explanation blue bibcodes open ADS page with paths to full text
Author name code: yuan
ADS astronomy entries on 2022-09-14
author:"Yuan, Ding"
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Title: Inter-Correlation Between Sunspot Oscillations and Their
Internal Structures
Authors: Fu, Libo; Zhu, Zizhan; Yuan, Ding; Wang, Jiaoyang; Feng,
Song; Anfinogentov, Sergey
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.
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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
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.
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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
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.
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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
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.
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Title: Dynamics of the Transversal Magnetic Fields in Photospheric
Quiet Regions
Authors: Liu, Yanxiao; Jiang, Chaowei; Yuan, Ding; Zuo, Pingbing
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 ×
10<SUP>15</SUP> 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.
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Title: Persistent fast kink magnetohydrodynamic waves detected in
a quiescent prominence
Authors: Li, Dong; Xue, Jianchao; Yuan, Ding; Ning, Zongjun
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.
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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.
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<SUP>-1</SUP>,
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.
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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
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.
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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.
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 (C<SUP>4+</SUP>) in collision with CO<SUB>2</SUB>, 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.
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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
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.
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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.
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.
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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.
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.
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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
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.
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Title: Slow-Mode Magnetoacoustic Waves in Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Yuan, Ding; Reale, Fabio;
Kolotkov, Dmitrii Y.; Srivastava, Abhishek K.
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.
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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
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.
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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
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 H<SUB>α</SUB> (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 H<SUB>α</SUB> data. We interpret this oscillatory signal as a
propagating slow sausage wave. The propagation speed is estimated at
about 8 km s<SUP>-1</SUP>. We infer that this sunspot's umbra could
have temperature as low as 2800-3500 K.
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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.
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. <BR /> Aims: Using
numerical simulations, we study Alfvén wave propagation and dissipation
in a magnetic flux tube and their heating effect. <BR /> 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. <BR /> 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<SUP>-1</SUP> 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. <BR />
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.
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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
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <P />Movie is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038433/olm">https://www.aanda.org</A>
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Title: Magnetic Connectivity between the Light Bridge and Penumbra
in a Sunspot
Authors: Feng, Song; Miao, Yuhu; Yuan, Ding; Qu, Zhongquan; Nakariakov,
Valery M.
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.
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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
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
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
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.
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Title: Multilayered Kelvin-Helmholtz Instability in the Solar Corona
Authors: Yuan, Ding; Shen, Yuandeng; Liu, Yu; Li, Hongbo; Feng,
Xueshang; Keppens, Rony
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.
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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
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<SUP>-1</SUP>. 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.
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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.
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
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).
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Title: Non-damping oscillations at flaring loops
Authors: Li, D.; Yuan, D.; Su, Y. N.; Zhang, Q. M.; Su, W.; Ning, Z. J.
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. <BR /> Aims: We combine the imaging and spectroscopic
measurements of available space missions, and investigate the properties
of non-damping oscillations at flaring loops. <BR /> 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. <BR /> 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<SUP>-1</SUP> and 1.9
km s<SUP>-1</SUP>, 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. <BR /> 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. <P />The movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832991/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: First Imaging Observation of Standing Slow Wave in Coronal
Fan Loops
Authors: Pant, V.; Tiwari, A.; Yuan, D.; Banerjee, D.
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<SUP>-1</SUP>. 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.
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
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.
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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.
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
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
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.
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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
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.
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 <SUB>0</SUB>) and
studying the density contrast ({δ }<SUB>ρ </SUB>) and correlation
length (L <SUB> c </SUB>) that characterize the randomness of the
equilibrium density profiles. For small-amplitude pulses, {δ }<SUB>ρ
</SUB> does not alter \bar{p} significantly. Large-amplitude pulses,
on the other hand, enhance the density contrast when {δ }<SUB>ρ
</SUB> is small but have a smoothing effect when {δ }<SUB>ρ
</SUB> is sufficiently large. We found that \bar{p} scales linearly
with L <SUB> c </SUB> 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.
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
∼10<SUP>9</SUP> 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
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.
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
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
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
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 <SUB> d </SUB>)
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 <SUB> d </SUB>
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.
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
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.
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<SUP>-1</SUP> 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
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.
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.
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.
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.
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
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.
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.
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.
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. <BR
/> 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. <BR /> 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. <BR />
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. <BR /> 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.
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. <BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP> to ~600
km s<SUP>-1</SUP>. 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.
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.
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
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.
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. <BR /> Aims: We design and test tools to reliably measure
the apparent phase speed of propagating disturbances in imaging data
sets. <BR /> 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). <BR /> 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<SUP>-1</SUP> and 49.0 ± 0.7 km
s<SUP>-1</SUP> 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. <BR /> 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.
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.
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.
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.
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.
2008GeCAS..72R.461K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: New <SUP>230</SUP>Th 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.
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.
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.
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.
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.
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.
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 32<SUP>o</SUP> × 32<SUP>o</SUP>
region located in the north east rim of Hellas (NEH) we obtain
C<SUB>NEH</SUB> ∼ 87%, and H<SUB>NEH</SUB> ∼ 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.
2003Sci...300..299Y Altcode:
The solar tidal deformation of Mars, measured by its k<SUB>2</SUB>
potential Love number, has been obtained from an analysis of Mars Global
Surveyor radio tracking. The observed k<SUB>2</SUB> 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 J<SUB>3</SUB>,
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 k<SUB>2</SUB> 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.
2002AGUFM.P62A0369Y Altcode:
The solar tidal deformation of Mars, measured by its k<SUB>2</SUB>
potential Love number, has been obtained from analysis of MGS radio
tracking. The observed k<SUB>2</SUB> =0.164+-0.016 is large enough to
rule out a solid iron core. The inferred core radius R<SUB>c</SUB>
(1600km<R<SUB>c<1900</SUB>km) 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 k<SUB>2m</SUB>
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 k<SUB>22</SUB>, 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
k<SUB>21</SUB> and k<SUB>22</SUB> coefficients primarily affect
the orbit node (k<SUB>21</SUB> has an annual variation) where it
is strongly mixed with seasonal changes in Mars' even zonal gravity
harmonics (J<SUB>2,</SUB> J<SUB>4</SUB>). The odd gravity harmonics
(J<SUB>3</SUB>, J<SUB>5</SUB>) are detected through seasonal changes in
orbit eccentricity where the influences of tides are weak. The observed
J<SUB>3</SUB>, J<SUB>5</SUB> 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.
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.
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.
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 k<SUB>2</SUB>=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.
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.
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.
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.
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 NmF<SUB>2</SUB> (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 hmF<SUB>2</SUB> 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
NmF<SUB>2</SUB> 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.
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.
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.
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.
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.
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.
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.
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.
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.
