Author name code: yuan ADS astronomy entries on 2022-09-14 author:"Yuan, Ding" ------------------------------------------------------------------------ Title: Inter-Correlation Between Sunspot Oscillations and Their Internal Structures Authors: Fu, Libo; Zhu, Zizhan; Yuan, Ding; Wang, Jiaoyang; Feng, Song; Anfinogentov, Sergey Bibcode: 2022arXiv220905982F Altcode: Three- and five-minute oscillations are commonly found in any sunspot. As they are modulated by the internal thermal and magnetic structures of a sunspot, therehence, they could be used as an effective tool for sunspot seismology. In this paper, we investigate the properties of oscillations in sunspot groups with varying size and magnetic field, and aim to establish the relationships between sunspot oscillations and its internal structure comparatively. We selected three groups of unipolar sunspot with approximately axial-symmetric magnetic field and calculated their Fourier spectra based on the Ultraviolet(UV)/Extreme ultraviolet(EUV) emission intensity variations recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA). We found that the distribution of three minute oscillation is defined by the joint effect of diverging magnetic field and the stratification of sunspot atmosphere. Its distribution could be modified by any invading magnetic structures in the umbra. Whereas the five minute oscillations are more prominent in small spots, it implies that five minute oscillation is very closely connected with umbral dynamics. Title: Length Scale of Photospheric Granules in Solar Active Regions Authors: Liu, Yan-Xiao; Jiang, Chao-Wei; Yuan, Ding; Zuo, Ping-Bing; Cao, Wen-Da Bibcode: 2022RAA....22h5008L Altcode: Investigating the length scales of granules could help understand the dynamics of granules in the photosphere. In this work, we detected and identified granules in an active region near disk center observed at wavelength of TiO (7057 Å) by the 1.6 m Goode Solar Telescope (GST). By a detailed analysis of the size distribution and flatness of granules, we found a critical size that divides the granules in motions into two regimes: convection and turbulence. The length scales of granules with sizes larger than 600 km follow Gauss function and demonstrate "flat" in flatness, which reveal that these granules are dominated by convection. Those with sizes smaller than 600 km follow power-law function and behave power-law tendency in flatness, which indicate that the small granules are dominated by turbulence. Hence, for the granules in active regions, they are originally convective in large length scale, and directly become turbulent once their sizes turn to small, likely below the critical size of 600 km. Comparing with the granules in quiet regions, they evolve with the absence of the mixing motions of convection and turbulence. Such a difference is probably caused by the interaction between fluid motions and strong magnetic fields in active regions. The strong magnetic fields make high magnetic pressure which creates pressure walls and slows down the evolution of convective granules. Such walls cause convective granules extending to smaller sizes on one hand, and cause wide intergranular lanes on the other hand. The small granules isolated in such wide intergranular lanes are continually sheared, rotated by strong downflows in surroundings and hereby become turbulent. Title: High-precision Multichannel Solar Image Registration Using Image Intensity Authors: Liang, Bo; Chen, Xi; Yu, Lan; Feng, Song; Guo, Yangfan; Cao, Wenda; Dai, Wei; Yang, Yunfei; Yuan, Ding Bibcode: 2022ApJS..261...10L Altcode: Solar images observed in different channels with different instruments are crucial to the study of solar activity. However, the images have different fields of view, causing them to be misaligned. It is essential to accurately register the images for studying solar activity from multiple perspectives. Image registration is described as an optimizing problem from an image to be registered to a reference image. In this paper, we proposed a novel coarse-to-fine solar image registration method to register the multichannel solar images. In the coarse registration step, we used the regular step gradient descent algorithm as an optimizer to maximize the normalized cross correlation metric. The fine registration step uses the Powell-Brent algorithms as an optimizer and brings the Mattes mutual information similarity metric to the minimum. We selected five pairs of images with different resolutions, rotation angles, and shifts to compare and evaluate our results to those obtained by scale-invariant feature transform and phase correlation. The images are observed by the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Furthermore, we used the mutual information and registration time criteria to quantify the registration results. The results prove that the proposed method not only reaches better registration precision but also has better robustness. Meanwhile, we want to highlight that the method can also work well for the time-series solar image registration. Title: Novel Data Analysis Techniques in Coronal Seismology Authors: Anfinogentov, Sergey A.; Antolin, Patrick; Inglis, Andrew R.; Kolotkov, Dmitrii; Kupriyanova, Elena G.; McLaughlin, James A.; Nisticò, Giuseppe; Pascoe, David J.; Krishna Prasad, S.; Yuan, Ding Bibcode: 2022SSRv..218....9A Altcode: 2021arXiv211213577A We review novel data analysis techniques developed or adapted for the field of coronal seismology. We focus on methods from the last ten years that were developed for extreme ultraviolet (EUV) imaging observations of the solar corona, as well as for light curves from radio and X-ray. The review covers methods for the analysis of transverse and longitudinal waves; spectral analysis of oscillatory signals in time series; automated detection and processing of large data sets; empirical mode decomposition; motion magnification; and reliable detection, including the most common pitfalls causing artefacts and false detections. We also consider techniques for the detailed investigation of MHD waves and seismological inference of physical parameters of the coronal plasma, including restoration of the three-dimensional geometry of oscillating coronal loops, forward modelling and Bayesian parameter inference. Title: Dynamics of the Transversal Magnetic Fields in Photospheric Quiet Regions Authors: Liu, Yanxiao; Jiang, Chaowei; Yuan, Ding; Zuo, Pingbing Bibcode: 2022ApJ...928..107L Altcode: Investigation of the properties of photospheric magnetic fields could shed light on the generation mechanism of small-scale magnetic fields in quiet regions. In this work, we studied the transversal magnetic fields by analyzing the linear polarization (LP) features with Sunrise IMaX data. We calculated the area coverage of LP features, and found that they are 16.1%, 8.6%, and 3% for signals above 3, 3.5, and 4.5 times of noise level, respectively. Those LP features extracted above 4.5 times of noise level are further analyzed. A proper value of 1.5 × 1015 Mx for the net magnetic flux contained in LP features is selected to divide the LP features into two types (I and II). Among all detected snapshot LP features, 86% of them are in type I and the rest are in type II. The length scales of LP features in these two types follow Gauss and power-law distributions, separately. For the topology of magnetic fields in type I, the magnetic flux patches might be footpoints of flux loops that root inside transversal magnetic fields with one unipolar thick leg or one thick leg together with one thin leg in opposite polarity. For those in type II, about 50% of them contain bipolar magnetic flux patches, but the rest appear without magnetic flux patches. Title: Persistent fast kink magnetohydrodynamic waves detected in a quiescent prominence Authors: Li, Dong; Xue, Jianchao; Yuan, Ding; Ning, Zongjun Bibcode: 2022SCPMA..6539611L Altcode: 2022arXiv220107535L Small-scale, cyclic, transverse motions of plasma threads are usually seen in solar prominences, which are often interpreted as magnetohydrodynamic (MHD) waves. Here, we observed small-scale decayless transverse oscillations in a quiescent prominence, and they appear to be omnipresent. The oscillatory periods of the emission intensity and a proxy for the line-of-sight Doppler shift are about half period of the displacement oscillations. This feature agrees well with the fast kink-mode waves in a flux tube. All the moving threads oscillate transversally spatially in phase and exhibit no significant damping throughout the visible segments, indicating that the fast kink MHD waves are persistently powered and ongoing dissipating energy is transferred to the ambient plasma in the quiet corona. However, our calculations suggest that the energy taken by the fast kink MHD waves alone can not support the coronal heating on the quiet Sun. Title: Charge-exchange X-Ray Signature in Laboratory Outflow Interaction with Neutrals Authors: Liang, G. Y.; Wei, H. G.; Yuan, D. W.; Zhong, J. Y.; Zhang, Z.; Wang, C.; Han, B.; Sun, W.; Yuan, X. X.; Xie, Z. Y.; Xiong, J.; Hutton, R.; Zhu, B. Q.; Zhu, J. Q.; Zhu, X. L.; Cui, W.; Wu, Y.; Ma, X. W.; Li, Y. T.; Zhao, G.; Zhang, J. Bibcode: 2022ApJ...925..150L Altcode: According to the principle of Euler similarity between laboratory and astrophysical plasmas, laboratory plasmas driven by high-power lasers have been used to simulate some aspects of astrophysical phenomena. And in doing so, they aid our understanding of shock heating, interaction structures, and the consequential evolution for astrophysical outflows within a short timescale (~ns). In this work, we experimentally investigated the mechanism of X-ray emission originating from a hot outflow (plasma) with a velocity of around 330 km s-1, impinging on a cold medium. A hybrid model was set up to understand the high-resolution X-ray spectra taken at the interaction region and to deduce that charge exchange takes place in such a laboratory miniature of astrophysical outflow interacting with dense molecular clouds, as in the cases of HH 248 and Cap in M82, for example. Effects from targets with multiple electrons are also explored. A brief analysis has been performed for our laboratory analog and astrophysical objects by a dimensionless ratio of the length scale between X-ray-emitting and charge-exchange regions. Title: Investigations of Sizes and Dynamical Motions of Solar Photospheric Granules by a Novel Granular Segmenting Algorithm Authors: Liu, Yanxiao; Jiang, Chaowei; Yuan, Ding; Zuo, Pingbing; Wang, Yi; Cao, Wenda Bibcode: 2021ApJ...923..133L Altcode: 2021ApJ...923..133Y; 2021arXiv211003951Y Granules observed in the solar photosphere are believed to be convective and turbulent, but the physical picture of the granular dynamical process remains unclear. Here we performed an investigation of granular dynamical motions of full length scales based on data obtained by the 1 m New Vacuum Solar Telescope and the 1.6 m Goode Solar Telescope. We developed a new granule segmenting method, which can detect both small faint and large bright granules. A large number of granules were detected, and two critical sizes, 265 and 1420 km, were found to separate the granules into three length ranges. The granules with sizes above 1420 km follow Gaussian distribution, and demonstrate flat in flatness function, which shows that they are non-intermittent and thus are dominated by convective motions. Small granules with sizes between 265 and 1420 km are fitted by a combination of power-law function and Gauss function, and exhibit nonlinearity in flatness function, which reveals that they are in the mixing motions of convection and turbulence. Mini granules with sizes below 265 km follow the power-law distribution and demonstrate linearity in flatness function, indicating that they are intermittent and strongly turbulent. These results suggest that a cascade process occurs: large granules break down due to convective instability, which transports energy into small ones; then turbulence is induced and grows, which competes with convection and further causes the small granules to continuously split. Eventually, the motions in even smaller scales enter in a turbulence-dominated regime. Title: Charge-exchange soft X-ray emission of highly charged ions with inclusion of multiple-electron capture Authors: Liang, G. Y.; Zhu, X. L.; Wei, H. G.; Yuan, D. W.; Zhong, J. Y.; Wu, Y.; Hutton, R.; Cui, W.; Ma, X. W.; Zhao, G. Bibcode: 2021MNRAS.508.2194L Altcode: 2021MNRAS.tmp.2341L Charge exchange has been recognized as a primary source of soft X-ray emission in many astrophysical outflow environments, including cometary and planetary exospheres impacted by the solar wind. Some models have been set up by using different data collections of charge-exchange cross-sections. However, multiple-electron transfer has not been included in these models. In this paper, we set up a charge-exchange model with the inclusion of double-electron capture (DEC), and make a detailed investigation of this process on X-ray emissions of highly charged carbon, nitrogen, oxygen, and neon ions by using available experimental cross-sections. We also study the effect of different n-selective cross-sections on soft X-ray emission by using available experimental n-distributions. This work reveals that DEC enhancement on line intensity is linearly proportional to the ratio of ion abundance in the solar wind. It is more obvious for soft X-rays from carbon ions (C4+) in collision with CO2, and the enhancement on line intensity can be up to 53 per cent with typical ion abundances [Advanced Composition Explorer (ACE)] in the solar wind. The synthetic spectra with parameters from the Ulysses mission for the solar wind reveal velocity dependence, target dependence, as well as the non-negligible contribution from the DEC. Title: Light bridges can suppress the formation of coronal loops Authors: Miao, Yuhu; Fu, Libo; Du, Xian; Yuan, Ding; Jiang, Chaowei; Su, Jiangtao; Zhao, Mingyu; Anfinogentov, Sergey Bibcode: 2021MNRAS.506L..35M Altcode: 2021arXiv210612833M A light bridge is a magnetic intrusion into a sunspot, it interacts with the main magnetic field and excites a variety of dynamical processes. In the letter, we studied magnetic connectivity between a light bridge and coronal loops rooted at the sunspot. We used the data of the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory(SDO) to study the features of sunspots with light bridges. It is found that if a light bridge anchors at the umbra-penumbra boundary, the coronal loops could not be formed around the anchoring point. If the a light bridge become detached from the penumbra, the coronal loop starts to form again. The vector magnetogram provided by the Helioseismic Magnetic Imager onboard SDO shows that the anchoring region of a light bridge usually have an accompanying opposite minor-polarities. We conjugate that the magnetic field line could connect to these opposite polarities and form short-range magnetic loops, and therefore, coronal loops that extend to long-range could not be formed. A model of light bridge is proposed to explain the magnetic connectivity between a light bridge and the coronal loops. This model could explain many physical processes associated with light bridges. Title: Kink Oscillations of Coronal Loops Authors: Nakariakov, V. M.; Anfinogentov, S. A.; Antolin, P.; Jain, R.; Kolotkov, D. Y.; Kupriyanova, E. G.; Li, D.; Magyar, N.; Nisticò, G.; Pascoe, D. J.; Srivastava, A. K.; Terradas, J.; Vasheghani Farahani, S.; Verth, G.; Yuan, D.; Zimovets, I. V. Bibcode: 2021SSRv..217...73N Altcode: 2021arXiv210911220N Kink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillations are observed in two different regimes. In the rapidly decaying regime, the apparent displacement amplitude reaches several minor radii of the loop. The damping time which is about several oscillation periods decreases with the increase in the oscillation amplitude, suggesting a nonlinear nature of the damping. In the decayless regime, the amplitudes are smaller than a minor radius, and the driver is still debated. The review summarises major findings obtained during the last decade, and covers both observational and theoretical results. Observational results include creation and analysis of comprehensive catalogues of the oscillation events, and detection of kink oscillations with imaging and spectral instruments in the EUV and microwave bands. Theoretical results include various approaches to modelling in terms of the magnetohydrodynamic wave theory. Properties of kink oscillations are found to depend on parameters of the oscillating loop, such as the magnetic twist, stratification, steady flows, temperature variations and so on, which make kink oscillations a natural probe of these parameters by the method of magnetohydrodynamic seismology. Title: Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures Authors: Zimovets, I. V.; McLaughlin, J. A.; Srivastava, A. K.; Kolotkov, D. Y.; Kuznetsov, A. A.; Kupriyanova, E. G.; Cho, I. -H.; Inglis, A. R.; Reale, F.; Pascoe, D. J.; Tian, H.; Yuan, D.; Li, D.; Zhang, Q. M. Bibcode: 2021SSRv..217...66Z Altcode: The phenomenon of quasi-periodic pulsations (QPPs) in solar and stellar flares has been known for over 50 years and significant progress has been made in this research area. It has become clear that QPPs are not rare—they are found in many flares and, therefore, robust flare models should reproduce their properties in a natural way. At least fifteen mechanisms/models have been developed to explain QPPs in solar flares, which mainly assume the presence of magnetohydrodynamic (MHD) oscillations in coronal structures (magnetic loops and current sheets) or quasi-periodic regimes of magnetic reconnection. We review the most important and interesting results on flare QPPs, with an emphasis on the results of recent years, and we present the predicted and prominent observational signatures of each of the fifteen mechanisms. However, it is not yet possible to draw an unambiguous conclusion as to the correct underlying QPP mechanism because of the qualitative, rather than quantitative, nature of most of the models and also due to insufficient observational information on the physical properties of the flare region, in particular the spatial structure of the QPP source. We also review QPPs in stellar flares, where progress is largely based on solar-stellar analogies, suggesting similarities in the physical processes in flare regions on the Sun and magnetoactive stars. The presence of QPPs with similar properties in solar and stellar flares is, in itself, a strong additional argument in favor of the likelihood of solar-stellar analogies. Hence, advancing our understanding of QPPs in solar flares provides an important additional channel of information about stellar flares. However, further work in both theory/simulations and in observations is needed. Title: The Causes of Peripheral Coronal Loop Contraction and Disappearance Revealed in a Magnetohydrodynamic Simulation of Solar Eruption Authors: Wang, Juntao; Jiang, Chaowei; Yuan, Ding; Zou, Peng Bibcode: 2021ApJ...911....2W Altcode: 2021arXiv210206877W The phenomenon of peripheral coronal loop contraction during solar flares and eruptions, recently discovered in observations, has gradually drawn the attention of solar physicists. However, its underlying physical mechanism is still uncertain. One possible mechanism is Hudson's implosion conjecture, which attributes the contraction of peripheral coronal loops to magnetic pressure reduction in the magnetic energy liberation core, while other researchers proposed alternative explanations. In previous observational studies we also note the disappearance of peripheral shrinking loops in the late phase, of which there is a lack of investigation and interpretation. In this paper, we exploit a full MHD simulation of solar eruption to study the causes of the two phenomena. It is found that the loop motion in the periphery is well correlated with magnetic energy accumulation and dissipation in the core, and the loop shrinkage is caused by a more significant reduction in magnetic pressure gradient force than in magnetic tension force, consistent with the implosion conjecture. The peripheral contracting loops in the late phase act as inflow to reconnect with central erupting structures, which destroys their identities and naturally explains their disappearance. We also propose a positive feedback between the peripheral magnetic reconnection and the central eruption. 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: Diagnosing a Solar Flaring Core with Bidirectional Quasi-periodic Fast Propagating Magnetoacoustic Waves Authors: Miao, Yuhu; Li, Dong; Yuan, Ding; Jiang, Chaowei; Elmhamdi, Abouazza; Zhao, Mingyu; Anfinogentov, Sergey Bibcode: 2021ApJ...908L..37M Altcode: 2021arXiv210112392M Quasi-periodic fast propagating (QFP) waves are often excited by solar flares, and could be trapped in the coronal structure with low Alfvén speed, so they could be used as a tool for diagnosing both the flaring core and magnetic waveguide. As the periodicity of a QFP wave could originate from a periodic source or be dispersively waveguided, it is a key parameter for diagnosing the flaring core and waveguide. In this paper, we study two QFP waves excited by a Geostationary Operational Environmental Satellite-class C1.3 solar flare occurring at active region NOAA 12734 on 2019 March 8. Two QFP waves were guided by two oppositely oriented coronal funnels. The periods of two QFP waves were identical and were roughly equal to the period of the oscillatory signal in the X-ray and 17 GHz radio emission released by the flaring core. It is very likely that the two QFP waves could be periodically excited by the flaring core. Many features of this QFP wave event are consistent with the magnetic tuning fork model. We also investigated the seismological application with QFP waves, and found that the magnetic field inferred with magnetohydrodynamic seismology was consistent with that obtained in the magnetic extrapolation model. Our study suggests that the QFP wave is a good tool for diagnosing both the flaring core and the magnetic waveguide. Title: Propagating slow sausage waves in a sunspot observed by the New Vacuum Solar Telescope Authors: Feng, Song; Deng, Zheng; Yuan, Ding; Xu, Zhi; Yang, Xiao Bibcode: 2020RAA....20..117F Altcode: 2020arXiv200203270F A sunspot is an ideal waveguide for a variety of magnetohydrodynamic waves, which carry a significant amount of energy to the upper atmosphere and could be used as a tool to probe the magnetic and thermal structure of a sunspot. In this study, we used the New Vacuum Solar Telescope and took high-resolution image sequences simultaneously in both TiO (7058±10 Å) and Hα (6562±2.5 Å) bandpasses. We extracted the area and total emission intensity variations of sunspot umbra and analyzed the signals with synchrosqueezing transform. We found that the area and emission intensity varied with both three and five minute periodicity. Moreover, the area and intensity oscillated in phase with each other, this fact hold in both TiO and Hα data. We interpret this oscillatory signal as a propagating slow sausage wave. The propagation speed is estimated at about 8 km s-1. We infer that this sunspot's umbra could have temperature as low as 2800-3500 K. Title: Numerical simulations of the lower solar atmosphere heating by two-fluid nonlinear Alfvén waves Authors: Kuźma, B.; Wójcik, D.; Murawski, K.; Yuan, D.; Poedts, S. Bibcode: 2020A&A...639A..45K Altcode: Context. We present new insight into the long-standing problem of plasma heating in the lower solar atmosphere in terms of collisional dissipation caused by two-fluid Alfvén waves.
Aims: Using numerical simulations, we study Alfvén wave propagation and dissipation in a magnetic flux tube and their heating effect.
Methods: We set up 2.5-dimensional numerical simulations with a semi-empirical model of a stratified solar atmosphere and a force-free magnetic field mimicking a magnetic flux tube. We consider a partially ionized plasma consisting of ion + electron and neutral fluids, which are coupled by ion-neutral collisions.
Results: We find that Alfvén waves, which are directly generated by a monochromatic driver at the bottom of the photosphere, experience strong damping. Low-amplitude waves do not thermalize sufficient wave energy to heat the solar atmospheric plasma. However, Alfvén waves with amplitudes greater than 0.1 km s-1 drive through ponderomotive force magneto-acoustic waves in higher atmospheric layers. These waves are damped by ion-neutral collisions, and the thermal energy released in this process leads to heating of the upper photosphere and the chromosphere.
Conclusions: We infer that, as a result of ion-neutral collisions, the energy carried initially by Alfvén waves is thermalized in the upper photosphere and the chromosphere, and the corresponding heating rate is large enough to compensate radiative and thermal-conduction energy losses therein. Title: Ultra-long and quite thin coronal loop without significant expansion Authors: Li, Dong; Yuan, Ding; Goossens, Marcel; Van Doorsselaere, Tom; Su, Wei; Wang, Ya; Su, Yang; Ning, Zongjun Bibcode: 2020A&A...639A.114L Altcode: 2020arXiv200602629L Context. Coronal loops are the basic building blocks of the solar corona. They are related to the mass supply and heating of solar plasmas in the corona. However, their fundamental magnetic structures are still not well understood. Most coronal loops do not expand significantly, but the diverging magnetic field would have an expansion factor of about 5-10 over one pressure scale height.
Aims: We investigate a unique coronal loop with a roughly constant cross section. The loop is ultra long and quite thin. A coronal loop model with magnetic helicity is presented to explain the small expansion of the loop width.
Methods: This coronal loop was predominantly detectable in the 171 Å channel of the Atmospheric Imaging Assembly (AIA). Then, the local magnetic field line was extrapolated within a model of the potential field source-surface. Finally, the differential emission measure analysis made from six AIA bandpasses was applied to obtain the thermal properties of this loop.
Results: This coronal loop has a projected length of roughly 130 Mm, a width of about 1.5 ± 0.5 Mm, and a lifetime of about 90 min. It follows an open magnetic field line. The cross section expanded very little (i.e., 1.5-2.0) along the loop length during its whole lifetime. This loop has a nearly constant temperature at about 0.7 ± 0.2 MK, but its density exhibits the typical structure of a stratified atmosphere.
Conclusions: We use the theory of a thin twisted flux tube to construct a model for this nonexpanding loop and find that with sufficient twist, a coronal loop can indeed attain equilibrium. However, we cannot rule out other possibilities such as footpoint heating by small-scale reconnection or an elevated scale height by a steady flow along the loop.

Movie is available at https://www.aanda.org Title: Magnetic Connectivity between the Light Bridge and Penumbra in a Sunspot Authors: Feng, Song; Miao, Yuhu; Yuan, Ding; Qu, Zhongquan; Nakariakov, Valery M. Bibcode: 2020ApJ...893L...2F Altcode: 2020arXiv200303976F A light bridge is a prominent structure commonly observed within a sunspot. Its presence usually triggers a wealth of dynamics in a sunspot and has a lasting impact on sunspot evolution. However, the fundamental structure of light bridges is still not well understood. In this study, we used the high-resolution spectropolarimetry data obtained by the Solar Optical Telescope on board the Hinode satellite to analyze the magnetic and thermal structure of a light bridge at AR 12838. We also combined the high-cadence $1700\,\mathring{\rm A} $ channel data provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory to study the dynamics on this bridge. We found a pair of blue and red Doppler shift patches at two ends of this bridge; this pattern appears to be the convective motion directed by the horizontal component of the magnetic field aligned with the spine of the bridge. Paired upward and downward motions imply that the light bridge could have a two-legged or undulating magnetic field. Significant 4 minute oscillations in the emission intensity of the $1700\,\mathring{\rm A} $ bandpass were detected at two ends, which overlapped the paired blue- and redshift patches. The oscillatory signals at the light bridge and the penumbra were highly correlated with each other. Although they are separated in space at the photosphere, the periodicity seems to have a common origin from underneath the sunspot. Therefore, we infer that the light bridge and penumbra could share a common magnetic source and become fragmented at the photosphere by magnetoconvection. Title: Two Quasi-periodic Fast-propagating Magnetosonic Wave Events Observed in Active Region NOAA 11167 Authors: Miao, Yuhu; Liu, Yu; Elmhamdi, A.; Kordi, A. S.; Shen, Y. D.; Al-Shammari, Rehab; Al-Mosabeh, Khaled; Jiang, Chaowei; Yuan, Ding Bibcode: 2020ApJ...889..139M Altcode: 2019arXiv191211792M We report a detailed observational study of two quasi-periodic fast-propagating (QFP) magnetosonic wave events that occurred on 2011 March 9 and 10, respectively. Interestingly, both the events have two wave trains (WTs): a strong main one (WT-1) and a small and weak secondary one (WT-2). Peculiar and common characteristics of the two events are observed, namely, (1) the two QFP waves are accompanied with brightenings during the whole stage of the eruptions; (2) both the two main WTs are nearly propagating along the same direction; (3) extreme-ultraviolet (EUV) waves are found to be associated with the two events. Investigating various aspects of the target events, we argue that (1) the second event is accompanied with a flux rope eruption during the whole stage; (2) the second event eruption produces a new filament-like dark feature; (3) the ripples of the two WT-2 QFP waves seem to result from different triggering mechanisms. Based on the obtained observational results, we propose that the funnel-like coronal loop system is indeed playing an important role in the two WT-1 QFP waves. The development of the second WT-2 QFP wave can be explained as due to the dispersion of the main EUV front. The coexistence of the two events offers thereby a significant opportunity to reveal what driving mechanisms and structures are tightly related to the waves. Title: A Compact Source for Quasi-periodic Pulsation in an M-class Solar Flare Authors: Yuan, Ding; Feng, Song; Li, Dong; Ning, ZongJun; Tan, Baolin Bibcode: 2019ApJ...886L..25Y Altcode: 2019arXiv191105217Y Quasi-periodic pulsations (QPPs) are usually found in the light curves of solar and stellar flares; they carry the features of time characteristics and plasma emission of the flaring core, and could be used to diagnose the coronas of the Sun and remote stars. In this study, we combined the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory and the Nobeyama Radioheliograph (NoRH) to observe an M7.7 class flare that occurred at active region 11520 on 2012 July 19. A QPP was detected both in the AIA 131 \mathringA bandpass and the NoRH 17 {GHz} channel; it had a period of about four minutes. In the spatial distribution of Fourier power, we found that this QPP originated from a compact source and that it overlapped with the X-ray source above the loop top. The plasma emission intensities in the AIA 131 \mathringA bandpass were highly correlated within this region. The source region is further segmented into stripes that oscillated with distinctive phases. Evidence in this event suggests that this QPP was likely to be generated by intermittent energy injection into the reconnection region. Title: Round-trip Slipping Motion of the Circular Flare Ribbon Evidenced in a Fan-spine Jet Authors: Shen, Yuandeng; Qu, Zhining; Zhou, Chengrui; Duan, Yadan; Tang, Zehao; Yuan, Ding Bibcode: 2019ApJ...885L..11S Altcode: 2019arXiv191005472S A solar jet that occurred on 2014 July 31, which was accompanied by a GOES C1.3 flare and a mini-filament eruption at the jet base, was studied by using observations taken by the New Vacuum Solar Telescope and the Solar Dynamic Observatory. Magnetic field extrapolation revealed that the jet was confined in a fan-spine magnetic system that hosts a null point at the height of about 9 Mm from the solar surface. An inner flare ribbon surrounded by an outer circular ribbon and a remote ribbon were observed to be associated with the eruption, in which the inner and remote ribbons, respectively located at the footprints of the inner and outer spines, while the circular one manifested the footprint of the fan structure. It is worth noting that the west part of the circular ribbon exhibited an interesting round-trip slipping motion, while the inner ribbon and the circular ribbon’s east part displayed a northward slipping motion. Our analysis results indicate that the slipping motions of the inner and the circular flare ribbons reflected the slipping magnetic reconnection process in the fan’s quasi-separatrix layer, while the remote ribbon was associated with the magnetic reconnection at the null point. In addition, the filament eruption was probably triggered by the magnetic cancellation around its south end, which further drove the slipping reconnection in the fan quasi-separatrix layer and the reconnection at the null point. Title: Multilayered Kelvin-Helmholtz Instability in the Solar Corona Authors: Yuan, Ding; Shen, Yuandeng; Liu, Yu; Li, Hongbo; Feng, Xueshang; Keppens, Rony Bibcode: 2019ApJ...884L..51Y Altcode: 2019arXiv191005710Y The Kelvin-Helmholtz (KH) instability is commonly found in many astrophysical, laboratory, and space plasmas. It could mix plasma components of different properties and convert dynamic fluid energy from large-scale structure to smaller ones. In this study, we combined the ground-based New Vacuum Solar Telescope (NVST) and the Solar Dynamic Observatories/Atmospheric Imaging Assembly (AIA) to observe the plasma dynamics associated with active region 12673 on 2017 September 9. In this multitemperature view, we identified three adjacent layers of plasma flowing at different speeds, and detected KH instabilities at their interfaces. We could unambiguously track a typical KH vortex and measure its motion. We found that the speed of this vortex suddenly tripled at a certain stage. This acceleration was synchronized with the enhancements in emission measure and average intensity of the 193 Å data. We interpret this as evidence that KH instability triggers plasma heating. The intriguing feature in this event is that the KH instability observed in the NVST channel was nearly complementary to that in the AIA 193 Å. Such a multithermal energy exchange process is easily overlooked in previous studies, as the cold plasma component is usually not visible in the extreme-ultraviolet channels that are only sensitive to high-temperature plasma emissions. Our finding indicates that embedded cold layers could interact with hot plasma as invisible matters. We speculate that this process could occur at a variety of length scales and could contribute to plasma heating. Title: Stereoscopic Observations of an Erupting Mini-filament-driven Two-sided-loop Jet and the Applications for Diagnosing a Filament Magnetic Field Authors: Shen, Yuandeng; Qu, Zhining; Yuan, Ding; Chen, Huadong; Duan, Yadan; Zhou, Chengrui; Tang, Zehao; Huang, Jin; Liu, Yu Bibcode: 2019ApJ...883..104S Altcode: 2019arXiv190803660S Ubiquitous solar jets or jet-like activities are generally regarded as an important source of energy and mass input to the upper solar atmosphere and the solar wind. However, their triggering and driving mechanisms are not completely understood. By taking advantage of stereoscopic observations with high temporal and spatial resolutions taken by the Solar Dynamic Observatory (SDO) and the Solar Terrestrial Relations Observatory (STEREO), we report an intriguing two-sided-loop jet that occurred on 2013 June 02, and was dynamically associated with the eruption of a mini-filament below an overlying large filament. Additionally, two distinct reconnection processes are identified during the formation stage. The SDO observations reveal that the two-sided-loop jet showed a concave shape with a projection speed of about 80-136 km s-1. From the other view angle, the STEREO observations clearly showed that the trajectories of the two arms of the two-sided-loop were along the cavity magnetic field lines hosting the large filament. Contrary to the well-accepted theoretical model, the present observation sheds new light on our understanding of the formation mechanism of two-sided-loop jets. Moreover, the eruption of the two-sided-loop jet not only supplied mass to the overlying large filament, but also provided a rare opportunity to diagnose the magnetic structure of the overlying large filament via the method of three-dimensional reconstruction. Title: Laboratory Analog of Heavy Jets Impacting a Denser Medium in Herbig-Haro (HH) Objects Authors: Liang, G. Y.; Zhong, J. Y.; Wei, H. G.; Yuan, D. W.; Zhang, Z.; Wang, C.; Han, B.; Zhu, B. J.; Jiang, W. M.; Peng, J. M.; Tao, T.; Hu, G. Y.; Wang, F. L.; Gao, X.; Zhu, B. Q.; Zhu, J. Q.; Ma, X. W.; Li, Y. T.; Zhao, G.; Zhang, J. Bibcode: 2018ApJ...868...56L Altcode: X-ray emissions in protostars play an important role in the chemistry of protostellar disks and in constraining the physics of jet formation. We have experimentally investigated the mechanism of X-ray emission in protostellar jets and modeled their interaction with the surrounding medium. The simulated supersonic jet is generated by intense laser beams irradiating a K-shaped target and then impacts an obstacle. We have successfully observed X-ray emission from the obstacle surface, and we find that it comes from the outflow material and not completely from the ambient medium heated by shock. Title: Investigating Sub-Pixel 45-Second Periodic Wobble in SDO/AIA Data from January to August 2012 Authors: Yuan, Ding; Liu, Wei; Walsh, Robert Bibcode: 2018SoPh..293..147Y Altcode: Artifacts could mislead interpretations in astrophysical observations. A thorough understanding of an instrument will help in distinguishing physical processes from artifacts. In this article, we investigate an artifact of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory. Time-series data and wavelet spectra revealed periodic intensity perturbations in small regions over the entire image in certain AIA extreme ultraviolet (EUV) passbands at a period of about 45 seconds. These artificial intensity variations are prominently detected in regions with sharp intensity contrast, such as sunspot light bridges. This artifact was caused by a periodic pointing wobble of the two AIA telescopes ATA 2 (193 and 211 Å channels) and ATA 3 (171 Å and UV channels), to a lesser extent, while the other two telescopes were not found to be affected. The peak-to-peak amplitude of the wobble was about 0.2 pixel in ATA 2 and 0.1 pixel in ATA 3. This artifact was intermittent and affected the data of seven months from 18 January to 28 August 2012, as a result of a thermal adjustment to the telescopes. We recommend that standard pointing-correction techniques, such as local correlation tracking, should be applied before any detailed scientific analysis that requires sub-pixel pointing accuracy. Specifically, this artificial 45-second periodicity was falsely interpreted as abnormal sub-minute oscillations in a light bridge of a sunspot (Yuan and Walsh in Astron. Astrophys.594, A101, 2016). Title: Non-damping oscillations at flaring loops Authors: Li, D.; Yuan, D.; Su, Y. N.; Zhang, Q. M.; Su, W.; Ning, Z. J. Bibcode: 2018A&A...617A..86L Altcode: 2018arXiv180603573L Context. Quasi-periodic oscillations are usually detected as spatial displacements of coronal loops in imaging observations or as periodic shifts of line properties (i.e., Doppler velocity, line width and intensity) in spectroscopic observations. They are often applied for remote diagnostics of magnetic fields and plasma properties on the Sun.
Aims: We combine the imaging and spectroscopic measurements of available space missions, and investigate the properties of non-damping oscillations at flaring loops.
Methods: We used the Interface Region Imaging Spectrograph (IRIS) to measure the spectrum over a narrow slit. The double-component Gaussian fitting method was used to extract the line profile of Fe XXI 1354.08 Å at the "O I" spectral window. The quasi-periodicity of loop oscillations were identified in the Fourier and wavelet spectra.
Results: A periodicity at about 40 s is detected in the line properties of Fe XXI 1354.08 Å, hard X-ray emissions in GOES 1-8 Å derivative, and Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while a phase shift of about π/2 is detected between the Doppler velocity and peak intensity. The amplitudes of Doppler velocity and line width oscillation are about 2.2 km s-1 and 1.9 km s-1, respectively, while peak intensity oscillates with amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period of about 155 s is identified in the Doppler velocity and peak intensity of the Fe XXI 1354.08 Å line emission, and AIA 131 Å intensity.
Conclusions: The oscillations at about 40 s are not damped significantly during the observation; this might be linked to the global kink modes of flaring loops. The periodicity at about 155 s is most likely a signature of recurring downflows after chromospheric evaporation along flaring loops. The magnetic field strengths of the flaring loops are estimated to be about 120-170 G using the magnetohydrodynamic seismology diagnostics, which are consistent with the magnetic field modeling results using the flux rope insertion method.

The movie associated to Fig. 1 is available at https://www.aanda.org Title: First Imaging Observation of Standing Slow Wave in Coronal Fan Loops Authors: Pant, V.; Tiwari, A.; Yuan, D.; Banerjee, D. Bibcode: 2017ApJ...847L...5P Altcode: 2017arXiv170806946P We observe intensity oscillations along coronal fan loops associated with the active region AR 11428. The intensity oscillations were triggered by blast waves that were generated due to X-class flares in the distant active region AR 11429. To characterize the nature of oscillations, we created time-distance maps along the fan loops and noted that the intensity oscillations at two ends of the loops were out of phase. As we move along the fan loop, the amplitude of the oscillations first decreased and then increased. The out-of-phase nature together with the amplitude variation along the loop implies that these oscillations are very likely to be standing waves. The period of the oscillations is estimated to be ∼27 minutes, damping time to be ∼45 minutes, and phase velocity projected in the plane of sky to be ∼65-83 km s-1. The projected phase speeds were in the range of the acoustic speed of coronal plasma at about 0.6 MK, which further indicates that these are slow waves. To the best of our knowledge, this is the first report on the existence of the standing slow waves in non-flaring fan loops. Title: Discrimination of the Spatial Distribution of Persistent EUV Oscillations in a Hot Waning Light Bridge Authors: Walsh, R. W.; Yuan, D. Bibcode: 2016AGUFMSH21E2578W Altcode: A light bridge is usually formed as a lower atmospheric structure in nascent or decaying sunspots; it divides the umbra into separate regions. Convection, which is normally suppressed by a sunspot's strong magnetic field, is partially restored and upflows are usually observed at the spine of a bridge with downflows (or return flows) at the two flanks. This study outlines observations a light bridge unusually sustained at coronal temperatures. Viewed in AR11520 on 12th July 2012 by the High Resolution Coronal Imager (HiC) and AIA/SDO, the EUV emission intensity exhibits two persistent oscillations. The approximate 5-minute oscillations are distributed along the spine of the light bridge whereas sub-minute oscillations are distinctively co-spatial along each bridge flank (though there is a distinct time-lag between them). This indicates strongly that (i) the oscillatory driver at the flanks is connected with the collective interactions between magnetic fields of the bridge and the sunspot itself and (ii) the internal magnetic structure of the bridge is twisted. The presentation will outline the distinct oscillatory maps generated and provide insight into determining the magnetic morphology until the bridge wans in EUV several hours later. Title: The Role of Kelvin-Helmholtz Instability for Producing Loop-top Hard X-Ray Sources in Solar Flares Authors: Fang, Xia; Yuan, Ding; Xia, Chun; Van Doorsselaere, Tom; Keppens, Rony Bibcode: 2016ApJ...833...36F Altcode: We propose a model for the formation of loop-top hard X-ray (HXR) sources in solar flares through the inverse Compton mechanism, scattering the surrounding soft X-ray (SXR) photons to higher energy HXR photons. We simulate the consequences of a flare-driven energy deposit in the upper chromosphere in the impulsive phase of single loop flares. The consequent chromosphere evaporation flows from both footpoints reach speeds up to hundreds of kilometers per second, and we demonstrate how this triggers Kelvin-Helmholtz instability (KHI) in the loop top, under mildly asymmetric conditions, or more toward the loop flank for strongly asymmetric cases. The KHI vortices further fragment the magnetic topology into multiple magnetic islands and current sheets, and the hot plasma within leads to a bright loop-top SXR source region. We argue that the magnetohydrodynamic turbulence that appears at the loop apex could be an efficient accelerator of non-thermal particles, which the island structures can trap at the loop-top. These accelerated non-thermal particles can upscatter the surrounding thermal SXR photons emitted by the extremely hot evaporated plasma to HXR photons. Title: Collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near critical density plasmas Authors: Liu, M.; Weng, S. M.; Li, Y. T.; Yuan, D. W.; Chen, M.; Mulser, P.; Sheng, Z. M.; Murakami, M.; Yu, L. L.; Zheng, X. L.; Zhang, J. Bibcode: 2016PhPl...23k3103L Altcode: 2016arXiv161106616L Laser-driven collisionless electrostatic shock formation and the subsequent ion acceleration have been studied in near critical density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near critical density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near critical density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strong time-oscillating electric field accompanying the laser-driven collisionless shock in a near critical density plasma. Title: Quasi-periodic Pulsations in Solar and Stellar Flares: An Overview of Recent Results (Invited Review) Authors: Van Doorsselaere, Tom; Kupriyanova, Elena G.; Yuan, Ding Bibcode: 2016SoPh..291.3143V Altcode: 2016SoPh..tmp..147V; 2016arXiv160902689V Quasi-periodic pulsations (or QPPs) are periodic intensity variations in the flare emission that occur across all wavelength bands. In this article, we review the observational and modelling achievements since the previous review on this topic by Nakariakov and Melnikov (Space Sci. Rev.149, 119, 2009). In recent years, it has become clear that QPPs are an inherent feature of solar flares because almost all flares exhibit QPPs. Moreover, it is now firmly established that QPPs often show multiple periods. We also review possible mechanisms for generating QPPs. Up to now, it has not been possible to conclusively identify the triggering mechanism or cause of QPPs. The lack of this identification currently hampers possible seismological inferences of flare plasma parameters. QPPs in stellar flares have been detected for a long time, and the high-quality data of the Kepler mission allows studying the QPP more systematically. However, it has not been conclusively shown whether the timescales of stellar QPPs are different or the same as those in solar flares. Title: Simultaneous Longitudinal and Transverse Oscillations in an Active-Region Filament Authors: Pant, Vaibhav; Mazumder, Rakesh; Yuan, Ding; Banerjee, Dipankar; Srivastava, Abhishek K.; Shen, Yuandeng Bibcode: 2016SoPh..291.3303P Altcode: 2016arXiv161103984P; 2016SoPh..tmp..185P We report on the co-existence of longitudinal and transverse oscillations in an active-region filament. On March 15, 2013, an M1.1 class flare was observed in Active Region AR 11692. A coronal mass ejection (CME) was found to be associated with the flare. The CME generated a shock wave that triggered the oscillations in a nearby filament, situated south-west of the active region as observed from National Solar Observatory (NSO) Global Oscillation Network Group (GONG) Hα images. In this work we report the longitudinal oscillations in the two ends of the filament, which co-existed with the transverse oscillations. We propose a scenario in which an incoming shock wave hits the filament obliquely and triggers both longitudinal and transverse oscillations. Using the observed parameters, we estimate the lower limit of the magnetic field strength. We use a simple pendulum model with gravity as the restoring force to estimate the radius of curvature. We also calculate the mass accretion rate that causes the filament motions to damp quite fast. Title: Abnormal oscillation modes in a waning light bridge Authors: Yuan, Ding; Walsh, Robert W. Bibcode: 2016A&A...594A.101Y Altcode: 2016arXiv160900596Y Context. A sunspot acts as a waveguide in response to the dynamics of the solar interior; the trapped waves and oscillations could reveal its thermal and magnetic structures.
Aims: We study the oscillations in a sunspot intruded by a light bridge, and the details of these oscillations could reveal the fine structure of the magnetic topology.
Methods: We used the Solar Dynamics Observatory/Atmospheric Imaging Assembly data to analyse the oscillations in the emission intensity of light bridge plasma at different temperatures, and we investigated their spatial distributions.
Results: The extreme ultraviolet emission intensity exhibits two persistent oscillations at five-minute and sub-minute ranges. The spatial distribution of the five-minute oscillation follows the spine of the bridge, whereas the sub-minute oscillations overlap with two flanks of the bridge. Moreover, the sub-minute oscillations are highly correlated in spatial domain, however, the oscillations at the eastern and western flanks are asymmetric with regard to the lag time. In the meantime, jet-like activities are only found at the eastern flank.
Conclusions: Asymmetries in the form of oscillatory pattern and jet-like activities are found between two flanks of a granular light bridge. Based on our study and recent findings, we propose a new model of twisted magnetic field for a light bridge and its dynamic interactions with the magnetic field of a sunspot. Title: Reflection of Propagating Slow Magneto-acoustic Waves in Hot Coronal Loops: Multi-instrument Observations and Numerical Modeling Authors: Mandal, Sudip; Yuan, Ding; Fang, Xia; Banerjee, Dipankar; Pant, Vaibhav; Van Doorsselaere, Tom Bibcode: 2016ApJ...828...72M Altcode: 2016arXiv160408133M Slow MHD waves are important tools for understanding coronal structures and dynamics. In this paper, we report a number of observations from the X-Ray Telescope (XRT) on board HINODE and Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA) of reflecting longitudinal waves in hot coronal loops. To our knowledge, this is the first report of this kind as seen from the XRT and simultaneously with the AIA. The wave appears after a micro-flare occurs at one of the footpoints. We estimate the density and temperature of the loop plasma by performing differential emission measure (DEM) analysis on the AIA image sequence. The estimated speed of propagation is comparable to or lower than the local sound speed, suggesting it to be a propagating slow wave. The intensity perturbation amplitude, in every case, falls very rapidly as the perturbation moves along the loop and eventually vanishes after one or more reflections. To check the consistency of such reflection signatures with the obtained loop parameters, we perform a 2.5D MHD simulation, which uses the parameters obtained from our observation as inputs, and perform forward modeling to synthesize AIA 94 Å images. Analyzing the synthesized images, we obtain the same properties of the observables as for the real observation. From the analysis we conclude that a footpoint heating can generate a slow wave which then reflects back and forth in the coronal loop before fading. Our analysis of the simulated data shows that the main agent for this damping is anisotropic thermal conduction. Title: Secondary Fast Magnetoacoustic Waves Trapped in Randomly Structured Plasmas Authors: Yuan, Ding; Li, Bo; Walsh, Robert W. Bibcode: 2016ApJ...828...17Y Altcode: 2016arXiv160606059Y Fast magnetoacoustic waves are an important tool for inferring parameters of the solar atmosphere. We numerically simulate the propagation of fast wave pulses in randomly structured plasmas that mimic the highly inhomogeneous solar corona. A network of secondary waves is formed by a series of partial reflections and transmissions. These secondary waves exhibit quasi-periodicities in both time and space. Since the temporal and spatial periods are related simply through the speed of the fast wave, we quantify the properties of secondary waves by examining the dependence of the average temporal period (\bar{p}) on the initial pulse width (w 0) and studying the density contrast ({δ }ρ ) and correlation length (L c ) that characterize the randomness of the equilibrium density profiles. For small-amplitude pulses, {δ }ρ does not alter \bar{p} significantly. Large-amplitude pulses, on the other hand, enhance the density contrast when {δ }ρ is small but have a smoothing effect when {δ }ρ is sufficiently large. We found that \bar{p} scales linearly with L c and that the scaling factor is larger for a narrower pulse. However, in terms of the absolute values of \bar{p}, broader pulses generate secondary waves with longer periods, and this effect is stronger in random plasmas with shorter correlation lengths. Secondary waves carry the signatures of both the leading wave pulse and the background plasma. Our study may find applications in magnetohydrodynamic seismology by exploiting the secondary waves detected in the dimming regions after coronal mass ejections or extreme ultraviolet waves. Title: Relativistic Electrons Produced by Reconnecting Electric Fields in a Laser-driven Bench-top Solar Flare Authors: Zhong, J. Y.; Lin, J.; Li, Y. T.; Wang, X.; Li, Y.; Zhang, K.; Yuan, D. W.; Ping, Y. L.; Wei, H. G.; Wang, J. Q.; Su, L. N.; Li, F.; Han, B.; Liao, G. Q.; Yin, C. L.; Fang, Y.; Yuan, X.; Wang, C.; Sun, J. R.; Liang, G. Y.; Wang, F. L.; Ding, Y. K.; He, X. T.; Zhu, J. Q.; Sheng, Z. M.; Li, G.; Zhao, G.; Zhang, J. Bibcode: 2016ApJS..225...30Z Altcode: Laboratory experiments have been carried out to model the magnetic reconnection process in a solar flare with powerful lasers. Relativistic electrons with energy up to megaelectronvolts are detected along the magnetic separatrices bounding the reconnection outflow, which exhibit a kappa-like distribution with an effective temperature of ∼109 K. The acceleration of non-thermal electrons is found to be more efficient in the case with a guide magnetic field (a component of a magnetic field along the reconnection-induced electric field) than in the case without a guide field. Hardening of the spectrum at energies ≥500 keV is observed in both cases, which remarkably resembles the hardening of hard X-ray and γ-ray spectra observed in many solar flares. This supports a recent proposal that the hardening in the hard X-ray and γ-ray emissions of solar flares is due to a hardening of the source-electron spectrum. We also performed numerical simulations that help examine behaviors of electrons in the reconnection process with the electromagnetic field configurations occurring in the experiments. The trajectories of non-thermal electrons observed in the experiments were well duplicated in the simulations. Our numerical simulations generally reproduce the electron energy spectrum as well, except for the hardening of the electron spectrum. This suggests that other mechanisms such as shock or turbulence may play an important role in the production of the observed energetic electrons. Title: Damping and power spectra of quasi-periodic intensity disturbances above a solar polar coronal hole Authors: Jiao, Fang-Ran; Xia, Li-Dong; Huang, Zheng-Hua; Li, Bo; Fu, Hui; Yuan, Ding; Chandrashekhar, Kalugodu Bibcode: 2016RAA....16...93J Altcode: 2016arXiv160204883J; 2016RAA....16f...8J We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 Å and 193 Å passbands, aiming to provide more insights into their physical nature. The damping and power spectra of the intensity disturbances with frequencies from 0.07 mHz to 10.5 mHz are investigated. The damping of the intensity disturbances tends to be stronger at lower frequencies, and their damping behavior below 980″ (for comparison, the limb is at 945″) is different from what happens above. No significant difference is found between the damping of the intensity disturbances in the AIA 171 Å and that in the AIA 193 Å. The indices of the power spectra of the intensity disturbances are found to be slightly smaller in the AIA 171 Å than in the AIA 193 Å, but the difference is within one standard deviation. An additional enhanced component is present in the power spectra in a period range of 8-40 min at lower heights. The power spectra of a spicule is highly correlated with its associated intensity disturbance, which suggests that the power spectra of the intensity disturbances might be a mixture of spicules and wave activities. We suggest that each intensity disturbance in the polar coronal hole is possibly a series of independent slow magnetoacoustic waves triggered by spicular activities. Title: Stochastic Transients as a Source of Quasi-periodic Processes in the Solar Atmosphere Authors: Yuan, Ding; Su, Jiangtao; Jiao, Fangran; Walsh, Robert W. Bibcode: 2016ApJS..224...30Y Altcode: 2016arXiv160308977Y Solar dynamics and turbulence occur at all heights of the solar atmosphere and could be described as stochastic processes. We propose that finite-lifetime transients recurring at a certain place could trigger quasi-periodic processes in the associated structures. In this study, we developed a mathematical model for finite-lifetime and randomly occurring transients, and found that quasi-periodic processes with periods longer than the timescale of the transients, are detectable intrinsically in the form of trains. We simulate their propagation in an empirical solar atmospheric model with chromosphere, transition region, and corona. We found that, due to the filtering effect of the chromospheric cavity, only the resonance period of the acoustic resonator is able to propagate to the upper atmosphere; such a scenario is applicable to slow magnetoacoustic waves in sunspots and active regions. If the thermal structure of the atmosphere is less wild and acoustic resonance does not take place, the long-period oscillations could propagate to the upper atmosphere. Such a case would be more likely to occur in polar plumes. Title: Forward Modeling of Standing Kink Modes in Coronal Loops. I. Synthetic Views Authors: Yuan, Ding; Van Doorsselaere, Tom Bibcode: 2016ApJS..223...23Y Altcode: 2016arXiv160301632Y Kink magnetohydrodynamic (MHD) waves are frequently observed in various magnetic structures of the solar atmosphere. They may contribute significantly to coronal heating and could be used as a tool to diagnose the solar plasma. In this study, we synthesize the Fe ix λ171.073 Å emission of a coronal loop supporting a standing kink MHD mode. The kink MHD wave solution of a plasma cylinder is mapped into a semi-torus structure to simulate a curved coronal loop. We decompose the solution into a quasi-rigid kink motion and a quadrupole term, which dominate the plasma inside and outside of the flux tube, respectively. At the loop edges, the line of sight integrates relatively more ambient plasma, and the background emission becomes significant. The plasma motion associated with the quadrupole term causes spectral line broadening and emission suppression. The periodic intensity suppression will modulate the integrated intensity and the effective loop width, which both exhibit oscillatory variations at half of the kink period. The quadrupole term can be directly observed as a pendular motion at the front view. Title: Forward Modeling of Standing Kink Modes in Coronal Loops. II. Applications Authors: Yuan, Ding; Van Doorsselaere, Tom Bibcode: 2016ApJS..223...24Y Altcode: 2016arXiv160207598Y Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses, and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation. Title: Forward Modeling of Propagating Slow Waves in Coronal Loops and Their Frequency-dependent Damping Authors: Mandal, Sudip; Magyar, Norbert; Yuan, Ding; Van Doorsselaere, Tom; Banerjee, Dipankar Bibcode: 2016ApJ...820...13M Altcode: 2016arXiv160200787M Propagating slow waves in coronal loops exhibit a damping that depends upon the frequency of the waves. In this study we aim to investigate the relationship of the damping length (L d ) with the frequency of the propagating wave. We present a 3D coronal loop model with uniform density and temperature and investigate the frequency-dependent damping mechanism for the four chosen wave periods. We include the thermal conduction to damp the waves as they propagate through the loop. The numerical model output has been forward modeled to generate synthetic images of SDO/AIA 171 and 193 Å channels. The use of forward modeling, which incorporates the atomic emission properties into the intensity images, allows us to directly compare our results with the real observations. The results show that the damping lengths vary linearly with the periods. We also measure the contributions of the emission properties on the damping lengths by using density values from the simulation. In addition to that we have also calculated the theoretical dependence of L d with wave periods and showed that it is consistent with the results we obtained from the numerical modeling and earlier observations. Title: Lunar Tidal Distortion from GRAIL and LLR Authors: Williams, J. G.; Konopliv, A. S.; Park, R. S.; Boggs, D. H.; Asmar, S. W.; Yuan, D. -N.; Watkins, M. M.; Smith, D. E.; Zuber, M. T. Bibcode: 2016LPI....47.1328W Altcode: Lunar tidal distortion is sensitive to structure. The Love number is determined by GRAIL data analysis and tidal dissipation is given by LLR analysis. Title: Forward modelling of optically thin coronal plasma with the FoMo tool Authors: Van Doorsselaere, Tom; Antolin, Patrick; Yuan, Ding; Reznikova, Veronika; Magyar, Norbert Bibcode: 2016FrASS...3....4V Altcode: The FoMo code was developed to calculate the EUV emission from optically thin coronal plasmas. The input data for FoMo consists of the coronal density, temperature and velocity on a 3D grid. This is translated to emissivity on the 3D grid, using CHIANTI data. Then, the emissivity is integrated along the line-of-sight to calculate the emergent spectral line that could be observed by a spectrometer. Moreover, the code has been extended to model also the radio emission from plasmas with a population of non-thermal particles. In this case, also optically thick plasmas may be modelled. The radio spectrum is calculated over a large wavelength range, allowing for the comparison with data from a wide range of radio telescopes. Title: Modeling of Reflective Propagating Slow-mode Wave in a Flaring Loop Authors: Fang, X.; Yuan, D.; Van Doorsselaere, T.; Keppens, R.; Xia, C. Bibcode: 2015ApJ...813...33F Altcode: 2015arXiv150904536F Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet 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. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s-1 in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves. Title: Signature of high-order azimuthal MHD body modes in sunspot's low atmosphere Authors: Yuan, Ding Bibcode: 2015RAA....15.1449Y Altcode: The five-minute oscillations inside sunspots appear to be the absorption of the solar p-mode. It is a potential tool to probe a sunspot's sub-structure. We studied the collective properties of five-minute oscillations in the power and phase distribution at the sunspot's umbra-penumbra boundary. The azimuthal distributions of the power and phase of five-minute oscillations enclosing a sunspot's umbra were obtained with images taken with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA). The azimuthal modes were quantified with periodogram analysis and justified with significance tests. The azimuthal nodal structures in an approximately axially symmetric sunspot AR 11131 (2010 Dec 08) were investigated. Mode numbers m = 2,3,4,7,10 were obtained in both 1700 Å and 1600 Å bandpasses. The 1600 Å channel also revealed an extra mode at m = 9. In the upper atmosphere (304 Å), fewer modes were detected at m = 3, 4, 7. The azimuthal modes in the sunspot's low atmosphere could be interpreted as high-order azimuthal MHD body modes. They were detected in the power and phase of the five-minute oscillations in sunspot AR 11131 with SDO/AIA data. Fewer modes were detected in the sunspot's upper atmosphere. Title: Forward Modeling of Standing Slow Modes in Flaring Coronal Loops Authors: Yuan, D.; Van Doorsselaere, T.; Banerjee, D.; Antolin, P. Bibcode: 2015ApJ...807...98Y Altcode: 2015arXiv150407475Y Standing slow-mode waves in hot flaring loops are exclusively observed in spectrometers and are used to diagnose the magnetic field strength and temperature of the loop structure. Owing to the lack of spatial information, the longitudinal mode cannot be effectively identified. In this study, we simulate standing slow-mode waves in flaring loops and compare the synthesized line emission properties with Solar Ultraviolet Measurements of Emitted Radiation spectrographic and Solar Dynamics Observatory/Atmospheric Imaging Assembly imaging observations. We find that the emission intensity and line width oscillations are a quarter period out of phase with Doppler shift velocity in both time and spatial domain, which can be used to identify a standing slow-mode wave from spectroscopic observations. However, the longitudinal overtones could only be measured with the assistance of imagers. We find emission intensity asymmetry in the positive and negative modulations this is because the contribution function pertaining to the atomic emission process responds differently to positive and negative temperature variations. One may detect half periodicity close to the loop apex, where emission intensity modulation is relatively small. The line-of-sight projection affects the observation of Doppler shift significantly. A more accurate estimate of the amplitude of velocity perturbation is obtained by de-projecting the Doppler shift by a factor of 1-2θ/π rather than the traditionally used {cos}θ . If a loop is heated to the hotter wing, the intensity modulation could be overwhelmed by background emission, while the Doppler shift velocity could still be detected to a certain extent. Title: Gravity Field of the Orientale Basin from the Gravity Recovery and Interior Laboratory (GRAIL) Mission Authors: Zuber, M. T.; Smith, D. E.; Goossens, S. J.; Andrews-Hanna, J. C.; Head, J. W.; Kiefer, W. S.; Asmar, S. W.; Konopliv, A. S.; Lemoine, F. G.; Matsuyama, I.; McGovern, P. J.; Melosh, H. J.; Neumann, G. A.; Nimmo, F.; Phillips, R. J.; Solomon, S. C.; Taylor, G. J.; Watkins, M. M.; Wieczorek, M. A.; Johnson, B. C.; Keane, J.; Miljkovic, K.; Park, R. S.; Soderblom, J. M.; Blair, D. M.; Mazarico, E.; Yuan, D. -N. Bibcode: 2015LPI....46.1447Z Altcode: 2015LPICo1832.1447Z The Endgame mapping strategy was designed to provide highest-resolution coverage over the Orientale basin to yield a gravity map of a multi-ring impact basin. Title: The Deep Lunar Interior from GRAIL Authors: Williams, J. G.; Konopliv, A. S.; Park, R. S.; Yuan, D. -N.; Asmar, S. W.; Watkins, M. M.; Smith, D. E.; Zuber, M. T. Bibcode: 2015LPI....46.1380W Altcode: 2015LPICo1832.1380W A solution for a very-high-resolution GRAIL gravity field determines lunar Love number and tidal dissipation Q, but does not detect the inner core. Title: Evolution of Fast Magnetoacoustic Pulses in Randomly Structured Coronal Plasmas Authors: Yuan, D.; Pascoe, D. J.; Nakariakov, V. M.; Li, B.; Keppens, R. Bibcode: 2015ApJ...799..221Y Altcode: 2014arXiv1411.4152Y We investigate the evolution of fast magnetoacoustic pulses in randomly structured plasmas, in the context of large-scale propagating waves in the solar atmosphere. We perform one-dimensional numerical simulations of fast wave pulses propagating perpendicular to a constant magnetic field in a low-β plasma with a random density profile across the field. Both linear and nonlinear regimes are considered. We study how the evolution of the pulse amplitude and width depends on their initial values and the parameters of the random structuring. Acting as a dispersive medium, a randomly structured plasma causes amplitude attenuation and width broadening of the fast wave pulses. After the passage of the main pulse, secondary propagating and standing fast waves appear. Width evolution of both linear and nonlinear pulses can be well approximated by linear functions; however, narrow pulses may have zero or negative broadening. This arises because narrow pulses are prone to splitting, while broad pulses usually deviate less from their initial Gaussian shape and form ripple structures on top of the main pulse. Linear pulses decay at an almost constant rate, while nonlinear pulses decay exponentially. A pulse interacts most efficiently with a random medium with a correlation length of about half of the initial pulse width. This detailed model of fast wave pulses propagating in highly structured media substantiates the interpretation of EIT waves as fast magnetoacoustic waves. Evolution of a fast pulse provides us with a novel method to diagnose the sub-resolution filamentation of the solar atmosphere. Title: Oscillations in a Sunspot with Light Bridges Authors: Yuan, Ding; Nakariakov, Valery M.; Huang, Zhenghua; Li, Bo; Su, Jiangtao; Yan, Yihua; Tan, Baolin Bibcode: 2014ApJ...792...41Y Altcode: 2014arXiv1407.1544Y The Solar Optical Telescope on board Hinode observed a sunspot (AR 11836) with two light bridges (LBs) on 2013 August 31. We analyzed a two-hour Ca II H emission intensity data set and detected strong five-minute oscillation power on both LBs and in the inner penumbra. The time-distance plot reveals that the five-minute oscillation phase does not vary significantly along the thin bridge, indicating that the oscillations are likely to originate from underneath it. The slit taken along the central axis of the wide LB exhibits a standing wave feature. However, at the center of the wide bridge, the five-minute oscillation power is found to be stronger than at its sides. Moreover, the time-distance plot across the wide bridge exhibits a herringbone pattern that indicates a counter-stream of two running waves, which originated at the bridge's sides. Thus, the five-minute oscillations on the wide bridge also resemble the properties of running penumbral waves. The five-minute oscillations are suppressed in the umbra, while the three-minute oscillations occupy all three cores of the sunspot's umbra, separated by the LBs. The three-minute oscillations were found to be in phase at both sides of the LBs. This may indicate that either LBs do not affect umbral oscillations, or that umbral oscillations at different umbral cores share the same source. It also indicates that LBs are rather shallow objects situated in the upper part of the umbra. We found that umbral flashes (UFs) follow the life cycles of umbral oscillations with much larger amplitudes. They cannot propagate across LBs. UFs dominate the three-minute oscillation power within each core; however, they do not disrupt the phase of umbral oscillation. Title: A Glimpse of Lunar Core Shape and Deep Gravity Field Authors: Williams, J. G.; Konopliv, A. S.; Lemoine, F. G.; Goossens, S.; Asmar, S. W.; Park, R. S.; Yuan, D. -N.; Boggs, D. H.; Mazarico, E.; Kiefer, W. S.; Wieczorek, M. A.; Watkins, M. M.; Smith, D. E.; Zuber, M. T. Bibcode: 2014LPI....45.2267W Altcode: A GRAIL S21 value implies a misalignment of principal axes derived by Lunar Laser Ranging. A fluid outer core shaped by internal gravity can affect axes. Title: A High-Resolution View of the Orientale Basin and Surroundings from the Gravity Recovery and Interior Laboratory (GRAIL) Authors: Zuber, M. T.; Smith, D. E.; Goossens, S. J.; Asmar, S. W.; Konopliv, A. S.; Lemoine, F. G.; Melosh, H. J.; Neumann, G. A.; Phillips, R. J.; Solomon, S. C.; Watkins, M. M.; Wieczorek, M. A.; Andrews-Hanna, J. C.; Head, J. W.; Kiefer, W. S.; McGovern, P. J.; Nimmo, F.; Taylor, G. J.; Besserer, J.; Johnson, B. C.; Milijkovic, K.; Soderblom, J. M.; Blair, D. M.; Kruizinga, G. L.; Mazarico, E.; Yuan, D. -N. Bibcode: 2014LPI....45.2061Z Altcode: A high-resolution view of the Orientale Basin and surroundings from the Gravity Recovery and Interior Laboratory (GRAIL). Title: Multi-height observations of magnetoacoustic cut-off frequency in a sunspot atmosphere Authors: Yuan, D.; Sych, R.; Reznikova, V. E.; Nakariakov, V. M. Bibcode: 2014A&A...561A..19Y Altcode: 2012arXiv1211.5196Y Context. The cut-off frequency of magnetoacoustic gravity (MAG) waves could be decreased by the inclined magnetic field, and therefore, low-frequency waves could penetrate into the upper atmosphere.
Aims: We observe the distribution of the cut-off frequency of compressive waves at various heights and reconstruct the magnetic field inclination, according to the MAG wave theory in a stratified atmosphere permeated by a uniform magnetic field.
Methods: We analysed the emission intensity oscillations of sunspot AR11131 (08 Dec. 2010) observed at the 1700 Å, 1600 Å, and 304 Å bandpasses of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), and computed the narrow-band power maps with the pixelised wavelet filtering method. The distribution of the cut-off frequency was defined as the median contour in the azimuthally-averaged oscillation power. The magnetic field inclination was estimated with the local cut-off frequency according to the MAG wave theory in the low-β limit and was compared to the potential field extrapolation.
Results: Shorter period oscillations dominate in the sunspot umbra, while longer period oscillations form an annular shape approximately concentric with the sunspot. Oscillations with longer periods are distributed further away from the sunspot centre. The 5 min oscillations appear to originate at or lower than the photosphere. The magnetic field inclinations determined with the cut-off frequency theory are about 30-40% larger than the values obtained by the potential field extrapolation.
Conclusions: The oscillation power distribution in a sunspot atmosphere reflects its magnetic and thermal structure. The cut-off frequency could be used to probe the magnetic field inclination, however, other factors have to be included to fully understand this phenomenon. The existence of return magnetic flux at the outer penumbra was evidenced by the cut-off frequency distribution. Title: Distinct propagating fast wave trains associated with flaring energy releases Authors: Yuan, D.; Shen, Y.; Liu, Y.; Nakariakov, V. M.; Tan, B.; Huang, J. Bibcode: 2013A&A...554A.144Y Altcode: Context. Large-scale fast waves with perturbation of the EUV emission intensity are well resolved in both temporal and spatial scale by SDO/AIA. These waves are prone to propagate along the magnetic field line.
Aims: We aim to probe the link between propagating fast wave trains and flaring energy releases. By measuring the wave parameters, we reveal their nature and investigate the potential to diagnose the energy source and waveguide.
Methods: The spatial and temporal evolution of the wave amplitude and propagating speed are studied. The correlation of individual wave trains with flare-generated radio bursts is tested.
Results: The propagating wave pattern comprises distinct wave trains with varying periods and wavelengths. This characteristic signature is consistent with the patterns formed by waveguide dispersion, when different spectral components propagate at different phase and group speeds. The wave train releases are found to be highly correlated in start time with the radio bursts emitted by the non-thermal electrons that were accelerated in bursty energy releases. The wave amplitude is seen to reach the maximum midway during its course. This can be caused by a combined effect of the waveguide spread in the transverse direction and density stratification. The transverse amplitude distribution perpendicular to the wave vector is found to follow approximately a Gaussian profile. The spatial structure is consistent with the kink mode that is polarised along the line-of-sight. The propagating speed is subject to deceleration from ~735-845 km s-1 to ~600 km s-1. This could be caused by the decrease in the local Alfvén speed and/or the projection effect. Title: Properties of the Lunar Interior: Preliminary Results from the GRAIL Mission Authors: Williams, J. G.; Konopliv, A. S.; Asmar, S. W.; Lemoine, F. G.; Melosh, H. J.; Neumann, G. A.; Phillips, R. J.; Smith, D. E.; Solomon, S. C.; Watkins, M. M.; Wieczorek, M. A.; Zuber, M. T.; Andrews-Hanna, J. C.; Head, J. W.; Kiefer, W. S.; McGovern, P. J.; Nimmo, F.; Taylor, G. J.; Weber, R. C.; Boggs, D. H.; Goossens, S. J.; Kruizinga, G. L.; Mazarico, E.; Park, R. S.; Yuan, D. -N. Bibcode: 2013LPI....44.3092W Altcode: 2013LPICo1719.3092W GRAIL analyses provide lunar gravity field, Love number, and moment of inertia with improved uncertainties. Title: Gravity Recovery and Interior Laboratory (GRAIL): Extended Mission and Endgame Status Authors: Zuber, M. T.; Smith, D. E.; Asmar, S. W.; Konopliv, A. S.; Lemoine, F. G.; Melosh, H. J.; Neumann, G. A.; Phillips, R. J.; Solomon, S. C.; Watkins, M. M.; Wieczorek, M. A.; Williams, J. G.; Andrews-Hanna, J. C.; Head, J. W.; Kiefer, W. S.; Matsuyama, I.; McGovern, P. J.; Nimmo, F.; Taylor, G. J.; Weber, R. C.; Goossens, S. J.; Kruizinga, G.; Mazarico, E.; Park, R. S.; Yuan, D. -N. Bibcode: 2013LPI....44.1777Z Altcode: 2013LPICo1719.1777Z The GRAIL extended mission has provided gravity models that are being used to map the upper crust of the Moon in unprecedented detail. Title: Energetic electron generation by magnetic reconnection in laboratory laser-plasma interactions Authors: Dong, Q. -L.; Yuan, D. -W.; Wang, S. -J.; Li, Y. T.; Liu, X.; Jiang, S. E.; Ding, Y. K.; Du, K.; Yu, M. -Y.; He, X. -T.; Tang, Y. J.; Zhu, J. Q.; Zhao, G.; Sheng, Z. -M.; Zhang, J.; Zhang Bibcode: 2012JPlPh..78..497D Altcode: The magnetic reconnection (MR) configuration was constructed by using two approaching laser-produced plasma bubbles. The characteristics of the MR current sheet were investigated. The driving energy of the laser pulse affects the type of the current sheet. The experiments present ``Y-type'' and ``X-type'' current sheets for larger and smaller driving energy, respectively. The energetic electrons were found to be well-collimated. The formation and ejection of plasmoid from the ``Y-type'' current sheet was expected to enhance the number of accelerated electrons. Title: Measuring the apparent phase speed of propagating EUV disturbances Authors: Yuan, D.; Nakariakov, V. M. Bibcode: 2012A&A...543A...9Y Altcode: Context. Propagating disturbances of the EUV emission intensity are commonly observed over a variety of coronal structures. Parameters of these disturbances, particularly the observed apparent (image-plane projected) propagation speed, are important tools for MHD coronal seismology.
Aims: We design and test tools to reliably measure the apparent phase speed of propagating disturbances in imaging data sets.
Methods: We designed cross-fitting technique (CFT), 2D coupled fitting (DCF) and best similarity match (BSM) to measure the apparent phase speed of propagating EUV disturbances in the running differences of time-distance plots (R) and background-removed and normalised time-distance plots (D).
Results: The methods were applied to the analysis of quasi-periodic EUV disturbances propagating at a coronal fan-structure of active region NOAA11330 on 27 Oct. 2011, observed with the Atmospheric Imaging Assembly (AIA) on SDO in the 171 Å bandpass. The noise propagation in the AIA image processing was estimated, resulting in the preliminary estimation of the uncertainties in the AIA image flux. This information was used in measuring the apparent phase speed of the propagating disturbances with the CFT, DCF and BSM methods, which gave consistent results. The average projected speed is measured at 47.6 ± 0.6 km s-1 and 49.0 ± 0.7 km s-1 for R and D, with the corresponding periods at 179.7 ± 0.2 s and 179.7 ± 0.3 s, respectively. We analysed the effects of the lag time and the detrending time in the running difference processing and the background-removed plot, on the measurement of the speed, and found that they are fairly weak.
Conclusions: The CFT, DCF and BSM methods are found to be reliable techniques for measuring the apparent (projected) phase speed. The samples of larger effective spatial length are more suitable for these methods. Time-distance plots with background removal and normalisation allow for more robust measurements, with little effect of the choice of the detrending time. Cross-fitting technique provides reliable measurements on good samples (e.g. samples with large effective detection length and recurring features). 2D coupled-fitting is found to be sensitive to the initial guess for parameters of the 2D fitting function. Thus DCF is only optimised in measuring one of the parameters (the phase speed in our application), while the period is poorly measured. Best similarity measure is robust for all types of samples and very tolerant to image pre-processing and regularisation (smoothing). Title: Estimating a High-Resolution Lunar Gravity Field and Time-Varying Core Signature Authors: Park, R. S.; Asmar, S. W.; Fahnestock, G. G.; Konopliv, A. S.; Kruizinga, G. L.; Lu, W.; Watkins, M.; Williams, J. G.; Yuan, D. Bibcode: 2011AGUFM.P44B..06P Altcode: An overall Gravity Recovery And Interior Laboratory (GRAIL) mission capability is presented based on a sensitivity analysis considering detailed spacecraft dynamics and kinematics models with realistic measurement uncertainties. Also shown is the effect of various perturbing forces, measurement models, and data arc lengths on overall estimation performance. The largest source of un-modeled error comes from the spacecraft thermal re-radiation force, and in order to characterize its error contribution, an a priori error constraint model is derived based on orbit geometry and expected force magnitude. The result shows that estimating a lunar gravity field is robust against both dynamics and kinematics errors and a nominal field of degree 300 or better can be determined according to the Kaula rule. The core signature, however, is more sensitive to modeling errors and satisfying the science requirement depends on how accurately the spacecraft dynamics can be modeled. Title: Leakage of long-period oscillations from the chromosphere to the corona Authors: Yuan, D.; Nakariakov, V. M.; Chorley, N.; Foullon, C. Bibcode: 2011A&A...533A.116Y Altcode: Long-period oscillations in a coronal diffuse structure are detected with the Transition Region And Coronal Explorer (TRACE). The EUV images of the NOAA active region 8253 are available in 171 Å and 195 Å bandpasses from 30 June to 4 July 1998. The average intensity variation is found to be connected with the CCD temperature, which varies with the orbital motion of the spacecraft. Hence, oscillations with the orbital period and its higher harmonics appear as artifacts in the light curves. After the exclusion of the orbital effects, we identified several long-period oscillations in the diffuse fan-like structure of the active region. Similar periodicities were detected in the radio emission from the chromospheric part of that active region, observed with the ground-based Nobeyama Radioheliograph (NoRH) in the 17 GHz channel. It was found that 0.221, 0.312 and 0.573 mHz oscillations were present in both EUV emission lines in the corona and the radio signal from the sunspot in the chromosphere, just beneath the active region. From the frequency values, the 1st and 3rd detected oscillations could be associated with the l = 2, n = -3 or l = 3, n = -5 and l = 1 gravity-driven solar interior modes, respectively. The appearance of these oscillations in the coronal part of the active region can be connected with the wave leakage or the evanescence of chromospheric oscillations. Title: Arctic Ocean Tides from GRACE Satellite Accelerations Authors: Killett, B.; Wahr, J. M.; Desai, S. D.; Yuan, D.; Watkins, M. M. Bibcode: 2010AGUFM.G51C0680K Altcode: Because missions such as TOPEX/POSEIDON don't extend to high latitudes, Arctic ocean tidal solutions aren't constrained by altimetry data. The resulting errors in tidal models alias into monthly GRACE gravity field solutions at all latitudes. Fortunately, GRACE inter-satellite ranging data can be used to solve for these tides directly. Seven years of GRACE inter-satellite acceleration data are inverted using a mascon approach to solve for residual amplitudes and phases of major solar and lunar tides in the Arctic ocean relative to FES 2004. Simulations are performed to test the inversion algorithm's performance, and uncertainty estimates are derived from the tidal signal over land. Truncation error magnitudes and patterns are compared to the residual tidal signals. Title: Using GRACE Satellite Acceleration Data to Recover Arctic Ocean Tides Authors: Killett, B.; Wahr, J.; Desai, S. D.; Yuan, D.; Watkins, M. Bibcode: 2008AGUFM.G22A..04K Altcode: Arctic ocean tidal solutions are not constrained by altimetry data because missions such as TOPEX/POSEIDON do not extend to high latitudes. The resulting errors in tidal models alias into the monthly GRACE gravity field solutions at all latitudes. Fortunately, it is possible to use the GRACE inter-satellite ranging data to solve for these tides directly. Five years of GRACE inter-satellite acceleration data are inverted to solve for the amplitude and phase of major solar and lunar tides in the Arctic ocean using a mascon approach. The resulting tidal amplitudes are compared to existing tidal models using in-situ data from coastal tide gauges and deep sea bottom pressure recorders. Simulations were performed to verify that the inversion algorithm works as designed. Title: Climate correlations across the MIS 5/4 boundary based on a stalagmite record from Dongge Cave, China Authors: Kelly, M. J.; Cheng, H.; Edwards, R. L.; Yuan, D. X. Bibcode: 2008GeCAS..72R.461K Altcode: No abstract at ADS Title: New 230Th dating methods applied to Chinese caves: Climate change on glacial to cultural timescales Authors: Edwards, R. L.; Cheng, H.; Wang, Y. J.; Yuan, D. X.; An, Z. S.; Kelly, M. J.; Dykoski, C. A.; Wang, X. F. Bibcode: 2008GeCAS..72R.237E Altcode: No abstract at ADS Title: Preliminary Analysis of Arctic Ocean Tides using GRACE Spacecraft Acceleration Data. Authors: Killett, B.; Desai, S.; Yuan, D.; Watkins, M.; Wahr, J. Bibcode: 2007AGUFM.U21C0629K Altcode: Arctic ocean tidal solutions are not constrained by altimetry data because missions such as TOPEX/POSEIDON do not extend to high latitudes. The resulting errors in tidal models alias into the monthly GRACE gravity field solutions at all latitudes. Fortunately, it is possible to use the GRACE inter-satellite ranging data to solve for these tides directly. Five years of GRACE inter-satellite acceleration data are inverted to solve for the amplitude and phase of major solar and lunar tides in the Arctic ocean using a mascon approach. The resulting tidal amplitudes are compared to existing tidal models. Title: Timing and nature of late Quaternary climate change from cave deposits Authors: Edwards, R. L.; Yuan, D. X.; An, Z. S.; Wang, Y. J.; Auler, A. S.; Cheng, H.; Rowe, H.; Wang, X. F.; Kelly, M. J.; Dykoski, C. A. Bibcode: 2006GeCAS..70Q.155E Altcode: No abstract at ADS Title: Marine isotope stage 8 millennial-scale variability as observed in the Asian monsoon Authors: Dykoski, C. A.; Edwards, R. L.; Cheng, H.; Yuan, D.; Wang, Y.; Rowe, H. Bibcode: 2006GeCAS..70R.153D Altcode: No abstract at ADS Title: Validating GRACE-derived static and dynamic gravity field models using long-term geodetic results from Laser ranging and DORIS data. Authors: Deleflie, F.; Willis, P.; Bertiger, W. I.; Berio, P.; Barlier, F.; Yuan, D. N.; Thompson, P. F. Bibcode: 2006cosp...36.1626D Altcode: 2006cosp.meet.1626D The GRACE mission led to a new generation of gravity field models called EIGEN and GGM modelling the static part of the Earth gravity field and also estimating seasonal effects related to mass redistribution in the whole Earth-Ocean-Atmosphere system The goal of this paper is to assess the improvement gained in accuracy when using these new gravity field models to fit orbital arcs of geodetic satellites processing Laser ranging or DORIS tracking data In particular we look at long-term Laser orbits solutions to derive any long-term improvement and at shorter term DORIS orbits looking for a potential removal of systematic seasonal effects In this paper we investigate the impact of the choice for a gravity field model used to propagate the equations of motion on the quality of the geodetic products We therefore use several gravity field models EGM96 GRIM5-S1 two EIGEN models as well as two GGM models We discuss the accuracy and the stability of the fit-derived products built since the beginning of the periods when tracking data are available fit-residuals station coordinates gravity field parameters in particular We also use monthly gravity field solutions elaborated at Jet Propulsion Laboratory JEM to evaluate if the DORIS or the SLR results can provide a more stable pseudo-geocenter determination and verify how annual systematic effects could be removed or not from weekly station coordinate determinations Title: Constraints on Mars' crustal structure from correlations of gravity and areoid with topography Authors: Kucinskas, A.; Yuan, D. -N.; Banerdt, W.; Sjogren, W. Bibcode: 2003EAEJA.....4392K Altcode: Spatial domain point correlations of gravity and areoid with topography on Mars are used to evaluate the extent of isostatic compensation (isostasy) for Martian surface features and constrain mean reference level crustal thickness for areas on the planet where Airy isostasy is a viable support mechanism. Regional correlations are carried out within long-wavelength spatial windows over the surface of Mars using point data values obtained from spherical harmonic solutions for Mars' global gravitational potential (Yuan et al., 2001) and topography (Smith et al., 1999) derived, respectively, from Mars Global Surveyor (MGS) Doppler tracking and altimetry data. We address the influence on Airy crustal thickness modeling results of departures from Mars' hydrostatic shape and areoid (essentially attributed to the Tharsis rise) by considering harmonic expansions for both gravity and topography defined by degrees 4 and 5 through 60. For a given data window location, a linear regression of Bouguer gravity anomalies versus gravity from uncompensated topography yields a regional degree of isostatic compensation C. We find that an appreciable portion of Martian surface topography is substantially isostatically compensated with 70% <= C <= 100% and a mean degree of compensation overline C ∼ 82%. Assuming Airy isostasy, areoid anomaly (N) versus topography variation (h) data within a given window are then compared, in the least squares sense, to theoretical (h,N) correlations for the Airy compensation model yielding a regional crustal thickness at the reference zero elevation H(h=0). For those areas on Mars which meet selection criteria based on significantly compensated topography (70% <= C <= 100%), physically meaningful reference crustal thickness (50 km <= H <= 130 km), and small rms for Airy model fit, we find a mean reference level crustal thickness overline H ∼ 80 km. Regions which satisfy these selection criteria are located essentially along the hemispheric dichotomy boundary zone and within the southern hemisphere highlands (Tharsis rise excluded) including most of the large Hellas impact basin and surroundings. For a 32o × 32o region located in the north east rim of Hellas (NEH) we obtain CNEH ∼ 87%, and HNEH ∼ 83 km, consistent with the obtained mean values. Without crustal recycling, magmatism could have created the thick present-day crust indicated by this study early in Mars' evolution, with a substantial fraction of radiogenic heat producing elements fractionated into the crust. Hypothesizing that the concentration of crustal radiogenic elements on Mars decreases exponentially with depth as for terrestrial continents results in a colder, high viscosity lower crust which could be maintained against relaxation for a significant part of Martian history. Title: Fluid Core Size of Mars from Detection of the Solar Tide Authors: Yoder, C. F.; Konopliv, A. S.; Yuan, D. N.; Standish, E. M.; Folkner, W. M. Bibcode: 2003Sci...300..299Y Altcode: The solar tidal deformation of Mars, measured by its k2 potential Love number, has been obtained from an analysis of Mars Global Surveyor radio tracking. The observed k2 of 0.153 +/- 0.017 is large enough to rule out a solid iron core and so indicates that at least the outer part of the core is liquid. The inferred core radius is between 1520 and 1840 kilometers and is independent of many interior properties, although partial melt of the mantle is one factor that could reduce core size. Ice-cap mass changes can be deduced from the seasonal variations in air pressure and the odd gravity harmonic J3, given knowledge of cap mass distribution with latitude. The south cap seasonal mass change is about 30 to 40% larger than that of the north cap. Title: The Size of Mars' Fluid Core From Mars k2 Love Number Obtained From Analysis of MGS Doppler Tracking. Authors: Yoder, C. F.; Konopliv, A. S.; Yuan, D. N.; Standish, E. M.; Folkner, W. M. Bibcode: 2002AGUFM.P62A0369Y Altcode: The solar tidal deformation of Mars, measured by its k2 potential Love number, has been obtained from analysis of MGS radio tracking. The observed k2 =0.164+-0.016 is large enough to rule out a solid iron core. The inferred core radius Rc (1600km<Rc<1900km) is remarkably independent of interior properties such as temperature, composition (as measured by the molar ratio Mg/(M+Fe)) and crustal thickness, even after correcting for atmospheric thermal tides, mantle anelasticity, spin pole nutations and seasonal changes in shape from ice cap ablation/accretion. One critical model feature is the ability to isolate the second degree and m'th order harmonic components: semidiurnal (m=2), diurnal (m=1) and long period (m=0) and solve for independent k2m parameters. Detection of tides depends on finding reliable, long period signatures since short period changes are too small. A crucial tidal signature is a secular drift in spacecraft orbit inclination related to the sun-synchronous spacecraft orbit and which is seen only in the m=2 tide. In order to minimize the effect of along-track changes on a solution for k22, the drag model solves for a daily coefficient and thus effectively minimizes the influence of the along-track residual signature on this solution parameter. The k21 and k22 coefficients primarily affect the orbit node (k21 has an annual variation) where it is strongly mixed with seasonal changes in Mars' even zonal gravity harmonics (J2, J4). The odd gravity harmonics (J3, J5) are detected through seasonal changes in orbit eccentricity where the influences of tides are weak. The observed J3, J5 amplitudes are consistent with estimates of ice cap mass only if the cap thickness increases with latitude and the south cap is significantly larger than the north cap. Title: JPL Mars Gravity Fields: Recent Model Changes and Results Authors: Konopliv, A. S.; Yuan, D.; Sjogren, W. S.; Yoder, C. F.; Standish, E. M.; Folkner, W. M. Bibcode: 2002AGUFM.P62A0368K Altcode: Over the past year there have been improvements in the models that affect the determination of the gravity field of Mars. The most notable change in the Mars gravity modeling is the change in the Mars orientation model. We have switched from the IAU coordinate system (either 1991 or 2000, e.g. Seidelmann et al., Celes. Mech. and Dyn. Astron. 82, 2002) to the coordinate system used by Mars Pathfinder (Folkner et al., Science 278, 1997). The new orientation model of Mars includes rigid-body nutation, seasonal spin variations, and polar motion. The Mars Pathfinder and Viking lander data have been merged with the MGS tracking data to help constrain the Mars orientation. Other model improvements include the Mars ephemeris and spacecraft component pointing. Together, these model changes have produced promising seasonal trends in the gravity field of Mars as well as detection of the tidal Love number and a new precession solution. In addition, four days of Mars Odyssey tracking data just after completion of aerobraking are included in the more recent gravity solution. This data contains some high frequency gravity information from a 200x500 km orbit with periapse near the equator. Title: GRACE Gravity Field Results from JPL Authors: Watkins, M. M.; Yuan, D.; Bertiger, W.; Kruizinga, G.; Romans, L.; Wu, S. Bibcode: 2002AGUFM.G12B..02W Altcode: The GRACE team at the Jet Propulsion Laboratory have over the past few years adapted the MIRAGE software used for deep space tracking data analysis and determination of the gravity field of planetary bodies such as Mars, Venus, the Moon, and 433 Eros, for GRACE applications. We have used this software to produce Earth gravity fields of unprecedented quality from a combination of the first GRACE K/Ka-band intersatellite tracking, GPS, accelerometer, and star camera data. In this paper we will present the results of that gravity field analysis, including the parameterization used, the spectral content of the residuals, the calibrated covariance, and performance in external tests such as orbit fits and sea surface topography. In addition, since the software and parameterization are independent of that used at the University of Texas and GFZ Potsdam, it provides a type of verification of the fields, and we will discuss the results of the intercomparison of the available gravity solutions. Title: Recent Gravity Models as a Result of the Lunar Prospector Mission Authors: Konopliv, A. S.; Asmar, S. W.; Carranza, E.; Sjogren, W. L.; Yuan, D. N. Bibcode: 2001Icar..150....1K Altcode: The lunar gravity field is determined from the tracking data of previous missions to the Moon with the 1998-1999 Lunar Prospector (LP) mission being the major contributor. LP provided the first measurement of the gravity field in a low polar circular orbit giving complete coverage at high resolution for the entire lunar nearside. However, since there is no direct measurement of the lunar farside from LP or any other mission, gravity details for the farside gravity are greatly limited. Even so, it has become apparent that there are mascons on the farside of the Moon together with the newly identified mascons in the LP data for the lunar nearside. The extended mission low-altitude data (at times less than 10 km above the surface) has gravity information for the nearside to nearly degree and order 180. The 100th-degree lunar gravity models (LP100J and LP100K) extract most of the information from the nominal 100-km altitude. A 165th degree model LP165P attempts to model the extended mission data with some but limited success. This model provides a smooth solution without aliasing when evaluated up to degree 110 allowing for resolution of numerous craters. In addition, a preliminary solution for the lunar Love number is k2=0.026±0.003. Title: A continuous-wave tunable solid-state blue laser based on intracavity sum-frequency mixing and pump-wavelength tuning Authors: Wang, C. Q.; Chow, Y. T.; Gambling, W. A.; Yuan, D. R.; Xu, D.; Zhang, G. H.; Jiang, M. H. Bibcode: 1999ApPhL..75.1821W Altcode: We report on continuous-wave tunable blue-light generation from a Nd:Y3Al15O12 laser by intracavity sum-frequency mixing of its fundamental laser line at 946 nm with the pump light from a tunable Ti:sapphire laser by use of cadmium-mercury-thiocyanate nonlinear crystal. The tunable range of the blue light was 434.4-437.5 nm, and the maximum output power at 436 nm was measured to be 310 μW. Title: CW dual-wavelength Nd:YAG laser at 946 and 938.5 nm and intracavity nonlinear frequency conversion with a CMTC crystal Authors: Wang, C. Q.; Chow, Y. T.; Yuan, D. R.; Xu, D.; Zhang, G. H.; Liu, M. G.; Lu, J. R.; Shao, Z. S.; Jiang, M. H. Bibcode: 1999OptCo.165..231W Altcode: We report on the efficient CW dual-wavelength operation of a Nd:YAG laser at 946 and 938.5 nm. A total output power of 527 mW was obtained with a slope efficiency of 34%. By inserting a cadmium mercury thiocyanate (CMTC) crystal into the Nd:YAG laser cavity, frequency-doubling of 946 nm and sum-frequency-generation of 946 with 938.5 nm were realised simultaneously. Blue light at 473 and 471.1 nm with an output power of 1.6 mW was obtained. Phase matching calculations were also done for the CMTC crystal. Title: Lunar Prospector 100th Degree Gravity Model Development Authors: Konopliv, A. S.; Yuan, D. N. Bibcode: 1999LPI....30.1067K Altcode: The latest Lunar Prospector gravity results will be presented. Currently under development is a 100th degree and order model that has higher resolution and more accurately represents the uncertainties on the farside and nearside than previous models. Title: Radar chain study of the May, 1995 storm Authors: Buonsanto, M. J.; González, S. a.; Pi, X.; Ruohoniemi, J. M.; Sulzer, M. P.; Swartz, W. e.; Thayer, J. P.; Yuan, D. N. Bibcode: 1999JASTP..61..233B Altcode: 1999JATP...61..233B We summarize the main features of the ionospheric F region as observed bythe Sondrestrom, Millstone Hill, Arecibo, and Jicamarca incoherent scatter radars during the 1-5May, 1995 CEDAR Storm Study interval. This paper apparently represents the first study of amajor storm interval using the current incoherent scatter radar chain supported by the U.S.National Science Foundation. We focus most attention on 2-3 May, and include additional datafrom IMP-8, the St. Johns magnetometer, SuperDARN, and global total electron content (TEC)maps from GPS. Three intervals of likely penetration of magnetospheric electric field from high tolow latitude are identified on 2 May. A unique feature of this storm are the strong daytimeequatorward wind surges in the neutral meridional wind observed at Millstone Hill. The first ofthese (at 14 UT on 2 May) is apparently due to a travelling atmospheric disturbance launched byintense frictional and Joule heating as observed at Sondrestrom. An evening enhancement in NmF2 (the dusk effect) is typically seen only on the first day of a geomagneticstorm. However, during this storm a strong dusk effect is seen at Millstone Hill on 2, 3, and 4May, associated with the equatorward wind surges. A penetrating eastward electric field alsocontributed to the dusk effect on 2 May. A large rise in hmF2 at Arecibo near0000 UT on 3 May is due to the same eastward electric field, which penetrates to the equator,causing a strong upward plasma drift at Jicamarca. This apparently results in a polewardexpansion of the equatorial anomaly zones as seen in GPS total electron content, and an increasein NmF2 at Arecibo to the largest value seen at midnight in several years. Title: Interior Structure and Seasonal Mass Redistribution of Mars from Radio Tracking of Mars Pathfinder Authors: Folkner, W. M.; Yoder, C. F.; Yuan, D. N.; Standish, E. M.; Preston, R. A. Bibcode: 1997Sci...278.1749F Altcode: No abstract at ADS Title: Comparison of ionospheric models for single-frequency radar altimeters Authors: Urban, T.; Shum, C.; Kruizinga, G.; Tapley, B.; Bilitza, D.; Yuan, D. Bibcode: 1997AdSpR..20.1769U Altcode: Relative performances of available ionospheric models for computing path delay corrections to radar altimeter range data have been assessed using altimeter crossover measurements computed for the single-frequency altimeter measurements collected by Geosat and ERS-1, and for the dual-frequency altimeter measurements collected by TOPEX/POSEIDON. The models studied include IRI-90, IRI-95, and JPL GIM. The models are further compared with the ionospheric delay computed from TOPEX/POSEIDON dual-frequency altimeter data. Crossover analyses indicate that IRI-95 is an improved model over IRI-90 for computing ionospheric delays for all three altimetric satellites during low to medium solar activity periods. It is found that smoothing of the TOPEX/POSEIDON dual-frequency ionospheric correction significantly improved the precision of the TOPEX/POSEIDON data. Title: Preparation and Properties of a Complex Crystal for Nonlinear Optical Applications: Cadmium Mercury Thiocyanate Authors: Jiang, M.; Yuan, D.; Liu, M.; Xu, D. Bibcode: 1996SPIE.2778..804J Altcode: No abstract at ADS Title: The Research of the Time Variation of H2O Master Authors: Yuan, D. L. Xiang T.; Yu, Z. Y. Bibcode: 1991Ap&SS.186...21Y Altcode: No abstract at ADS Title: An Improved Model for the Earth's Gravity Field Authors: Shum, C. K.; Tapley, B. D.; Yuan, D. N.; Ries, J. C.; Schutz, B. E. Bibcode: 1990ggg..conf...97S Altcode: No abstract at ADS Title: Determination of the gravitational coefficient of the Earth from near-Earth satellites Authors: Ries, J. C.; Eanes, R. J.; Huang, C.; Schutz, B. E.; Shum, C. K.; Tapley, B. D.; Watkins, M. M.; Yuan, D. N. Bibcode: 1989GeoRL..16..271R Altcode: Laser range, doppler and altimeter data collected from 14 near-Earth satellites have been combined to determine the value of the geocentric gravitational coefficient (GM) of the Earth. A long-arc solution using 3 years of laser range data to Lageos was used in a separate determination in which the effects of general relativity were investigated. The value of GM (including the mass of the atmosphere) was determined to be 398600.4405 km³/sec² when all corrections for general relativity are taken into account. The uncertainty (1-σ) in the value of GM is estimated to be 0.001 km³/sec². Title: Circulation from a joint gravity field solution determination of the general ocean Authors: Tapley, B. D.; Nerem, R. S.; Shum, C. K.; Ries, J. C.; Yuan, D. N. Bibcode: 1988GeoRL..15.1109T Altcode: With the development of satellite altimetry, it is possible to infer the geostrophic velocity of the surface ocean currents, if the geoid and the position of the satellite are known accurately. Errors in current geoid models and orbit computations, both due primarily to errors in the Earth's gravity field model, have limited the use of altimeter data for this purpose. The objective of this investigation is to demonstrate that altimeter data can be used in a joint solution to simultaneously estimate the quasi-stationary sea surface topography, ζ, and the model for the gravity field. Satellite tracking data from twelve satellites were used along with Seasat altimeter data for the solution. The estimated model of ζ compares well at long wavelengths with the hydrographic model of ζ. Covariance analysis indicates that the geoid is separable from ζ up to degree 9, at which point geoid error is comparable to the signal of ζ. Title: An improved model for the earth's gravity field. Authors: Tapley, B. D.; Schutz, B. E.; Shum, C. K.; Ries, J. C.; Yuan, D. N. Bibcode: 1988agfm.conf..125T Altcode: Two gravity models, PTGF2 and PTGF2A, each complete to degree and order 36 plus resonant coefficients, were generated. Ground-based tracking data collected by 15 satellites and Seasat altimeter crossover data were used to determine the PTGF2 gravity field model. PTGF2A contains direct altimeter data in addition to all the data in PTGF2. Evaluations based on orbit fits and gravity anomaly residuals indicate that the gravity models have achieved a significant advancement over previously existing gravity models.