Author name code: hoeksema ADS astronomy entries on 2022-09-14 author:"Hoeksema, Todd" ------------------------------------------------------------------------ Title: Understanding Solar Cycle Magnetic Evolution with Properties of Solar Active Regions Authors: Liu, Y.; Hoeksema, T.; Zhao, J.; DeRosa, M. L.; Sun, X. Bibcode: 2020AGUFMSH0020015L Altcode: Understanding the solar cycle is a fundamental and important objective in solar physics. Recent studies have revealed correlations between variations of the poleward transport of photospheric magnetic fields with properties of both magnetic field in solar active regions as well as their decay products. Features such as poleward surges often play an outsized role in advecting flux away from the activity belts into polar regions, and therefore affect solar cycle activity. This report describes our plans and reviews preliminary results investigating the effects of active region-modified zonal and meridional flows on flux evolution and the solar cycle. Title: The Solar Orbiter magnetometer Authors: Horbury, T. S.; O'Brien, H.; Carrasco Blazquez, I.; Bendyk, M.; Brown, P.; Hudson, R.; Evans, V.; Oddy, T. M.; Carr, C. M.; Beek, T. J.; Cupido, E.; Bhattacharya, S.; Dominguez, J. -A.; Matthews, L.; Myklebust, V. R.; Whiteside, B.; Bale, S. D.; Baumjohann, W.; Burgess, D.; Carbone, V.; Cargill, P.; Eastwood, J.; Erdös, G.; Fletcher, L.; Forsyth, R.; Giacalone, J.; Glassmeier, K. -H.; Goldstein, M. L.; Hoeksema, T.; Lockwood, M.; Magnes, W.; Maksimovic, M.; Marsch, E.; Matthaeus, W. H.; Murphy, N.; Nakariakov, V. M.; Owen, C. J.; Owens, M.; Rodriguez-Pacheco, J.; Richter, I.; Riley, P.; Russell, C. T.; Schwartz, S.; Vainio, R.; Velli, M.; Vennerstrom, S.; Walsh, R.; Wimmer-Schweingruber, R. F.; Zank, G.; Müller, D.; Zouganelis, I.; Walsh, A. P. Bibcode: 2020A&A...642A...9H Altcode: The magnetometer instrument on the Solar Orbiter mission is designed to measure the magnetic field local to the spacecraft continuously for the entire mission duration. The need to characterise not only the background magnetic field but also its variations on scales from far above to well below the proton gyroscale result in challenging requirements on stability, precision, and noise, as well as magnetic and operational limitations on both the spacecraft and other instruments. The challenging vibration and thermal environment has led to significant development of the mechanical sensor design. The overall instrument design, performance, data products, and operational strategy are described. Title: The Science Case for the $4{\pi}$ Perspective: A Polar/Global View for Studying the Evolution & Propagation of the Solar Wind and Solar Transients Authors: Vourlidas, A.; Gibson, S.; Hassler, D.; Hoeksema, T.; Linton, M.; Lugaz, N.; Newmark, J. Bibcode: 2020arXiv200904880V Altcode: To make progress on the open questions on CME/CIR propagation, their interactions and the role and nature of the ambient solar wind, we need spatially resolved coverage of the inner heliosphere -- both in-situ and (critically) imaging -- at temporal scales matching the evolutionary timescales of these phenomena (tens of minutes to hours), and from multiple vantage points. The polar vantage is uniquely beneficial because of the wide coverage and unique perspective it provides. The ultimate goal is to achieve full $4\pi$ coverage of the solar surface and atmosphere by 2050. Title: The Solaris Solar Polar Mission Authors: Hassler, Donald M.; Newmark, Jeff; Gibson, Sarah; Harra, Louise; Appourchaux, Thierry; Auchere, Frederic; Berghmans, David; Colaninno, Robin; Fineschi, Silvano; Gizon, Laurent; Gosain, Sanjay; Hoeksema, Todd; Kintziger, Christian; Linker, John; Rochus, Pierre; Schou, Jesper; Viall, Nicholeen; West, Matt; Woods, Tom; Wuelser, Jean-Pierre Bibcode: 2020EGUGA..2217703H Altcode: The solar poles are one of the last unexplored regions of the solar system. Although Ulysses flew over the poles in the 1990s, it did not have remote sensing instruments onboard to probe the Sun's polar magnetic field or surface/sub-surface flows.We will discuss Solaris, a proposed Solar Polar MIDEX mission to revolutionize our understanding of the Sun by addressing fundamental questions that can only be answered from a polar vantage point. Solaris uses a Jupiter gravity assist to escape the ecliptic plane and fly over both poles of the Sun to >75 deg. inclination, obtaining the first high-latitude, multi-month-long, continuous remote-sensing solar observations. Solaris will address key outstanding, breakthrough problems in solar physics and fill holes in our scientific understanding that will not be addressed by current missions.With focused science and a simple, elegant mission design, Solaris will also provide enabling observations for space weather research (e.g. polar view of CMEs), and stimulate future research through new unanticipated discoveries. Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth System Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan; Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao, Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa, Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale; Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland, Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander; Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens, Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent; Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet, Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth, Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha Bibcode: 2018arXiv181008728N Altcode: The authors of this report met on 28-30 March 2018 at the New Jersey Institute of Technology, Newark, New Jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. Their objective was to identify challenges in the path towards building an effective framework to achieve transformative advances in the understanding and forecasting of the Sun-Earth system from the upper convection zone of the Sun to the Earth's magnetosphere. The workshop aimed to develop a research roadmap that targets the scientific challenge of coupling observations and modeling with emerging data-science research to extract knowledge from the large volumes of data (observed and simulated) while stimulating computer science with new research applications. The desire among the attendees was to promote future trans-disciplinary collaborations and identify areas of convergence across disciplines. The workshop combined a set of plenary sessions featuring invited introductory talks and workshop progress reports, interleaved with a set of breakout sessions focused on specific topics of interest. Each breakout group generated short documents, listing the challenges identified during their discussions in addition to possible ways of attacking them collectively. These documents were combined into this report-wherein a list of prioritized activities have been collated, shared and endorsed. Title: Using the Deep Space Gateway to Build the Next Generation Heliophysics Research Grid Authors: Vourlidas, A.; Ho, G. C.; Cohen, I. J.; Korendyke, C. M.; Tun-Beltran, S.; Plunkett, S. P.; Newmark, J.; St Cyr, O. C.; Hoeksema, T. Bibcode: 2018LPICo2063.3055V Altcode: The Heliophysics Research Grid (HRG) consists of in situ and imaging sensors, distributed in key locations in the heliosphere for research and to support space exploration needs. The Deep Space Gateway enables the HRG as a storage and staging hub for HRG launches. Title: Q-Maps: A Synoptic Data Product for Investigating Coronal Connectivity Authors: Sun, Xudong; Hoeksema, Todd; Liu, Yang; Mikic, Zoran; Titov, Viacheslav Bibcode: 2017shin.confE..73S Altcode: No abstract at ADS Title: Achieving Consistent Vector Magnetic Field Measurements from SDO/HMI Authors: Schuck, P. W.; Scherrer, Phil; Antiochos, Spiro; Hoeksema, Todd Bibcode: 2016usc..confE..71S Altcode: NASA's Solar Dynamics Observatory (SDO) is delivering vector magnetic field observations of the full solar disk with unprecedented temporal and spatial resolution; however, the satellite is in a highly inclined geosynchronous orbit. The relative spacecraft-Sun velocity varies by ±3 km/s over a day which introduces significant orbital artifacts in the Helioseismic Magnetic Imager (HMI) data. We have recently demonstrated that the orbital artifacts contaminate all spatial and temporal scales in the data and developed a procedure for mitigating these artifacts in the Doppler data obtained from the Milne-Eddington inversions in the HMI Pipeline. Simultaneously, we have found that the orbital artifacts may be introduced by inaccurate estimates for the free-spectral ranges (FSRs) of the optical elements in HMI. We describe our approach and attempt to minimize orbital artifacts in the hmi.V_720 Dopplergram series by adjusting the FSRs for the optical elements of HMI within their measurement uncertainties of ±1%. introduces major orbital artifacts in the Helioseismic Magnetic Imager (HMI) data. We have recently demonstrated that the orbital artifacts contaminate all spatial and temporal scales in the data and developed a procedure for mitigating these artifacts in the Doppler data obtained from the Milne-Eddington inversions in the HMI Pipeline. Simultaneously, we have found that the orbital artifacts may be introduced by inaccurate estimates for the free-spectral ranges (FSRs) of the optical elements in HMI. We describe our approach and attempt to minimize orbital artifacts in the hmi.V_720 Dopplergram series by adjusting the FSRs for the optical elements in HMI within their measurement uncertainties of ±1%. Title: Unexpectedly Large Lorentz-Force Impulse Observed During a Solar Eruption Authors: Sun, Xudong; Fisher, George; Torok, Tibor; Hoeksema, Todd; Li, Yan; CGEM Team Bibcode: 2016shin.confE.158S Altcode: For fast coronal mass ejections (CMEs), the acceleration phase takes place in the low corona; the momentum process is presumably dominated by the Lorentz force. Using ultra-high-cadence vector magnetic data from the Helioseismic and Magnetic Imager (HMI) and numerical simulations, we show that the observed fast-evolving photospheric field can be used to characterize the impulse of the Lorentz force during a CME. While the peak Lorentz force concurs with the maximum ejecta acceleration, the observed total force impulse surprisingly exceeds the CME momentum by over an order of magnitude. We conjecture that most of the Lorentz force impulse is "trapped" in the thin layer of the photosphere above the HMI line-formation height and is counter-balanced by gravity. This implies a consequent upward plasma motion which we coin "gentle photospheric upwelling". The unexpected effect dominates the momentum processes, but is negligible for the energy budget, suggesting a complex coupling between different layers of the solar atmosphere during CMEs. Title: Predicting the Interplanetary Magnetic Field using Approaches Based on Data Mining and Physical Models Authors: Riley, P.; Russell, C. T.; de Koning, C. A.; Biesecker, D. A.; Linker, J.; Owens, M. J.; Lugaz, N.; Martens, P.; Angryk, R.; Reinard, A.; Ulrich, R. K.; Horbury, T. S.; Pizzo, V. J.; Liu, Y.; Hoeksema, T. Bibcode: 2015AGUFMSH14A..06R Altcode: An accurate prediction of the interplanetary magnetic field, and, in particular, its z-component (Bz) is a crucial capability for any space weather forecasting system, and yet, thus far, it has remained largely elusive (a point exemplified by the fact that no prediction center currently provides a forecast for Bz). In this presentation, we discuss the various physical processes that can produce non-zero values of Bz and summarize a selection of promising approaches that may ultimately lead to reliable forecasts of Bz. We describe the first steps we have taken to develop a framework for assessing these techniques, and show preliminary results of their efficacy. Title: Why Is the Great Solar Active Region 12192 CME-Poor? Authors: Sun, Xudong; Bobra, Monica G.; Hoeksema, Todd; Liu, Yang; Li, Yan; Shen, Chenglong; Couvidat, Sebastien; Norton, Aimee A.; Fisher, George H. Bibcode: 2015TESS....140802S Altcode: Solar active region (AR) 12192 of October 2014 hosts the largest sunspot group in 24 years. It is the most prolific flaring site of Cycle 24, but surprisingly produced no coronal mass ejection (CME) from the core region during its disk passage. Here, we study the magnetic conditions that prevented eruption and the consequences that ensued. We find AR 12192 to be "big but mild"; its core region exhibits weaker non-potentiality, stronger overlying field, and smaller flare-related field changes compared to two other major flare-CME-productive ARs (11429 and 11158). These differences are present in the intensive-type indices (e.g., means) but generally not the extensive ones (e.g., totals). AR 12192's large amount of magnetic free energy does not translate into CME productivity. The unexpected behavior suggests that AR eruptiveness is limited by some relative measure of magnetic non-potentiality over the restriction of background field, and that confined flares may leave weaker photospheric and coronal imprints compared to their eruptive counterparts. Title: Causes of Major Change in the Heliospheric Field Authors: Hoeksema, Todd Bibcode: 2015TESS....111002H Altcode: The fundamental polarity structure of the heliospheric magnetic field is determined in the solar corona and depends on the photospheric magnetic field. Most of the time the shape of the field evolves slowly from one solar rotation to the next. Modest perturbations are caused by the emergence of new flux, whose configuration generally matches the large-scale patterns that already exist. However, a few times during the solar cycle a radical change occurs when new flux permanently disrupts the large-scale pattern. Such times are often associated with increased numbers of coronal mass ejections. The new pattern typically strengthens and can endure for many years. This investigation identifies the reconfigurations detected in the modeled coronal field during the last several solar cycles and investigates their photospheric sources in Cycles 23 and 24 using magnetic field observations from WSO, MDI, and HMI. Title: A Multi-Observatory Inter-Comparison of Line-of-Sight Synoptic Solar Magnetograms Authors: Riley, P.; Ben-Nun, M.; Linker, J. A.; Mikic, Z.; Svalgaard, L.; Harvey, J.; Bertello, L.; Hoeksema, T.; Liu, Y.; Ulrich, R. Bibcode: 2014SoPh..289..769R Altcode: The observed photospheric magnetic field is a crucial parameter for understanding a range of fundamental solar and heliospheric phenomena. Synoptic maps, in particular, which are derived from the observed line-of-sight photospheric magnetic field and built up over a period of 27 days, are the main driver for global numerical models of the solar corona and inner heliosphere. Yet, in spite of 60 years of measurements, quantitative estimates remain elusive. In this study, we compare maps from seven solar observatories (Stanford/WSO, NSO/KPVT, NSO/SOLIS, NSO/GONG, SOHO/MDI, UCLA/MWO, and SDO /HMI) to identify consistencies and differences among them. We find that while there is a general qualitative consensus, there are also some significant differences. We compute conversion factors that relate measurements made by one observatory to another using both synoptic map pixel-by-pixel and histogram-equating techniques, and we also estimate the correlation between datasets. For example, Wilcox Solar Observatory (WSO) synoptic maps must be multiplied by a factor of 3 - 4 to match Mount Wilson Observatory (MWO) estimates. Additionally, we find no evidence that the MWO saturation correction factor should be applied to WSO data, as has been done in previous studies. Finally, we explore the relationship between these datasets over more than a solar cycle, demonstrating that, with a few notable exceptions, the conversion factors remain relatively constant. While our study was able to quantitatively describe the relationship between the datasets, it did not uncover any obvious "ground truth." We offer several suggestions for how this may be addressed in the future. Title: Hot Spine Loops and the Nature of a Late-Phase Solar Flare Authors: Sun, Xudong; Hoeksema, Todd; Liu, Yang Bibcode: 2013enss.confE..24S Altcode: The fan-spine magnetic topology is thought to be responsible for many curious emission signatures in solar explosive events. A spine field line links topologically separate flux domains and possibly their evolutionary trends, but direct observational evidence of such structure has been rare. Here we report a unique event observed by the Solar Dynamic Observatory (SDO) where a set of hot coronal loops (over 10 MK) that developed during the rising phase of the flare connected to a quasi-circular chromospheric ribbon at one end and a remote brightening at the other. Magnetic field extrapolation suggest these loops are tracers of the spine field line. The sequential brightening of the ribbon and the increasing number of hot loops suggest that continuous slipping and null-point type reconnection were at work, transferring flux from below the fan dome to the exterior. This event also features an extreme-ultraviolet (EUV) late phase - a second emission peak observed in the warm EUV lines (2-7 MK) hours after the flare. Observations indicate that the initially confined process transitioned to a fluxrope eruption near the flare peak. The eruption opened the overlying field and drastically accelerated the energy release. Slow cooling of the large post-flare arcades naturally explains the sequential delay of the late-phase peak in increasingly cooler EUV lines. Our result demonstrates the crucial nature of magnetic coupling between systems of different sizes - a minor topological change may lead to violent eruptions on a much larger scale. Title: Using Electric Fields to drive simulations of the solar coronal magnetic field Authors: Fisher, George H.; Cheung, Mark; DeRosa, Marc; Kazachenko, Maria; Welsch, Brian; Hoeksema, Todd; Sun, Xudong Bibcode: 2012shin.confE..47F Altcode: The availability of high-cadence vector magnetograms and Doppler flow information measured from the HMI instrument on SDO make it possible to determine the electric field at the solar photosphere. This electric field, in turn, can be used to drive time-dependent simulations of the magnetic field in the solar corona, employing the MHD equations, or simpler time-dependent models such as the magneto-frictional (MF) model. Here, we demonstrate these concepts by using electric fields determined from HMI data to drive a time-dependent MF model of the solar corona in the volume overlying the photosphere near NOAA AR 11158. Title: A Portrait of the Magnetic Sun: Observation and Modeling at Global and Active Region Scales Authors: Sun, Xudong; Hoeksema, T.; Liu, Y.; Zhao, X.; Hayashi, K. Bibcode: 2012AAS...22032206S Altcode: The solar magnetic field contains a vast amount of energy that powers the dynamic atmosphere. On the large scale, the dipole-like field waxes and wanes, reversing polarity in each activity cycle. Its strength and evolution history strongly modulate solar wind speed, heliospheric open flux, and their sources. On the smaller scale, active regions with non-potential kilogauss field often exhibit explosive behaviors that directly affect space weather conditions. Thanks to space-borne observatories such as MDI and HMI, it is possible to monitor the photospheric field constantly. The ability to diagnose the coronal field is also improving due to the advances of extrapolation models. This dissertation talk briefly summarizes the large scale magnetic field and solar wind structures of Cycle 23 based on the MDI data archive and potential field models. I then focus on a recent major active region observed by HMI. The vector magnetogram sequence, complemented by a non-linear force-free field extrapolation, portrays in detail the 3D current and energy evolution leading to major eruptions with good spatial and temporal resolution. Future work will include better constrained coronal field modeling and more accurate estimation of the energy, as well as the coupling between the small and large scale fields. Title: Recurrent Eruptions in a Quadrupolar Magnetic Configuration Observed by SDO Authors: Sun; Xudong; Hoeksema, Todd; Liu, Yang; Hayashi, Keiji Bibcode: 2012decs.confE..91S Altcode: The active region AR11158 generated the first X-class flare of the current solar cycle as well as over a dozen CMEs over the course of a few days. Interestingly, most of these CMEs originated from a complex quadrupolar magnetic configuration on the eastern side rather than the center of the region where a major filament situated. A couple of pores emerged relatively late during the AR development but rapidly altered the magnetic connectivities, accumulating a large amount of electric current and free energy at the eruption site. HMI vector magnetograms and a non-linear force-free field extrapolation are used to explore the coronal field structures that favor the subsequent eruptions. AIA observation of the brightening flare loops and footpoint pairs provides further evidence for the interpretation. Title: Evolution of Magnetic Field and Energy in A Major Eruptive Active Region Based on SDO/HMI Observation Authors: Sun, Xudong; Hoeksema, Todd; Liu, Yang; Wiegelmann, Thomas; Hayashi, Keiji; Chen, Qingrong; Thalmann, Julia Bibcode: 2011sdmi.confE..63S Altcode: We report the evolution of magnetic field and its energy in NOAA AR 11158 based on a vector magnetogram series from the Helioseismic and Magnetic Imager (HMI). Fast flux emergence and strong shearing motion created a quadrupolar sunspot complex that produced several major eruptions, including the first X-class flare of solar cycle 24. Extrapolated non-linear force-free coronal field shows substantial electric current and free energy increase during early flux emergence along a newly-formed, low-lying filament with a typical 1000 G field strength and 0.45 Mm^(-1) alpha-parameter at its center. The computed magnetic free energy reaches a maximum of 2.62E32 erg, about 50% stored below 6 Mm. This free energy decreases by 0.33E32 erg within 1 hour of the X-class flare, which is likely an underestimation of the actual energy loss. During the flare, photospheric field changed rapidly: the horizontal field was enhanced by 28% in the AR core region. Such change is consistent with the conjectured coronal field "implosion", and is in line with both the reconnection signatures and the coronal loop retraction observed by the Atmospheric Image Assembly (AIA). Extrapolation indicates that the coronal field relaxes more rapidly with height after the flare and becomes overall less energetic. These preliminary results demonstrate the capability to quantitatively study the AR field topology and energetics using SDO data- although difficulties still abound. Title: Evolution of Magnetic Field in the Flaring Active Region 11158 Observed by SDO/HMI Authors: Sun, Xudong; Hoeksema, T.; Liu, Y.; Wiegelmann, T.; Hayashi, K. Bibcode: 2011SPD....42.2101S Altcode: 2011BAAS..43S.2101S We report the evolution of the magnetic field in NOAA AR11158 over 5 days (2011 Feb 12-16) using preliminary vector magnetograms from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). This region consisted of two pairs of major sunspots and displayed a complex quadrupolar field topology. It produced multiple major flares and eruptions, including the first X-class flare of the current solar cycle. Strong shear motion and flux emergence were both present, with apparent emergence preceding each major flare. We reconstruct the coronal field from a series of vector data using a non-linear force-free (NLFF) extrapolation. The estimated free magnetic energy shows a great increase during the early emergence of the current-carrying flux, while a significant, permanent decrease ( 0.5e32 erg, or 20%) is found after the X-class flare despite continuous flux injection. We relate this decrease to a previously reported, sudden change of the photospheric field after the flare. The extrapolated coronal field structure correspondingly becomes more "compact": the low-lying of field appears more sheared and stores more free energy, and higher-altitude field decays faster with height and becomes more potential. The coronal field overall becomes less-energetic. Title: HMI: First Results Authors: Centeno, R.; Tomczyk, S.; Borrero, J. M.; Couvidat, S. Hayashi, K.; Hoeksema, T.; Liu, Y.; Schou, J. Bibcode: 2011ASPC..437..147C Altcode: 2010arXiv1012.3796C The Helioseismic and Magnetic Imager (HMI) has just started producing data that will help determine what the sources and mechanisms of variability in the Sun's interior are. The instrument measures the Doppler shift and the polarization of the Fe I 6173 Å line, on the entire solar disk at a relatively-high cadence, in order to study the oscillations and the evolution of the full vector magnetic field of the solar Photosphere. After the data are properly calibrated, they are given to a Milne-Eddington inversion code (VFISV, Borrero et al. 2010) whose purpose is to infer certain aspects of the physical conditions in the Sun's Photosphere, such as the full 3-D topology of the magnetic field and the line-of-sight velocity at the solar surface. We will briefly describe the characteristics of the inversion code, its advantages and limitations -both in the context of the model atmosphere and the actual nature of the data-, and other aspects of its performance on such a remarkable data load. Also, a cross-comparison with near-simultaneous maps from the Spectro-Polarimeter (SP) onboard Hinode will be made. Title: Understanding Solar Eruptions with SDO/HMI Measuring Photospheric Flows, Testing Models, and Steps Towards Forecasting Solar Eruptions Authors: Schuck, Peter W.; Linton, M.; Muglach, K.; Hoeksema, T. Bibcode: 2010AAS...21640214S Altcode: 2010BAAS...41Q.875S The Solar Dynamics Observatory (SDO) is carrying the first full-disk imaging vector magnetograph, the Helioseismic and Magnetic Imager (HMI), into an inclined geosynchronous orbit. This magnetograph will provide nearly continuous measurements of photospheric vector magnetic fields at cadences of 90 seconds to 12 minutes with 1" resolution, precise pointing, and unfettered by atmospheric seeing. The enormous data stream of 1.5 Terabytes per day from SDO will provide an unprecedented opportunity to understand the mysteries of solar eruptions. These ground-breaking observations will permit the application of a new technique, the differential affine velocity estimator for vector magnetograms (DAVE4VM), to measure photospheric plasma flows in active regions. These measurements will permit, for the first time, accurate assessments of the coronal free energy available for driving CMEs and flares. The details of photospheric plasma flows, particularly along magnetic neutral-lines, are critical to testing models for initiating coronal mass ejections (CMEs) and flares. Assimilating flows and fields into state-of-the art 3D MHD simulations that model the highly stratified solar atmosphere from the convection zone to the corona represents the next step towards achieving NASA's Living with a Star forecasting goals of predicting "when a solar eruption leading to a CME will occur." Our presentation will describe these major science and predictive advances that will be delivered by SDO/HMI. Title: The magnetic field at the heliospheric base during solar minimum Authors: Zhao, X.; Hoeksema, T. Bibcode: 2009AGUFMSH13B1534Z Altcode: What is the base of the heliosphere? and where is the heliospheric base located? There appears no generally accepted answer to the questions. We define the heliospheric base as the spherical surface where all open magnetic field lines have become radial and start to gradually wind into Archimedes spirals. Both observationally and in models it seems clear that all of the coronal magnetic field above the cusp points of coronal streamers is open. However, except at the cusp points (located near 2.5 solar radii in most magnetostatic models), the open field lines are not generally radial. The non-radial coronal plasma expansion, especially during solar minimum, is supposed to be caused primarily by the transverse magnetic pressure gradient [Smith and Balogh, 1995]. The pressure gradient approaches zero at the Alfven critical point, so the height of the Alfven critical point, at about 15 solar radii, provides a reasonable estimate of the above-defined heliospheric base. If the non-radial coronal expansion is indeed caused mainly by the magnetic pressure gradient, the open magnetic flux is expected to be uniformly distributed at the heliospheric base. The fast latitude scans of the inner heliosphere by the Ulysses spacecraft have confirmed that distribution of open magnetic flux (i.e., the radial component of the magnetic field, Br, multiplied by the square of the radial distance) is independent of latitude [Smith and Balogh, 1995; 2008]. The STEREO A and B spacecraft in 2007.6-2008.6 were well separated in longitude. We compare the two sets of rotation-averages of unsigned daily open magnetic flux observed by the STEREO A and B during this period. We find that statistically the two sets of observations agree very well, suggesting the absence of a significant gradient in longitude as well. We calculate the strength of the radial magnetic field component at 15 solar radii using the horizontal-current current-sheet source-surface (HCCSSS) coronal field model applied to photospheric magnetic field observations [Zhao & Hoeksema, 1995; 2001]. The model successfully reproduces a uniform Br, the same as observed by Ulysses, STEREO A, and STEREO B. The result further confirms that the heliospheric base is located at the Alfven critical point at about 15 solar radii. Title: Spatial Structures of Polar Magnetic Field During the Last Solar Cycle Authors: Sun, Xudong; Hoeksema, T. Bibcode: 2009SPD....40.1103S Altcode: The Sun's polar field is closely related to the large scale coronal structure. It is important for coronal modeling and greatly affects the result. However, the polar field is not well observed because the ecliptic lies near the Sun's equator. In this study, we make use of the data from various observatories (MDI/WSO/MWO/Hinode) to study its spatial structures during the last solar cycle. The result is useful to improve the polar field extrapolation schemes. Title: Distributing space weather monitoring instruments and educational materials worldwide for IHY 2007: The AWESOME and SID project Authors: Scherrer, Deborah; Cohen, Morris; Hoeksema, Todd; Inan, Umran; Mitchell, Ray; Scherrer, Philip Bibcode: 2008AdSpR..42.1777S Altcode: The International Heliophysical Year (IHY) aims to advance our understanding of the fundamental processes that govern the Sun, Earth, and heliosphere. The IHY Education and Outreach Program is dedicated to inspiring the next generation of space and Earth scientists as well as spreading the knowledge, beauty, and relevance of our solar system to the people of the world. In our Space Weather Monitor project we deploy a global network of sensors to high schools and universities to provide quantitative diagnostics of solar-induced ionospheric disturbances, thunderstorm intensity, and magnetospheric activity. We bring real scientific instruments and data in a cost-effective way to students throughout the world. Instruments meet the objectives of being sensitive enough to produce research-quality data, yet inexpensive enough for placement in high schools and universities. The instruments and data have been shown to be appropriate to, and usable by, high school age and early university students. Data contributed to the Stanford data center is openly shared and partnerships between groups in different nations develop naturally. Students and teachers have direct access to scientific expertise. The result is a world-wide collaboration of scientists, teachers, and students to investigate the variability of the ionosphere. The research-quality AWESOME (Atmospheric Weather Electromagnetic System of Observation, Modeling, and Education) instruments have been selected as a participating program by the United Nations Basic Space Science Initiative (UNBSSI). The IHY Committee for International Education and Public Outreach has designated the simpler SID (Sudden Ionospheric Disturbance) monitors to be provided to teacher/student teams in each of the 192 countries of the world. Title: A Determination of the Value and Variability of the Sun's Open Magnetic Flux using a Global MHD Model Authors: Riley, P.; Mikic, Z.; Linker, J.; Harvey, J. W.; Hoeksema, T.; Liu, Y.; Bertello, L. Bibcode: 2008AGUSMSH44A..03R Altcode: The underlying value and variation of the Sun's open, unsigned magnetic flux is of fundamental scientific importance, yet its properties remain poorly known. For example, do long term (on the time-scale of ~ 100 years) changes in the strength of the solar magnetic field exist and do they persist through the heliosphere? If present, they may have a direct impact on space climate, including implications for the transport of cosmic rays (CRs), and as such, may affect technology, space, and even terrestrial climate. Global MHD models are capable of reproducing the structure of the large-scale solar and interplanetary magnetic field (at least in the absence of transient phenomena such as Coronal Mass Ejections), and should, in principle, be able to address this topic. However, they rely - and depend crucially - on boundary conditions derived from observations of the photospheric magnetic field. In spite of ~ 40 years of measurements, accurate estimates of the radial component of the photospheric magnetic field remain difficult to make. In this study, we attempt to find a "ground truth" estimate of the photospheric magnetic field by carefully comparing both disk magnetograms and diachronic (previously known as synoptic) maps from 6 different observatories (KPVT, SOLIS, GONG, MDI, WSO, and MWO). We find that although there is a general consensus between several of them, there are also some significant discrepancies. Using data from these observatories, we compute global heliospheric solutions for a selection of epochs during the last 3 solar cycles and compare the results with in situ observations. We apply these results to several topics related to the Sun's open flux. Title: Modeling Solar Wind Using the Newly Calibrated MDI Magnetic Field: 1996-2008 Authors: Sun, X.; Hoeksema, T. Bibcode: 2008AGUSMSP51A..12S Altcode: The Wang-Sheeley-Arge (WSA) model is regularly used to predict the solar wind speed and interplanetary magnetic field polarity (IMF) at 1 AU. As the only input to the model, photospheric magnetic observations can affect the result to a significant extent. In this paper, we employ the newly calibrated MDI data (1996-2008) and a reasonable polar field extrapolation to test an objective scheme for predicting the solar wind parameters. The results are statistically evaluated and compared with those based on older MDI data and other sources. In order to study the model dependence, we use three different models to infer the coronal field: the potential field source surface (PFSS) model, Schatten current sheet (SCS) model and horizontal-current current-sheet source-surface (HCCSSS) model. They sometimes produce different coronal field structures and perform variously in different phases of the solar cycle. Title: The Sun as the Source of Heliospheric "Space Weather": A CISM Integrated Model Perspective and STEREO Inspiration Authors: Luhmann, J. G.; Li, Y.; Lynch, B.; Lee, C. O.; Huttunen, E.; Liu, Y.; Toy, V.; Odstrcil, D.; Riley, P.; Linker, J.; Mikic, Z.; Arge, C.; Petrie, G.; Zhao, X.; Liu, Y.; Hoeksema, T.; Owens, M.; Galvin, A.; Simunac, K.; Howard, R.; Vourlidas, A.; Jian, L. K.; Russell, C. T. Bibcode: 2008AGUSMSH31C..01L Altcode: Models developed under the Center for Integrated Space weather Modeling (CISM) represent one effort that is underway to realistically simulate the Sun's physical controls over interplanetary conditions, or heliospheric "space weather", in three dimensions. This capability is critical for interpreting the latest observations from STEREO, whose goal is to enable connections to be made between what is observed in the heliosphere via distributed in-situ measurements and what is observed in the corona and heliosphere via imaging from separated 1 AU perspectives. The ways in which the CISM models are enabling the exploitation of STEREO and other observations toward increased understanding of the solar wind and coronal activity and its consequences are described. In particular, the models allow the identification of the sources of structures in the solar wind, and analyses of how the coronal context of the observed CMEs plays a key role in determining the ultimate terrestrial (and other planetary) response . Title: Mechanisms of the solar activity cycle Authors: Hoeksema, Todd Bibcode: 2006AdSpR..38..831H Altcode: No abstract at ADS Title: Three-Dimensional Magnetohydrodynamic Simulation of a Global Solar Corona Using a Temperature Distribution Map Obtained from SOHO EIT Measurements Authors: Hayashi, Keiji; Benevolenskaya, Elena; Hoeksema, Todd; Liu, Yang; Zhao, Xue Pu Bibcode: 2006ApJ...636L.165H Altcode: The temperature at the base of the solar corona is one of the important factors in determining the solar coronal structure. In this Letter, we performed the time-dependent magnetohydrodynamic (MHD) simulation for the solar corona utilizing the temperature map derived from the multiwavelength observation by the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) and the magnetic field map from the Michelson Doppler Imager (MDI) on SOHO. We analyzed the difference in three-dimensional magnetic field topology obtained when the uniform base temperature adopted in standard simulations is replaced by the observation-based, nonuniform temperature distribution. The differences in the magnetic field topology obtained as the response of the solar corona to the changes of the temperature at the coronal base depict the role of the plasma conditions at the coronal base in the dynamics of the global solar corona. This work is our first effort to utilize the data of the solar coronal plasma as the boundary condition to enhance the MHD simulations of a solar corona. Title: Comparison of Photospheric Footpoints of Open Magnetic Field Regions using CSSS and PFSS models Authors: Poduval, B.; Hoeksema, T.; Zhao, X. Bibcode: 2005AGUSMSH13A..10P Altcode: Comparison of Photospheric Footpoints of Open Magnetic Field Regions using CSSS and PFSS models The Current--Sheet Source Surface (CSSS) model developed by Zhao and Hoeksema (1995) assumes a cusp surface at the cusp point of coronal streamers at around 2.5 Rsun, which divides the corona into three regions, one bounded by the photosphere and the cusp surface, the second, between the cusp surface and the source surface, and the third, the region beyond the source surface. In this model the source surface can be placed closer to the Alfven critical point which is a great advantage over the traditional Potential Field Source Surface (PFSS) models, where it is at 2.5 Rsun. The source surface magnetic field obtained by CSSS model exhibits little latitudinal variation, which is consistent with the Ulysses observation of the interplanetary magnetic field (IMF). On the other hand, the source surface field computed using the PFSS model shows a latitudinal structure. We have carried out a comparative study of the photospheric footpoints of open magnetic fields obtained dusing the two models. The magnetic neutral line was found to be coinciding in the two models, as expected. There are significant differences in the locations and sizes of the open field regions on the photosphere, and they are not always consistent with the observations of coronal holes. We present the results of the comparison. Title: Potential Field Source Surface Model and Solar Wind Prediction Authors: Poduval, B.; Zhao, X.; Hoeksema, T. Bibcode: 2005AGUSMSH23C..03P Altcode: Various magnetic activities of the Sun causes disturbances in the near-Earth enviornment as well as on the weather and technology on Earth. "Addressing these disturbances and predicting them well in advance are the main task of Space Weather research. Much of the solar side of Space Weather is concerned with the accurate prediction of solar wind and its properties which are closely related to the coronal magnetic field. Since a direct measurement of the coronal magnetic field is still limited to strong field regions, solar wind predictions are based on theoretical models of the corona. The primary prediction scheme of the solar wind speed currently used at SEC is based on the empirical relationship between the flux tube expansion (FTE) factor obtained using Potential Field Source Surface (PFSS) model of the corona and the solar wind speed near the Earth. Though successful, this scheme has significant discrepancies. We have studied, using the near-Earth saltellites data as well as near--Sun Helios data, the possible causes of these discrepancies. In our study, FTE at the source surface were obtained using two different coronal models: PFSS model and the Current--Sheet Source Surface (CSSS) model. We present the results of this investigation and a comparison of the two models. Title: A Solar Wind Source Tracking Concept for Inner Heliosphere Constellations of Spacecraft Authors: Luhmann, J. G.; Li, Yan; Arge, C. N.; Hoeksema, Todd; Zhao, Xuepu Bibcode: 2003AIPC..679..168L Altcode: During the next decade, a number of spacecraft carrying in-situ particles and fields instruments, including the twin STEREO spacecraft, ACE, WIND, and possibly Triana, will be monitoring the solar wind in the inner heliosphere. At the same time, several suitably instrumented planetary missions, including Nozomi, Mars Express, and Messenger will be in either their cruise or orbital phases which expose them at times to interplanetary conditions and/or regions affected by the solar wind interaction. In addition to the mutual support role for the individual missions that can be gained from this coincidence, this set provides an opportunity for evaluating the challenges and tools for a future targeted heliospheric constellation mission. In the past few years the capability of estimating the solar sources of the local solar wind has improved, in part due to the ability to monitor the full-disk magnetic field of the Sun on an almost continuous basis. We illustrate a concept for a model and web-based display that routinely updates the estimated sources of the solar wind arriving at inner heliospheric spacecraft. Title: g-mode detection: Where do we stand? Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.; Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema, T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T. Bibcode: 2001ESASP.464..467A Altcode: 2001soho...10..467A We review the recent developments in determining the upper limits to g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We address how this limit can be improved by way of new helioseismic instruments and/or new collaborations, hopefully providing in the not too distant future unambiguous g-mode detection. Title: Study of the Effect of Active Regions on the Solar Irradiance During Solar Minimum Authors: Domingo, V.; Sanchez, L.; Appourchaux, T.; Froehlich, C.; Wehrli, C.; Hoeksema, T.; Pap, J. Bibcode: 1997SPD....28.0206D Altcode: 1997BAAS...29..893D We have determined both the size of the area that contributes to the solar irradiance increase around an active region and the angular distribution of the radiance excess in it, using data obtained during about one year around solar minimum (April 1996 - April 1997). During the solar minimum and the early raising phase of the new maximum it is possible to study the effect of isolated active regions while there are few of them. The result of this study will be important to separate the contribution of the active regions to the solar irradiance change during the solar cycle from any underlying long term effect, if there is one. The solar radiance measured by the Low-resolution Oscillations Imager (LOI) of the VIRGO instrument and by the MDI instrument aboard SOHO is used to determine the dimension of the radiating area. The increase in irradance is determined by the Sun Photometers (SPM) and Radiometers on the VIRGO instrument. Title: Initial Results from SOI/MDI High Resolution Magnetograms Authors: Title, A.; Tarbell, T.; Frank, Z.; Schrijver, C.; Shine, R.; Wolfson, J.; Zayer, I.; Scherrer, P.; Bush, R.; Deforest, C.; Hoeksema, T. Bibcode: 1996AAS...188.6915T Altcode: 1996BAAS...28..938T The Michelson Doppler Imager (MDI) on SoHO takes magnetogram s with resolutions of 1.2 (high resolution) and 4 (full disk) arcseconds. Movies of 16 hour duration have been constructed in full disk and high resolution mode. High resolution movies of the south polar region also have been obtained. In sums of nine high resolution magnetograms it is possible to detect fields as low as 5 gauss and total fluxes as low as 5 10(1) 6 Mx. In mid latitude regions new flux is observed to emerge everywhere. At all latitudes below 60 degrees flux is mixed on the scale of supergranulation. In the polar region above 60 degrees only fields of a single polarity are observed above the detection limit. Title: VIRGO: Experiment for Helioseismology and Solar Irradiance Monitoring Authors: Fröhlich, Claus; Romero, José; Roth, Hansjörg; Wehrli, Christoph; Andersen, Bo N.; Appourchaux, Thierry; Domingo, Vicente; Telljohann, Udo; Berthomieu, Gabrielle; Delache, Philippe; Provost, Janine; Toutain, Thierry; Crommelynck, Dominique A.; Chevalier, André; Fichot, Alain; Däppen, Werner; Gough, Douglas; Hoeksema, Todd; Jiménez, Antonio; Gómez, Maria F.; Herreros, José M.; Cortés, Teodoro Roca; Jones, Andrew R.; Pap, Judit M.; Willson, Richard C. Bibcode: 1995SoPh..162..101F Altcode: The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar `constant', two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given. Title: P-Mode Frequencies of Degree L = 3 TO 5 Authors: Pantel, A.; Hoeksema, T.; Fossat, E.; Scherrer, P.; Gelly, B.; Grec, G.; Loudagh, S.; Schmider, F. X. Bibcode: 1995ESASP.376b.381P Altcode: 1995soho....2..381P; 1995help.confP.381P No abstract at ADS Title: Solar Core Rotation: Latest IRIS Results Authors: Fossat, E.; Lazrek, M.; Loudagh, S.; Pantel, A.; Gelly, B.; Grec, G.; Schmider, F. X.; Pallé, P. L.; Régulo, C.; Ehgamberdiev, S.; Khalikov, S.; Hoeksema, T. Bibcode: 1995ESASP.376b.261F Altcode: 1995help.confP.261F; 1995soho....2..261F No abstract at ADS Title: Analysis of the heliospheric current sheet at Earth's orbit and model comparisons Authors: Lepping, R. P.; Szabo, A.; Peredo, M.; Hoeksema, T. Bibcode: 1995sowi.conf...95L Altcode: IMP 8 magnetic field data for the first half of the year 1994, i.e., for about 6 solar rotations, are analyzed around regions of sector boundary crossings with the purpose of obtaining both gross- and fine-scale characteristics of the related heliospheric current sheets separating the observed sectors. For purposes of estimating the attitudes of the normals to the sector boundaries. analysis intervals (sometimes 30 min or more in length) allowing the field to fully complete an excursion of about 180 deg were used in the study, which consisted of variance analyses of the field within those intervals. The resulting boundary normals were analyzed and compared to known (generic) models of projected heliospheric current sheets and to a coronal field model for the same time period. One of the most outstanding features of the resulting ensemble of estimated boundary normals for this period is that they strongly prefer low inclinations, indicating that the observations do not support a 1 AU model that predicts a current sheet whose surface is approximately parallel with the sun's equator, such as the 'sombrero' model. They instead support a model that predicts a relatively high inclination current sheet at 1 AU. Also the normals assume a surprisingly large range of longitudes, somewhat favoring those consistent with a Parker model (45 deg and 225 deg) and/or radial alignment (0 deg and 180 deg). These boundary structures, as defined, are shown typically to be as broad as several hundred proton gyroradii, but having embedded within them very thin structures associated with stronger currents. Such thin structures have normals usually differing markedly from the gross boundary. For some crossings there are indications of a wave-like structure in the current sheet as it passed the spacecraft. Title: Inference of 3-dimensional structure underlying large-scale coronal events observed by YOHKOH and ULYSSES Authors: Slater, G. L.; Freeland, S. L.; Hoeksema, T.; Zhao, X.; Hudson, H. S. Bibcode: 1995sowi.confQ..63S Altcode: The Yohkoh/SXT images provide full-disk coverage of the solar corona, usually extending before and after one of the large-scale eruptive events that occur in the polar crown These produce large arcades of X-ray loops, often with a cusp-shaped coronal extension, and are known to be associated with coronal mass ejections. The Yohkoh prototype of such events occurred 12 Nov. 1991. This allows us to determine heights from the apparent rotation rates of these structures. In comparison v with magnetic-field extrapolations from Wilcox Solar Observatory. use use this tool to infer the three dimensional structure of the corona in particular cases: 24 Jan. 1992, 24 Feb. 1993, 14 Apr. 1994, and 13 Nov. 1994. The last event is a long-duration flare event. Title: The Solar Oscillation Imager-Michelson Doppler Imager for SoHO Authors: Title, A.; Tarbell, T.; Wolfson, J.; Scherrer, P.; Bush, R.; Hoeksema, T. Bibcode: 1992AAS...180.0606T Altcode: 1992BAAS...24Q.737T No abstract at ADS Title: Optical Components of the Solar Oscillations Imager-Michelson Doppler Imager Authors: Tarbell, T.; Rosenberg, W.; Pope, T.; Huff, L.; Torgerson, D.; Title, A.; Wolfson, J.; Scherrer, P.; Bush, R.; Hoeksema, T. Bibcode: 1992AAS...180.0607T Altcode: 1992BAAS...24R.737T No abstract at ADS Title: Empirically derived solar wind conditions near the sun. Authors: Suess, S. T.; Dryer, M.; Wilcox, J. M.; Hoeksema, T.; Henning, H. Bibcode: 1983BAAS...15Q.874S Altcode: No abstract at ADS