggesting that many of these non-thermal velocities are likely the result of non-thermal motions of cooling plasma visible in both active and quiet regions; however the active region distribution does exhibit a more pronounced high velocity tail with a secondary bump which could .be the result of a component resulting from heating of the coronal plasma. Title: Three-Dimensional Magnetohydrodynamic Models of Twisted Multithreaded Coronal Loop Oscillations Authors: Ofman, L. Bibcode: 2009ApJ...694..502O Altcode: The multithreaded structure of active region coronal loops was deduced from past spectroscopic observations. Recent high-resolution observations by Transition Region and Coronal Explorer and Hinode satellites provided direct evidence that active region loops consist of multiple magnetic threads filled with plasma with higher density than neighboring loop material. High-resolution observations of loops near a flare site suggest that the threads are twisted or tangled, the magnetic field is not force free, and flows are present. To better understand these observations, we developed for the first time a three-dimensional magnetohydrodynamic model of twisted multithreaded loops that oscillate as a result of an impulsive event. The twist is induced by applying a rotating velocity field at the footpoint of the initially parallel set of threads, and parallel flow is included. The oscillations of the twisted loops are excited by a fast magnetosonic pulse. The evolution and the damping of the fast magnetosonic wave excited in the twisted multithreaded loop are compared to oscillations of a four-parallel-threaded loop. It was found that twisted loop oscillations result in filamented current and velocity structure that cannot be described by the fundamental kink mode. When parallel flow is present, the oscillation induces nonlinear compressive modulation of the flow and density in the threads. The twisted loop oscillates and damps faster than the parallel-threaded loop. The results of the study demonstrate the effects of the twist, internal loop structure, and flow on the evolution of the waves in coronal active region loops. Title: Three-dimensional MHD modeling of waves in active region loops Authors: Ofman, Leon; Selwa, Małgorzata Bibcode: 2009IAUS..257..151O Altcode: Observations show that MHD waves are one of the most important universal processes in the heliosphere. These waves are likely to play an important role in energy transfer in the heliosphere, and they can be used as a diagnostic tool of the properties of the local magneto-fluid environment. Recent observations by TRACE and Hinode satellites provide ample evidence of oscillations in coronal active region loops. The oscillations were interpreted as fast (kink), slow, and Alfvén modes, and the properties of the waves were used for coronal seismology. However, due to the complex interactions of the various modes in the inhomogeneous active region plasma, and due to nonlinearity, idealized linear theory is inadequate to properly describe the waves. To overcome this theoretical shortcoming we developed 3D MHD models of waves in active region loops. We investigated the effects of 3D active region magnetic and density structure on the oscillations and the wave dissipation, and we investigated the oscillation of individual loops. Some loops were constructed to contain several threads and twist. Here, we present the results of our models, and show how they can be used to understand better the properties of the waves, and of the active regions. Title: Development of Solar Wind Model Driven by Empirical Heat Flux and Pressure Terms Authors: Sittler, E. C.; Ofman, L.; Selwa, M. A.; Kramar, M. Bibcode: 2008AGUFMSH13B1537S Altcode: We are developing a time stationary self-consistent 2D MHD model of the solar corona and solar wind as suggested by Sittler et al. (2003). Sittler & Guhathakurta (1999) developed a semi-empirical steady state model (SG model) of the solar wind in a multipole 3-streamer structure, with the model constrained by Skylab observations. Guhathakurta et al. (2006) presented a more recent version of their initial work. Sittler et al. (2003) modified the SG model by investigating time dependent MHD, ad hoc heating term with heat conduction and empirical heating solutions. Next step of development of 2D MHD models was performed by Sittler & Ofman (2006). They derived effective temperature and effective heat flux from the data-driven SG model and fit smooth analytical functions to be used in MHD calculations. Improvements of the Sittler & Ofman (2006) results now show a convergence of the 3-streamer topology into a single equatorial streamer at altitudes > 2 RS. This is a new result and shows we are now able to reproduce observations of an equatorially confined streamer belt. In order to allow our solutions to be applied to more general applications, we extend that model by using magnetogram data and PFSS model as a boundary condition. Initial results were presented by Selwa et al. [2008]. We choose solar minimum magnetogram data since during solar maximum the boundary conditions are more complex and the coronal magnetic field may not be described correctly by PFSS model. As the first step we studied the simplest 2D MHD case with variable heat conduction, and with empirical heat input combined with empirical momentum addition for the fast solar wind. We use realistic magnetic field data based on NSO/GONG data, and plan to extend the study to 3D. This study represents the first attempt of fully self-consistent realistic model based on real data and including semi-empirical heat flux and semi-empirical effective pressure terms. References: Sittler E. C. Jr. and Guhathakurta M., 1999, ApJ, 523, 812-826 Sittler E. C. Jr., Ofman L., Gibson S., Guhathakurta M., Davila J., Skoug R., Fludra A., Holzer T., 2003, Solar Wind 10, 113 Sittler, E. C. Jr. and Ofman L., 2006, ILWS, GOA, India Guhathakurta, M., E. C. Sittler Jr. and L. Ofman, JGR, Vol 111, A11215, 2006. Selwa, M., L. Ofman, E. C. Sittler Jr. and M. Kramar, Development of solar wind model driven by empirical heat flux, SHINE Meeting, 2008. Title: The role of AR topology on excitation, trapping and damping of individual loop oscillations Authors: Selwa, M. A.; Ofman, L. Bibcode: 2008AGUFMSH13A1517S Altcode: We investigate the role of magnetic field topology on individual dense loop oscillation by the means of 3D MHD numerical simulations of two models of idealized active regions (AR's). The first model of AR is initialized as a straight cylinder surrounded by the fieldlines of the same length and orientation. The second model consists of a force-free dipole magnetic configuration and contains a loop with a higher density than its surroundings. Dipole fieldlines have position dependent length and orientation. We study different ways of excitation of transverse loop oscillations by an external pulse and by a nearly eigenmode excitation implemented inside the loop. We find that perturbation acting directly on a single loop excites oscillations both in cylindrical and dipole loop. However, the leakage of the wave energy is larger in a curved loop compared to straight loop. External excitation of the whole AR is efficient in the excitation of oscillation in the straight cylindrical AR, but results in less efficient excitation in the case of dipole AR loop. We claim that excitation of collective motion of straight fieldlines having the same wave-periods and planes of the oscillations requires much less energy than excitation of dipole fieldlines having position-dependent orientation and wave-periods and being excited individually, not having a collective mode of oscillation. We conclude that coherent motion of straight fieldlines is one of the factors that decreases the energy leakage from an oscillating loop, while individual motions of dipole fieldlines require more energy from the source to produce the loop oscillations, and also lead to higher damping rate compared to the straight field case. Title: Acceleration and heating of solar wind ions by turbulent wave spectrum Authors: Ofman, L. Bibcode: 2008AGUFMSH43A1648O Altcode: We model the heating and the acceleration of multi-ion plasma of the solar wind by turbulent spectrum of Alfvénic fluctuations in the resonant and nonresonant frequency range. The modeling effort is guided by the observed properties of the spectrum and the measured physical parameters of the solar wind plasma in the heliosphere in-situ, as well as close to the sun from remote sensing observations. We start with 2.5D multifluid model that includes ion-cyclotron terms to study the nonresonant wave heating and acceleration, and proceed with 2D hybrid model that extends into the resonant frequency range. In addition to protons the model includes helium ions, and other heavy ions, and the results of the turbulent Alfvénic wave spectrum is compared to observation. In the hybrid model the protons and heavy ions are treated kinetically, while the electrons are included as neutralizing background fluid. This model allows to extend the study to resonant frequency range, and explore the nonlinear saturation of the heating for resonant and nonresonant waves. The models are used to explore the effect of non-homogeneous background density across the magnetic field, and of ion beams on the heating by turbulent wave spectrum. Title: 3D MHD Simulations of Excitation and Damping of Vertical Kink Waves in Coronal Active Region Loops Authors: Selwa, M.; Ofman, L. Bibcode: 2008ASPC..397..189S Altcode: We present numerical results of a three dimensional MHD model of an idealized active region field. The active region is initialized as a force-free dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. We study different ways of exciting vertical kink oscillations by velocity: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. These properties are varied in the parametric studies. We find that vertical kink oscillations amplitude is significantly amplified in comparison to horizontal kink oscillations amplitude for exciters located centrally (symmetrically) below the loop, which explains why the pure vertical kink mode is so rarely observed in comparison to the horizontally polarized one. We observe that vertical kink waves in 3D stratified geometry are damped mainly due to wave leakage. We compare our simulation with TRACE observational data and find qualitative agreement. We plan to search for vertical kink modes in Hinode data, and compare to our models. Title: Standing fast magnetoacoustic kink waves of solar coronal loops with field-aligned flow Authors: Gruszecki, M.; Murawski, K.; Ofman, L. Bibcode: 2008A&A...488..757G Altcode: Aims: We refer to the recent observational data of Hinode, which detected weakly-attenuated coronal loop oscillations in the presence of background flow (Ofman & Wang 2008, A&A, 482, L9). Vertical loop oscillations that lasted for three wave periods were reported with a wave period P = 113 ± 2 s, attenuation time τ = 560 ± 260 s, and wave amplitude A{max} = 0.67 ± 0.12 Mm. Ofman & Wang (2008) estimated the flow speed within the range of 74-123 km s-1. We consider impulsively generated standing fast magnetoacoustic kink waves of a straight solar coronal slab with field-aligned internal flow. We aim to determine the influence of such flow on the spatial and temporal signatures of these waves.
Methods: The time-dependent, ideal magnetohydrodynamic equations are solved numerically.
Results: The numerical results show that as a result of wave scattering on inhomogeneous flow kink waves experience stronger attenuation than for a still plasma, while P remains weakly altered by this flow. Numerically evaluated values of A{max} and P are close to the observational data. A value of τ is about two times smaller than observed. Title: Three-dimensional Magnetohydrodynamic Wave Behavior in Active Regions: Individual Loop Density Structure Authors: McLaughlin, J. A.; Ofman, L. Bibcode: 2008ApJ...682.1338M Altcode: We present the numerical results from a three-dimensional (3D) nonlinear MHD simulation of wave activity in an idealized active region in which individual, realistic loop density structure is included. The active region is modeled by an initially force-free, dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. This study represents an extension to the model of Ofman & Thompson. As found in their work, we see that fast wave propagation is distorted by the Alfvén speed profile and that the wave propagation generates field line oscillations, which are rapidly damped. We find that the addition of a high-density loop significantly changes the behavior inside that loop, specifically in that the loop can support trapped waves. We also find that the impact of the fast wave impulsively excites both horizontal and vertical loop oscillations. From a parametric study of the oscillations, we find that the amplitude of the oscillations decreases with increasing density contrast, whereas the period and damping time increase. This is one of the key results presented here: that individual loop density structure can influence the damping rate, and specifically that the damping time increases with increasing density contrast. All these results were compared with an additional study performed on a straight coronal loop with similar parameters. Through comparison with the straight loop, we find that the damping mechanism in our curved loop is wave leakage due to curvature. The work performed here highlights the importance of including individual loop density structure in the modeling of active regions and illustrates the need for obtaining accurate density measurements for coronal seismology. Title: Hinode observations of transverse waves with flows in coronal loops Authors: Ofman, L.; Wang, T. J. Bibcode: 2008A&A...482L...9O Altcode: Aims: We report the first evidence for transverse waves in coronal multithreaded loops with cool plasma ejected from the chromosphere flowing along the threads. These observations are good candidates for coronal seismology.
Methods: We analyzed observations made with Solar Optical Telescope (SOT) on board the Hinode satellite in the Ca II H line filter.
Results: The oscillations are visible for about 3 periods, with a period lasting about 2 min, with weak damping. We see the oscillations in thin threads (~0.5 arcsec) of cool plasma flowing in the coronal loops with speeds in the range 74-123 km s-1.
Conclusions: Observations indicate that the waves exhibit different properties in the various threads. In some threads, the waves are nearly standing fundamental kink modes with a phase speed of about 1250 km s-1, whereas the dynamics of other threads is consistent with propagating fast magnetosonic waves. Based on the observed wave and loop properties and the assumed active region loop density in the range (1-5) × 109 cm-3, the estimated energy flux is sufficient to heat the loops to coronal temperatures, and the average magnetic field in the threads is estimated as 20 ± 7 G. Title: Identification of types of kink modes in coronal loops: principles and application to TRACE results Authors: Wang, T.; Solanki, S.; Selwa, M.; Ofman, L. Bibcode: 2008AGUSMSP31C..08W Altcode: We explore the possible signatures of different types of kink modes (horizontal and vertical oscillations in their fundamental mode and second harmonic) which may arise in coronal loops. Based on the 3D geometrical parameters of 14 TRACE loops of transverse oscillations, we simulate qualitatively the loop displacements due to these types of kink mode oscillations. We find that for many combinations of viewing and loop geometry it is not straightforward to distinguish between the two types of kink modes. We have also considered Doppler signatures and found that these can in principle help to obtain unique identifications of the oscillation modes. We then compared the simulated spatial signatures with the observations for 14 TRACE loops. We find that two cases of loop oscillations previously identified as a fundamental horizontal mode appear to be a fundamental vertical mode, while in two other cases it is not possible to clearly distinguish between a horizontal oscillation of the fundamental mode and the second-harmonic, and in six cases it is not possible to clearly distinguish between a fundamental horizontal mode and a second-harmonic vertical mode. In addition, for the particular case that the oscillating loop has a S-shape, we find that the fundamental vertical oscillation can take on the appearance of the horizontal second harmonic due to projection effects. We also present numerical results of three dimensional MHD model of an idealized active region field with S-shaped field-lines. The active region is initialized as a force-free dipole magnetic configuration with uniform density and contains a loop with a higher density than its surroundings. We introduce a velocity pulse which models the impact of a flare on surrounding fields. Both the qualitative study and the MHD simulation support the conclusion of the presence of fundamental mode of vertical kink oscillations in an S-shaped loop. Our interpretation can naturally solve the puzzle of the absence of the fundamental mode and the apparent presence of second harmonic oscillations observed in a TRACE loop by De Moortel and Brady (2007). Title: Three dimensional MHD models of twisted multi-threaded loop oscillations Authors: Ofman, L. Bibcode: 2008AGUSMSP41C..07O Altcode: The multi-threaded structure of active region coronal loops was deduced from past spectroscopic observations. Recent high resolution observations by TRACE and Hinode provide direct evidence that active region loops consist of multiple magnetic threads filled with plasma with higher density than neighboring loop material. High resolution observations of loops near a flare site suggest that the threads are twisted, and the magnetic field is not force-free. To better understand these observations I developed 3D MHD model of twisted multi-threaded loop oscillations. The twist is induced by applying rotating velocity field at the foot-point of the initially parallel set of threads. The oscillations of the twisted loops are excited by a fast magnetosonic pulse. The evolution and the damping of the fast magnetosonic wave excited in the twisted multi-threaded loop is compared to the wave in single threaded loop, and to parallel threaded loop. The results of the study show the effect of the twist and internal loop structure on the damping of the waves. *Visiting Associate Professor, Tel Aviv University Title: 3D MHD model of kink waves in a loop anchored in a realistic active region Authors: Selwa, Malgorzata; Ofman, Leon; Wang, Tongjiang; Solanki, Sami Bibcode: 2008cosp...37.2804S Altcode: 2008cosp.meet.2804S We present numerical results of three dimensional MHD model of the active region field. The active region is initialized using MDI data of 15 May 2001, 02:57 UT and potential extrapolation of the magnetic field with gravitationally stratified density and contains a loop with a higher density than its surroundings. The potential model imitates the original TRACE AR quite well, however, the choice of particular loop within AR is inaccurate due to limitation of the plane-of-the-sky view. This study represents an extension to the model of Ofman (2007). We introduce a velocity pulse based on TRACE observations to model the impact of a flare on surrounding fields, and study the resulting loop oscillations. The flare is initialized as a semispherical velocity pulse at the bottom of AR and corresponds to the event between loop's footpoints captured by TRACE. We investigate the influence of a realistic dense loop on the excitation and damping of the oscillations and compare our results with TRACE observations. By the means of 3D computer simulation we confirm that considering combination of viewing and loop geometry and Doppler signatures it is straightforward to distinguish between at least two types of kink modes: horizontal and vertical in the real loop observed by Aschwanden et al. (2002). We find that oscillation previously identified as a fundamental horizontal mode (Aschwanden et al. 2002) appears to be a fundamental vertical mode. As such vertical kink oscillations are not as rare compared to horizontal ones as previously thought. Title: Oscillation of twisted multi-threaded loops in coronal active regions Authors: Ofman, Leon Bibcode: 2008cosp...37.2274O Altcode: 2008cosp.meet.2274O Recent high resolution observations by Hinode satellite shows that coronal active region loops near the site of a flare are multi-threaded structures that are oscillating, and may be twisted non-force-free structures. The physical properties of the threads are not identical, and the oscillations can vary in each thread. I report the results of three-dimensional MHD simulation of a twisted non-force-free multi-threaded loop, that exhibits damped oscillations. The loop was initialized with four threads of high density plasma (compared to surrounding corona), and the twist was obtained by inducing rotation velocity field centered at one footpoint. The resulting twisted structure was impacted by a fast magnetosonic pulse that produced damped oscillations in the structure. I compare the results of the twisted multi-threaded loop model to oscillations of a straight (untwisted) multi-threaded loop, and to Hinode observations of oscillating coronal loop structures. I find that the twist affects the oscillations considerably, which suggest a new method for diagnostic of the non-force-free field. Title: 3D simulations of damping of waves in a loop anchored in a dipole active region: does resonant absorption take place in realistic loops? Authors: Selwa, M. A.; Ofman, L. Bibcode: 2007AGUFMSH53A1056S Altcode: We present numerical results of three dimensional MHD model of an idealized active region field. The active region is initialized as a force-free dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. This study represents an extension to the model of McLaughlin & Ofman (2007). We examine the impact of different density profiles of the loop on damping of kink waves by introducing a velocity pulse which models the impact of a flare on surrounding fields. We compare our results with a straight cylinder model of the loop which can be solved analytically. We study the resulting loop oscillations and compare our results with TRACE observations. Title: Propagating Alfven waves in Coronal Loops Observed by Hinode Authors: Ofman, L.; Wang, T. Bibcode: 2007AGUFMSH52C..02O Altcode: Observations made with Solar Optical Telescope (SOT) on board the Hinode satellite reveal that coronal loop with flowing cool chromospheric material exhibit periodic oscillation. Additional related observations were obtained by EIS imaging spectrometer. The oscillations are visible for about 3 periods in multiple strands of the loops in transverse direction to the loop axis, suggesting that these are Alfvén waves propagating along the strands of the loop. The period of the oscillations is about 2 minutes and the damping time is on the order of 1000 seconds. The flow velocity of the cool material and the phase speed of the waves were determined directly, by comparing frames of the observed time sequence. The phase speed agrees with the expected speed of standing waves for the observed loop length and period. We find that MHD model of the waves in a coronal loop is in good agreement with observations. We also find that the energy flux in the observed waves appears to be sufficient to heat the loop to coronal temperatures. Title: Numerical Simulations of Slow Standing Waves in a Curved Solar Coronal Loop Authors: Selwa, M.; Ofman, L.; Murawski, K. Bibcode: 2007ApJ...668L..83S Altcode: We consider slow standing waves that are impulsively excited in a curved solar coronal loop. The numerical model we implement includes the effect of nonlinearity in the frame of two-dimensional ideal magnetohydrodynamics. We discuss the role of curved magnetic field lines and of the slow and fast pulses overlapping at one of the loop's footpoints in the excitation and attenuation of slow standing waves. We find that slow waves can be excited faster in curved loops than in slabs due to the combined effect of the pulse inside and outside the loop. Title: The Energetics of the Slow Solar Wind Authors: Ofman, L. Bibcode: 2007ASPC..369..569O Altcode: Observations and numerical models show that the slow solar wind is associated with coronal streamers. However, the exact heating and acceleration mechanism of the slow wind is unknown. Moreover, the energization mechanism is likely to be different for electrons, protons, and heavy ions. Some of the main objectives of Solar-B is to understand the opening of magnetic field and heating of the coronal plasma that forms the solar wind. Recent results of three-fluid numerical models of the slow solar wind heating and acceleration in coronal streamers are shown. The possible heating mechanisms of electrons, protons, and heavy ions in the slow wind, and the formation of open flux in streamers is discussed. The relation of the numerical results to past observations by SOHO, and Ulysses spacecraft, and future observations with Solar-B is discussed. Title: Attenuation of Alfvén waves in straight and curved coronal slabs Authors: Gruszecki, M.; Murawski, K.; Solanki, S. K.; Ofman, L. Bibcode: 2007A&A...469.1117G Altcode: Aims:We consider impulsively generated Alfvén waves in coronal loops to investigate the role of energy leakage on wave attenuation, which includes lateral leakage, leakage into dense photospheric regions and nonlinear driving of magnetosonic waves.
Methods: A coronal loop is modelled either as a straight magnetic slab or as a curved slab of smooth mass density profiles. We perform numerical simulations of 2.5D ideal magnetohydrodynamic equations to determine the signatures of Alfvén waves.
Results: The numerical results show that lateral leakage of Alfvén waves is significant in comparison to leakage into the photospheric regions for realistic corona to photospheric density ratios. Energy leakage is enhanced by curvature of magnetic field lines and for large amplitude Alfvén waves for which nonlinear driving of magnetosonic waves is more significant than in the linear regime. Title: Two-dimensional hybrid model of wave and beam heating of multi-ion solar wind plasma Authors: Ofman, L.; ViñAs, A. F. Bibcode: 2007JGRA..112.6104O Altcode: 2007JGRA..11206104O We study the heating and the acceleration of protons and heavy ions by waves in the solar wind, as well as the nonlinear influence of heavy ions on the wave structure, using a two-dimensional (2-D) hybrid model. Protons and heavy ions are treated kinetically by solving their equations of motion in the self-consistent electric and magnetic fields of the waves, while electrons are treated as a neutralizing background fluid. We use the 2-D hybrid code to investigate more realistic 2-D plasma model than previous 1-D simulation and analytical studies, which allows parallel as well as obliquely propagating waves and localized driver. Using the hybrid code, we consider for the first time the heating and acceleration of protons and heavy ions by a driven-input spectrum of Alfvén/cyclotron waves and by heavy ion beam in the multispecies coronal plasma in two spatial dimensions. We find that the ion beam is more efficient in generating temperature anisotropy than the driven wave spectrum in our model. We discuss the observational implication of the results to the solar wind. Title: The Influence Of Helium Ions And Heating On Coronal Streamer Structure Authors: Ofman, Leon Bibcode: 2007AAS...210.3001O Altcode: 2007BAAS...39..142O The magnetic and compositional structure and dynamics of a coronal streamer is investigated using thermally conductive multi-fluid model. The variation of proton density, and He I/He II abundances is studied as a function of latitude and height. The effects of various heating rates, and heating profiles on the formation, and the compositional structure of streamers are studied. The dependence of the acceleration profile of the multi-component slow solar wind, as well as the properties of the differential ion outflow on the heat input is investigated numerically and compared to observations. Title: Coronal Heating and Acceleration of the Solar Wind Authors: Ofman, L. Bibcode: 2007ASPC..370...82O Altcode: The heating of the solar corona to millions of degrees have puzzled solar physicist for decades. The related process of solar wind acceleration is also not well understood. Although, the exact physical mechanisms of these processes are being debated, current spectroscopic, and white light observations of the corona provide important constrains on the possible models. I provide a brief overview of the relevant observations by Ulysses, SOHO, and RHESSI spacecrafts, and discuss the theoretical models of the possible heating and acceleration mechanisms. I show the results of computations that lead towards the understanding of these processes. Title: 2d Simulations Of Excitation And Damping Of Vertical Kink Waves Authors: Selwa, Malgorzata; Murawski, K.; Solanki, S. K.; Ofman, L. Bibcode: 2007AAS...210.9115S Altcode: 2007BAAS...39S.206S We consider different kinds of excitation of fast vertical kink standing waves in a solar coronal loop that is embedded in a potential arcade. The two dimensional numerical model we implement includes the effects of field line curvature and nonlinearity on the excitation and damping of standing fast magnetosonic waves. We investigate the effects of a driven sinusodial pressure pulse and compare it with an impulsive excitation by a pressure pulse that impacts the overlaying loop. The results of the numerical simulations reveal wave signatures which are characteristic of vertical loop oscillations seen in recent TRACE observational data. Title: 3d Simulations Of Excitation And Damping Of Waves In A Dipole Active Region Authors: Selwa, Malgorzata; Ofman, L.; McLaughlin, J. Bibcode: 2007AAS...210.9114S Altcode: 2007BAAS...39R.206S We present numerical results of three dimensional MHD model of an idealized active region field. The active region is initialized as a force-free dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. This study represents an extension to the model of McLaughlin & Ofman (2007). We examine the impact of a different density profiles of the loop on excitation and damping of kink waves by introducing a velocity or pressure pulse which models the impact of a flare on surrounding fields. We study the resulting loop oscillations and compare our results with TRACE observations. Title: Understanding coronal heating and solar wind acceleration: Case for in situ near-Sun measurements Authors: McComas, D. J.; Velli, M.; Lewis, W. S.; Acton, L. W.; Balat-Pichelin, M.; Bothmer, V.; Dirling, R. B.; Feldman, W. C.; Gloeckler, G.; Habbal, S. R.; Hassler, D. M.; Mann, I.; Matthaeus, W. H.; McNutt, R. L.; Mewaldt, R. A.; Murphy, N.; Ofman, L.; Sittler, E. C.; Smith, C. W.; Zurbuchen, T. H. Bibcode: 2007RvGeo..45.1004M Altcode: The solar wind has been measured directly from 0.3 AU outward, and the Sun's atmosphere has been imaged from the photosphere out through the corona. These observations have significantly advanced our understanding of the influence of the Sun's varying magnetic field on the structure and dynamics of the corona and the solar wind. However, how the corona is heated and accelerated to produce the solar wind remains a mystery. Answering these fundamental questions requires in situ observations near the Sun, from a few solar radii (R S ) out to ~20 R S , where the internal, magnetic, and turbulent energy in the coronal plasma is channeled into the bulk energy of the supersonic solar wind. A mission to make such observations has long been a top priority of the solar and space physics community. The recent Solar Probe study has proven that such a mission is technically feasible and can be accomplished within reasonable resources. Title: Three-dimensional MHD Model of Wave Activity in a Coronal Active Region Authors: Ofman, L. Bibcode: 2007ApJ...655.1134O Altcode: MHD wave activity associated with a flare was observed in coronal active region AR 8270 in the extreme ultraviolet (EUV) by the Transition Region and Coronal Explorer (TRACE) satellite on 1998 July 14. In this study, a three-dimensional MHD model of the active region field was initialized using a National Solar Observatory (NSO) Kitt Peak magnetogram and potential extrapolation of the magnetic field, together with gravitationally stratified density. To model the observed wave activity following the flare, a velocity pulse was launched into a model active region from below. It was found that the global oscillations in the model active region are in good qualitative agreement with observations. The main difference between the observations and the model is in the oscillation of several individual loops that damp on longer timescales compared to the corresponding magnetic field line oscillation damping in the model. Title: Observing The He II Off-Limb Corona From Solar Orbiter Authors: Giordano, S.; Fineschi, S.; Ofman, L.; Mancuso, S.; Abbo, L. Bibcode: 2007ESASP.641E..31G Altcode: The SOLar Orbiter, SOLO, represents a unique platform for off-limb solar corona observations, because of the near-Sun, helio-synchronous and out-of-ecliptic perspective. We discuss as the simultaneous monochromatic imaging of the UltraViolet spectral lines emitted by the neutral hydrogen (HI) and singly ionized helium ions (HeII) in solar corona in addition to the visible light imaging allows to use the Doppler dimming diagnostics to derive velocity maps of the full corona and the maps of the abundance of helium relative to hydrogen. We compute the expected HeII 303. 78 A, HI Lyα 1215. 56 A and Visible Light emissivity for a coronal model derived from a MHD computation of the coronal physical parameters, such as electron and ions density, kinetic temperatures and outflow velocity in the region from 1. 2 to 5. 0 solar radii. The UV lines are Doppler dimmed in presence of outflows, moreover we take into account the possibility of pumping effect on the He II line due to nearby Si XI 303. 32 A spectral line which can excited the He II line for plasma speeds around 450 km/s. We study as the helium coronal diagnostics from the out-of-ecliptic and helio-synchronous observations can moreover address the understanding of the processes leading to the elemental composition of the coronal streamers and hole boundaries, as example to establish roles of gravitational settling and Coulomb drag. Title: 3D MHD Model of Waves in an Active Region Authors: Ofman, L.; McLaughlin, J. Bibcode: 2006AGUFMSH33B0416O Altcode: Wave activity associated with flares and CME's have been observed with SOHO, TRACE, and other satellites. The propagation and dissipation of the waves provide information on the coronal magnetic structures. In particular, MHD waves were observed in coronal active region AR8270 following a flare with TRACE on July 14, 1998. In this study, three dimensional MHD model of the active region field was constructed using National Solar Observatory (NSO) Kitt Peak magnetogram and potential extrapolation of the magnetic field, together with gravitationally stratified density as the initial state. The model was evolved to steady state, and a velocity pulse with amplitude of ~100 km/sec was launched into the active region from below to mimic the observed effect of the flare. It was found that the global oscillations in the model active region are in good qualitative agreement with observations. The main difference between the observations and the model is in the oscillation of several individual loops that damp on longer time scale, compared to the corresponding magnetic field line oscillation damping in the model. We investigate the effects of global active region magnetic structure, as well as local loop structure on the trapping and damping of waves in the active region. Title: Numerical simulations of vertical oscillations of a multi-stranded coronal loop Authors: Gruszecki, M.; Murawski, K.; Selwa, M.; Ofman, L. Bibcode: 2006A&A...460..887G Altcode: Aims. We consider impulsively generated oscillations in a 2D model of a curved solar coronal arcade loop that consists of up to 5 strands of dense plasma.
Methods: . First we do a simulation for a loop which consists of two curved strands. We evaluate by means of numerical simulations the influence of the distance between the strands and their number on wave period, attenuation time, and amplitudes of standing kink waves.
Results: . The results of the numerical simulations reveal that only strands which are very close to each other (distance comparable to the strand width) considerably change the collective behavior of kink oscillations. More distant strands also exhibit weak coupling of the oscillations. However, their behavior can essentially be explained in terms of separate oscillating loops. We compare the numerical results with recent TRACE observational findings, and find qualitative agreement.
Title: 3D MHD Wave Behavior in Active Regions: Trapped Modes Authors: McLaughlin, J. A.; Ofman, L. Bibcode: 2006AGUFMSH33B0413M Altcode: We present the numerical results of a fast magnetoacoustic wave propagating within an idealized active region. The active region is modeled by an initially force-free, dipole magnetic configuration with gravitationally stratified density and contains a loop with a higher density than its surroundings. This study represents an extension to the model of Ofman &Thompson (2002). As found in their work, we see that fast wave propagation is distorted by the Alfvén speed profile and that the wave propagation generates fieldline oscillations and these oscillations are rapidly damped. Inside the high density loop, we find that the amplitude of these oscillations decreases as the density contrast, ξ, increases. We also find that the high density loop undergoes both vertical and horizontal oscillations. We calculate how the rate of wave damping in our loop varies with ξ and find a local minimum at about ξ=2.5, and we argue that this is evidence of wave trapping. Thus, this work illustrates the importance of obtaining accurate loop density measurements for coronal seismology. Title: Semi-Empirically Derived Heating Function of the Corona-Heliopshere During the Whole- Sun Month Authors: Guhathakurta, M.; Sittler, E.; Ofman, L. Bibcode: 2006AGUFMSH23B0354G Altcode: In spite of many recent developments in observations and models of the solar corona, the exact form of the heating function of the solar wind plasma is unknown. Here we attempt to make some progress on that problem by applying a previously developed simplified magnetohydrodynamic model to a unique synthesis of remote sensing coronal observations from SOHO and Spartan 201 and in-situ data from Ulysses during the quiescent phase of solar cycle 23 (1995-1997) which also included the Whole Sun Month (August/September, 1996) study period. Our analysis provides for the first time an empirically derived estimate of the heat flux and temperature profile of the corona and interplanetary medium as a function of latitude and radial distance for this data set. Our results suggest that the effective heat flux and temperature may include thermal and non-thermal components possibly providing as much as half of the total heat input. The primary contribution of our analysis is that parameters calculated from our model provide insight into the energy deposition profile and the model results can be used as a test of observations of flow speed and temperature using different observational techniques for this period. The main limitations of the model are calculations of the magnetic field in equatorial regions, and the neglect of force balance across field lines. Title: Semiempirically derived heating function of the corona heliosphere during the Whole Sun Month Authors: Guhathakurta, M.; Sittler, E. C.; Ofman, L. Bibcode: 2006JGRA..11111215G Altcode: In spite of many recent developments in observations and models of the solar corona, the exact form of the heating function of the solar wind plasma is unknown. Here we attempt to make some progress on that problem by applying a previously developed simplified magnetohydrodynamic model to a unique synthesis of remote sensing coronal observations from SOHO and Spartan 201, and in-situ data from Ulysses spacecraft during the quiescent phase of solar cycle 23 (1995-1997) which also included the Whole Sun Month (August/September 1996) study period. Our analysis provides for the first time an empirically derived estimate of the heat flux and temperature profile of the corona and interplanetary medium over the solar polar regions as a function of latitude and radial distance for this data set. The latitudinal and radial variation is extended to include the equatorial regions but with less fidelity given the significant structure associated with the streamer belt. Our results suggest that both thermal and nonthermal heating terms contribute to the temperature and heat flux in the low corona, particularly above the poles, with the non-thermal component possibly providing as much as half of the total heat input. Title: Improved input to the empirical coronal mass ejection (CME) driven shock arrival model from CME cone models Authors: Xie, H.; Gopalswamy, N.; Ofman, L.; St. Cyr, O. C.; Michalek, G.; Lara, A.; Yashiro, S. Bibcode: 2006SpWea...410002X Altcode: We study the Sun-Earth travel time of interplanetary shocks driven by coronal mass ejections (CMEs) using empirical cone models. Three different cone models have been used to obtain the radial speeds of the CMEs, which are then used as input to the empirical shock arrival (ESA) model to obtain the Sun to Earth travel time of the shocks. We compare the predicted and observed shock transit times and find that the accuracy of the ESA model is improved by applying CME radial speeds from the cone models. There are two ways of calculating the shock travel time: using the ESA model or using the simplified ESA formula obtained by an exponential fit to the ESA model. The average mean error in the travel time with the cone model speeds is 7.8 hours compared to 14.6 hours with the sky plane speed, which amounts to an improvement of 46%. With the ESA formula, the corresponding mean errors are 9.5 and 11.7 hours, respectively, representing an improvement of 19%. The cone models minimize projection effects and hence can be used to obtain CME radial speeds. When input to the ESA model, the large scatter in the shock travel time is reduced, thus improving CME-related space weather predictions. Title: Three-Dimensional MHD Models of Waves in Active Regions: Application to Coronal Seismology Authors: McLaughlin, J. A.; Ofman, L. Bibcode: 2006ESASP.617E.102M Altcode: 2006soho...17E.102M We present results from three-dimensional MHD simulations of the behaviour of MHD waves in 3D models of coronal active regions and loops. The models of the active regions are constructed by using a dipole magnetic field and gravitationally stratified coronal density structure. We compare the main features of the model with those seen recently by the SOHO and TRACE satellites and investigate the application of the results to coronal seismology. We discuss the possible applications of STEREO data to the improvement of our model. Title: Waves In Active Regions: Comparing Observations And 3D MHD Models Authors: Ofman, Leon; McLaughlin, J. Bibcode: 2006SPD....37.1802O Altcode: 2006BAAS...38..246O Recent TRACE observations of active regions in EUV shows waveactivity in coronal active regions following impulsive events.Motivated by these observations we construct 3D MHD models of theactive regions using photospheric magnetic field as boundarycondition from SOHO MDI or Kitt Peak data, and nonuniform densitystructure to model individual loops. We introduce several forms ofvelocity and density pulses to model the effects of impulsiveevents, such as flares, and follow the evolution of the modelactive region. We find good agreement between the observedevolution of active regions, and the 3D MHD models. Thus, wedemonstrate that the 3D MHD models can be used for coronalseismology. In the near future STEREO data may provide improvedinput for these models. Title: Oscillations of Hard X-Ray Flare Emission Observed by RHESSI: Effects of Super-Alfvénic Beams? Authors: Ofman, L.; Sui, L. Bibcode: 2006ApJ...644L.149O Altcode: Recent Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) observations of hard X-ray (>25 keV) emission from several flares show damped oscillations with periods of 2-4 minutes and damping times of several tens of minutes. We analyze the observations of the 2005 January 19 flare that show the quasi-periodic, damped oscillations, and we propose a physical mechanism for this phenomenon. Namely, we suggest that super-Alfvénic beams in the vicinity of the reconnection region lead to the excitation of the oscillations. The oscillations damp as the flows and the reconnecting magnetic fields dissipate during the decay phase of the flare. We show the results of 2.5-dimensional viscoresistive MHD simulations of this mechanism, and we find qualitative agreement with the RHESSI observations. In addition, we find that the flows destabilize the current sheet, which leads to an increased reconnection rate compared to the case without the beams. Title: 3d Mhd Wave Behavior In Active Regions: Modeling Techniques Authors: McLaughlin, James A.; Ofman, L. Bibcode: 2006SPD....37.0116M Altcode: 2006BAAS...38..218M We have performed simulations of three-dimensional MHD wave propagation in models of coronal active regions. Here, we present descriptions of the methodology and techniques that are used in the construction of such simulations. These include:1) The MHD equations solved and the velocity perturbations used to simulate, for example, incoming EIT waves.2) The construction of the active region model using extrapolations of the observed photospheric magnetic field and gravitational stratification of the coronal density structure.3) The inclusion of the density structure of individual, realistic coronal loops using a new technique.We also discuss the application of the model to coronal seismology and the possibility of using STEREO data to the improvement of the simulations. Title: 3D MHD models of waves in active regions: application to coronal seismology Authors: McLaughlin, J. A.; Ofman, L. Bibcode: 2006AGUSMSH52A..06M Altcode: We present results from three-dimensional MHD simulations of the behavior of MHD waves in realistic models of coronal active regions. The models of the active regions are constructed by using the observed photospheric magnetic field and gravitationally stratified coronal density structure with individual loops. We compare the main features of the model with those seen recently by the SOHO and TRACE satellites, and investigate the application of the results to coronal seismology. We discuss the possible application of STEREO data to the improvement of our model. Title: 2D MHD model of the solar corona and solar wind: Recent results Authors: Sittler, E. C., Jr.; Ofman, L. Bibcode: 2006ilws.conf..128S Altcode: We have been developing a self-consistent 2D MHD steady-state model of the solar corona and solar wind. This model is empirically constrained by 2D maps of the effective temperature, Teff , and heat flux, qeff , as originally derived by Sittler and Guhathakurta or SG model. The SG model has been applied to Mark II K-coronameter data, Skylab, Spartan and SOHO/LASCO white light coronagraph data, plus plasma and magnetic field Ulysses data. Our model uses the MHD conservation equations of mass, momentum and energy with a multipole expansion of the coronal magnetic field up to octupole term as the initial state for the MHD solutions. At present our MHD solutions are confined between the coronal base at 1.03 RS and 5 RS and will be expanded to larger heliocentric distances in the future. In order to make our MHD solutions more tractable, we have fit smooth analytical functions to Teff and qeff derived from the data-driven SG model. We will present solutions under these conditions, some of the difficulties we have had to deal with and show the future direction of our research. Title: Magnetohydrodynamic waves throughout the heliosphere Authors: Ofman, L. Bibcode: 2006cosp...36.2675O Altcode: 2006cosp.meet.2675O Magnetohydrodynamic waves are observed in the solar corona the solar wind and in planetary magnetospheres and play an important role in energy transport in heliospheric plasma Observations of the MHD waves serve as a diagnostic tool of heliospheric dynamical processes and of the magnetized plasma structures throughout the heliosphere Thus the observations and the theoretical studies of MHD waves advances our understanding of important heliospherical processes which governs the sun s influence on earth I will present an overview of current observations of MHD waves throughout the heliosphere and of recent theoretical and computational models of MHD waves in heliospheric plasma I will discuss how cross-disciplinary international collaborative study of the universal MHD wave processes in the heliosphere can be carried out during IHY 2007 Title: Wave acceleration of the fast solar wind Authors: Ofman, Leon Bibcode: 2006AdSpR..38...64O Altcode: Observations show that the solar wind exhibits two modes of outflow: the slow (∼400 km s -1), high density, highly variable wind that emerges from equatorial solar regions, and the high latitude, fast (∼800 km s -1), low density, steady solar wind. The bi-modal solar wind outflow is most evident near minima of solar activity. Theoretical studies of the fast solar wind in open magnetic structures motivated by SOHO, Ulysses, and Helios observations indicate that both, high frequency kinetic waves, and low frequency MHD waves play a role in its acceleration and heating. Ion-cyclotron waves have been suggested as the main energy source of the solar wind. However, there are theoretical difficulties with the ion-cyclotron wave heating of the protons, and these waves do not heat electrons. Low frequency MHD waves are still the best candidates to transport momentum and energy far from the Sun, to accelerate the solar wind on large spatial scales. I will present recently developed two-dimensional three-fluid model that includes explicit wave acceleration, and visco-resistive dissipation. The model describes electrons, protons, and minor ions as three coupled fluids that are heated by different heating processes with the parameters constrained by observations. I will present the results of 2.5D three-fluid simulations of the fast solar wind plasma that combine the effects of MHD waves self-consistently, and ion-cyclotron waves parametrically on the acceleration and heating processes. I will present the results of hybrid kinetic models of ion-cyclotron wave heating of the heavy ions in the solar wind plasma. Title: A 3D Numerical Toolkit for Modeling the Heliosphere Authors: Spicer, D. S.; Davila, J. M.; Ofman, L. Bibcode: 2005AGUFMSH11A0258S Altcode: We present results from a numerical toolkit that can be used by observers, analysts, and modelers to study solar activity and its effect on the heliosphere. The core of the toolkit is a 3D AMR unstructured mesh high order Godunov code that was orginally designed to model the magnetospheric-ionospheric system. We plan to make the code available in portable code form through the CCMC. Title: Two-dimensional hybrid modeling of wave heating in the solar wind plasma Authors: Ofman, L.; Vinas, A. Bibcode: 2005AGUFMSH53A1253O Altcode: We study the heating and the acceleration of protons, and heavy ions by waves in the solar wind, as well as the nonlinear influence of heavy ions on the wave structure using a 2D hybrid model. Protons and heavy ions are treated kinetically by solving their equations of motion in the self-consistent electric and magnetic fields of the waves, while electrons are treated as a neutralizing background MHD fluid. We use the 2D hybrid code to investigate more realistic obliquely propagating waves, boundary conditions, and background field structures, than previous 1D-simulation and analytical studies. Using the 2D hybrid code we consider for the first time the heating and acceleration of protons and heavy ions by a driven-input spectrum of Alfvén/cyclotron waves in the multi-species coronal plasma. We discuss the observational implication of the results to the solar wind, as well as the relation to the acceleration of stellar winds with hot magnetized coronae. Title: Solar Probe: Humanity's First Visit to a Star (Invited) Authors: McComas, D. J.; Velli, M.; Lewis, W. S.; Acton, L. W.; Balat-Pichelin, M.; Bothmer, V.; Dirling, R. B.; Eng, D. A.; Feldman, W. C.; Gloeckler, G.; Guhathakurtha, M.; Habbal, S. R.; Hassler, D. M.; Mann, I.; Maldonado, H. M.; Matthaeus, W. H.; McNutt, R. L.; Mewaldt, R. A.; Murphy, N.; Ofman, L.; Potocki, K. A.; Sittler, E. C.; Smith, C. W.; Zurbuchen, T. H. Bibcode: 2005ESASP.592..279M Altcode: 2005ESASP.592E..42M; 2005soho...16E..42M No abstract at ADS Title: Multifluid Models of the Solar Wind Authors: Ofman, L. Bibcode: 2005ESASP.592..205O Altcode: 2005ESASP.592E..32O; 2005soho...16E..32O No abstract at ADS Title: High-frequency Alfvén waves in multi-ion coronal plasma: Observational implications Authors: Ofman, L.; Davila, J. M.; Nakariakov, V. M.; ViñAs, A. -F. Bibcode: 2005JGRA..110.9102O Altcode: 2005JGRA..11009102O We investigate the effects of high-frequency (of order ion gyrofrequency) Alfvén and ion-cyclotron waves on ion emission lines by studying the dispersion of these waves in a multi-ion coronal plasma. For this purpose we solve the dispersion relation of the linearized multifluid and Vlasov equations in a magnetized multi-ion plasma with coronal abundances of heavy ions. We also calculate the dispersion relation using nonlinear one-dimensional hybrid kinetic simulations of the multi-ion plasma. When heavy ions are present the dispersion relation of parallel propagating Alfvén cyclotron waves exhibits the following branches (in the positive Ω - k quadrant): right-hand polarized nonresonant and left-hand polarized resonant branch for protons and each ion. We calculate the ratio of ion to proton velocities perpendicular to the direction of the magnetic field for each wave modes for typical coronal parameters and find strong enhancement of the heavy ion perpendicular fluid velocity compared with proton perpendicular fluid velocity. The linear multifluid cold plasma results agree with linear warm plasma Vlasov results and with the nonlinear hybrid simulation model results. In view of our findings we discuss how the observed nonthermal line broadening of minor ions in coronal holes may relate to the high-frequency wave motions. Title: Semi-Empirical Model of Electron Heat Flux: Soho and Ulysses Observations Authors: Sittler, E. C., Jr.; Skoug, Ruth; Ofman, Leon; Fludra, Andrezej Bibcode: 2005ESASP.592..445S Altcode: 2005soho...16E..78S; 2005ESASP.592E..78S No abstract at ADS Title: MHD Waves and Heating in Coronal Holes Authors: Ofman, Leon Bibcode: 2005SSRv..120...67O Altcode: Coronal holes have been identified as source regions of the fast solar wind, and MHD wave activity has been detected in coronal holes by remote sensing, and in situ in fast solar wind streams. I review some of the most suggestive wave observations, and discuss the theoretical aspects of MHD wave heating and solar wind acceleration in coronal holes. I review the results of single fluid 2.5D MHD, as well as multi-fluid 2.5D MHD models of waves in coronal holes, the heating, and the acceleration of the solar wind be these waves. Title: Modeling Wave Activity in Coronal Active Regions Authors: Ofman, L. Bibcode: 2005AGUSMSH13B..02O Altcode: Wave activity in coronal active regions has been detected recently in EUV and as Doppler velocity oscillations by SOHO, and in EUV by TRACE. The properties of the waves are determined by the excitation mechanism, and by the local physical conditions, such as magnetic field strength and geometry, temperature, and density. It has been demonstrated that the phase speeds of the various wave modes can be determined from observations. Using 3D MHD model I investigate the generation, propagation, and damping of MHD waves in active regions, with the goal of developing a diagnostic tool of active region physical properties. Photospheric magnetograms were used as the boundary conditions for the magnetic field model, and the initial state was constructed using force-free extrapolation, and gravitationally stratified density. Here I expand previous studies, and investigate possible excitation mechanism, as well as the damping of the transverse oscillations due to resistivity, and leakage. I also investigate the generation, propagation, and damping of longitudinal oscillations in the active region loops. In the present study improved boundary and initial conditions are developed, and the effects of chromospheric coupling on the excitation and damping of the waves are investigated. Title: Improved Empirical CME Arrival Time Model Via Cone Model Authors: Xie, H.; Gopalswamy, N.; Ofman, L.; Michalek, G.; Lara, A.; Yashiro, S. Bibcode: 2005AGUSMSH53A..09X Altcode: In this study, we compare the results obtained from two cone models and carry out the statistical study of the distribution of the actual size and space speed of Coronal Mass Ejections (CMEs). We improved the existing empirical CME arrival (ECA) model, based on previously developed empirical models and provided the prediction of CME transit time from the Sun to the Earth. The previous ECA model was in good agreement with the observations for high-speed CMEs. However, the agreement was not as good for low-speed events. One of possible reasons may be due to errors caused by the significant scatter of CME projection speeds in low projected-speed events. Using the cone models we reduced the errors and improved the accuracy of the ECA model by applying the cone models to halo CMEs erupted from near disk center of the Sun (within < 30 deg.) to determine the actual speed. We found that both cone models provide similar improved accuracy for the arrival time. Title: Three dimensional MHD models of active region loops Authors: Ofman, Leon Bibcode: 2005AdSpR..36.1572O Altcode: Present imaging and spectroscopic observations of active region loops allow to determine many physical parameters of the coronal loops, such as the density, temperature, velocity of flows in loops, and the magnetic field. However, due to projection effects many of these parameters remain ambiguous. Three dimensional (3D) imaging in EUV by the STEREO spacecraft will help to resolve the projection ambiguities, and the observations could be used to setup 3D MHD models of active region loops to study the dynamics and stability of active regions. Here the results of 3D MHD models of active region loops, and the progress towards more realistic 3D MHD models of active regions are presented. In particular the effects of impulsive events on the excitation of active region loop oscillations, and the generation, propagations and reflection of EIT waves are shown. It is demonstrated how 3D MHD models together with 3D EUV observations can be used as a diagnostic tool for active region loop physical parameters, and to advance the science of the sources of solar coronal activity. Title: Coronal Heating in Open vs. Closed Field Authors: Ofman, L. Bibcode: 2004ESASP.575...41O Altcode: 2004soho...15...41O No abstract at ADS Title: Transverse Oscillations in a Coronal Loop Arcade Authors: Verwichte, E.; Nakariakov, V. M.; Ofman, L.; Deluca, E. E. Bibcode: 2004ESASP.575..460V Altcode: 2004soho...15..460V No abstract at ADS Title: Alfvén waves in the solar corona, the solar wind, and the magnetosphere Authors: Ofman, L. Bibcode: 2004AGUFMSM44A..02O Altcode: Observations and theoretical models show that Alfvén waves play an important role in many physical processes taking place in the plasma of the "local cosmos." For example, Alfvén waves are still the major candidates for the acceleration and heating of the fast solar wind, since they were proposed nearly 4 decades ago. Recently, MHD waves were observed in coronal loops in the EUV with the TRACE satellite. The SOHO, and TRACE instrument provide evidence for slow magnetosonic waves in coronal plumes. In-situ Helios and Ulysses spacecraft find ample evidence for the presence of propagating Alfvén waves in the solar wind. The CLUSTER mission provides for the first time multi-point view of the magnetospheric and solar wind plasma environment, and in particular high cadence magnetic field measurements with the Fluxgate Magnetometer (FGM), that enables to study the properties of Alfvén waves in various parts of the magnetosphere simultaneously. I will discuss the observations and modeling of Alfvén waves starting from the low corona (loops), continuing into the solar wind, the magnetosphere, and to the auroral ionosphere. I will present the results of MHD, multifluid, and hybrid models of low-frequency (MHD), as well as kinetic Alfvén waves in the plasma in various parts of the "local cosmos", and I will discuss the role Alfvén waves play in the energization of the plasma, and as a diagnostic tool of the plasma physical processes. Title: Characteristics of transverse oscillations in a coronal loop arcade Authors: Verwichte, E.; Nakariakov, V. M.; Ofman, L.; Deluca, E. E. Bibcode: 2004SoPh..223...77V Altcode: TRACE observations from 15 April 2001 of transverse oscillations in coronal loops of a post-flare loop arcade are investigated. They are considered to be standing fast kink oscillations. Oscillation signatures such as displacement amplitude, period, phase and damping time are deduced from 9 loops as a function of distance along the loop length. Multiple oscillation modes are found with different amplitude profile along the loop length, suggesting the presence of a second harmonic. The damping times are consistent with the hypothesis of phase mixing and resonant absorption, although there is a clear bias towards longer damping times compared with previous studies. The coronal magnetic field strength and coronal shear viscosity in the loop arcade are derived. Title: Parallel electric field in the auroral ionosphere: excitation of acoustic waves by Alfvén waves Authors: Israelevich, P.; Ofman, L. Bibcode: 2004AnGeo..22.2797I Altcode: Available from http://www.copernicus.org/site/EGU/annales/22/8/2797.htm?FrameEngine=false; Title: Multiple ions resonant heating and acceleration by Alfvén/cyclotron fluctuations in the corona and the solar wind Authors: Xie, Hong; Ofman, Leon; ViñAs, Adolfo Bibcode: 2004JGRA..109.8103X Altcode: We study the interaction between protons, multiple minor ions (O5+, He++), and a given Alfvén/cyclotron fluctuation spectra in the corona and the solar wind. One-dimensional hybrid simulations are performed in initially homogeneous, collisionless, magnetized plasma with waves propagating parallel to the background magnetic field. The self-consistent hybrid simulations and linear Vlasov theory are used to study the effect of the driving spectrum, ion drift velocity, and microinstabilities on the coronal plasma and solar wind heating. The simulation results provide a clear picture of wave-particle interaction and successfully explain (1) how the driving spectrum frequency range and the power law index affect the resonant heating, (2) how ion double-peak distribution is formed and how differential flows affect the resonant interaction via the change of the resonant wave dispersion relation, and (3) how local microinstabilities affect minor ion heating and constraint the values of plasma parameters observed in the solar wind. Title: Three-fluid model of the heating and acceleration of the fast solar wind Authors: Ofman, L. Bibcode: 2004JGRA..109.7102O Altcode: A new three-fluid, two-dimensional, wave-driven model that includes, for the first time, heat conduction, viscous, and resistive dissipation for protons and electrons in two-dimensional coronal hole is presented. The fast solar wind model includes electron, proton, and He++ or O5+ ion fluids. The heating of the solar wind plasma due to MHD waves is modeled as follows: A broadband spectrum of low-frequency Alfvén waves is launched from the base of the corona. The waves deposit momentum and heat into the plasma to produce the fast solar wind. The values of the resistivity and shear viscosity coefficients required to produce the hot and fast solar wind consistent with observations are orders of magnitude larger than classical values. An empirical heating term that represents the contribution of additional heating processes, such as resonant heating by ion cyclotron waves, is included for the heavy ions and for protons in three out of four cases in the present study. Title: Loop Density Enhancement by Nonlinear Magnetohydrodynamic Waves Authors: Terradas, J.; Ofman, L. Bibcode: 2004ApJ...610..523T Altcode: We study the possibility that waves in coronal loops can produce density enhancements at loop tops. The mechanism involved is the ponderomotive force of standing magnetohydrodynamic (MHD) waves. We study the effect of large-amplitude waves in loops by first using a simple second-order one-dimensional MHD model for which analytical expressions are available. This simple model shows how Alfvén waves can excite density fluctuations on slow timescales. Next, we solve the time-dependent nonlinear 2.5-dimensional MHD equations in an arcade model, in order to study the effect of nonuniform Alfvén speed along the loop on large-amplitude waves. Finally, we solve the nonlinear three-dimensional MHD equations in a flux-tube configuration. Waves are launched by an initial transverse velocity profile in the loop, with footpoints fixed in the photosphere. We find that large initial disturbances produce a pressure imbalance along the loop, which results in an upflow from its legs. The accumulation of mass at the top of the oscillating loop can produce significant density enhancements for typical coronal conditions. In a later stage, the pressure gradient becomes dominant and inhibits the concentration of mass at the loop top. We find that oscillating loops observed by the EUV telescope on board TRACE on 1998 July 14 exhibit emission measure enhancements consistent with this mechanism. Title: Development of MHD Wave Diagnostic and Models of Coronal Active Regions Authors: Ofman, L.; Thompson, B. J.; Davila, J. M. Bibcode: 2004AAS...204.9504O Altcode: 2004BAAS...36..826O We investigate the generation, propagation, and damping of MHD waves in active regions, with the goal to develop a diagnostic tool of active region structure, dynamics, and stability. We used 3D MHD model to study the generation and the propagation of EIT waves in a simple model of an active regions, and the interaction of EIT waves with the active region magnetic field. We model the oscillation of active region loops numerically using the 3D MHD model active regions. Such oscillations have been recently observed by TRACE. We use photospheric magnetograms as the boundary conditions for the magnetic field model, and construct an initial field using force-free extrapolation. Finite plasma temperature, density, and gravity are included in the model. We construct loop density structures in the model, guided by TRACE and EIT observations in the EUV. We demonstrate that by comparing the results of the MHD models of waves in an active region to observations we will be able to construct a diagnostic tool for the physical properties of the active regions, such as magnetic field and density structure. Title: Multiple Ions Resonant Heating and acceleration by Alfvén/cyclotron Fluctuations in the corona and the solar Wind Authors: Hong, X.; Ofman, L. Bibcode: 2004AAS...204.7201H Altcode: 2004BAAS...36R.798H We study the interaction between protons, multiple minor ions (O5+, He++) and a given Alfvén/cyclotron fluctuations spectra in the corona and the solar wind. One-dimensional hybrid simulations are performed in initially homogeneous, collisionless, magnetized plasma with waves propagating parallel to the background magnetic field. The self-consistent hybrid simulations and linear Vlasov theory are used to study how multiple minor species and the differential drift velocity may affect the resonance interaction between cyclotron waves and the solar wind protons. The results of the simulations provide a clear picture of wave-particle interaction under various plasma conditions, which can explain 1) how multiple minor ions affect the resonant heating of the coronal plasma and the solar wind by a given wave spectrum, relative drift velocity, and micro-instability; 2) how energy is distributed and transferred among waves and different ion species; 3) the growth and damping of different beam micro-instability modes, including both, right-hand and left-hand waves; 4) the formation of ion double-peak distribution and He++ anisotropy in the solar wind. Title: Cone model for halo CMEs: Application to space weather forecasting Authors: Xie, Hong; Ofman, Leon; Lawrence, Gareth Bibcode: 2004JGRA..109.3109X Altcode: In this study, we present an innovative analytical method to determine the angular width and propagation orientation of halo Coronal Mass Ejections (CMEs). The relation of CME actual speed with apparent speed and its components measured at different position angle has been investigated. The present work is based on the cone model proposed by [2002]. We have improved this model by (1) eliminating the ambiguity via a new analytical approach, (2) using direct measurements of projection onto the plane of the sky (POS), (3) determining the actual radial speeds from projection speeds at different position angles to clarify the uncertainty of projection speeds in previous empirical models. Our analytical approach allows us to use coronagraph data to determine accurately the geometrical features of POS projections, such as major axis, minor axis, and the displacement of the center of its projection, and to determine the angular width and orientation of a given halo CME. Our approach allows for the first time the determination of the actual CME speed, width, and source location by using coronagraph data quantitatively and consistently. The method greatly enhances the accuracy of the derived geometrical and kinematical properties of halo CMEs, and can be used to optimize Space Weather forecasts. The applied model predications are in good agreement with observations. Title: Theoretical Aspects of Wave Acceleration in Open Magnetic Structures Authors: Ofman, L. Bibcode: 2004ESASP.547..345O Altcode: 2004soho...13..345O Theoretical studies of the solar wind outflow in open magnetic structures motivated by SOHO observations indicate that both, high frequency ion-cyclotron waves and low frequency MHD waves play a role in the acceleration and heating of the solar wind plasma. In particular, the high temperature anisotropy of O5+ ions deduced from SOHO UVCS observations suggests that resonant heating due to ion cyclotron waves is important in minor ions. However, there are theoretical difficulties with the ion-cyclotron wave heating model of protons. It appears that low-frequency waves are still required to transport energy and to accelerate the solar wind on large scales. In addition, the source of electron heating is still an open question. I will review some of the recent wave heating models of the fast solar wind. I will discuss the threefluid model, that describes electrons, protons, and heavy ions as coupled fluids. This description allows to model different properties and heating processes for each particle species and to model the high temperature of the heavy ions in accordance with observations. I will show the results of 2.5D three-fluid, simulations of the solar wind plasma that combine the effects of MHD waves selfconsistently, and ion-cyclotron waves empirically as the sources of energy. I will review several results of hybrid kinetic models of ion-cyclotron wave heating and relaxation of heavy ion anisotropy. Title: The origin of the slow solar wind in coronal streamers Authors: Ofman, L. Bibcode: 2004AdSpR..33..681O Altcode: The highly variable slow solar wind has been associated with low-latitude regions of the heliosphere most clearly by the Ulysses spacecraft. Although, it is evident today that the slow solar wind originates in coronal helmet streamers, the mechanism of the slow solar wind acceleration, and the origin of the variability are still being debated. The combination of new observations and numerical modeling are beginning to address these questions. I will discuss how recent in-situ observations by Ulysses, white light and EUV observations by the LASCO and UVCS instruments on SOHO advanced our understanding of the streamer structure, dynamics, and stability. I will briefly review the current state of numerical MHD modeling of streamers, and the possible mechanisms that may produce the highly variable slow wind. I will present the results of recent heat-conductive MHD modeling of multiple streamer slow solar wind with heating function constrained by observations. I will show how multi-fluid numerical modeling of the slow solar wind in streamers helps to identify the regions of the slow solar wind outflow. Title: 3D MHD Simulation of the Interaction of Fast Magnetosonic Waves and a Coronal Active Region Authors: Terradas, J.; Ofman, L. Bibcode: 2004ESASP.547..469T Altcode: 2004soho...13..469T We present a three-dimensional MHD simulation of the local interaction between fast magnetoacoustic waves and a coronal active region observed with the Transition Region and Coronal Explorer (TRACE) on June 13, 1998. The 3D MHD model is initiated with the active region magnetic field calculated from the extrapolation of photospheric magnetograms. The corona is assumed to be isothermal and resistive dissipation is included in the model. We compare the main features of the simulated wave with the wave observed with TRACE. We find that many aspects of the simulation match the observations. In particular, we show how the wave's trajectory is modified, undergoing strong reflection and refraction away from the active region. Title: 3D MHD Models of Active Region Loops Authors: Ofman, L. Bibcode: 2004cosp...35.4568O Altcode: 2004cosp.meet.4568O Present imaging and spectroscopic observations of active region loops allow to determine many physical parameters of the coronal loops, such as the density, temperature, velocity of flows in loops, and possibly the magnetic field. However, due to projection effects many of these parameters remain ambiguous. Three dimensional imaging in EUV by the STEREO spacecraft will help to resolve the projection ambiguities, and the observations could be used to setup 3D MHD models of active region loops to study the dynamics and stability. Here I present the results of 3D MHD models of active region loops, and the progress toward more realistic 3D MHD models of active regions. In particular I show the effects of impulsive events on the excitation of active region loop oscillations, and the generation, propagations and reflection of EIT waves. I show how 3D MHD models together with 3D EUV observations can be used as a diagnostic tool for active region loop physical parameters, and to advance the science of the sources of solar coronal activity. Title: Looptop Density Enhancement By Nonlinear Magnetohydrodynamic Waves Authors: Terradas, J.; Ofman, L. Bibcode: 2003AGUFMSH42B0539T Altcode: We discuss the possibility that disturbances generated in flares can produce the emission measure enhancement at the top of coronal loops observed by the Transition Region and Coronal Explorer ({TRACE}). The mechanism involved is the ponderomotive force of standing waves in the loops. We study the effect of large amplitude waves in loops using first a simple one-dimensional model for which analytical expressions are available, and second by solving the time dependent nonlinear magnetohydrodynamic (MHD) equations in a more realistic three-dimensional configuration. Waves are launched by an initial transverse velocity profile in the loop with footpoints fixed in the photosphere. We find that large initial disturbances can provide an imbalance along the loop, which results in an upflow from the legs of the loop. The accumulation of mass at the top of the loop produces a strong density enhancement. In a later stage, the pressure gradient becomes dominant and inhibits the concentration of mass at the loop apex. Title: Alfvén Waves in Multi-ion Coronal Plasma: Observational Implications Authors: Ofman, L.; Nakariakov, V. M.; Davila, J. M. Bibcode: 2003AGUFMSH11D1129O Altcode: We investigate low-frequency Alfvén waves in a multi-ion coronal plasma by deriving the dispersion relation of the linearized three-fluid equations in magnetized plasma with coronal parameters. We study the effect of collisions on the velocity amplitude of minor ions due to the Alfvén waves compared to the proton wave amplitude. We find that in the collisionless plasma the minor ion velocity is reduced by the factor Z/A compared to protons, where Z is the ion charge, and A is mass in units of proton mass. When the collision frequency is much larger then the Alfvén wave frequency the velocity amplitude of the minor ions is equal to the proton velocity amplitude. We show the effects of minor ions and collisions on the dispersion relation of Alfvén waves in the three fluid plasma. In view of our results we show how the observed nonthermal line broadening of minor ions relates to the wave motions of protons as a function of heliocentric distance, and the plasma physical parameters. Title: Development of 2D MHD Self-Consistent Empirical Model of the Corona and Solar Wind Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Holzer, T.; Davila, J.; Guhathakurta, M. Bibcode: 2003AGUFMSH42D..07S Altcode: We are developing a 2D MHD self-consistent empirical model of the solar corona and solar wind. We constrain the solution using empirically determined estimates of the effective pressure for the momentum equation and effective heat flux for the energy equation provided from coronagraph data and Ulysses plasma and magnetic field data. Our solutions are steady state and do not use a polytrope which we know is not valid in the solar corona. We have been able to achieve preliminary convergence. We will present the results of an error analysis. Our results are presently only valid during solar minimum, but are generalizing so it can be used during the transition toward solar maximum (i.e., three current sheets). We will also present some preliminary results which will allow us to apply our solutions to solar maximum conditions. Title: Multiple Ions Resonant Heating and Acceleration by Alfven/cyclotron Fluctuations in the Solar Wind Authors: Xie, H.; Ofman, L. Bibcode: 2003AGUFMSH11D1133X Altcode: We study the interaction between protons, and multiple minor ions (O5+, He++) and a given cyclotron resonant spectra in coronal hole plasma. One-dimensional hybrid simulations are performed in initially homogeneous, collisionless, magnetized plasma with waves propagating parallel to the background magnetic field. The self-consistent hybrid simulations are used to study how multiple minor species may affect the resonance interaction between a spectrum of waves and the solar wind protons. The results of the simulations provide a clear picture of wave-particle interaction under various coronal conditions, which can explain 1) how multiple minor ions affect the resonant heating and the temperature anisotropy of the solar wind protons by a given wave spectrum; 2) how energy is distributed and transferred among waves and different ion species; 3) the growth and damping of different beam microinstability modes, including both inward and outward waves; 4) the formation of proton double-peak distribution in the solar wind. Title: Flows in coronal loops driven by Alfvén waves: 1.5 MHD simulations with transparent boundary conditions Authors: Grappin, R.; Léorat, J.; Ofman, L. Bibcode: 2003AIPC..679..750G Altcode: We investigate time-dependent siphon flows in coronal loops driven by Alfvén waves. We consider a 1.5 D isothermal, MHD model in which the coordinate is the abscissa along the loop, with an external gravity field reversing sign in the middle, and a uniform magnetic field parallel to the x-axis. We use transparent boundary conditions, meant to describe the upper part of the loop. The reaction of the loop to Alfvén waves depends entirely on whether we allow or not incoming parallel velocity fluctuations: only in the latter case do transonic flows arise, but the flow is in that case generated by a nonlinear coupling of the waves with the boundaries. Title: Development of Multidimensional MHD Model for the Solar Corona and Solar Wind Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guhathakurta, M.; Davila, J.; Skoug, R.; Fludra, A.; Holzer, T. Bibcode: 2003AIPC..679..113S Altcode: We are developing a time stationary self-consistent 2D MHD model of the solar corona and solar wind that explicitly solves the energy equation, using a semi-empirical 2D MHD model of the corona to provide an empirically determined effective heat flux qeff (i.e., the term effective means the possible presence of wave contributions). But, as our preliminary results indicate, in order to achieve high speed winds over the poles we also need to include the empirically determined effective pressure Peff as a constraint in the momentum equation, which means that momentum addition by waves above 2 RS are required to produce high speed winds. At present our calculations do not include the Peff constraint. The estimates of Peff and qeff come from the semi-empirical 2D MHD model of the solar corona by Sittler and Guhathakurta (1999a,2002) which is based on Mk-III, Skylab and Ulysses observations. For future model development we plan to use SOHO LASCO, CDS, EIT, UVCS and Ulysses data as constraints for our model calculations. The model by Sittler and Guhathakurta (1999a, 2002) is not a self-consistent calculation. The calculations presented here is the first attempt at providing a self-consistent calculation based on empirical constraints. Title: Damped Oscillations of Multithreaded Coronal Loops: results of 3D MHD Simulations Authors: Ofman, L.; Terradas, J. Bibcode: 2003SPD....34.0108O Altcode: 2003BAAS...35..806O Recently, scaling laws of the damping time of coronal loop oscillations were constructed from TRACE observations in the EUV of damped coronal loop oscillations (Ofman and Aschwanden 2002). The scaling laws suggest that the damping of the oscillations is due to phase mixing with anomalously high viscosity or resistivity. The phase mixing dissipation scenario is most likely realized due to the multithread structure of the coronal loops as suggested by observations. We develop a resistive 3D MHD model of an active region coronal loop in low-beta plasma. We model the damping of an active region coronal loop oscillations using the resistive 3D MHD equations. The oscillations are excited by a model "EIT wave" that hits the loop. We investigate the evolution and the damping of the oscillations in a multithreaded loop and compare the results with a cylindrical loop. We find that the damping time is strongly dependent on the resistivity for the multithreaded loop, while for the cylindrical loop the damping time is weakly dependent on resistivity, in agreement with previous analytical results. We investigate the effects of boundary conditions, resistivity, and loop parameters on the damping rate in the multithreaded loop. Title: Winds from ``Non-Coronal'' and ``Hybrid'' Stars Driven by MHD Waves Authors: Airapetian, V. S.; Carpenter, K.; Ofman, L. Bibcode: 2003AAS...202.3214A Altcode: 2003BAAS...35..745A Observations obtained with IUE, HST and FUSE provide extensive data on atmospheric heating and wind dynamics for late-type luminous stars. The physical processes which drive winds in these stars are poorly understood, despite decades of study. In our previous study we have shown that observational signatures of winds can be interpreted by our model of winds driven by propagated Alfvén waves in stellar atmospheres and launched at a single frequency at the wind base (Airapetian et al. 2000). We extend our MHD calculations of winds from luminous late-type stars to include an Alfvén wave driver with a broad-band frequency range. The calculations are applied to ``non-coronal'' (α Tau) and ``hybrid'' (β Dra) giant stars to consistently reproduce the observed velocity profiles of the winds, its terminal velocity, the turbulent broadening of UV lines and mass loss rates. The nature of wind variability in luminous late-type stars is discussed. We also present the preliminary results of our first MHD and LTE radiative transfer calculations to model the UV spectra from the K5 giant, α Tau.

This research is supported by the NASA Research grant from GSFC No. NAG5-12869. Title: Observations of Slow Solar Wind Outflow in Coronal Streamers and the Relation to Current Sheet Structure Authors: Strachan, L.; Ofman, L.; Panasyuk, A. V. Bibcode: 2003SPD....34.0602S Altcode: 2003BAAS...35Q.817S UVCS/SOHO observations have allowed measurements of the slow solar wind outflow in streamers by using O VI emission at 1032 and 1037 Å (Strachan et al 2002). Here we analyze the UVCS data to obtain more detailed outflow velocities of O 5+ in the legs and stalks of streamers. According to MHD models current sheets are believed to exist in the stalks and legs of coronal streamers, and the slow solar wind outflow speed peaks at same locations. In this work we compare the observations of outflow velocities to the velocities predicted by three-fluid model that includes O 5+. We present some preliminary data and discuss constraints on the observed and model values of the streamer parameters. Title: Nanoflare Frequency Distribution Scaling from Wave Heating: Results of Nonlinear Loop Modeling Authors: Davila, J. M.; Ofman, L.; Davila, J. M.; Ofman, L. Bibcode: 2003SPD....34.1601D Altcode: 2003BAAS...35..832D The statistics of nanoflare events observed by TRACE in the EUV and Yohkoh in soft X-rays exhibits a power law relation between the peak thermal energy and the number of events per energy interval. Using 1D coronal loop model with nonlinear coupling to the chromosphere (Ofman, Klimchuk, and Davila 1998) we calculate the distribution of heating events due to the dissipation of waves driven by a random Alfven wave source. Initial results show that the number of heating events per energy bin scale with energy with the power of 2+/- 0.4. The scaling is consistent with the observed value of 1.86+/-0.07 at 171Å and 1.81+/-0.10 at 195Å found with TRACE (Aschwanden and Parnell 2002). Thus, we conclude that in the nanonflare energy range (E<1028 erg) the observed frequency distribution of peak energy is consistent with wave heating. Title: 3D MHD Simulation of the Interaction of Fast Magnetoacoustic Waves and Coronal Active Regions Authors: Terradas, J.; Ofman, L. Bibcode: 2003SPD....34.0109T Altcode: 2003BAAS...35..806T Following the work of Ofman and Thompson (2002), we present a three-dimensional MHD simulation of the local interaction between fast magnetosonic waves and coronal active regions. In order to have a realistic simulation, in the present work the active region is modeled by an initially potential magnetic field configuration calculated from the extrapolation of photospheric magnetograms. The density is gravitationally stratified and we also include resistive dissipation in the model. We compare the main features of the simulated wave with a wave observed with the Transition Region and Coronal Explorer (TRACE). We find that many aspects of the simulation match the observations. In particular, we show how the wave's trajectory is modified, undergoing strong reflection and refraction away from the active region. We also discuss how we can use the simulations as a tool to understand the three-dimensional topology and stability of active regions, in anticipation of the STEREO mission. Title: Consequences of proton and alpha anisotropies in the solar wind: Hybrid simulations Authors: Gary, S. Peter; Yin, Lin; Winske, Dan; Ofman, Leon; Goldstein, Bruce E.; Neugebauer, Marcia Bibcode: 2003JGRA..108.1068G Altcode: Alfvén fluctuations propagating away from the Sun in the solar corona and solar wind transfer energy via cyclotron resonances to ions of successively larger charge-to-mass ratios. This can yield T⟂/T∥ > 1 for each ion species, where the subscripts refer to directions relative to the background magnetic field. If these anisotropies become sufficiently large, they drive electromagnetic ion cyclotron instabilities. This paper describes two-dimensional hybrid simulations of a collisionless, homogeneous, magnetized plasma to study the consequences of scattering by enhanced field fluctuations from such instabilities. The ions in the simulations consist of majority protons and minority alpha particles with initial bi-Maxwellian velocity distributions and representative solar wind parameters including a nonzero alpha/proton relative speed. The simulations show that both helium and proton cyclotron instabilities reduce the driving anisotropy, reduce initial differences between the proton and alpha particle anisotropies, and, as a new result, usually reduce initial alpha/proton speeds. These results are somewhat different from theoretical predictions of ion scattering by interaction with outward propagating Alfvén-cyclotron waves but are consistent with observations from Ulysses. Title: Empirically Constrained Multidimensional MHD Model for the Solar Corona and Solar Wind Authors: Sittler, E. C.; Ofman, L.; Gibson, S.; Guthathakurta, M.; Skoug, R.; Fludra, A.; Davila, J.; Holzer, T. Bibcode: 2002AGUFMSH21A0502S Altcode: We are developing a time stationary self-consistent 2D MHD model of the solar corona and solar wind that explicitly solves the energy equation, using a semi-empirical 2D MHD model of the corona to provide an empirically determined effective heat flux qeff (i.e., the term effective means the possible presence of wave contributions) for the energy equation and effective pressure Peff for the momentum equation. Preliminary results indicated that in order to achieve high speed winds over the poles we not only needed to use qeff in the energy equation, but also needed to include the empirically determined effective pressure Peff as a constraint in the momentum equation, which means that momentum addition by waves above 2 RS are required to produce high speed winds. A solution which only included qeff showed high acceleration over the poles below 2 RS, but then drooped above that radial distance indicating we needed momentum addition above that height to get high speed flows over the poles. We will show new results which include the added constraint of Peff in the momentum equation. This method will allows us to estimate the momentum addition term due to waves as a function of height and latitude within the corona. The estimates of Peff and qeff come from the semi-empirical 2D MHD model of the solar corona by Sittler and Guhathakurta (1999, 2002) which is based on Mk-III, Skylab and Ulysses observations. For future model development we plan to use SOHO LASCO, CDS, EIT, UVCS, Spartan 201-05 and Ulysses data as constraints for our model calculations. The model by Sittler and Guhathakurta (1999, 2002) is not a self-consistent calculation. The calculations presented here are a continuing effort to provide a self-consistent calculation based on empirical constraints. Title: Doppler oscillations in hot coronal loops Authors: Curdt, W.; Wang, T. J.; Innes, D. E.; Solanki, S. K.; Dammasch, I. E.; Kliem, B.; Ofman, L. Bibcode: 2002ESASP.506..581C Altcode: 2002ESPM...10..581C; 2002svco.conf..581C Recently, a new kind of damped oscillations of hot coronal loops was revealed by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on SOHO. Such events seem to be a common feature observed in active region loops, seen very often when these lines brighten. The oscillations always have an impulsive trigger and are strongly damped while they cool down. However, in lines formed at coronal temperatures of ≍2 MK never any signature of these oscillations has been observed. In this study, we present the main properties of Doppler oscillations derived from a statistical study of 17 flare-like events, and a comparison with TRACE transverse loop oscillations. We also discuss the oscillation modes and their damping mechanism. Title: Kink oscillations of coronal loops as a tool for the determination of coronal magnetic field Authors: Nakariakov, Valery; Ofman, Leon Bibcode: 2002ESASP.506..461N Altcode: 2002svco.conf..461N; 2002ESPM...10..461N We develop a new method for the determination of the absolute value of the magnetic field strength in coronal closed magnetic structures, based on the analysis of flare-generated oscillations of coronal loops. Interpretation of the quasi-harmonic oscillations observed in terms of global standing kink waves allows to connect the period of the oscillations and the loops length with the magnetic field strength in the loops. Improved diagnostic of the loop length, the oscillation period, and the plasma density in the loop will significantly improve the method's precision. Title: Consequences of proton and alpha anisotropies in the solar wind: Hybrid simulations Authors: Gary, S. P.; Yin, L.; Winske, D.; Ofman, L.; Goldstein, B. E.; Neugebauer, M. Bibcode: 2002AGUFMSH12A0390G Altcode: Alfvén-like fluctuations in the solar corona and solar wind may cascade from lower to higher frequencies where they transfer energy via cyclotron resonances to ions of successively higher charge-to-mass-ratios. This yields Tperpendicular to }/T{∥ > 1 for each ion species, where the subscripts refer to directions relative to the background magnetic field. If sufficiently large, these anisotropies drive electromagnetic ion cyclotron instabilities. This manuscript describes the use of two-dimensional hybrid simulations of a collisionless, homogeneous, magnetized plasma with both protons and alpha particles to study the consequences of scattering by enhanced field fluctuations from such instabilities. The most important new results are that both helium and proton cyclotron instabilities reduce initial differences between the proton and alpha particle anisotropies, and also reduce initial alpha/proton relative speeds. These simulation results are different from theoretical predictions of ion responses to their direct interaction with cascading Alfvén/cyclotron waves, but are consistent with observations from the Ulysses spacecraft. Title: EUV Dimmings: Simple or Enigmatic? Authors: Thompson, B.; Biesecker, D. A.; Ofman, L.; St. Cyr, O. C.; Wills-Davey, M. J. Bibcode: 2002AGUFMSH52A0488T Altcode: EUV dimmings are large-scale depletions in coronal EUV emission associated with coronal mass ejections. Their occurrence is nearly perfect in correlation with fast CMEs. Many of the EUV dimming observations appear to correspond well in appearance and behavior to SXR dimmings. It has been assumed that the dimmings are merely the location of the CME mass removal in the corona, and that their similar appearance to coronal holes is because they are transient coronal holes with fieldlines opened by the coronal mass ejection. However, not all CMEs have dimmings, and large-scale EUV dimmings have also been caused by heating of local plasma, and due to absorption by cool material "clouds" evolving in the wake of an eruption. Additionally, there are several ways in which these regions "heal," presumably due to the closing down of the open field lines. The presentation will include a range of EUV dimming observations, a discussion of their origin, and what they might imply about the nature of the associated CMEs. Title: Resonant heating and acceleration of ions in coronal holes driven by cyclotron resonant spectra Authors: Ofman, L.; Gary, S. P.; ViñAs, A. Bibcode: 2002JGRA..107.1461O Altcode: Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats and accelerates the ions in the solar wind. Velocity distributions of minor ions derived from SOHO Ultraviolet Cronagraph Spectrometer (UVCS) observations in coronal holes indicate that the minor ion temperature anisotropy is T⟂/T∣∣ > 10 and that outflow speeds are higher than those of the solar wind protons. Here one-dimensional hybrid simulations of initially homogeneous, collisionless plasmas are used to study a model of coronal plasmas including kinetic protons, a tenuous component of oxygen ions, and massless fluid electrons. Spectra of ion cyclotron resonant Alfvén waves are imposed on the system to study the resultant heating of both ion species. We investigate the effects of various power spectra of the form f-1 or f-5/3 and vary the input frequency range. We find that the ion heating strongly depends on the power contained in the frequency range of the input spectrum that can resonate with the ions. The minor O5+ ions are easily heated and become anisotropic due to various forms of the spectra. The protons remain nearly isotropic and are weakly heated in most cases in this study. We investigate the self-consistent fluctuation spectrum generated by the response of the ions and the non-Maxwellian features in the velocity distribution. Title: Acceleration and Heating of the Fast Solar Wind by Ion-Cyclotron and MHD Waves Authors: Ofman, L. Bibcode: 2002AGUFMSH12A0417O Altcode: The basic plasma properties of the fast solar wind as deduced from observations suggest that both, high frequency ion-cyclotron waves, and low frequency MHD waves play a role in the acceleration and heating of the coronal hole plasma. The heating due to high-frequency waves is particularly important in minor ions, such as O5+. I will present the results of 3-fluid, simulations of the solar wind plasma that combine the effects of ion-cyclotron, and MHD waves. The low frequency waves are included self-consistently as the source of momentum and heating of protons and electrons. Additional heat and momentum input terms due to ion-cyclotron waves are included in protons and minor ions. The 3-fluid gyrotropic model allows for Tperpendicular to >T_∥ of the ions in accordance with observations. The heating term that contributes mostly to the perpendicular temperature of minor ions is constructed using the saturated state of the hybrid kinetic model of the solar wind plasma at several locations in the coronal hole, with the plasma β and other parameters varying with radial distance. Iterative update of these parameters is planed in a future study. The temperature anisotropy estimated from SOHO UVCS spectral observations is used to constrain the hybrid kinetic modeling. Ulysses and Helios observations are used to constrain the asymptotic solar wind speed and mass flux. Title: Hot Coronal Loop Oscillations Observed by SUMER: Slow Magnetosonic Wave Damping by Thermal Conduction Authors: Ofman, L.; Wang, Tongjiang Bibcode: 2002ApJ...580L..85O Altcode: Recently, strongly damped Doppler shift oscillations of hot (T>6 MK) coronal loops were observed with the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory. The oscillations are interpreted as signatures of slow-mode magnetosonic waves excited impulsively in the loops. Using a one-dimensional MHD code, we model the oscillations and the damping of slow magnetosonic waves in a model coronal loop. We find that because of the high temperature of the loops, the large thermal conduction, which depends on temperature as T2.5, leads to rapid damping of the slow waves on a timescale comparable to observations (5.5-29 minutes). The scaling of the dissipation time with period agrees well with SUMER observations of 35 cases in 17 events. We also find that the decay time due to compressive viscosity alone is an order of magnitude longer than the observed decay times. Title: Estimating random transverse velocities in the fast solar wind from EISCAT Interplanetary Scintillation measurements Authors: Canals, A.; Breen, A. R.; Ofman, L.; Moran, P. J.; Fallows, R. A. Bibcode: 2002AnGeo..20.1265C Altcode: Interplanetary scintillation measurements can yield estimates of a large number of solar wind parameters, including bulk flow speed, variation in bulk velocity along the observing path through the solar wind and random variation in transverse velocity. This last parameter is of particular interest, as it can indicate the flux of low-frequency Alfvén waves, and the dissipation of these waves has been proposed as an acceleration mechanism for the fast solar wind. Analysis of IPS data is, however, a significantly unresolved problem and a variety of a priori assumptions must be made in interpreting the data. Furthermore, the results may be affected by the physical structure of the radio source and by variations in the solar wind along the scintillation ray path. We have used observations of simple point-like radio sources made with EISCAT between 1994 and 1998 to obtain estimates of random transverse velocity in the fast solar wind. The results obtained with various a priori assumptions made in the analysis are compared, and we hope thereby to be able to provide some indication of the reliability of our estimates of random transverse velocity and the variation of this parameter with distance from the Sun.

Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma; instruments and techniques) Title: Damping Time Scaling of Coronal Loop Oscillations Deduced from Transition Region and Coronal Explorer Observations Authors: Ofman, L.; Aschwanden, M. J. Bibcode: 2002ApJ...576L.153O Altcode: The damping mechanism of recently discovered coronal loop transverse oscillations provides clues to the mechanism of coronal heating. We determine the scaling of the damping time with the parameters of the loops observed in extreme ultraviolet by the Transition Region and Coronal Explorer. We find excellent agreement of the scaling power to the power predicted by phase mixing and poor agreement with the power predicted by the wave leakage or ideal decay of the cylindrical kink mode mechanisms. Phase mixing leads to rapid dissipation of the Alfvén waves due to the variation of the Alfvén speed across the wave front and formation of small scales. Our results suggest that the loop oscillations are dissipated by phase mixing with anomalously high viscosity. Title: Interaction of EIT Waves with Coronal Active Regions Authors: Ofman, L.; Thompson, B. J. Bibcode: 2002ApJ...574..440O Altcode: Large-scale coronal waves associated with flares were first observed by the Solar and Heliospheric Observatory (SOHO) Extreme ultraviolet Imaging Telescope (EIT). We present the first three-dimensional MHD modeling of the interaction of the EIT waves with active regions and the possibility of destabilization of an active region by these waves. The active region is modeled by an initially force-free, bipolar magnetic configuration with gravitationally stratified density. We include finite thermal pressure and resistive dissipation in our model. The EIT wave is launched at the boundary of the region, as a short time velocity pulse that travels with the local fast magnetosonic speed toward the active region. We find that the EIT wave undergoes strong reflection and refraction, in agreement with observations, and induces transient currents in the active region. The resulting Lorentz force leads to the dynamic distortion of the magnetic field and to the generation of secondary waves. The resulting magnetic compression of the plasma induces flows, which are particularly strong in the current-carrying active region. We investigate the effect of the magnetic field configuration and find that the current-carrying active region is destabilized by the impact of the wave. Analysis of the three-dimensional interaction between EIT waves and active regions can serve as a diagnostic of the active region coronal magnetic structure and stability. Title: Self-consistent 2D MHD modeling of multi-streamer coronal structures Authors: Ofman, L.; Sittler, E. C.; Gibson, S.; Holzer, T. E.; Guhathakurta, M. Bibcode: 2002AGUSMSH21B..02O Altcode: Recently, a semi-empirical 2D MHD model of the solar corona was constructed by Sittler and Guhathakurta [1999]. The model uses an empirical electron density and empirical magnetic field during solar minimum as input to the conservation equations of mass, momentum, and energy to derive an empirical effective heat flux, or empirical heating function. This semi-empirical model is not a self-consistent calculation. We explore the possibility of developing a self-consistent model that uses the empirical heating function as a constraint for the calculations. This allows us to solve the energy equation without use of a polytrope which we know does not apply near the Sun. For our initial attempt we use the empirically derived magnetic field model obtained from observed streamer topologies and Ulysses boundary conditions to initialize our self-consistent 2D MHD model of the solar corona. We solve the thermally conductive energy equations with an empirical heating function, and obtain 3-streamer structure with self-consistent magnetic field, current-sheets, solar wind outflow, density, and temperature. We compare the results of the thermally conductive model to the polytropic model, and to the empirical model. We find that the self-consistent magnetic field structure is more realistic then the empirical model. We find that the thermally conductive streamers result in more diffuse current-sheets than in the polytropic model. We also find that the heating function reduces the heliocentric distance of the streamers' cusp, and produces more rapid acceleration of the solar wind in the thermally conductive model then in the polytropic model, consistent with observations. We investigate the effect of various forms of the heating function, and of an empirically derived heat flux on the solutions. Title: Chromospheric Leakage of Alfvén Waves in Coronal Loops Authors: Ofman, L. Bibcode: 2002ApJ...568L.135O Altcode: The recently observed rapid damping of coronal loop oscillations generated discussion regarding the physical mechanism responsible for the damping, with the leakage into the chromosphere suggested as one of the possible mechanisms. I study the leakage of Alfvén waves into the chromospheric footpoints of a coronal loop using the nonlinear viscoresistive 1.5-dimensional MHD model. The waves were launched by an initial transverse velocity profile in the loop. I find that the leakage time of long-wavelength transverse oscillations, such as the ones observed recently by the Transition Region and Coronal Explorer (TRACE), is 5 times longer than the observed damping time of the oscillations. For the loop recently observed by TRACE, I conclude that the observed damping of the long-wavelength oscillations is not due to leakage into the chromosphere. However, depending on particular chromospheric and coronal properties, chromospheric leakage may be significant in some events of coronal loop oscillations. Title: The Origin of the Slow Solar Wind in Coronal Streamers Authors: Ofman, L. Bibcode: 2002cosp...34E.825O Altcode: 2002cosp.meetE.825O The highly variable slow solar wind has been associated with low-latitude regions of the heliosphere most clearly by the Ulysses spacecraft. Although, it is clear today that the slow solar wind is associated with coronal helmet streamers, the mechanism of the slow solar wind acceleration, and the origin of its variability are still being debated. The combination of new observations and numerical modeling began to address these questions. I will discuss how recent white light and EUV observations of streamers by the LASCO and UVCS instruments on SOHO advanced our understanding of the streamer structure, dynamics, and stability. I will briefly review the current state of numerical MHD modeling of streamers, and the possible mechanisms that may produce the highly variable slow wind. I will show how multifluid numerical modeling of the slow solar wind in streamers helps to identify the regions of the slow solar wind outflow. I will present the results of recent attempts of self-consistent MHD modeling of multiple streamer slow solar wind with empirical heating function constrained by observations. Title: Resonant Heating and Acceleration of Ions in Coronal Holes by High-Frequency Wave Spectrum Authors: Ofman, L.; Gary, S. P.; Vinas, A. Bibcode: 2001AGUFMSH11A0696O Altcode: Recent observations and models suggest that the resonant absorption of ion cyclotron waves heats and accelerates the ions in the solar wind. Velocity distributions of minor ions derived from SOHO UVCS observations in coronal holes indicate that the minor ion temperature anisotropy >10 and outflow speeds is higher then the solar wind protons. Using 1D hybrid code we investigate the effects of differential flow and anisotropy on the stability of the solar wind plasma. We investigate the heating and the acceleration of the solar wind plasma ions by including an input spectrum of the form f-1 and f-5/3. We find that the ion heating strongly depends on the power contained in the frequency range of the power-law spectrum that can resonate with the ions. The heating also depends on the plasma β , and the abundance of the minor ions. We investigate the self-consistent fluctuations spectrum generated by the response of the ions. We have used second-order theory (Gary and Tokar 1985) to evaluate the rates of proton heating, anisotropy formation, and acceleration, and have compared these predictions against the simulation results. Title: New Observations of Oscillating Coronal Loops Authors: Reeves, K. K.; Shoer, J.; Deluca, E. E.; Winebarger, A. R.; Ofman, L.; Davila, J. M. Bibcode: 2001AGUFMSH11A0704R Altcode: One of the most promising discoveries of the TRACE mission is the first observations of transverse oscillations in coronal loops (Aschwanden et al 1999, Nakariakov et al 1999). Loops are set into motion from nearby flares, oscillate with a well defined frequency and decay on a time scale of 10 minutes. While the theoretical study of MHD waves in the corona has a long history, observational support has dramatically increased over the past 10 years as coronal instruments have improved. The transverse oscillations have been identified as standing kink modes for the 14-July-1998 observations cited above. In this paper we present clear evidence for a decaying global kink modes observed by TRACE on 15-Apr-2001. Six different loops have been observed to oscillate with a frequency in the range: 15-20 mHz (compared with 4 mHz for 14-July-1998) and a decay time in the range: 8-23 minutes (compared with 11 minutes for the earlier event). The implications for these results for coronal diagnostics and solar coronal seismology will be discussed. Title: Publicly Available Numerical Codes for Modeling the X-ray and Microwave Emissions from Solar and Stellar Activity Authors: Holman, G. D.; Mariska, J. T.; McTiernan, J. M.; Ofman, L.; Petrosian, V.; Ramaty, R. Bibcode: 2001AAS...199.9302H Altcode: 2001BAAS...33.1444H We have posted numerical codes on the Web for modeling the bremsstrahlung x-ray emission and the gyrosynchrotron radio emission from solar and stellar activity. In addition to radiation codes, steady-state and time-dependent Fokker-Planck codes are provided for computing the distribution and evolution of accelerated electrons. A 1-D hydrodynamics code computes the response of the stellar atmosphere (chromospheric evaporation). A code for modeling gamma-ray line spectra is also available. On-line documentation is provided for each code. These codes have been developed for modeling results from the High Energy Solar Spectroscopic Imager (HESSI) along with related microwave observations of solar flares. Comprehensive codes for modeling images and spectra of solar flares are under development. The posted codes can be obtained on NASA/Goddard's HESSI Web Site at http://hesperia.gsfc.nasa.gov/hessi/modelware.htm This work is supported in part by the NASA Sun-Earth Connection Program. Title: Reconnection remnants in the magnetic cloud of October 18-19, 1995: A shock, monochromatic wave, heat flux dropout, and energetic ion beam Authors: Collier, Michael R.; Szabo, A.; Farrell, W. M.; Slavin, J. A.; Lepping, R. P.; Fitzenreiter, R.; Thompson, B.; Hamilton, D. C.; Gloeckler, G.; Ho, G. C.; Bochsler, P.; Larson, D.; Ofman, L. Bibcode: 2001JGR...10615985C Altcode: Evidence is presented that the Wind spacecraft observed particle and field signatures on October 18-19, 1995, due to reconnection near the foot points of a magnetic cloud (i.e., between 1 and 5 solar radii). These signatures include (1) an internal shock traveling approximately along the axis of the magnetic cloud, (2) a simple compression of the magnetic field consistent with the foot point magnetic fields being thrust outward at speeds much greater than the solar wind speed, (3) an electron heat flux dropout occurring within minutes of the shock, indicating a topological change resulting from disconnection from the solar surface, (4) a very cold 5 keV proton beam, and (5) an associated monochromatic wave. We expect that given observations of enough magnetic clouds, Wind and other spacecraft will see signatures similar to the ones reported here indicating reconnection. However, these observations require the spacecraft to be fortuitously positioned to observe the passing shock and other signatures and will therefore be associated with only a small fraction of magnetic clouds. Consistent with this, a few magnetic clouds observed by Wind have been found to possess internal shock waves. Title: Electromagnetic heavy ion cyclotron instability: Anisotropy constraint in the solar corona Authors: Gary, S. Peter; Yin, Lin; Winske, Dan; Ofman, Leon Bibcode: 2001JGR...10610715G Altcode: The electromagnetic proton cyclotron anisotropy instability is driven by T⊥p/T∥p>1 where p represents protons and the directional subscripts denote directions relative to the background magnetic field. Fluctuating field growth leads to wave-particle scattering, which in turn imposes an upper bound on the anisotropy of the form T⊥p/T∥p-1=Sp/β∥pαp, where β∥p≡8πnpkBT∥p/Bo2, and the fitting parameters Sp<~1 and αp~=0.4. Recent SOHO observations indicate that minority heavy ions are substantially hotter and more anisotropic than protons in the solar corona. Here linear theory and hybrid simulations have been carried out in a model of a homogeneous, magnetized, collisionless plasma with anisotropic minority oxygen ions (denoted by subscript O). These calculations show that the electromagnetic oxygen ion cyclotron anisotropy instability also leads to wave-particle scattering, which constrains that anisotropy by the form T⊥O/T∥O-1=SO/[(mp/mO)β~∥O]αo, where β~∥O≡8πnekBT∥O/Bo2, So~10 and αO~0.4. This constraint should be observable in the solar corona. Title: Three-Fluid 2.5-dimensional Magnetohydrodynamic Model of the Effective Temperature in Coronal Holes Authors: Ofman, L.; Davila, J. M. Bibcode: 2001ApJ...553..935O Altcode: Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations show that protons and minor ions are hot (Tp>106 K, Ti>107 K) and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfvénic fluctuations in the solar wind. Using the three-fluid 2.5-dimensional MHD model, we have shown that the unresolved Alfvénic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. However, Alfvén waves with realistic amplitudes cannot reproduce the O5+ perpendicular temperature and anisotropy deduced from UVCS observations. This suggests that the minor ions are heated by a different mechanism than protons. Title: Determination of the coronal magnetic field by coronal loop oscillations Authors: Nakariakov, V. M.; Ofman, L. Bibcode: 2001A&A...372L..53N Altcode: We develop a new method for the determination of the absolute value of the magnetic field strength in coronal closed magnetic structures, based on the analysis of flare-generated oscillations of coronal loops. Interpretation of the oscillations observed in terms of global standing kink waves allows to connect the period of the oscillations and the loops length with the magnetic field strength in the loops. For loop oscillations observed with TRACE on 14th July 1998 and 4th July 1999, we estimate the magnetic field strength as 4-30 G. Using TRACE 171 Å and 195 Å images of the loop, taken on 4th July 1999 to determine the plasma density, we estimate the magnetic field in the loop as 13+/- 9 G. Improved diagnostic of the loop length, the oscillation period, and the plasma density in the loop will significantly improve the method's precision. Title: Multifluid and Hybrid Modeling of Waves in Coronal Holes: Implications for Heating Theories Authors: Ofman, L.; Davila, J. M. Bibcode: 2001AGUSM..SH22E01O Altcode: Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) observations show that protons and minor ions are hot (Tp>106 K, Ti>107 K) and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfvénic fluctuations in the solar wind. Using the three-fluid 2.5D MHD model we have shown that the unresolved Alfvénic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. However, \Alfven waves with realistic amplitudes can not reproduce the O5+ perpendicular temperature and anisotropy deduced from UVCS observations. We use the hybrid model to investigate constrains on the anisotropy of the minor ions. Our results suggests that the minor ions are heated and accelerated by high-frequency waves ( ~103 Hz), while proton heating occurs by low frequency waves ( ~10-3 Hz). Title: Interaction of EIT Waves with Coronal Active Regions Authors: Ofman, L. Bibcode: 2001AGUSM..SH31D11O Altcode: We use 3D MHD modeling to investigate the interaction of the EIT waves with active regions. The active region is modeled by an initially force-free, bipolar, magnetic configuration. We include gravity, finite thermal pressure, and resistive dissipation in our model. The EIT wave is launched at the boundary of the region, as short time velocity pulse that travels with the local fast magnetosonic speed ( ~ 250 km/s) towards the active region. We investigate the effect of the pulse amplitude and direction relative to the active region magnetic field orientation. We find that the EIT wave reconnects with the active region magnetic field, and induces transient currents. The currents and the resulting Lorenz force lead to the dynamic distortion of the active region magnetic field, and the generation of secondary waves that propagate away from the active regions. The Lorenz force compresses the plasma and induces flow along the magnetic flux tubes producing active region loops. Analysis of the interaction between the EIT wave and the active region can serve as a diagnostic of the active region coronal magnetic structure. We show animations of the interaction of the EIT waves with the active regions. Title: Constraints on the O+5 Anisotropy in the Solar Corona Authors: Ofman, L.; Viñas, A.; Gary, S. P. Bibcode: 2001ApJ...547L.175O Altcode: Velocity distributions of O+5 ions derived from Ultraviolet Coronagraph Spectrometer (UVCS) observations in coronal holes indicate that the O+5 ions are highly anisotropic (T⊥i/T∥i~30-300 at 3.5 Rsolar). The observations provide empirical values for the electron density and the ion temperatures. It is well known that the electromagnetic ion cyclotron instability is driven by temperature anisotropy. The instability leads to the rapid decrease of anisotropy and transfer of part of the kinetic energy of the particles into the magnetic field fluctuations. Here we use linear theory and hybrid simulations combined with the empirical values of the densities and the temperatures to investigate the ion cyclotron instability of the anisotropic minor ions in the coronal hole plasma. We find that an initial O+5 anisotropy of 50 decreases by an order of magnitude within ~300-900 proton cyclotron periods. Thus, the ion cyclotron instability constrains the anisotropy of O+5 ions that can be sustained in the solar corona without continuous perpendicular heating. Title: Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes Authors: Ofman, Leon Bibcode: 2001STIN...0132396O Altcode: The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear. time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that nonlinear waves are generated in coronal holes by torsional Alfvén waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the, fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature. and magnetic field geometry,) that will become available from the recently launched SOHO spacecraft. Title: Three-fluid 2.5D MHD models of waves in solar coronal holes and the relation to SOHO/UVCS observations Authors: Ofman, L. Bibcode: 2000AIPC..537..119O Altcode: 2000wdss.conf..119O The physical properties of the minor ions in the corona provide clues on the coronal heating and solar wind acceleration mechanism. Recent observations show that protons and minor ions are hot (Tp>106 K, Ti>108 K) and anisotropic in coronal holes. A possible cause of the large perpendicular motions is unresolved Alfvénic fluctuations in the solar wind. Using the three-fluid 2.5D MHD model I have shown that the unresolved Alfvénic fluctuations lead to apparent proton temperature and anisotropy consistent with UVCS observations. I show the calculated dependence of the apparent kinetic temperatures of protons and O5+ ions with heliocentric distance and compare the results to the UVCS observations. . Title: Imaging the Sun in extreme ultraviolet and in X-rays with spaceborne instruments Authors: Ofman, Leon Bibcode: 2000OptPN..11...54O Altcode: No abstract at ADS Title: Source regions of the slow solar wind in coronal streamers Authors: Ofman, L. Bibcode: 2000GeoRL..27.2885O Altcode: Recent SOHO/UVCS observations of the O5+ ion line emission at 1032Å in coronal streamers indicate that the emission is stronger by an order of magnitude at the edges (legs) of streamers than in the central core of streamers. In contrast, the brightness of the Ly-α emission peaks in the core of streamers. I have developed the first 2.5D, three-fluid numerical MHD model of the slow solar wind flow in a coronal streamer. Using the model I find that the enhancement of the oxygen line emission occurs due to the enhanced abundances of O5+ ions in the legs of streamer caused by the Coulomb friction with the outflowing protons. Thus, the enhanced O5+ emission traces the source regions of the slow solar wind in coronal streamers. The identification of these regions helps to understand the origins and the composition of the slow solar wind. Title: Three-dimensional MHD modeling of an impulsive excitation of a coronal loop motivated by TRACE observations Authors: Ofman, L.; Davila, J. M. Bibcode: 2000SPD....31.0604O Altcode: 2000BAAS...32..838O Recently, decaying transversal oscillations of bright coronal loops in the 171 Angstroms and 195 Angstroms emission lines were observed with the imaging telescope on-board the TRACE satellite. The loop oscillations were excited impulsively by a solar flare in the adjacent active region. Using 3D MHD model of the loop the period and the decay rate of the oscillations, together with the loop geometry, density, and temperature can be used to determine the average magnetic field of the loop, and the magnetic or viscous Reynolds number (R). Recently, Nakariakov et al. (1999) used the R1/5 heating time scaling to determine the range of the dissipation coefficients in the loop observed with TRACE. Using the linearized 3D MHD model we investigate the coupling of the decaying transverse mode and the internal Alfvén mode, and examine the relation between the decay time of the transverse oscillations and the heating time of the loop for a range of Reynolds numbers, and wavenumbers. We use the nonlinear 3D MHD model with more realistic loop geometry, boundary conditions, and mode coupling to study the relaxation of the impulsively excited coronal loop oscillation. We find that when the Reynolds number is large (R=104) the nonlinear effects become important at the resonant dissipation layer, and the heating time decreases compared to the linear case. We plan to expand the nonlinear 3D model to include the effects of gravity, and loop curvature to better model the loop oscillations observed by TRACE. LO would like to acknowledge support by the NASA SR&T, and the HPCC programs. Title: Three-dimensional MHD modeling of an impulsive excitation of a coronal loop motivated by TRACE observations. Authors: Ofman, L.; Davila, J. M. Bibcode: 2000BAAS...32..837O Altcode: No abstract at ADS Title: Dissipation of Slow Magnetosonic Waves in Coronal Plumes Authors: Ofman, L.; Nakariakov, V. M.; Sehgal, N. Bibcode: 2000ApJ...533.1071O Altcode: Recently, slow magnetosonic waves were identified in polar plumes, at heights up to about 1.2 Rsolar using the Extreme Ultraviolet Imaging Telescope (EIT) observations of quasi-periodic EUV intensity fluctuations, and higher in the corona using the Ultraviolet Coronagraph Spectrometer (UVCS) white-light channel. First, we derive the linear dispersion relation for the slow waves in the viscous plasma. Next, we derive and solve an evolutionary equation of the Burgers type for the slow waves, incorporating the effects of radial stratification, quadratic nonlinearity, and viscosity. Finally, we model the propagation and dissipation of slow magnetosonic waves in polar plumes using one-dimensional and two-dimensional MHD codes in spherical geometry. The waves are launched at the base of the corona with a monochromatic source. We find that the slow waves nonlinearly steepen as they propagate away from the Sun into the solar wind. The nonlinear steepening of the waves leads to enhanced dissipation owing to compressive viscosity at the wave fronts. The efficient dissipation of the slow wave by compressive viscosity leads to damping of the waves within the first solar radii above the surface. We investigate the parametric dependence of the wave properties. Title: Propagation and Dissipation of Slow Magnetosonic Waves in Coronal Plumes Authors: Ofman, L. Bibcode: 2000ASPC..205..147O Altcode: 2000ltse.conf..147O Recently, slow magnetosonic waves were identified in polar plumes at heights of up to ~1.2Rodot using the Extreme Ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) spacecraft. We model the propagation of these waves in solar polar coronal plumes, and the dissipation of the waves by compressive viscosity. First, we estimate the damping rate of the waves using linear theory. Next, we model the slow magnetosonic wave with a 2D MHD code in spherical geometry and assume azimuthal symmetry of the plumes. We find that the slow magnetosonic waves generated at the base of the plumes by periodic compressions propagate outward and dissipate in the plumes. The background atmosphere includes Parker's flow and the corresponding density stratified by gravity close to the Sun. The stratification leads to the nonlinear steepening, and to enhanced dissipation over the linear rate of the waves. The dissipation may contribute to the heating and the acceleration of the solar wind. By observing the density structure of the plumes during an eclipse it may be possible to learn more about these waves. Title: UVCS WLC Observations of Compressional Waves in the South Polar Coronal Hole Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L. Bibcode: 2000ApJ...529..592O Altcode: Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) white light channel (WLC) observations of the south polar coronal hole plumes and interplume regions produce signatures of quasi-periodic variations in the polarized brightness (pB) at a heliocentric distance of 1.9 solar radii (Rsolar). The Fourier power spectrum of the pB time series shows significant peaks at about 1.6-2.5 mHz and additional smaller peaks at longer and shorter timescales. Wavelet analysis of the pB time series shows that the coherence time of the fluctuations is about 30 minutes. The new observations strongly suggest that the fluctuations are compressional wave packets propagating in the coronal hole high above the limb. The presence of compressional waves may have important implications that help to explain the heating of coronal holes and the fast solar wind acceleration. Title: Nonlinear dissipative spherical Alfvén waves in solar coronal holes Authors: Nakariakov, V. M.; Ofman, L.; Arber, T. D. Bibcode: 2000A&A...353..741N Altcode: The weakly nonlinear dynamics of linearly polarized, spherical Alfvén waves in coronal holes is investigated. An evolutionary equation, combining the effects of spherical stratification, nonlinear steepening and dissipation due to shear viscosity is derived. The equation is a spherical analog of the scalar Cohen-Kulsrud-Burgers equation. Three main stages of the wave evolution are distinguished: geometrical amplification, wave breaking and enhanced dissipation. The wave dissipation is dramatically increased by the nonlinear transfer of energy to smaller scales. The scenario of the nonlinear dissipation is practically independent of viscosity. The dissipation rate is stronger for highest amplitudes, and depends weakly on the wave period and the temperature of the atmosphere. Waves with periods less than 300 s and initial amplitudes about 2-3% of the Alfvén speed at the base of the corona are subject to the nonlinear steepening and dissipation in less than 10 solar radii. For the Alfvén waves with amplitudes less than 25 km s-1 at the base of the corona, the maximum amplitude of up to 200 km s-1 is reached at several solar radii. The nonlinear distortion of the wave shape is accompanied by the generation of longitudinal motions and density perturbations. Title: Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes Authors: Ofman, Leon Bibcode: 2000STIN...0021484O Altcode: The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear, time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that solitary-like waves are generated in coronal holes nonlinearly by torsional Alfven waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature, and magnetic field geometry) that will become available from the recently launched SOHO spacecraft. Title: Winds from Luminous Late-Type Stars. I. The Effects of Nonlinear Alfvén Waves Authors: Airapetian, V. S.; Ofman, L.; Robinson, R. D.; Carpenter, K.; Davila, J. Bibcode: 2000ApJ...528..965A Altcode: We present the results of magnetohydrodynamic (MHD) modeling of winds from luminous late-type stars using a 2.5-dimensional, nonlinear MHD computer code. We assume that the wind is generated within an initially hydrostatic atmosphere and is driven by torsional Alfvén waves generated at the stellar surface. Two cases of atmospheric topology are considered: case I has longitudinally uniform density distribution and isotropic radial magnetic field over the stellar surface, and case II has an isotropic, radial magnetic field with a transverse density gradient, which we refer to as an ``atmospheric hole.'' We use the same set of boundary conditions for both models.The calculations are designed to model a cool luminous star, for which we assume an initial hydrostatic pressure scale height of 0.072 R*, an Alfvén wave speed of 92 km s-1 at the surface, and a wave period of 76 days, which roughly corresponds with the convective turnover time. For case I the calculations produce a wind with terminal velocity of ~22 km s-1 and a mass loss rate comparable to the expected value of 10-6 Msolar yr-1. For case II we predict a two-component wind: a fast (25 km s-1) and relatively dense wind outside of the atmospheric hole and a slow (15 km s-1), rarefied wind inside of the hole. Title: Numerical Simulations of Trapped Slow Magnetosonic Waves in Solar Coronal Plumes Authors: Ofman, L.; Deforest, C. E. Bibcode: 2000AdSpR..25.1909O Altcode: Recent observations of polar plumes in the southern solar coronal hole by the Extreme ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft show signatures of quasi-periodic compressional waves. Here, we present the results of a nonlinear, 2D MHD simulation of the slow magnetosonic waves in plumes for typical coronal conditions consistent with observations. Our numerical simulations confirm the interpretation of the observed intensity fluctuations as propagating slow magnetosonic waves. On March 7 1996 DeForest and Gurman (1998) detected quasi-periodic intensity variations of 10-20% in the EIT Fe IX and X line emission at 171A&ring that propagate outward in several polar plumes at 75-150 km s-1 with a period of 10-15 minutes. The observed propagation velocity agrees well with the expected sound velocity inside the plumes. The lower phase speed in the plumes than in the ambient plasma leads to partial trapping of the slow magnetosonic waves in the plumes. The slow magnetosonic waves may contribute to the heating of the lower corona by compressive dissipation Title: Dissipation and Steepening of Slow Magnetosonic Waves in Polar Plumes and the Effect on the Solar Wind Close to the Sun Authors: Ofman, L. Bibcode: 1999ESASP.446..515O Altcode: 1999soho....8..515O Recently, slow magnetosonic waves were identified in polar plumes at heights up to about 1.2Rs, using Extreme ultraviolet Imaging Telescope (EIT) observations of quasi-periodic EUV intensity fluctuations (Ofman, Nakariakov, DeForest 1999). We model the propagation and dissipation of slow magnetosonic waves in polar plumes using 2D MHD code in spherical geometry. We find that outward propagating slow magnetosonic waves may become trapped due to transverse density and temperature structure of the plumes. The slow waves nonlinearly steepen in the gravitationally stratified plumes. The nonlinear steepening of the waves leads to enhanced acceleration of the subsonic solar wind due to momentum transfer, and to the enhances dissipation due to compressive viscosity at the wave-fronts. The slow waves can contribute to the heating of coronal holes close to the Sun (r<2Rs), a region where the shear Alfven wave heating is inefficient. Title: Alfvén wave phase mixing driven by velocity shear in two-dimensional open magnetic configurations Authors: Ruderman, M. S.; Goldstein, M. L.; Roberts, D. A.; Deane, A.; Ofman, L. Bibcode: 1999JGR...10417057R Altcode: Phase mixing of torsional Alfvén waves in axisymmetric equilibrium magnetic configurations with purely poloidal magnetic field and stationary flow along the field lines in resistive viscous plasmas is studied. The characteristic wavelength along the magnetic field lines is assumed to be much smaller than the characteristic scale of inhomogeneity in the magnetic field direction, and the WKB method is used to obtain an analytic solution describing phase mixing. The general solution is applied to a particular configuration with the radial magnetic field and flow under the assumptions that the magnetic field and density are independent of the polar angle in the spherical coordinates and the flow velocity is independent of the radial coordinate. The only source of phase mixing in this configuration is velocity shear. The analytical solution is compared with a numerical simulation of the fully nonlinear resistive MHD equations. The numerical and analytical results are in good agreement. Consequences for wave energy deposition into the solar corona and solar wind and for the evolution of the Alfvén wave energy spectrum are discussed. Title: TRACE observation of damped coronal loop oscillations: Implications for coronal heating Authors: Nakariakov, V. M.; Ofman, L.; Deluca, E. E.; Roberts, B.; Davila, J. M. Bibcode: 1999Sci...285..862N Altcode: The imaging telescope on board the Transition Region and Coronal Explorer (TRACE) spacecraft observed the decaying transversal oscillations of a long [(130 ± 6) × 106 meters], thin [diameter (2.0 ± 0.36) × 106 meters], bright coronal loop in the 171 angstrom FeIX emission line. The oscillations were excited by a solar flare in the adjacent active region. The decay time of the oscillations is 14.5 ± 2.7 minutes for an oscillation with a frequency 3.90 ± 0.13 millihertz. The coronal dissipation coefficient is estimated to be eight to nine orders of magnitude larger than the theoretically predicted classical value. The larger dissipation coefficient may solve existing difficulties with wave heating and reconnection theories. Title: Alfvén wave phase mixing driven by velocity shear in two dimensions Authors: Ruderman, M. S.; Goldstein, M. L.; Roberts, D. A.; Deane, A.; Ofman, L. Bibcode: 1999AIPC..471..337R Altcode: 1999sowi.conf..337R We investigate the role of velocity shears in producing strong phase mixing and damping of Alfvén waves. We show that phase mixing damps waves in regions of strong velocity shear, thus providing a possible source of heat to the solar corona and solar wind. We compare the linear solutions with direct numerical solution of the three-dimensional equations of compressible (resistive) magnetohydrodynamics (MHD). In regions far removed from the velocity shear, the simulations show that the radial evolution of the wave amplitudes follows closely WKB theory. In the shear layer, strong damping occurs in the numerical simulations, quantitatively close to that computed from the linearized analysis. Title: Two-fluid 2.5D MHD model of the fast solar wind and the effective proton temperature Authors: Ofman, L.; Davila, J. M. Bibcode: 1999AIPC..471..405O Altcode: 1999sowi.conf..405O Recent SOHO/UVCS observations indicate that the perpendicular proton and ion temperatures are much larger than electron temperatures (Kohl et al. 1997). In the present study we simulate numerically the solar wind flow in a coronal hole with the two-fluid approach. For simplicity, we neglect electron inertia. We investigate the effects of electron and proton temperatures on the solar wind acceleration by nonlinear waves. In the model the nonlinear waves are generated by Alfvén waves with frequencies in the 10-3 Hz range, driven at the base of the coronal hole. The resulting electron and proton flow profile exhibits density and velocity fluctuations. The fluctuations may steepen into shocks as they propagate away from the sun. We construct the proton velocity distribution and a synthetic Ly-α line profile by including the combined effects of temperature and velocity fluctuations in the model, and compare them to the UVCS observations. Title: Temporal Evolution and Physical Properties of North Polar Coronal Hole from SPARTAN 201-05, SOHO, TRACE and Mk3 Authors: Guhathakurta, M.; Deforest, C.; Fisher, R. R.; Ofman, L.; Kucera, T.; Gibson, S.; Spartan201 Team Bibcode: 1999AAS...194.3203G Altcode: 1999BAAS...31..870G Polar coronal rays/plumes as long lived structures that extend out to 6 R_sun were first observed during the first flight of SPARTAN 201 spacecraft during April 11-12 of 1993. In this paper we will present detail observations from the WLC aboard Spartan 201 spacecraft (31 Oct.- 2 Nov.,1998) of the north polar coronal hole and comapre its physical properties to the past three Spartan missions. We will present comparisons of the Spartan WL observations with the Mk3 pB observations, SOHO LASCO and EIT observations, and finally the high resolution TRACE 171 Angstroms observations, to characterize the north polar coronal hole all the way from the base of the corona out to 30 R_sun. We will also look for signatures of waves (quasi-period variations) in the coronal hole plumes and interplume regions in the high cadence Spartan pB observations obtained during this mission. Title: A Numerical Package for Modeling Solar Flares and Interpreting HESSI Data Authors: Holman, G. D.; Mariska, J. T.; McTiernan, J. M.; Ofman, L.; Petrosian, V.; Ramaty, R. R. Bibcode: 1999AAS...194.8008H Altcode: 1999BAAS...31..966H HESSI, the High Energy Solar Spectroscopic Imager, will observe the x-ray and gamma-ray emission from solar flares with an unprecedented combination of spectral, spatial, and temporal resolution. The quantitative interpretation of the HESSI data will require a level of numerical modeling not generally demanded by previous observations. In view of this, we are developing an integrated package of modular numeric codes and models for the analysis and interpretation of these data. The package will focus on the energetic electrons produced during the impulsive phase of flares. It will compute both the bremsstrahlung x-ray/gamma-ray emission and the gyrosynchrotron radio emission from model flare configurations and initial electron distributions. Steady-state and time-dependent Fokker-Planck codes will compute the transport of suprathermal electrons. A hydrodynamic code will compute the response of the flare plasma in the model configurations. The proposed computational package will allow for comprehensive modeling of energized electrons in different flare scenarios. The predicted emissions can be compared directly with HESSI and radio images and spectra. The package will provide the necessary framework for comparing electron acceleration models with HESSI data. This work is supported in part by the NASA Sun-Earth Connection Program. Title: Determination of the Reynolds number from TRACE Observation of Damped Coronal Loop Oscillations Induced by a Flare Authors: Ofman, L.; Nakariakov, V. M.; Deluca, E.; Roberts, B.; Davila, J. M. Bibcode: 1999AAS...194.7909O Altcode: 1999BAAS...31..964O The Transition Region and Coronal Expolorer (TRACE) observes the solar corona with unprecedented spatial and temporal resolution. We analyzed active region loop observation in the 171 Angstroms Fe IX emission line, and report the direct observations of damped transverse oscillations of a long (130+/-6 Mm) thin (diameter 2+/-0.36 Mm) bright active region loop. The oscillations were detected following a flare in the adjacent active region. We determined the oscillation frequency and the decay time by the least-square fit of an exponentially decaying sinusoidal function. Using the dispersion relation for the transverse oscillations, and the observed loop geometry we estimated the Alfven crossing time in the loop. The Alfven time can be used to determine the magnetic field strength in the loop if the density is known. All parts of the loop were observed to oscillate transversly in-phase, implying that the ocillation is a global mode of the loop. Using dissipative MHD model for resonant absorption of global mode oscillations for the coronal loop we determined the Reynolds number that produces the observed damping rate of the observed global mode. The value of the Reynolds number is in the 10(5-10^6) range, which is eight to nine orders of magnitude smaller than the classical coronal value. We discuss the important implication of the small Reynolds number on coronal heating theories. Title: Slow Magnetosonic Waves in Coronal Plumes Authors: Ofman, L.; Nakariakov, V. M.; DeForest, C. E. Bibcode: 1999ApJ...514..441O Altcode: Recent observations of polar plumes in the southern solar coronal hole by the Extreme-Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft show signatures of quasi-periodic compressional waves with periods of 10-15 minutes. The relative wave amplitude was found to increase with height in the plumes up to about 1.2 Rsolar. Using a one-dimensional linear wave equation for the magnetosonic wave, we show that the waves are propagating and that their amplitude increases with height. The observed propagation velocity agrees well with the expected sound velocity inside the plumes. We present the results of the first nonlinear, two-dimensional, magnetohydrodynamic (MHD) simulation of the magnetosonic waves in plumes for typical coronal conditions consistent with observations and gravitationally stratified solar corona. We find numerically that outward-propagating slow magnetosonic waves are trapped, and nonlinearly steepen in the polar plumes. The nonlinear steepening of the magnetosonic waves may contribute significantly to the heating of the lower corona by compressive dissipation. Title: Signatures of Nonlinear Waves in Coronal Plumes and Holes Authors: Ofman, Leon Bibcode: 1999STIN...0119003O Altcode: In recent Ultraviolet Coronagraph Spectrometer/Solar and Heliospheric Observatory (UVCS/SOHO) White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9-2.45 solar radii. The motivation for the observation is the 2.5D Magnetohydrodynamics (MHD) model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. To help identify the waves observed with the UVCS/WLC we model the propagation and dissipation of slow magnetosonic waves in polar plumes using 1D MHD code in spherical geometry, We find that the slow waves nonlinearly steepen in the gravitationally stratified plumes. The nonlinear steepening of the waves leads to enhanced dissipation due to compressive viscosity at the wave-fronts. Title: Two-fluid 2.5D MHD Simulations of the Fast Solar Wind in Coronal Holes and the Relation to UVCS Observations Authors: Davila, J. M.; Ofman, L. Bibcode: 1999SSRv...87..165D Altcode: Recent SOHO/UVCS observations indicate that the perpendicular proton and ion temperatures are much larger than electron temperatures. In the present study we simulate numerically the solar wind flow in a coronal hole with the two-fluid approach. We investigate the effects of electron and proton temperatures on the solar wind acceleration by nonlinear waves. In the model the nonlinear waves are generated by Alfvén waves with frequencies in the 10-3 Hz range, driven at the base of the coronal hole. The resulting electron and proton flow profile exhibits density and velocity fluctuations. The fluctuations may steepen into shocks as they propagate away from the sun. We calculate the effective proton temperature by combining the thermal and wave velocity of the protons, and find qualitative agreement with the proton kinetic temperature increase with height deduced from the UVCS Ly-α observations by Kohl et al. (1998). Title: SOHO Observations of Density Fluctuations in Coronal Holes Authors: Ofman, L.; Romoli, M.; Noci, G.; Poletto, G.; Kohl, J. L.; Howard, R. A.; Cyr, C. St.; Deforest, C. E. Bibcode: 1999SSRv...87..287O Altcode: In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power spectrum peaks in the 10 12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations. Title: Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L. Bibcode: 1998ApJ...507L.189O Altcode: In the Letter ``Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind'' by L. Ofman, M. Romoli, G. Poletto, G. Noci, and J. L. Kohl (ApJ, 491, L111 [1997]), there was an error in the data reduction of the polarized brightness (pB). It was assumed that the cadence of the data and the exposure time are equal. However, the correct cadence is30 s longer than the exposure time because of the time it takes the polarizer to change orientation between exposures. This error does not affect the main result of the Letter, i.e., the detection of quasi-periodic density fluctuations in the solar wind. However, the correct cadences of the data in Table 1 are 30 s longer. This correction can be taken into account in Figure 1 by multiplying the times by 1.5 and dividing the frequencies by the same factor. Thus, the highest peak in the power spectrum is at 1.8+/-0.07 mHz (the corresponding period is 9.3+/-0.4 minutes). The correction factor is 1.1 in Figure 2 because of the longer exposure time in this observation. Title: SUMER Observations of the Evolution and the Disappearance of a Solar Prominence Authors: Ofman, L.; Kucera, T. A.; Mouradian, Z.; Poland, A. I. Bibcode: 1998SoPh..183...97O Altcode: The mechanisms that lead to the formation and the disappearance of prominences are poorly understood, at present. An arch-shaped prominence was observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO) on 31 March-1 April 1996. The observations were performed at three wave-bands in the Lyman continuum. Ten successive images were obtained at 41-minute time intervals. Based on computed models of Gouttebroze, Heinzel, and Vial (1993), we have determined the temperature distribution of the prominence using the intensity ratio of 876 Å and 907 Å. The observed time sequence shows that parts of the prominence disappear possibly by heating, while other parts exhibit heating and cooling with apparent outward motion. We model the heat input with the linearized MHD equations using a prescribed initial density and a broad-band spectrum of Alfvén waves. We find a good qualitative agreement with observations. In the model the prominence is heated by the resonant absorption of Alfvén waves with frequencies that match the resonant condition for a particular flux tube structure that is determined by the magnetic field topology and plasma density. Title: Solar wind acceleration by large-amplitude nonlinear waves: Parametric study Authors: Ofman, L.; Davila, J. M. Bibcode: 1998JGR...10323677O Altcode: We investigate the parametric dependence of the solar wind acceleration by large-amplitude nonlinear (LAN) magnetohydrodynamic waves. For this purpose we model numerically the self-consistent problem of the solar wind with waves by solving time-dependent, nonlinear, resistive 2.5-dimensional (three-dimensional with azimuthal symmetry) MHD equations driven by Alfvén waves. We find that when the Alfvén wave amplitude is above a parameter-dependent threshold, LAN waves are generated in the model coronal hole. For typical coronal parameters the solar wind speed and density fluctuate considerably on a timescale of ~10-40 min and with an amplitude of up to several hundred kmilometers per second near the Sun (r<~10RS) in agreement with recent interplanetary scintillation observations. The solar wind speed is inversely dependent on the driving frequency in the range 0.35-3 mHz. The amplitude of the velocity fluctuations increases with the amplitude of the magnetic field and the driving Alfvén waves at the base of the corona and decreases with the coronal temperature. We found that for the same typical solar wind and Alfvén wave parameters and an isothermal initial atmosphere, the WKB model predicts 30% higher flow velocities far from the Sun (32RS) than our self-consistent wave model with high-frequency Alfvén waves (f=2.78mHz), conforming to the WKB approximation. However, our model predicts significantly higher average flow speed near the Sun. When low-frequency non-WKB waves drive the wind, our model predicts 25% higher solar wind speed than the WKB model far from the Sun. This result of our model is in agreement with linear studies of solar wind acceleration by Alfvén waves that take into account Alfvén wave reflection. Title: Observation of Prominence Heating and the Heating Mechanism Authors: Ofman, L.; Mouradian, Z.; Kucera, T. A.; Poland, A. I. Bibcode: 1998ASPC..150..159O Altcode: 1998IAUCo.167..159O; 1998npsp.conf..159O No abstract at ADS Title: A Self-consistent Model for the Resonant Heating of Coronal Loops: The Effects of Coupling with the Chromosphere Authors: Ofman, L.; Klimchuk, J. A.; Davila, J. M. Bibcode: 1998ApJ...493..474O Altcode: We present the first model of resonant heating of coronal loops that incorporates the dependence of the loop density on the heating rate. By adopting the quasi-static equilibrium scaling law ρ ~ Q5/7, where ρ is the density and Q is the volumetric heating rate, we are able to approximate the well-known phenomena of chromospheric evaporation and chromospheric condensation, which regulate the coronal density. We combine this scaling law with a quasi-nonlinear MHD model for the resonant absorption of Alfvén waves in order to study the spatial and temporal dependence of the heating. We find that the heating is concentrated in multiple resonance layers, rather than in the single layer of previous models, and that these layers drift throughout the loop to heat the entire volume. These newfound properties are in much better agreement with coronal observations. Title: Atmospheric Dynamics of Luminous Late-Type Stars Authors: Airapetian, V. S.; Ofman, L.; Robinson, R. D.; Carpenter, K.; Davila, J. Bibcode: 1998ASPC..154.1569A Altcode: 1998csss...10.1569A We present first results of magnetohydrodynamic (MHD) calculations of winds from luminous late-type stars using an existing, 2.5D, non-linear MHD code recently developed by Ofman & Davila (e.g., Ofman & Davila 1997). We assume that the wind is initiated in a hydrostatic atmosphere with an isothermal pressure scale height of 0.072 R* and a ``chromospheric hole'' modeled by a transverse density structure and a radial magnetic field. To ensure that we are accurately assessing the terminal velocity of the wind, we carried out the calculations to a height of 20 stellar radii. We find that in the higher density (low Alfven velocity) regions outside of the ``chromospheric hole'' the Alfven waves are freely propagating. Ponderomotive forces associated with these waves drive radial, compressive motions and contribute to stellar wind acceleration. The compressive motions then excite slow magnetosonic waves which non-linearly steepen into solitary waves that propagate on top of a background flow. This situation is similar to solar coronal hole models. In the lower density ``chromospheric hole'' region the Alfven wave are strongly reflected, and produce a substantial outflow, with both radial and azimuthal velocities approaching the local Alfven speed. Our results are in qualitative agreement with observational signatures of winds in cool, luminous late-type stars. Title: Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L. Bibcode: 1997ApJ...491L.111O Altcode: Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light channel (WLC) observations on board the Solar and Heliospheric Observatory (SOHO) indicate quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes. This is the first observation of possible signatures of compressional waves high above the limb (at heliocentric distances in the range 1.9-2.45 Rsolar). The Fourier power spectrum of the pB time series at 1.9 Rsolar shows significant peak at about 6 minutes and possible fluctuations on longer timescales (20-50 minutes). The observation at 1.9 Rsolar is the only currently available WLC data set with sufficient cadence to resolve the 6 minute period. These preliminary observations may result from density fluctuations caused by compressional waves propagating in polar coronal holes. We stress that our results are preliminary, and we plan future high-cadence observations in both plume and interplume regions of coronal holes. Recently, Ofman & Davila used a 2.5 D MHD model and found that Alfvén waves with an amplitude of 20-70 km s-1 at the base of the coronal hole can generate nonlinear, high-amplitude compressional waves that can contribute significantly to the acceleration of the fast solar wind. The nonlinear solitary-like waves appear as fluctuations in the density and the radial outflow velocity and contribute significantly to solar wind acceleration in open magnetic field structures. The motivation for the reported observations is the MHD model prediction. Title: IPS Observations of the Solar Wind Velocity and the Acceleration Mechanism Authors: Ofman, L.; Davila, J. M.; Coles, W. A.; Grall, R. R.; Klinglesmith, M. T. Bibcode: 1997ESASP.415..361O Altcode: 1997cpsh.conf..361O No abstract at ADS Title: Fast Solar Wind Acceleration by Nonlinear Waves in Coronal Holes Authors: Ofman, L.; Davila, J. M. Bibcode: 1997AAS...191.7414O Altcode: 1997BAAS...29.1326O We use the 2.5D (3D with azimuthal symmetry) MHD equations to model numerically the solar wind acceleration in a nonhomogeneous coronal hole. We investigate the parametric dependence of the solar wind acceleration by nonlinear MHD waves with a monochromatic and a broad band driving source. We find that when the Alfven wave amplitude is above a parameter dependent threshold , large amplitude nonlinear longitudinal waves are generated and contribute to the radial acceleration. The calculated solar wind speed and density fluctuates considerably on a time scale of tens of minutes with an amplitude of up to several hundred km/s near the sun (4R_sun<r<10R_sun). The amplitude of the fluctuations decreases with the distance from the sun. Using the monochromatic driver we find that the solar wind speed and the amplitude of the nonlinear waves is inversely dependent on the driving frequency in the range 0.3-3 mHz. The acceleration due to the broad band driver depends on the power spectrum of the driver. The amplitude of the nonlinear waves and the acceleration increases with the magnitude of the magnetic field and decreases with the temperature of the coronal hole. Title: A Self-Consistent Model for the Resonant Heating of Coronal Loops: the Effects of Coupling with the Chromosphere Authors: Klimchuk, J. A.; Ofman, L.; Davila, J. M. Bibcode: 1997SPD....28.0504K Altcode: 1997BAAS...29..909K The physical nature of coronal heating remains one of the great problems of solar physics. One of the several theories that are being pursued is the resonant absorption of MHD waves. While promising in several respects, this theory has suffered from a glaring deficiency: the computed heating is incompatible with both the assumed density and the observed structure of coronal loops. We present the first model of resonant heating of coronal loops that incorporates the dependence of the loop density on the heating rate. By adopting the quasi-static equilibrium scaling law rho ~ Q(5/7) , where rho is the density and Q is the volumetric heating rate, we are able to approximate the well-known phenomena of chromospheric evaporation and chromospheric condensation, which regulate the coronal density. We combine this scaling law with a linearized MHD model for the resonant absorption of Alfven waves to study the spatial and temporal dependence of the heating. We find that the heating is concentrated in multiple resonance layers, rather than the single layer of previous models, and that these layers drift throughout the loop to heat the entire volume. These new properties are in much better agreement with coronal observations, including recent observations from the CDS and EIT instruments on SOHO, as well as earlier observations from the SXT instrument on Yohkoh. Title: Do First Results from SOHO UVCS Indicate That the Solar Wind Is Accelerated by Solitary Waves? Authors: Ofman, L.; Davila, J. M. Bibcode: 1997ApJ...476L..51O Altcode: The Ultraviolet Coronagraph Spectrometer (UVCS) on board the recently launched US-European Solar and Heliospheric Observatory (SOHO) satellite has found O VI and H I emission lines with a broad component that corresponds to ~300 km s-1 unresolved motions at about 0.7 solar radii above the photosphere. These motions appear to be independent of ion mass. We suggest that the large Doppler broadening of the ion emission lines observed by the UVCS are signatures of solitary waves in the solar wind plasma. According to our recent 2.5-dimensional (i.e., three-dimensional with azimuthal symmetry) MHD simulations, these waves may contribute significantly to the solar wind acceleration and may generate velocity fluctuations with a magnitude that agrees with the above observations. Title: Solar Wind Acceleration by Solitary Waves in Coronal Holes Authors: Ofman, L.; Davila, J. M. Bibcode: 1997ApJ...476..357O Altcode: Coronal holes are well-known sources of the high-speed solar wind; however, the exact acceleration mechanism of the fast wind is still unknown. We solve numerically the time-dependent, nonlinear, resistive 2.5-dimensional MHD equations and find that solitary waves are generated in coronal holes nonlinearly by torsional Alfvén waves. The solitary wave phase velocity was found to be slightly above the sound speed in the coronal hole; for example, with the driving Alfvén wave amplitude vd ~ 36 km s-1 and plasma β = 5%, the solitary wave phase speed is ~185 km s-1. We show with a more simplified analytical model of the coronal hole that sound waves are generated nonlinearly by Alfvén waves. We find numerically that these waves steepen nonlinearly into solitary waves. In addition, ohmic heating takes place in the coronal hole inhomogeneities owing to phase-mixing of the torsional Alfvén waves. When solitary waves are present, the solar wind speed and density fluctuate considerably on timescales of ~20-40 minutes in addition to the Alfvénic fluctuations. The solitary wave-driven wind might be in better qualitative agreement with observations than the thermally driven and WKB Alfvén wave solar wind models. Title: Possible Signatures of Nonlinear MHD Waves in the Solar Wind: UVCS Observatio ns and Models Authors: Ofman, L.; Romoli, M.; Davila, J. M.; Poletto, G.; Kohl, J.; Noci, G. Bibcode: 1997ESASP.404..571O Altcode: 1997cswn.conf..571O No abstract at ADS Title: Solitary waves in coronal holes-predicted signatures close to the sun Authors: Ofman, L.; Davila, J. M. Bibcode: 1997AIPC..385..227O Altcode: 1997recs.conf..227O Coronal holes are well known sources of the high speed solar wind, however, the exact acceleration mechanism of the wind is still unknown. We find that solitary waves may be generated in coronal holes nonlinearly by Alfvén waves. The solitary waves may efficiently accelerate the fast solar wind in addition to thermal conduction. We solve numerically the time-dependent, nonlinear, resistive 2.5-D MHD equations in spherical geometry with azimuthal symmetry to model solar wind acceleration by waves in coronal holes. Torsional Alfvén waves are driven at the base of the model coronal hole and propagate into the corona. Ohmic heating layers are found to occur at the coronal hole boundaries due to phase-mixing of the torsional Alfvén waves. The nonlinear coupling of the perpendicular (to the background magnetic field) components of the velocity and the magnetic field to the radial component of the momentum equation leads to the acceleration of the solar wind in the radial direction and to the generation of solitary waves. The solitary wave phase velocity was found to be above the sound speed in the coronal hole, with the driving Alfvén wave amplitude vd~25 km s-1, and plasma β=2.5%. We discuss the implication of our results to the proposed in-situ observations in the region r<10Rs with the future solar probe mission. Title: A New Mechanism for Solar Wind Acceleration Authors: Ofman, L.; Davila, J. M. Bibcode: 1997IAUJD..19E..34O Altcode: We investigate the parametric dependence of a new solar wind acceleration mechanism by nonlinear magneto-hydrodynamic waves, by solving numerically the time-dependent, nonlinear, resistive 2.5-D MHD equations. We find that large amplitude nonlinear longitudinal waves are generated in coronal holes by torsional Alfven waves for a broad range of parameters in the 10^6 K magnetized plasma. The structure and the dependence of the phase speed on the amplitude of these waves are similar to solitary waves. We find that the solar wind speed and density fluctuate considerably on a time scales of ~20-40 min with an amplitude of several hundred km s^{-1}. The amplitude of the radial velocity fluctuations increases with the amplitude of the driving torsional Alfven waves at the base of the corona and the magnetic field strength, decreases with the temperature, and nearly independent of the driving frequency. The typical driving frequency of the Alfven waves is in the mHz range, determined by wave reflection in the radially stratified coronal hole, with an amplitude of 30-60 km s^{-1}. For typical coronal hole parameters the nonlinear wave driven wind accelerates to more than twice the Parker's solar wind speed and is in qualitative agreement with recent SOHO observations. Title: Heating of coronal holes by the resonant absorption and dissipation of Alfvén waves Authors: Ofman, L.; Davila, J. M. Bibcode: 1996AIPC..382..149O Altcode: Coronal hole regions are well known sources of high-speed solar wind, however to account for the observed properties of the solar wind a source of energy must be included in addition to heat conduction. Alfvén waves were suggested as the possible source of heating that accelerates the solar wind. We investigate the heating and propagation of Alfvén waves in coronal holes via 2-D MHD simulation in slab geometry. Resonance heating layers are found to occur when shear Alfvén waves are driven at the coronal boundary and a continuous density profile is assumed for the coronal hole. The heating is enhanced by phase mixing when coronal hole inhomogeneities (i.e., plumes) are included. We investigate the dependence of the heating rate on the driver frequency and the Lundquist number S and find a good agreement with the analytical S1/3 scaling of the dissipation length for uniform background magnetic field. We find that when S=104 the low frequency Alfvén waves can be a significant source of heating of coronal holes at several solar radii. At larger values of S nonlinear effects may reduce the effective dissipation length. We also find that the radial dependence of the heating rate has the same form as the observed scale height temperature radial profiles observed by SPARTAN 201-01. Title: Acceleration of the Solar Wind by Solitary Waves in Coronal Holes Authors: Ofman, L.; Davila, J. M. Bibcode: 1996AAS...188.8602O Altcode: 1996BAAS...28..963O Coronal holes are well known sources of the high speed solar wind, however, the exact acceleration mechanism of the wind is still unknown. We solve numerically the time-dependent, nonlinear, resistive 2(1)/(2)-D MHD equations and find that solitons are generated in coronal holes nonlinearly by torsional Alfven waves. Initially, the ponderomotive force due to Alfven waves excites longitudinal magnetosonic waves by coupling to the radial component of the momentum equation. Next, these waves steepen into solitons that accelerate the solar wind to supersonic speed in the radial direction even in a low-beta plasma. The solitary wave phase velocity was found to be slightly above the sound speed in the coronal hole; for example, with the driving Alfven wave amplitude v_d~40 km s(-1) , and plasma beta =5% the soliton phase speed ~ 200 km s(-1) . We investigate the parametric dependence of the soliton wavelength and frequency on the plasma beta , and on the driving Alfven wave amplitude and frequency. More simplified analytical model of the coronal hole leads to the Benjamin-Ono equation that predicts the generation of solitons analytically. The compressive dissipation of solitary waves may contribute significantly to coronal hole heating. In addition, Ohmic heating takes place near the coronal hole boundaries due to phase-mixing of the torsional Alfven waves in the inhomogeneous regions. When solitary waves are present the solar wind fluctuates considerably on long time scales and on small spatial scales in addition to the Alfvenic fluctuations. This is in better qualitative agreement with observations than the thermally driven and WKB Alfven wave solar wind models. Title: Are thermal sudden disappearances of prominences driven by resonant absorption of Alfven waves? Authors: Ofman, L.; Mouradian, Z. Bibcode: 1996A&A...308..631O Altcode: In the present study we propose the resonant absorption of Alfven waves as the heating mechanism that leads to thermal sudden disappearances (DBt) of prominences. The physical parameters of prominence flux tubes are used with the low-{be}, linearized, resistive magnetohydrodynamic (MHD) model to calculate the heating times of prominences for a range of wavenumbers. The heating time dependence on the wavenumbers is compared to the measured times for DBt of quiescent prominences and a qualitative agreement is found. We find that present observational evidence is in qualitative agreement with the predictions of the resonant absorption heating mechanism for DBt of prominences. However, more observations of DBt are required to establish the heating mechanism with a higher degree of certainty. Title: Signatures of Global Mode Alfven Resonance Heating in Coronal Loops Authors: Ofman, L.; Davila, J. M.; Shimizu, T. Bibcode: 1996ApJ...459L..39O Altcode: The Yohkoh Soft X-Ray Telescope (SXT) observations of active region coronal loops transient brightening is analyzed, and the scaling of the thermal energy release with loop lengths is found to be Eth ~ L1.60+/-0.09. The numerically determined scaling of the global mode heating rate for the resonant absorption of Alfven waves, H ~ L, is found to agree with the heating rate deduced from the observed thermal energy scaling, provided that the magnetic field scales as B ~ L-0.70+/-0.05 and the waves are driven with a omega -1 spectrum. Previous analytical and numerical studies have shown that the heating due to resonant absorption of Alfven waves is most efficient at the global mode frequency. In agreement with these studies, we suggest that coronal loop transient X-ray brightenings occur when a given length coronal loop is perturbed at its global mode frequency by random footpoint motions, which results in more efficient heating of the loop. Title: Nonlinear Excitation of Global Modes and Heating in Randomly Driven Coronal Loops Authors: Ofman, L.; Davila, J. M. Bibcode: 1996ApJ...456L.123O Altcode: We solve the nonlinear three-dimensional MHD equations for fully compressible, low- beta , resistive plasma to model resonant Alfven wave heating of a coronal loop. Alfven waves are driven in the loop by a (pseudo)random time-dependent forcing with a bounded amplitude. We find that global modes are excited and resonantly heat the loop in the nonlinear regime in three dimensions. Resonant heating occurs in several narrow layers accompanied by high velocity and magnetic field shear. The narrow dissipation layers are affected by the self-consistent velocity shear and are carried around by the flow. Consequently, the topology of the perpendicular magnetic field and the ohmic heating regions differs significantly from the linear or single-frequency driver regimes, and the heating is spread more uniformly inside the loop. The heating rate varies significantly on a timescale of one to several global mode periods. We conclude that, in solar active regions, random field-line motions can excite global mode oscillations and resonantly heat the loops with a time-varying heating rate. Title: Alfvén wave heating of coronal holes and the relation to the high-speed solar wind Authors: Ofman, L.; Davila, J. M. Bibcode: 1995JGR...10023413O Altcode: Coronal hole regions are well-known sources of high-speed solar wind; however, to account for the observed properties of the solar wind, a source of energy must be included in addition to heat conduction. Alfvén waves were suggested as the possible source of heating that accelerates the solar wind. We investigate the heating and propagation of the fast and shear Alfvén waves in coronal holes via numerical solution of the time-dependent, linearized, resistive, low-β, two-dimensional MHD equations in slab geometry. The waves are driven at the lower boundary of the coronal hole and propagate into the corona. We find that fast waves are partially reflected at the coronal hole boundary and significant part of the wave energy leaks out of the coronal hole. We compare the calculated wavelengths and the attenuation rate of the fast waves in the leaky waveguide formed by the coronal hole with the analytical ideal MHD solutions for ky=0, where ky is the perpendicular wavenumber, and find an excellent agreement. When ky≠0 the fast waves couple to the shear Alfvén waves and transfer energy across field lines.

Resonance heating layers are found to occur when shear Alfvén waves are driven and a continuous density profile is assumed for the coronal hole. When resonance absorption is considered, the leakage is small compared to the heating rate. The heating is enhanced by phase mixing when coronal hole inhomogeneities (i.e., plumes) are included. We investigate the dependence of the heating rate on the driver frequency and the Lundquist number S and find a good agreement with the analytical S1/3 scaling of the dissipation length. We find that when S=104 the low-frequency Alfvén waves can be a significant source of heating of coronal holes at several solar radii. At larger values of S, nonlinear effects might reduce the effective dissipation length. We discuss the relation of our results to the observed properties of high-speed solar wind and coronal holes. Title: Nonlinear resonant absorption of Alfvén waves in three dimensions, scaling laws, and coronal heating Authors: Ofman, L.; Davila, J. M. Bibcode: 1995JGR...10023427O Altcode: The nonlinear evolution of the resonant absorption of standing and propagating Alfvén waves in an inhomogeneous plasma is studied via solution of the time-dependent, three-dimensional, low-β, resistive MHD equations over a wide parameter range. When the nonlinear effects become important, the velocities at the dissipation layer were found to be lower than the linear scaling of S1/3 would predict, where S is the Lundquist number. Highly sheared velocities that are subject to the Kelvin-Helmholtz-like instability were found at the narrow dissipation layers. Three-dimensional Kelvin-Helmholtz-like vortices appear at and near the dissipation layers and propagate along the slab of plasma when traveling Alfvén wave solution are considered. The narrow resonant heating layers are deformed by the self-consistent shear flow. In the solar active regions where the resonant absorption of Alfvén waves is believed to occur, the instability may lead to turbulent enhancement of the dissipation parameters and account for the observed turbulent velocities inferred from the nonthermal broadening of x-ray and EUV emission lines. The self consistent J×B force changes significantly the density structure of the loop that leads to a shift in the global mode frequency response of the loop and a subsequent drop in the heating rate. In the solar corona the density evolution of the loop is likely to be dominated by evaporation of material from the transition region. Title: Reply to “Comment on nonlinear studies of coronal heating by the resonant absorption of Alfvén waves” by J. V. Hollweg Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1995GeoRL..22.2679O Altcode: No abstract at ADS Title: Observations and physical interpretations of the solar wind flow properties as obtained from white light coronagraph aboard SPARTAN 201-01 Authors: Guhathakurta, Madhulika; Fisher, Richard; Ofman, Leon Bibcode: 1995sowi.conf...64G Altcode: The solar corona was observed with an externally occulted White Light Coronagraph (WLC) carried on the SPARTAN 201-1 spacecraft on 11-12 Apr. 1993. With observations from WLC and the ground based Mauna Loa White Light Coronagraph, a large number of polar plumes both in the north and south polar holes were traced from 1.16 to 5.5 Rs. Flow properties of the solar wind in coronal holes have been determined (Habbal et al., 1995) by using a two fluid model constrained by density profiles and scale height temperatures from the white light observations, and interplanetary measurements of the flow speed and proton mass flux from Ulysses' south polar passage. Provisions for acceleration by Alfven waves, as well as electron and proton heating, are included in the momentum and the energy equations respectively. The model computations fit remarkably well the empirical constraints of the two different density structures (plumes and coronal holes) for a range of input parameters. In this study we investigate the physical nature of the heating function used in the two-fluid model. Alfven waves have been suggested as the possible source of heating that accelerates the solar wind (Ofman and Davila, 1995). We utilize the density contrast observed in WLC data in the plume and ambient coronal hole region to estimate the Alfven wave frequencies responsible for heating these structures. The source heating function utilized in the two fluid model of the solar wind acceleration will be compared with the resonant Alfven wave heating function. Title: Heating of coronal holes by the resonant absorption and dissipation of Alfven waves and its relation to solar wind acceleration Authors: Ofman, L.; Davila, J. M. Bibcode: 1995sowi.confQ..66O Altcode: Coronal hole regions are well known sources of high-speed solar wind, however to account for the observed properties of the solar wind a source of momentum and heat must be included. Alfven waves were suggested as the possible source of heating that accelerates the solar wind. We investigate the propagation of the Alfven waves in coronal holes via numerical solution of the linearized 2-D resistive MHD equations in slab geometry. The Alfven waves are driven at the lower boundary of the coronal hole and propagate into the corona. The waves are reflected at the coronal hole boundary and part of the wave energy leaks out of the coronal hole. We compare the calculated wavelengths and the attenuation rate of the fast mode Alfven waves in the leaky waveguide formed by the coronal hole with the analytical ideal MHD solutions. The formation of resonance heating layers is found to occur when shear Alfven waves propagate in an inhomogeneous coronal hole. The heating is enhanced when fast mode waves couple to the shear Alfven waves. The narrow heating layers are formed near the location of the ideal resonance, which might occur near the coronal hole boundary for a nearly constant density coronal hole, surrounded by a higher density plasma. We investigate the dependence of the heating on the driver frequency, the Lundquist number, and on the heliocentric distance. and find that the low frequency Alfven waves can be an efficient source of heating at large distances from the Sun. We discuss the relation of our results to the observed properties of high-speed solar wind and coronal holes. Title: Coronal Heating by the Resonant Absorption of Alfven Waves: Wavenumber Scaling Laws Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1995ApJ...444..471O Altcode: The importance of global modes in coronal loop heating is well established. In the present work the scaling of the global-mode resonant heating rate with the perturbation wavenumbers is studied with the numerical solution of the linearized time-dependent MHD equations for a full compressible, low-beta, resistive plasma using an implicit integration scheme. The numerical simulations demonstrate that the dissipation on inhomogeneities in the background Alfven speed occurs in narrow resonant layer with the highest heating rate at the global-mode frequency. The global-mode heating rate H r was found to scale as H (Sub r) approximately k y 1.03 when k z = 0.1, and as H r approximately k y -1.93 when k z = 0.75, where k y and k z are the wavenumbers in the perpendicular and parallel to the magnetic field directions, respectively, while the dependence of H r on k z is more complex. The quality factor Q of the MHD resonance cavity scales as Q approximately k y -1.8 for k z = 0.75 and as Q approximately k y -1.46 for k z = 0.1. The numerically determined heating rate scaling, the global-mode fequency, and the quality factor are in good agreement with the analytical linear theory. The magnitude of the perturbed velocities was found to decrease with k y. Assuming typical coronal loop parameters (B 0 = 100-200 G, upsilon A = 2000-4000 km/s), the Alfven waves can supply the required heating to a low-Q loops. Title: Heating of Coronal Holes by the Resonant Absorption and Dissipation of Alfvén Waves Authors: Ofman, L.; Davila, J. M. Bibcode: 1995SPD....26..907O Altcode: 1995BAAS...27..974O No abstract at ADS Title: Magnetic Reconnection and Current-Sheet Formation at X-type Neutral Points Authors: Steinolfson, R. S.; Ofman, L.; Morrison, P. J. Bibcode: 1995GMS....86..189S Altcode: 1995spcb.book..189S Numerical solutions of the nonlinear, resistive magnetohydrodynamic (MHD) equations are used to study the evolution of a perturbed or stressed x-type neutral point. By performing individual simulations for both compressible and incompressible plasmas, we are able to demonstrate that the important physics for this problem involves just the interaction between the plasma flow velocity and the magnetic field and that the thermodynamics has a relatively passive effect. We have also done separate simulations for both solid, conducting wall boundary conditions at a fixed distance from the x-point and for open boundary conditions that adjust as required by the evolving solution within the boundaries. With solid, conducting wall boundary conditions, our solutions for azimuthally symmetric disturbances agree (for essentially linear perturbations) with those obtained in previous analytic linear studies. In this case the stressed x-point relaxes back to the unstressed state on a time scale somewhat shorter than the time scale for the linear resistive tearing mode. Perturbations that are not azimuthally symmetric can relax even faster than the symmetric modes. When the conditions at the boundary are free to adjust, the disturbances grow in amplitude on an Alfvén time scale with the eventual formation of a current sheet separating two y-points. This rapid growing behavior is, of course, in sharp contrast to the relatively slow decaying solutions obtained with closed boundaries. The growing solutions qualitatively agree with previous analytic x-point solutions that have been suggested as an explanation for the rapid energy conversion in flares and substorms. Title: Nonlinear studies of coronal heating by the resonant absorption of Alfvén waves Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1994GeoRL..21.2259O Altcode: The first nonlinear study of the instability of the resonant absorption is presented in this paper. The nonlinear evolution of the resonant absorption of Alfvén waves in an inhomogeneous plasma is studied via solution of the time-dependent 3-D, low-β, resistive MHD equations. Highly sheared velocities that are subject to the Kelvin-Helmholtz like instability are found at the narrow dissipation layers. Three dimensional Kelvin-Helmholtz like vortices appear at and near the dissipation layers and propagate along the slab of plasma. The narrow resonant heating layers are deformed by the self-consistent shear flow. In the solar active regions where the resonant absorption of Alfvén waves is believed to occur the instability may lead to turbulent enhancement of the dissipation parameters and account for the observed turbulent velocities inferred from the non-thermal broadening of x-ray and EUV emission lines. Title: Coronal Heating by the Resonant Absorption of Alfven Waves Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1994scs..conf..473O Altcode: 1994IAUCo.144..473O Nonlinear evolution and stability of the resonant absorption layer is considered by solving the time-dependent 3D, low-β, resistive MHD equations with the Lax-Wendroff explicit method. The narrow resonant heating layers are deformed by the self-consistent shear flow. When the driver amplitude is small compared to the average Alfvén speed the dissipation layer appears to be stable and the driver-period-averaged ohmic heating rate saturates at a slightly higher than the linear rate. When the driver amplitude is large (Fd ≍ 1) the resonant heating may become unstable. Title: Coronal Heating by the Resonant Absorption of Alfven Waves: The Effect of Viscous Stress Tensor Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1994ApJ...421..360O Altcode: The time-dependent linearized magnetohydrodynamics (MHD) equations for a fully compressible, low-beta, viscoresistive plasma are solved numerically using an implicit integration scheme. The full viscosity stress tensor (Braginskii 1965) is included with the five parameters etai i = 0 to 4. In agreement with previous studies, the numerical simulations demonstrate that the dissipation on inhomogeneities in the background Alfven speed occurs in a narrow resonant layer. For an active region in the solar corona the values of etai are etao = 0.65 g/cm/s, eta1 = 3.7 x 10-12 g/cm/s, eta2 = 4 eta1, eta3 = 1.4 x 10-6 g/cm/s, eta4 = 2 eta3, with n = 1010/cu cm, T = 2 x 106 K, and B = 100 G. When the Lundquist number S = 104 and R1 much greater than S (where R1 is the dimensionless shear viscous number) the width of the resistive dissipation layer dr is 0.22a (where a is the density gradient length scale) and dr approximately S-1/3. When S much greater than R1 the shear viscous dissipation layer width dr scales as R1-1/3. The shear viscous and the resistive dissipation occurs in an overlapping narrow region, and the total heating rate is independent of the value of the dissipation parameters in agreement with previous studies. Consequently, the maximum values of the perpendicular velocity and perpendicular magnetic field scale as R1-1/3. It is evident from the simulations that for solar parameters the heating due to the compressive viscosity (R0 = 560) is negligible compared to the resistive and the shear viscous (R1) dissipation and it occurs in a broad layer of order a in width. In the solar corona with S approximately equals 104 and R1 approximately equals 1014 (as calculated from the Braginskii expressions), the shear viscous resonant heating is of comparable magnitude to the resistive resonant heating. Title: Nonlinear Evolution of Coronal Heating by the Resonant Absorption of Alfven Waves Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1993AAS...183.5904O Altcode: 1993BAAS...25.1386O The nonlinear 3-D MHD equations for a fully compressible, low-beta, visco-resistive plasma are solved numerically using the Lax-Wendroff integration scheme (the explicit integration scheme was found to converge considerably faster in terms of physical time per CPU time than the Alternating Direction Implicit method). The calculations are initiated with the solutions of the linearized version of the MHD equations (Ofman, Davila, and Steinolfson 1994, Ap.J., in press), with inhomogeneous background density, and a constant magnetic field. The numerical simulations demonstrate that the narrow dissipation layer is affected by the self-consistent velocity shear: i.e., the regions of high ohmic heating are carried around by the flow. Consequently, the topology of the perpendicular magnetic field and the ohmic heating regions differs significantly from the linear case. Additional harmonics of the driver frequency appear in the temporal oscillations with the dominant frequency of double the driver frequency. When the Lundquist number is S=10(3) the average width of the resistive dissipation layer is 0.4a (where a is the density gradient length scale) and consistent with the linear results. When the driver amplitude is small compared to the average Alfven speed the dissipation layer appears to be stable and the ohmic heating rate is enhanced by about 15% over the linear heating rate. When the driver amplitude is comparable to the average Alfven speed the nonlinear effects dominate the evolution and the resonant heating layer may become unstable. A parametric study of the instability is presented. The effect of the self-consistent velocity on the instability is considered by generalizing the linear theory (Davila 1987) to include shear flow and solving the linearized dispersion relation of the resonant absorption with the background shear flow. (*) NRC-NAS Resident Research Associate. Title: Magnetic Reconnection at Stressed X-Type Neutral Points Authors: Ofman, L.; Morrison, P. J.; Steinolfson, R. S. Bibcode: 1993ApJ...417..748O Altcode: The reconnection and relaxation of two-dimensional stressed (nonpotential) X-type neutral point magnetic fields are studied via solution of the nonlinear resistive two-dimensional MHD equations and by analytical solution of the linear eigenvalue problem. Previous linear studies (Craig & McClymont 1991; Hassam 1992; Craig & Watson 1992), have shown that such stressed fields may relax on a time substantially shorter (i.e., ∼ |log η|2, where η is the resistivity) than the usual time scale for linear reconnection (i.e., η3/5. We have generalized the linear dispersion relation for azimuthally nonsymmetric perturbations and have found that for modes with azimuthal mode numbers m > 0, the relaxation can occur at a rate faster than that for n = m = 0, where n is the radial "quantum" number. All of the results presented are for frozen-in (line-tied) boundary conditions at some distance from the X-point, and we emphasize that these boundary conditions are essential in order to obtain our solutions. We find that for nearly azimuthally symmetric magnetic perturbations the fields relax incompressibly and nonlinearly to the unstressed X-type neutral point at a rate close to that predicted by linear theory. Also, fully compressible nonlinear MHD simulations have been performed, which show that the interaction between the plasma flow velocity and the magnetic field is the important physical effect, while the inclusion of thermodynamics does not affect the evolution considerably. A Liapunov functional for the nonlinear incompressible two-dimensional resistive MHD equations is derived to show that the current-free X-point configuration is a global equilibrium to which general initial conditions relax. Title: Coronal Heating by the Resonant Absorption of Alfven Waves: The Effects of Viscous Stress Tensor Authors: Ofman, L.; Davila, J. M.; Steinolfson, R. S. Bibcode: 1993BAAS...25.1202O Altcode: No abstract at ADS Title: Reconnection of Magnetic Fields with Stressed X-type Neutral Points Authors: Ofman, L.; Steinolfson, R. S.; Morrison, P. J. Bibcode: 1992AAS...180.5503O Altcode: 1992BAAS...24..819O The reconnection of two-dimensional stressed X-type neutral point magnetic fields is studied via solution of the nonlinear resistive MHD equations and by analytical solution of the linear eigenvalue problem. Previous linear studies [I. Craig and A. McClymont, Ap. J. 371, L41 (1991); A. Hassam, Ap. J. submitted (1991)] have shown that such stressed fields may relax on a time substantially shorter than the usual time scale for liner reconnection (i.e. eta (3/5) ). We find that for azimuthally symmetric (m=0) and nonsymmetric (m>0) perturbations, the fields relax to the unstressed X-type neutral point at a rate close to that predicted by linear theory, provided the fields at the boundaries are fixed, and there is no flow through the boundaries. If outflowing boundary conditions are imposed, we find that the perturbed X-point evolves into a sheet current within several Alfven times. This process is of the type proposed to explain solar flare discharges [J. Dungey, Phil. Mag. 44 354 (1953)]. Title: Nonlinear Evolution of the Resistive Tearing Mode Instability with Shear Flow and Viscosity Authors: Ofman, L.; Morrison, P. J.; Steinolfson, R. S. Bibcode: 1991BAAS...23.1042O Altcode: No abstract at ADS Title: Determination of force-free magnetic fields above the photosphere using three-component boundary conditions - Moderately non-linear case Authors: Cuperman, S.; Ofman, L.; Semel, M. Bibcode: 1990A&A...230..193C Altcode: The calculation of the magnetic field components and the tracing of the magnetic field lines above the photosphere are considered within the framework of the nonlinear force-free field model, upon using three-component magnetic fields as boundary conditions. This vertical integration represents an extrapolation in the small and is free of any implicit or explicit assumption in the large. As a study case, an analytical model providing magnetic field components at a surface (representing the photosphere) and above it is used. Magnetic field components and magnetic field lines at z greater than 0 are obtained. Their comparison with the analytical ones provides a measure of the calculational accuracy. The method is demonstrated for the case of moderately nonlinear force-free forces. Title: Resistive Tearing Mode Instability with Shear Flow and Viscosity Authors: Ofman, L.; Steinolfson, R. S.; Chen, X. L.; Morrison, P. J. Bibcode: 1990BAAS...22..853O Altcode: No abstract at ADS Title: Thermally Conductive Magnetohydrodynamic Flows in Helmet-Streamer Coronal Structures Authors: Cuperman, S.; Ofman, L.; Dryer, M. Bibcode: 1990ApJ...350..846C Altcode: The behavior of thermally conductive plasma flows in helmet-streamer coronal structures is investigated within the framework of the axisymmetric nonrotating one-fluid MHD model. Continuous subsonic-supersonic solutions satisfying observed boundary conditions at the sun as well as the vanishing of the temperature at infinity are obtained and presented. Special attention is paid to the combined effects of conductive flow (and corresponding thermal force) and rapidly diverging magnetic field on the critical points. In this, the heliocentric distance of the neutral point determining the separation between closed and open field lines (cusp) is treated as a free parameter. These thermally conductive solutions are contrasted with those provided by corresponding isothermal models. Title: The absolute value and sign of the function alpha(r) in the force-free magnetic field modelling of photospheric observations Authors: Cuperman, S.; Ofman, L.; Semel, M. Bibcode: 1990A&A...227..227C Altcode: A relatively simple method for the determination of the quantity α = J/B characterizing the force-free magnetic fields based on photospheric vector magnetic fields is presented. Magnetic configurations for which the sign of α does not change are considered.

The method consists of two steps, namely: (a) Expression of force-free field equations in terms of the observed quantities Bz, B2x, B2y and BxBy and determination of |α|; (b) Selection of the proper sign of α (corresponding to the magnetic configuration under consideration) by (i) solving the FFF equations under the assumptions α = - |α| and α = +|α|, (ii) using the two types of solutions to calculate the surface energy integral ES(z) = ∫ (B2x + B2y + B2x)ds, and (iii) retaining the sign that leads to a decrease with height (z) of Es(z).

The proposed method is tested by considering three different FFF magnetic configurations for which analytical solutions exist. Title: Extrapolation of photospheric potential magnetic fields using oblique boundary values - A simplified approach Authors: Cuperman, S.; Ofman, L.; Semel, M. Bibcode: 1990A&A...227..583C Altcode: The problem of extrapolating photospheric potential magnetic fields is addressed using the oblique line-of-sight component B1(rs) as a boundary condition and reducing it to that for the normal line-of-sight component Bz(rs). The observed B1(rs) component is used along with the direction cosines of the line-of-sight alpha, beta, and gamma to calculate semianalytically the photospheric components Bx(rs) and By(rs). All these values are used to find the normal photospheric component Bx(rs). Finally, using the distribution Bz(rs) as boundary values, the relatively simpler problem corresponding to the case in which the normal components are known is solved. The method is tested on the case of an analytical model configuration for which exact solutions in the half-space above the photosphere exist. Title: Reply Authors: Cuperman, S.; Ofman, L.; Dryer, M. Bibcode: 1989JGR....9410153C Altcode: No abstract at ADS Title: Determination of constant-alpha force-free magnetic fields above the photosphere using three-component boundary conditions Authors: Cuperman, S.; Ofman, L.; Semel, M. Bibcode: 1989A&A...216..265C Altcode: The constant-α, force-free magnetic field equations are numerically integrated for the case in which all three field components are specified at the photo sphere and used as boundary conditions. Test-cases successfully compare the numerical results with exact analytical values. Title: On the dispersion of ion cyclotron waves in H+-He++ solar wind-like magnetized plasmas Authors: Cuperman, S.; Ofman, L.; Dryer, M. Bibcode: 1988JGR....93.2533C Altcode: We investigate by computer simulation experiments the nonlinear behavior of mixed H+-He++ plasma systems under the particular physical conditions found by the linear theory to allow the parallel propagation of only weakly damped electromagnetic ion cyclotron waves at the alpha particle cyclotron frequency. Here the waves are generated by anisotropic proton populations. The essentially nonlinear results of our computer simulations indicate a strong damping of the parallel propagating electromagnetic ion cyclotron waves and a significant dip in the energy spectrum, both centered cyclotron waves and a significant dip in the energy spectrum, both centered at about ω=Ωα. Title: On the Dispersion of Ion Cyclotron Waves in Magnetized H+ -He++ Solar Wind-Like Plasmas Authors: Cuperman, S.; Ofman, L.; Dryer, M. Bibcode: 1987sowi.conf..346C Altcode: No abstract at ADS Title: Nonlinear aspects of collective, electromagnetic interactions in magnetized plasmas with anisotropic protons and isotropic alpha particles Authors: Cuperman, S.; Ofman, L.; Dryer, M. Bibcode: 1986JPlPh..36..387C Altcode: We use computer simulation experiments to investigate the nonlinear behaviour of plasmas with a mixture of anisotropic protons and isotropie alpha particles, embedded in a static magnetic field. Specifically, we study the linearly predicted ‘stop-band’ for the propagation of the proton-produced electromagnetic ion cyclotron waves in conjunction with the energization of the heavier ions by the same waves. For this, three cases are considered: (1) proton + electron plasma; (2) proton + electron + cold alpha particle plasma, and (3) proton + electron + warm alpha particle plasma. Among the main results obtained we mention the following, (a) In the presence of significant relative He2+ concentrations (either cold or warm) all proton-produced left-polarized waves having frequencies above the alpha-particle gyrofrequency are practically suppressed, during the entire nonlinear evolution of the system, indicating that particle-wave-particle interactions are confined to the low-frequency branch of the waves, (b) The ‘remnant’ wave energy, i.e. that part of the wave energy not transferred to the particles, decreases significantly when going from case 1 to case 3. (c) Nevertheless, in all three cases, the initial proton thermal anisotropy relaxes to the same quasi-equilibrium value ( 1·5). (d) The cold alpha particles in case 2 are strongly heated by their non-resonant interaction with the proton-produced ion cyclotron electromagnetic waves, (e) In contrast, the initially warm isotropic alpha particles in case 3 are heated by resonant interaction with the proton-produced waves, resulting in an increase in the perpendicular energy and a decrease in the parallel energy. The physical processes involved in the collisionless interaction of these mixed protons and heavier ions (alpha particles) are discussed.