explanation      blue bibcodes open ADS page with paths to full text
Author name code: tian
ADS astronomy entries on 2022-09-14
author:"Tian, Hui"

---------------------------------------------------------
Title: Statistical investigation of the kinematic and thermal
    properties of supra-arcade downflows observed during a solar flare
Authors: Tan, Guangyu; Hou, Yijun; Tian, Hui
2022MNRAS.tmp.2292T    Altcode: 2022arXiv220814737T
  Supra-arcade downflows (SADs) are dark structures descending towards
  post-reconnection flare loops observed in extreme ultraviolet or X-ray
  observations and are closely related to magnetic reconnection during
  solar flares. Due to the lack of statistical study on SADs in a single
  flare, evolutions of kinematic and thermal properties of SADs during
  the flare process still remain obscure. In this work, we identified 81
  SADs in a flare that occurred on 2013 May 22 using observations of the
  Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  (SDO). The kinematic properties of each SAD, including the appearance
  time, height, projective velocity, and acceleration were recorded. We
  found that the appearance heights of SADs become larger during the
  flare, which is likely due to the lift of the bottom of the plasma
  sheet. In the flare decay phase, the region where SADs mainly appear
  moves from the north part to the south side possibly related to
  a secondary eruption in the south side. The trajectories of most
  SADs can be fitted by one or two deceleration processes, while some
  special ones have positive accelerations during the descent. For the
  thermal properties, we selected 54 SADs, whose front and body could be
  clearly distinguished from the surrounding during the entire descent,
  to perform Differential Emission Measure analysis. It is revealed that
  the temperatures of the SAD front and body tend to increase during
  their downward courses, and the relationship between the density and
  temperature indicates that the heating is mainly caused by adiabatic
  compression.

---------------------------------------------------------
Title: Magnetoseismology for the solar corona: from  10 Gauss to
    coronal magnetograms
Authors: Yang, Zihao; Gibson, Sarah; He, Jiansen; Del Zanna, Giulio;
   Tomczyk, Steven; Morton, Richard; McIntosh, Scott; Wang, Linghua;
   Karak, Bidya Binay; Samanta, Tanmoy; Tian, Hui; Chen, Yajie; Bethge,
   Christian; Bai, Xianyong
2022cosp...44.2490Y    Altcode:
  Magnetoseismology, a technique of magnetic field diagnostics based
  on observations of magnetohydrodynamic (MHD) waves, has been widely
  used to estimate the field strengths of oscillating structures in
  the solar corona. However, previously magnetoseismology was mostly
  applied to occasionally occurring oscillation events, providing
  an estimate of only the average field strength or one-dimensional
  distribution of field strength along an oscillating structure. This
  restriction could be eliminated if we apply magnetoseismology to the
  pervasive propagating transverse MHD waves discovered with the Coronal
  Multi-channel Polarimeter (CoMP). Using several CoMP observations of
  the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
  the plasma density and wave phase speed in the corona, which allow us
  to map both the strength and direction of the coronal magnetic field
  in the plane of sky. We also examined distributions of the electron
  density and magnetic field strength, and compared their variations
  with height in the quiet Sun and active regions. Such measurements
  could provide critical information to advance our understanding of the
  Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

---------------------------------------------------------
Title: A new post-hoc flat field measurement method for the Solar
    X-ray and Extreme Ultraviolet Imager onboard the Fengyun-3E satellite
Authors: Song, Qiao; Bai, Xianyong; Chen, Bo; Hu, Xiuqing; Chen,
   Yajie; Hou, Zhenyong; Zhang, Xiaofan; He, Lingping; Song, Kefei;
   Zhang, Peng; Wang, Jing-Song; Zhang, Xiaoxin; Zong, Weiguo; Dun,
   Jinping; Tian, Hui; Deng, Yuanyong
2022arXiv220701829S    Altcode:
  The extreme ultraviolet (EUV) observations are widely used in
  solar activity research and space weather forecasting since they
  can observe both the solar eruptions and the source regions of
  the solar wind. Flat field processing is indispensable to remove
  the instrumental non-uniformity of a solar EUV imager in producing
  high-quality scientific data from original observed data. Fengyun-3E
  (FY-3E) is a meteorological satellite operated in Sun-synchronous orbit,
  and the routine EUV imaging data from the Solar X-ray and Extreme
  Ultraviolet Imager (X-EUVI) onboard FY-3E has the characteristics
  of concentric rotation. Taking advantage of the concentric rotation,
  we propose a post-hoc flat field measurement method for its EUV 195
  channel in this paper. This method removes small-scale and time-varying
  component of the coronal activities by taking the median value for
  each pixel along the time axis of a concentric rotation data cube,
  and then derives large-scale and invariable component of the quiet
  coronal radiation, and finally generates a flat field image. Analysis
  shows that our method is able to measure the instrumental spot-like
  non-uniformity possibly caused by contamination on the detector, which
  mostly disappears after the in-orbit self-cleaning process. It can
  also measure the quasi-periodic grid-like non-uniformity, possibly
  from the obscuration of the support mesh on the rear filter. After
  flat field correction, these instrumental non-uniformities from the
  original data are effectively removed. X-EUVI 195 data after dark and
  flat field corrections are consistent with the 193 channel data from
  SDO/AIA, verifying the suitability of the method. Our method is not
  only suitable for FY-3E/X-EUVI but also a candidate method for the
  flat field measurement of future solar EUV telescopes.

---------------------------------------------------------
Title: Sun-as-a-star spectroscopic observations of the line-of-sight
    velocity of a solar eruption on 2021 October 28
Authors: Xu, Yu; Yang, Zihao; Tian, Hui; Chamberlin, Phillip; Gao,
   Yuhang; Bai, Xianyong
2022cosp...44.1387X    Altcode:
  The propagation direction and the actual speed of the coronal
  mass ejection (CME), which are the most decisive factors for its
  geo-effectiveness, are difficult to determine through single-perspective
  imaging observations. Here we show that Sun-as-a-star spectroscopic
  observations, together with imaging observations, could allow us
  to achieve this goal. Using observations of the Extreme-ultraviolet
  Variability Experiment (EVE) onboard the Solar Dynamics Observatory,
  we found clear blue-shifted secondary emission components of
  extreme ultraviolet spectral lines during a solar eruption on 2021
  Oct. 28. From simultaneous imaging observations, we found that the
  secondary components are caused by mass ejection from the flare
  site. We estimated the line-of-sight (LOS) velocity of the ejecta
  both from the double Gaussian fitting method and the red-blue (RB)
  asymmetry analysis. The results of both methods agree well with
  each other, and the average LOS velocity of the plasma is around 420
  km/s. The plane-of-sky (POS) velocity, around 560 km/s, from the Solar
  Terrestrial Relation Observatory-A (STEREO-A) view is measured using
  the 30.4 nm images series taken by the Extreme Ultraviolet Imager
  onboard STEREO-A. The actual velocity of the ejecta is then computed
  by combining the imaging and spectroscopic observations, which turns
  out to be around 569 km/s with an angel of around 42.4$^\circ$ to the
  west of the Sun-Earth line. Our analysis suggests that the heating
  of the plasma to a temperature of around 0.2 MK causes the filament
  region to become as bright as the flare one, which leads to the obvious
  blue-shifted components in the transition region line profiles.

---------------------------------------------------------
Title: Cross-Loop Propagation of a Quasi-Periodic Extreme-Ultraviolet
    Wave Triggered by a Solar Eruption
Authors: Sun, Zheng; Chen, P. F.; Tian, Hui; Yao, Shuo; Hou, Zhenyong;
   Chen, Hechao; Gao, Yuhang
2022cosp...44.2499S    Altcode:
  Extreme-ultraviolet (EUV) waves refer to large-scale disturbances
  propagating outward from sites of solar eruptions in EUV narrow-band
  imaging observations of the Sun. These waves are normally single pulses
  propagating radially from the eruption sites. Using observations
  from the Atmospheric Imaging Assembly (AIA) on board the Solar
  Dynamics Observatory, we report a very rare case of EUV wave,
  which is characterized by quasi-periodic propagation across coronal
  loops. Excited by an M1.7-class solar flare occurring at NOAA active
  region 12887 on 2 November 2021, the wave exhibits slow and fast
  components. The slow component, whose average speed is about 103
  km/s, appears to originate from the opening of coronal loops at one
  footpoint. The fast component represents a relatively large disturbance,
  propagating across the coronal loops at an average speed of about
  308 km/s. There is no significant decrease in the speeds of both
  components. A wavelet analysis reveals that the periods of the slow and
  fast components are both ~132 s, which is close to the period of the
  quasi-periodic pulsations (QPP) at the flare ribbon, ~158 s. We suggest
  that the slow component is caused by successive opening and expansion
  of coronal loops, and that the fast component represents fast-mode
  magnetoacoustic wave trains triggered by the loop expansion. The
  quasi-periodic loop opening is likely accompanied by an intermittent
  energy release process that heats the flare ribbon quasi-periodically.

---------------------------------------------------------
Title: Detection of flare-associated plasma flows in the stellar
    corona of EV Lac with X-ray spectroscopy
Authors: Chen, Hechao; Tian, Hui; Lu, Hong-Peng; Hou, Zhenyong; Xu,
   Yu; Wu, Yuchuan
2022cosp...44.1385C    Altcode:
  Stellar flares are characterized by sudden enhancement of
  electromagnetic radiation from the atmospheres of stars. Compared
  to their solar counterparts, our knowledge on the coronal plasma
  dynamics during stellar flares and their connection to coronal mass
  ejections remains very limited. With time-resolved high-resolution
  X-ray spectroscopic observations of three strong stellar flares
  on an active M dwarf EV Lac from the CHANDRA X-ray observatory, we
  detected noticeable flare-associated plasma flows through Doppler shift
  measurements of strong coronal emission lines from ions such as O VIII
  (3 MK), Mg XII (10 MK), and Si XIV (16 MK). The plasma flow pattern in
  the decay phase of one flare event, including a weak redshift (below
  90 km s$ ^{-1}$) in the Si XIV line and persistent blueshifts (around
  70-120 km s$ ^{-1}$) in the O VIII and Mg XII lines, indicates that
  this event may occur with a possible filament eruption and shrinking
  high-temperature post-flare loops. Moreover, evidences for explosive
  and gentle chromospheric evaporation were found in another two flares,
  respectively. For the explosive one, we simultaneously detected hot
  evaporating flows with a velocity up to 150 km s$ ^{-1}$ in the Si XIV
  line and cooler condensation downflows with a velocity of 40-75 km s$
  ^{-1}$ in the O VIII and Mg XII lines; for the gentle one, only weak
  evaporating flows with a velocity of 50-80 km s$ ^{-1}$ appear in
  the Si XIV and Mg XII lines. During this two flares, variable line
  emission fluxes in He-like triplets of Si XIII further reveal an
  increase of electron density from 10$ ^{12}$ up to 10$ ^{13}$ cm$
  ^{-3}$ and a temperature rise from 3 MK up to 6$-$7 MK.

---------------------------------------------------------
Title: Transient small-scale brightenings in the quiet solar corona:
    a model for campfires observed with Solar Orbiter
Authors: Chen, Yajie; Peter, Hardi; Berghmans, David; Tian, Hui;
   Auchère, Frédéric; Przybylski, Damien
2022cosp...44.2557C    Altcode:
  Recent observations by the Extreme Ultraviolet Imager (EUI) on
  board Solar Orbiter have revealed prevalent small-scale transient
  brightenings in the quiet solar corona termed "campfires". To
  understand the generation mechanism of these coronal brightenings,
  we constructed a self-consistent and time-dependent quiet-Sun
  model extending from the upper convection zone to the lower corona
  using a realistic three-dimensional radiation magnetohydrodynamic
  simulation. From the model we have synthesized the coronal emission
  in the EUI 174 passband. We identified several transient coronal
  brightenings similar to those in EUI observations. The size and
  lifetime of these coronal brightenings are mostly 0.5-4 Mm and ~2 min,
  respectively. These brightenings are generally located at a height of
  2-4 Mm above the photosphere, and the local plasma is often heated
  above 1 MK. By examining the magnetic field structures before and
  after the occurrence of brightenings, we concluded that these coronal
  brightenings are generated by component magnetic reconnection between
  interacting bundles of magnetic field lines or neighboring field lines
  within highly twisted flux ropes. Occurring in the coronal part of
  the atmosphere, these events generally reveal no obvious signature
  of flux emergence or cancellation in photospheric magnetograms. These
  transient coronal brightenings may play an important role in heating
  of the local coronal plasma.

---------------------------------------------------------
Title: On the detectability of solar and stellar coronal mass
    ejections through asymmetries of extreme-ultraviolet spectral line
    profiles
Authors: Yang, Zihao; Guo, Yang; Tian, Hui; Chen, Yajie; Chen, Hechao;
   Gao, Yuhang; Bai, Xianyong; Zhu, Yingjie; Zhang, Jiale
2022cosp...44.1383Y    Altcode:
  Coronal mass ejections (CMEs) are the largest-scale eruptive phenomena
  in the solar system. Associated with enormous plasma ejections and
  energy release, CMEs have an important impact on the solar-terrestrial
  environment. CMEs can also occur on other stars and will greatly
  impact the habitability of the orbiting exoplanets around the hosting
  stars. Therefore, the detection of stellar CMEs and how stellar CMEs
  affect the space environments are indispensable when evaluating the
  habitability of exoplanets. Observationally, solar CMEs could result
  in the asymmetries of spectral line profiles. However, few studies have
  concentrated on whether we can detect solar and stellar CME signals and
  accurately diagnose CME properties through line profile asymmetries. In
  this work, we constructed a geometric CME model and derived the
  analytical expressions for full-disk integrated extreme ultraviolet
  (EUV) line profiles during CMEs. For different CME properties and
  instrumental conditions, full disk-integrated line profiles were
  synthesized. We further evaluated the detectability and diagnostic
  potential of CMEs from the synthetic line profiles. Our investigations
  provide important constraints on the future design of spectrographs
  for solar and stellar CME detections through EUV line asymmetries.

---------------------------------------------------------
Title: Decayless oscillations in solar coronal bright points
Authors: Gao, Yuhang; van Doorsselaere, Tom; Tian, Hui; Chen, Yajie
2022cosp...44.2496G    Altcode:
  Decayless kink oscillations of solar coronal loops (or decayless
  oscillations for short) have attracted great attention since their
  discovery. Coronal bright points (CBPs) are mini-active regions and
  consist of loops with a small size. However, decayless oscillations
  in CBPs have not been widely reported. In this study, we identified
  this kind of oscillations in some CBPs using 171 \r{A}, images taken
  by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
  Observatory (SDO). After using the motion magnification algorithm to
  increase oscillation amplitudes, we made time-distance maps to identify
  the oscillatory signals. We also estimated the loop lengths and velocity
  amplitudes. We analyzed 23 CBPs, and found 31 oscillation events in 16
  of them. The oscillation periods range from 1 to 8 minutes (on average
  about 5 minutes), and the displacement amplitudes have an average value
  of 0.07 Mm. The average loop length and velocity amplitude are 23 Mm
  and 1.57 km s$ ^{-1}$, respectively. Relationships between different
  oscillation paraments are also examined. Additionally, we performed
  a simple forward model to illustrate how these sub-pixel oscillation
  amplitudes (less than 0.4 Mm) could be detected. Results of the model
  confirm the reliability of our data processing methods. Our study
  shows for the first time that decayless oscillations are common in
  small-scale loops of CBPs. These oscillations may play an important
  role in coronal heating in the quiet Sun and coronal holes. They also
  allow for seismological diagnostics of the Alfv\'{e}n speed and magnetic
  field strength in the corona.

---------------------------------------------------------
Title: Coronal Microjets in Quiet-sun Regions Observed with the
    Extreme Ultraviolet Imager Onboard Solar Orbiter
Authors: Hou, Zhenyong; He, Jiansen; Berghmans, David; Teriaca, Luca;
   Wang, Linghua; Schuehle, Udo; Tian, Hui; Chen, Yajie; Chen, Hechao;
   Gao, Yuhang; Bai, Xianyong
2022cosp...44.2536H    Altcode:
  We report the smallest coronal jets ever observed in the quiet Sun
  with recent high resolution observations from the High Resolution
  Telescopes (HRI-EUV and HRI-Lyα) of the Extreme Ultraviolet
  Imager (EUI) onboard Solar Orbiter. In the HRI-EUV (174 Å) images,
  these microjets usually appear as nearly collimated structures with
  brightenings at their footpoints. Their average lifetime, projected
  speed, width, and maximum length are 4.6 min, 62 km $s^{-1}$, 1.0 Mm,
  and 7.7 Mm, respectively. Inverted-Y shaped structures and moving blobs
  can be identified in some events. A subset of these events also reveal
  signatures in the HRI-Lyα (H I Lyα at 1216 Å) images and the extreme
  ultraviolet images taken by the Atmospheric Imaging Assembly onboard the
  Solar Dynamics Observatory. Our differential emission measure analysis
  suggests a multi-thermal nature and an average density of ~1.4x10^9
  $cm^{-3}$ for these microjets. Their thermal and kinetic energies were
  estimated to be ~3.9x10$^{24}$ erg and ~2.9x10$^{23}$ erg, respectively,
  which are of the same order of the released energy predicted by the
  nanoflare theory. Most events appear to be located at the edges of
  network lanes and magnetic flux concentrations, suggesting that these
  coronal microjets are likely generated by magnetic reconnection between
  small-scale magnetic loops and the adjacent network field.

---------------------------------------------------------
Title: Broadening and red asymmetry of Halpha line profiles observed
    by LAMOST during a stellar flare on an M-type star
Authors: Wu, Yuchuan; He, Han; Zhang, Liyun; Tian, Hui; Lu, Hong-Peng;
   Chen, Hechao; Xu, Yu; Shi, Jianrong; Wang, Haifeng
2022cosp...44.1384W    Altcode:
  Stellar flares are characterized by sudden enhancement of
  electromagnetic radiation in stellar atmospheres. So far much of our
  understanding of stellar flares comes from photometric observations,
  from which plasma motions in flare regions could not be detected. From
  the spectroscopic data of LAMOST DR7, we have found one stellar
  flare that is characterized by an impulsive increase followed by a
  gradual decrease in the H$\alpha$ line intensity on an M4-type star,
  and the total energy radiated through H${\alpha}$ is estimated to be
  on the order of $10^{33}$ erg. The H$\alpha$ line appears to have
  a Voigt profile during the flare, which is likely caused by Stark
  pressure broadening due to the dramatic increase of electron density
  and/or opacity broadening due to the occurrence of strong non-thermal
  heating. Obvious enhancement has been identified at the red wing of the
  H$\alpha$ line profile after the impulsive increase of the H$\alpha$
  line intensity. The red wing enhancement corresponds to plasma moving
  away from the Earth at a velocity of 100$-$200 km s$^{-1}$. According
  to the current knowledge of solar flares, this red wing enhancement
  may originate from: (1) flare-driven coronal rain, (2) chromospheric
  condensation, or (3) a filament/prominence eruption that either with a
  non-radial backward propagation or with strong magnetic suppression. The
  total mass of the moving plasma is estimated to be on the order of
  $10^{15}$ kg.

---------------------------------------------------------
Title: Possible detection of coronal mass ejections on late-type
    main-sequence stars in LAMOST medium-resolution spectra
Authors: Lu, Hong-Peng; Tian, Hui
2022cosp...44.1381L    Altcode:
  Context. Stellar coronal mass ejections (CMEs) are the main source
  of the stellar space weather and they could affect the habitability
  of neighboring planets. Large-sample time-domain spectral data are
  currently unavailable for the detection of stellar CMEs. Aims. This work
  aims to detect stellar CMEs from spectra continuously observed through
  the LAMOST Medium-Resolution Spectroscopic Survey (LAMOST-MRS). Our
  sample includes 1,379,408 LAMOST-MRS spectra of 226,194 late-type
  main-sequence stars (T$ _{eff}$ < 6000 K, log[g/(cm s$ ^{-2}$)] >
  4). Methods. We first identified stellar CME candidates by examining
  the asymmetry of H$\alpha$ lines, and then performed double Gaussian
  fitting for H$\alpha$ contrast profiles (differences between CME
  spectra and reference spectra) of the CME candidates to analyze the
  temporal variation of the asymmetric component. Results. Four stellar
  CME candidates were detected, one of which originates from a G-type
  Sun-like star, and the other three are from M-type dwarfs. The Mg I
  triplet (5168.94 Å, 5174.13 Å, 5185.10 Å) and the H$\alpha$ line of
  candidate 1 exhibit a blue wing enhancement, and the corresponding
  Doppler shift of this enhancement shows a gradually increasing
  trend. The host star of candidate 2 is a G5-type Sun-like star. The
  emission of the H$\alpha$ blue wing of this candidate gradually
  increases, and the corresponding maximum Doppler velocity is close to
  the stellar surface escape velocity. The H$\alpha$ line shows an obvious
  blue wing enhancement in candidate 3. In candidate 4, the H$\alpha$
  line shows an obvious red wing enhancement, and the corresponding
  maximum Doppler velocity exceeds the surface escape velocity of the
  host star. The lower limit of the CME mass was estimated to be 8.84
  × $10^{17}$ g to 3.02 × $10^{20}$ g for these four candidates.

---------------------------------------------------------
Title: Possible detection of coronal mass ejections on late-type
    main-sequence stars in LAMOST medium-resolution spectra
Authors: Lu, Hong-peng; Tian, Hui; Zhang, Li-yun; Karoff, Christoffer;
   Chen, He-chao; Shi, Jian-rong; Hou, Zhen-yong; Chen, Ya-jie; Xu, Yu;
   Wu, Yu-chuan; Cao, Dong-tao; Wang, Jiang-tao
2022A&A...663A.140L    Altcode: 2022arXiv220509972L
  Context. Stellar coronal mass ejections (CMEs) are the primary driver
  of exoplanetary space weather and may affect the habitability of
  exoplanets. However, detections of possible stellar CME signatures are
  extremely rare. <BR /> Aims: This work aims to detect stellar CMEs from
  time-domain spectra observed through the LAMOST Medium-Resolution
  Spec-troscopic Survey (LAMOST-MRS). Our sample includes 1 379
  408 LAMOST-MRS spectra of 226 194 late-type main-sequence stars
  (T<SUB>eff</SUB> &lt; 6000 K, log[g/(cm s<SUP>−2</SUP>)] &gt;
  4.0). <BR /> Methods: We first identified stellar CME candidates by
  examining the asymmetries of Hα line profiles and then performed double
  Gaussian fitting for Hα contrast profiles (differences between the
  CME spectra and reference spectra) of the CME candidates to analyse the
  temporal variation in the asymmetric components. <BR /> Results: Three
  stellar CME candidates were detected on three M dwarfs. The Hα and Mg I
  triplet lines (at 5168.94 Å, 5174.13 Å, and 5185.10 Å) of candidate
  1 all exhibit a blue-wing enhancement, and the corresponding Doppler
  shift of this enhancement shows a gradually increasing trend. The Hα
  line also shows an obvious blue-wing enhancement in candidate 2. In
  candidate 3, the Hα line shows an obvious red-wing enhancement,
  and the corresponding projected maximum velocity exceeds the surface
  escape velocity of the host star. The lower limit of the CME mass
  is estimated to be ~8 × 10<SUP>17</SUP> g to 4 × 10<SUP>18</SUP>
  g for these three candidates.

---------------------------------------------------------
Title: Three-dimensional Propagation of the Global EUV Wave associated
    with a solar eruption on 2021 October 28
Authors: Hou, Zhenyong; Wang, Jing-Song; Zhang, Xiaoxin; Zhang, Peng;
   Chen, Bo; Tian, Hui; Chen, Yajie; Chen, Hechao; Bai, Xianyong; Xu, Yu
2022cosp...44.2484H    Altcode:
  We present a case study for the global extreme ultraviolet (EUV) wave
  and its chromospheric counterpart `Moreton-Ramsey wave' associated
  with the second X-class flare in Solar Cycle 25 and a halo coronal
  mass ejection (CME). The EUV wave was observed in the H$\alpha$
  and EUV passbands with different characteristic temperatures. In the
  171\,\AA\ and 193/195\,\AA\ images, the wave propagates circularly
  with an initial velocity of 600--720\,km\,s$^{-1}$ and a deceleration
  of 110--320\,m\,s$^{-2}$. The local coronal plasma is heated from
  log(T/K)$\approx$5.9 to log(T/K)$\approx$6.2 during the passage of the
  wavefront. The H$\alpha$ and 304\,\AA\ images also reveal signatures
  of wave propagation with a velocity of 310--540\,km\,s$^{-1}$. With
  multi-wavelength and dual-perspective observations, we found that the
  wavefront likely propagates forwardly inclined to the solar surface
  with a tilt angle of $\sim$53.2$^{\circ}$. Our results suggest that
  this EUV wave is a fast-mode magnetohydrodynamic wave or shock driven
  by the expansion of the associated CME, whose wavefront is likely
  a dome-shaped structure that could impact the upper chromosphere,
  transition region and corona.

---------------------------------------------------------
Title: Detection of Flare-induced Plasma Flows in the Corona of EV
    Lac with X-Ray Spectroscopy
Authors: Chen, Hechao; Tian, Hui; Li, Hao; Wang, Jianguo; Lu, Hongpeng;
   Xu, Yu; Hou, Zhenyong; Wu, Yuchuan
2022ApJ...933...92C    Altcode: 2022arXiv220514293C
  Stellar flares are characterized by sudden enhancement of
  electromagnetic radiation from the atmospheres of stars. Compared to
  their solar counterparts, our knowledge on the coronal plasma dynamics
  of stellar flares and their connection to coronal mass ejections
  remains very limited. With time-resolved high-resolution spectroscopic
  observations from the Chandra X-ray Observatory, we detected noticeable
  coronal plasma flows during several stellar flares on a nearby dMe
  star EV Lac. In the observed spectra of O VIII (3 MK), Fe XVII (6
  MK), Mg XII (10 MK), and Si XIV (16 MK) lines, these flare-induced
  upflows/downflows appear as significant Doppler shifts of several tens
  to 130 km s<SUP>-1</SUP> , and the upflow velocity generally increases
  with temperature. Variable line ratios of the Si XIII triplet reveal
  that this plasma flows in most flares are accompanied by an increase
  in the coronal plasma density and temperature. We interpret these
  results as X-ray evidence of chromospheric evaporation on EV Lac. In
  two successive flares, the plasma flow pattern and a sharp increase
  of the measured coronal density are highly suggestive of explosive
  evaporation. The transition from redshifts to blueshifts in such an
  explosive evaporation occurs at a temperature of at least 10 MK,
  much higher than that observed in solar flares (~1 MK). However,
  in one flare the cool and warm upflows appear to be accompanied by
  a decreasing plasma density, which might be explained by a stellar
  filament/prominence eruption coupled to this flare. These results
  provide important clues to understanding the coronal plasma dynamics
  during flares on M dwarfs.

---------------------------------------------------------
Title: Global Hg cycle over Ediacaran-Cambrian transition and its
    implications for environmental and biological evolution
Authors: Wu, Yaowen; Yin, Runsheng; Li, Chao; Chen, Di; Grasby,
   Stephen E.; Li, Tengfei; Ji, Sui; Tian, Hui; Peng, Ping'an
2022E&PSL.58717551W    Altcode:
  The Ediacaran-Cambrian (E-C) transition witnessed remarkable
  environmental changes, the extinction of the Ediacaran biota, and
  subsequent rapid diversification of Cambrian animals. However, the
  linkages between environmental and biological evolution are still under
  debate at this critical time. Here, we present new Hg abundance and Hg
  isotopes in sediments from South China, which are then combined with
  those published from the Indian craton to explore the co-evolution
  of environment and complex life during the E-C transition. In
  both areas, high Hg/TOC ratios and near-zero Δ<SUP>199</SUP>Hg of
  the Late Ediacaran sediments suggest enhanced volcanism, whereas
  relatively high Hg/TOC ratios and positive Δ<SUP>199</SUP>Hg shift
  upsection indicate volcanic-sourced atmospheric Hg(II) deposition in
  the earliest Cambrian. The dramatically decreasing Hg/TOC ratios and
  positive Δ<SUP>199</SUP>Hg of early Cambrian Age 2 to 3 sediments
  indicate scavenging of dissolved seawater Hg(II) by organic matter
  particulates. Our Hg results suggest volcanism may have likely
  played a significant role in the extinction of Ediacaran biota and
  global negative carbon excursions near the E-C boundary. Furthermore,
  our Hg data provides new evidence of extensive OM burial in the early
  Cambrian Age 2 to 3 oceans, leading to a rapid increase of Earth-surface
  O<SUB>2</SUB> levels that coincided with appearance of more complex
  large-body animals. Our study provides new insights of the global Hg
  cycle into the co-evolution of the environment and complex life at
  this critical time.

---------------------------------------------------------
Title: Implications for Additional Plasma Heating Driving the
    Extreme-ultraviolet Late Phase of a Solar Flare with Microwave
    Imaging Spectroscopy
Authors: Zhang, Jiale; Chen, Bin; Yu, Sijie; Tian, Hui; Wei, Yuqian;
   Chen, Hechao; Tan, Guangyu; Luo, Yingjie; Chen, Xingyao
2022ApJ...932...53Z    Altcode: 2022arXiv220503518Z
  Extreme-ultraviolet late phase (ELP) refers to the second
  extreme-ultraviolet (EUV) radiation enhancement observed in certain
  solar flares, which usually occurs tens of minutes to several hours
  after the peak of soft X-ray emission. The coronal loop system that
  hosts the ELP emission is often different from the main flaring arcade,
  and the enhanced EUV emission therein may imply an additional heating
  process. However, the origin of the ELP remains rather unclear. Here
  we present the analysis of a C1.4 flare that features such an ELP,
  which is also observed in microwave wavelengths by the Expanded Owens
  Valley Solar Array. Similar to the case of the ELP, we find a gradual
  microwave enhancement that occurs about 3 minutes after the main
  impulsive phase microwave peaks. Radio sources coincide with both foot
  points of the ELP loops and spectral fits on the time-varying microwave
  spectra demonstrate a clear deviation of the electron distribution
  from the Maxwellian case, which could result from injected nonthermal
  electrons or nonuniform heating to the footpoint plasma. We further
  point out that the delayed microwave enhancement suggests the presence
  of an additional heating process, which could be responsible for the
  evaporation of heated plasma that fills the ELP loops, producing the
  prolonged ELP emission.

---------------------------------------------------------
Title: Can We Detect Coronal Mass Ejections through Asymmetries of
    Sun-as-a-star Extreme-ultraviolet Spectral Line Profiles?
Authors: Yang, Zihao; Tian, Hui; Bai, Xianyong; Chen, Yajie; Guo,
   Yang; Zhu, Yingjie; Cheng, Xin; Gao, Yuhang; Xu, Yu; Chen, Hechao;
   Zhang, Jiale
2022ApJS..260...36Y    Altcode: 2022arXiv220403683Y
  Coronal mass ejections (CMEs) are the largest-scale eruptive phenomena
  in the solar system. Associated with enormous plasma ejections and
  energy releases, CMEs have an important impact on the solar-terrestrial
  environment. Accurate predictions of the arrival times of CMEs at
  the Earth depend on precise measurements of their 3D velocities,
  which can be achieved by using simultaneous line-of-sight (LOS)
  and plane-of-sky (POS) observations. Besides the POS information from
  routine coronagraph and extreme-ultraviolet (EUV) imaging observations,
  spectroscopic observations could unveil the physical properties of
  CMEs, including their LOS velocities. We propose that spectral line
  asymmetries measured by Sun-as-a-star spectrographs can be used for
  routine detections of CMEs and estimations of their LOS velocities
  during their early propagation phases. Such observations can also
  provide important clues for the detection of CMEs on other solar-like
  stars. However, few studies have concentrated on whether we can detect
  CME signals and accurately diagnose CME properties through Sun-as-a-star
  spectral observations. In this work, we construct a geometric CME
  model and derive the analytical expressions for full disk-integrated
  EUV line profiles during CMEs. For different CME properties and
  instrumental configurations, the full disk-integrated line profiles
  are synthesized. We further evaluate the detectability and diagnostic
  potential of CMEs from the synthetic line profiles. Our investigations
  provide important constraints on the future design of Sun-as-a-star
  spectrographs for CME detections through EUV line asymmetries.

---------------------------------------------------------
Title: Sun-as-a-star Spectroscopic Observations of the Line-of-sight
    Velocity of a Solar Eruption on 2021 October 28
Authors: Xu, Yu; Tian, Hui; Hou, Zhenyong; Yang, Zihao; Gao, Yuhang;
   Bai, Xianyong
2022ApJ...931...76X    Altcode: 2022arXiv220411722X
  The propagation direction and true velocity of a solar coronal
  mass ejection, which are among the most decisive factors for its
  geo-effectiveness, are difficult to determine through single-perspective
  imaging observations. Here we show that Sun-as-a-star spectroscopic
  observations, together with imaging observations, could allow us
  to solve this problem. Using observations of the Extreme Ultraviolet
  Variability Experiment onboard the Solar Dynamics Observatory, we found
  clear blueshifted secondary emission components in extreme-ultraviolet
  spectral lines during a solar eruption on 2021 October 28. From
  simultaneous imaging observations, we found that the secondary
  components are caused by a mass ejection from the flare site. We
  estimated the line-of-sight (LOS) velocity of the ejecta from both the
  double Gaussian fitting method and the red-blue asymmetry analysis. The
  results of both methods agree well with each other, giving an average
  LOS velocity of the plasma of ~423 km s<SUP>-1</SUP>. From the 304 Å
  image series taken by the Extreme ultraviolet Imager onboard the Solar
  Terrestrial Relation Observatory-A (STEREO-A) spacecraft, we estimated
  the plane-of-sky velocity from the STEREO-A viewpoint to be around
  587 km s<SUP>-1</SUP>. The full velocity of the bulk motion of the
  ejecta was then computed by combining the imaging and spectroscopic
  observations, which turns out to be around 596 km s<SUP>-1</SUP> with
  an angle of 42.°4 to the west of the Sun-Earth line and 16.°0 south
  to the ecliptic plane.

---------------------------------------------------------
Title: Doppler shifts of spectral lines formed in the solar transition
    region and corona
Authors: Chen, Yajie; Peter, Hardi; Przybylski, Damien; Tian, Hui;
   Zhang, Jiale
2022A&A...661A..94C    Altcode: 2022arXiv220304691C
  Context. Emission lines formed in the transition region and corona
  dominantly show redshifts and blueshifts, respectively. <BR
  /> Aims: We investigate the Doppler shifts in a 3D radiation
  magnetohydrodynamic (MHD) model of the quiet Sun and compare these
  to observed properties. We concentrate on Si IV 1394 Å originating
  in the transition region and examine the Doppler shifts of several
  other spectral lines at different formation temperatures. <BR />
  Methods: We constructed a radiation MHD model extending from the upper
  convection zone to the lower corona using the MURaM code. In this
  quiet Sun model, the magnetic field is self-consistently maintained
  by the action of a small-scale dynamo in the convection zone, and it
  is extrapolated to the corona as an initial condition. We synthesized
  the profiles of several optically thin emission lines, which formed at
  temperatures from the transition region into the corona. We investigated
  the spatial structure and coverage of redshifts and blueshifts and how
  this changes with the line-formation temperature. <BR /> Results: The
  model successfully reproduces the observed change of average net Doppler
  shifts from redshifted to blueshifted from the transition region into
  the corona. In particular, the model shows a clear imbalance of area
  coverage of redshifts versus blueshifts in the transition region of
  ca. 80% to 20%, even though it is even a bit larger on the real Sun. We
  determine that (at least) four processes generate the systematic Doppler
  shifts in our model, including pressure enhancement in the transition
  region, transition region brightenings unrelated to coronal emission,
  boundaries between cold and hot plasma, and siphon-type flows. <BR
  /> Conclusions: We show that there is not a single process that is
  responsible for the observed net Doppler shifts in the transition
  region and corona. Because current 3D MHD models do not yet fully
  capture the evolution of spicules, which is one of the key ingredients
  of the chromosphere, most probably these have yet to be added to the
  list of processes responsible for the persistent Doppler shifts.

---------------------------------------------------------
Title: VizieR Online Data Catalog: WD binary pathways survey. V. Gaia
    WD+AFGK binaries (Ren+, 2020)
Authors: Ren, J. -J.; Raddi, R.; Rebassa-Mansergas, A.; Hernandez,
   M. S.; Parsons, S. G.; Irawati, P.; Rittipruk, P.; Schreiber, M. R.;
   Gansicke, B. T.; Torres, S.; Wang, H. -J.; Zhang, J. -B.; Zhao, Y.;
   Zhou, Y. -T.; Han, Z. -W.; Wang, B.; Liu, C.; Liu, X. -W.; Wang, Y.;
   Zheng, J.; Wang, J. -F.; Zhao, F.; Cui, K. -M.; Shi, J. -R.; Tian, H.
2022yCat..19050038R    Altcode:
  We observed 93 white dwarf and A-, F-, G-, or K-type main-sequence
  star (WD+AFGK) candidates during 23 nights, spanning 2017-Dec-12 to
  2018-Jun-27, from the Xinglong 2.16m telescope (XL216). The instrument
  terminal we used was the High Resolution fiber-fed Spectrograph (HRS),
  thus providing Echelle spectra of a 49800 resolving power for a fixed
  slit width of 0.19mm, and covering the ~3650-10000Å wavelength
  range. <P />Eight nights of observations (between 2017-Jul-06 and
  2018-Jan-16) were carried out using the Echelle spectrograph attached
  to the 2.12m telescope at the San Pedro Martir Observatory in Baja
  California, Mexico. The corresponding resolving power is R~20000 for
  a slit width of 2.8", covering the 3650-7300Å wavelength range. <P
  />Finally, we obtained 264 high-resolution spectra for 104 WD+AFGK
  candidates, each of them having at least two spectra obtained on
  different nights. <P />(4 data files).

---------------------------------------------------------
Title: Decayless Oscillations in Solar Coronal Bright Points
Authors: Gao, Yuhang; Tian, Hui; Van Doorsselaere, Tom; Chen, Yajie
2022ApJ...930...55G    Altcode: 2022arXiv220317034G
  Decayless kink oscillations of solar coronal loops (or decayless
  oscillations for short) have attracted great attention since their
  discovery. Coronal bright points (CBPs) are mini-active regions and
  consist of loops with a small size. However, decayless oscillations
  in CBPs have not been widely reported. In this study, we identified
  this kind of oscillations in some CBPs using 171 Å images taken
  by the Atmospheric Imaging Assembly on board the Solar Dynamics
  Observatory. After using the motion magnification algorithm to increase
  oscillation amplitudes, we made time-distance maps to identify the
  oscillatory signals. We also estimated the loop lengths and velocity
  amplitudes. We analyzed 23 CBPs and found 31 oscillation events in 16
  of them. The oscillation periods range from 1 to 8 minutes (on average
  about 5 minutes), and the displacement amplitudes have an average value
  of 0.07 Mm. The average loop length and velocity amplitude are 23 Mm and
  1.57 km s<SUP>-1</SUP>, respectively. Relationships between different
  oscillation parameters are also examined. Additionally, we performed a
  simple model to illustrate how these subpixel oscillation amplitudes
  (less than 0.4 Mm) could be detected. Results of the model confirm
  the reliability of our data processing methods. Our study shows for
  the first time that decayless oscillations are common in small-scale
  loops of CBPs. These oscillations allow for seismological diagnostics
  of the Alfvén speed and magnetic field strength in the corona.

---------------------------------------------------------
Title: Broadening and Redward Asymmetry of Hα Line Profiles Observed
    by LAMOST during a Stellar Flare on an M-type Star
Authors: Wu, Yuchuan; Chen, Hechao; Tian, Hui; Zhang, Liyun; Shi,
   Jianrong; He, Han; Lu, Hongpeng; Xu, Yu; Wang, Haifeng
2022ApJ...928..180W    Altcode: 2022arXiv220302292W
  Stellar flares are characterized by sudden enhancement of
  electromagnetic radiation in stellar atmospheres. So far, much of our
  understanding of stellar flares has come from photometric observations,
  from which plasma motions in flare regions could not be detected. From
  the spectroscopic data of LAMOST DR7, we have found one stellar
  flare that is characterized by an impulsive increase followed by a
  gradual decrease in the Hα line intensity on an M4-type star, and the
  total energy radiated through Hα is estimated to be of the order of
  10<SUP>33</SUP> erg. The Hα line appears to have a Voigt profile during
  the flare, which is likely caused by Stark pressure broadening due to
  the dramatic increase in electron density and/or opacity broadening due
  to the occurrence of strong nonthermal heating. Obvious enhancement
  has been identified in the red wing of the Hα line profile after
  the impulsive increase in the Hα line intensity. The red-wing
  enhancement corresponds to plasma moving away from the Earth at
  a velocity of 100-200 km s<SUP>-1</SUP>. According to our current
  knowledge of solar flares, this red-wing enhancement may originate
  from: (1) flare-driven coronal rain, (2) chromospheric condensation,
  or (3) a filament/prominence eruption either with nonradial backward
  propagation or with strong magnetic suppression. The total mass of
  the moving plasma is estimated to be of the order of 10<SUP>15</SUP> kg.

---------------------------------------------------------
Title: Three-dimensional Propagation of the Global Extreme-ultraviolet
    Wave Associated with a Solar Eruption on 2021 October 28
Authors: Hou, Zhenyong; Tian, Hui; Wang, Jing-Song; Zhang, Xiaoxin;
   Song, Qiao; Zheng, Ruisheng; Chen, Hechao; Chen, Bo; Bai, Xianyong;
   Chen, Yajie; He, Lingping; Song, Kefei; Zhang, Peng; Hu, Xiuqing;
   Dun, Jinping; Zong, Weiguo; Song, Yongliang; Xu, Yu; Tan, Guangyu
2022ApJ...928...98H    Altcode: 2022arXiv220213051H
  We present a case study for the global extreme-ultraviolet (EUV) wave
  and its chromospheric counterpart the Moreton-Ramsey Wave associated
  with the second X-class flare in Solar Cycle 25 and a halo coronal
  mass ejection (CME). The EUV wave was observed in the Hα and EUV
  passbands with different characteristic temperatures. In the 171 Å
  and 193/195 Å images, the wave propagates circularly with an initial
  velocity of 600-720 km s<SUP>-1</SUP> and a deceleration of 110-320
  m s<SUP>-2</SUP>. The local coronal plasma is heated from log(T/K)
  ≍ 5.9 to log(T/K) ≍ 6.2 during the passage of the wave front. The
  Hα and 304 Å images also reveal signatures of wave propagation with
  a velocity of 310-540 km s<SUP>-1</SUP>. With multiwavelength and
  dual-perspective observations, we found that the wave front likely
  propagates forwardly inclined to the solar surface with a tilt angle
  of ~53°.2. Our results suggest that this EUV wave is a fast-mode
  magnetohydrodynamic wave or shock driven by the expansion of the
  associated CME, whose wave front is likely a dome-shaped structure
  that could impact the upper chromosphere, transition region, and corona.

---------------------------------------------------------
Title: Coronal condensation as the source of transition-region
    supersonic downflows above a sunspot
Authors: Chen, Hechao; Tian, Hui; Li, Leping; Peter, Hardi; Chitta,
   Lakshmi Pradeep; Hou, Zhenyong
2022A&A...659A.107C    Altcode: 2021arXiv211201354C
  Context. Plasma loops or plumes rooted in sunspot umbrae often harbor
  downflows with speeds of 100 km s<SUP>−1</SUP>. These downflows
  are supersonic at transition region temperatures of ∼0.1 MK. The
  source of these flows is not well understood. <BR /> Aims: We aim
  to investigate the source of sunspot supersonic downflows (SSDs)
  in active region 12740 using simultaneous spectroscopic and imaging
  observations. <BR /> Methods: We identified SSD events from multiple
  raster scans of a sunspot by the Interface Region Imaging Spectrograph,
  and we calculated the electron densities, mass fluxes, and velocities
  of these SSDs. The extreme-ultraviolet (EUV) images provided by the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and
  the EUV Imager onboard the Solar Terrestrial Relations Observatory were
  employed to investigate the origin of these SSDs and their associated
  coronal rain. <BR /> Results: Almost all the identified SSDs appear
  at the footpoints of sunspot plumes and are temporally associated
  with the appearance of chromospheric bright dots inside the sunspot
  umbra. Dual-perspective EUV imaging observations reveal a large-scale
  closed magnetic loop system spanning the sunspot region and a remote
  region. We observed that the SSDs are caused by repeated coronal
  rain that forms and flows along these closed magnetic loops toward the
  sunspot. One episode of coronal rain clearly indicates that reconnection
  near a coronal X-shaped structure first leads to the formation of
  a magnetic dip. Subsequently, hot coronal plasma catastrophically
  cools from ∼2 MK in the dip region via thermal instability. This
  results in the formation of a transient prominence in the dip, from
  which the cool gas mostly slides into the sunspot along inclined
  magnetic fields under the gravity. This drainage process manifests
  as a continuous rain flow, which lasts for ∼2 h and concurrently
  results in a nearly steady SSD event. The total mass of condensation
  (1.3 × 10<SUP>14</SUP> g) and condensation rate (1.5 × 10<SUP>10</SUP>
  g s<SUP>−1</SUP>) in the dip region were found to be sufficient to
  sustain this long-lived SSD event, which has a mass transport rate of
  0.7 − 1.2 × 10<SUP>10</SUP> g s<SUP>−1</SUP>. <BR /> Conclusions:
  Our results demonstrate that coronal condensation in magnetic dips
  can result in the quasi-steady sunspot supersonic downflows. <P
  />Movies associated to Figs. 1, 3, 6, 7, and 11 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202142093/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Stellar parameters of a Young
    Stellar Snake (Tian, 2020)
Authors: Tian, H. -J.
2022yCat..19040196T    Altcode:
  In this study, we mainly use the astrometric and photometric data from
  Gaia DR2. <P />(1 data file).

---------------------------------------------------------
Title: VizieR Online Data Catalog: LAMOST Time-Domain survey, first
    results (Wang+, 2021)
Authors: Wang, S.; Zhang, H. -T.; Bai, Z. -R.; Yuan, H. -L.; Xiang,
   M. -S.; Zhang, B.; Hou, W.; Zuo, F.; Du, B.; Li, T. -D.; Yang, F.;
   Cui, K. -M.; Wang, Y. -L.; Li, J.; Kovalev, M.; Li, C. -Q.; Tian,
   H.; Zong, W. -K.; Han, H. -G.; Liu, C.; Luo, A. -L.; Shi, J. -R.;
   Fu, J. -N.; Bi, S. -L.; Han, Z. -W.; Liu, J. -F.
2022yCatp040002104W    Altcode:
  We performed this survey with both the LRS and MRS observations. For
  LRS observation, the wavelength coverage is 3650-9000Å (Luo et al.,
  2015RAA....15.1095L). For MRS observation, the blue and red arms cover
  wavelength ranges from 4950Å to 5350Å and from 6300Å to 6800Å,
  respectively (Liu et al., 2020, in prep. arXiv:2005.07210). The LRS
  survey of each plate was observed with 3-10 single 600s exposures in
  one observation night; the MRS survey of each plate was observed with
  3-8 single 1200s exposures. <P />(6 data files).

---------------------------------------------------------
Title: Research Progress of Decayless Oscillations in the Solar Corona
Authors: Gao, Y. H.; Tian, H.; Guo, M. Z.; Li, B.
2022AcASn..63....1G    Altcode:
  Decayless transverse kink oscillations of solar coronal loops (or
  decayless oscillations for short) have attracted great attention since
  their discovery. In contrast to the previously reported decaying kink
  oscillations, they are not associated with any external impulsive
  events and are found to show no obvious decay of amplitude. Besides,
  their ubiquitous existence suggests that they might play an important
  role in the process of coronal heating and diagnostics of the
  properties of coronal loops. In this review, we summarize the research
  progress of decayless oscillations. The observational results include
  their amplitude, period, scaling rules, polarization and multiple
  harmonics. We also introduce different types of theoretical models on
  their generation mechanisms. Moreover, we also give some examples of
  their application in coronal seismology. In the last section of this
  review, we discuss future perspectives on the research of decayless
  oscillations.

---------------------------------------------------------
Title: Magnetoseismology for the solar corona: from  10 Gauss to
    coronal magnetograms
Authors: Yang, Zihao; Bethge, Christian; Tian, Hui; Tomczyk, Steven;
   Morton, Richard; Del Zanna, Giulio; McIntosh, Scott; Karak, Bidya
   Binay; Gibson, Sarah; Samanta, Tanmoy; He, Jiansen; Chen, Yajie; Bai,
   Xianyong; Wang, Linghua
2021AGUFMSH12C..07Y    Altcode:
  Magnetoseismology, a technique of magnetic field diagnostics based
  on observations of magnetohydrodynamic (MHD) waves, has been widely
  used to estimate the field strengths of oscillating structures in
  the solar corona. However, previously magnetoseismology was mostly
  applied to occasionally occurring oscillation events, providing
  an estimate of only the average field strength or one-dimensional
  distribution of field strength along an oscillating structure. This
  restriction could be eliminated if we apply magnetoseismology to the
  pervasive propagating transverse MHD waves discovered with the Coronal
  Multi-channel Polarimeter (CoMP). Using several CoMP observations of
  the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
  the plasma density and wave phase speed in the corona, which allow us
  to map both the strength and direction of the coronal magnetic field
  in the plane of sky. We also examined distributions of the electron
  density and magnetic field strength, and compared their variations
  with height in the quiet Sun and active regions. Such measurements
  could provide critical information to advance our understanding of the
  Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

---------------------------------------------------------
Title: Magnitude and Uncertainty of Nitrous Oxide Emissions From
North America Based on Bottom-Up and Top-Down Approaches: Informing
    Future Research and National Inventories
Authors: Xu, R.; Tian, H.; Pan, N.; Thompson, R. L.; Canadell,
   J. G.; Davidson, E. A.; Nevison, C.; Winiwarter, W.; Shi, H.; Pan,
   S.; Chang, J.; Ciais, P.; Dangal, S. R. S.; Ito, A.; Jackson, R. B.;
   Joos, F.; Lauerwald, R.; Lienert, S.; Maavara, T.; Millet, D. B.;
   Raymond, P. A.; Regnier, P.; Tubiello, F. N.; Vuichard, N.; Wells,
   K. C.; Wilson, C.; Yang, J.; Yao, Y.; Zaehle, S.; Zhou, F.
2021GeoRL..4895264X    Altcode:
  We synthesized N<SUB>2</SUB>O emissions over North America using 17
  bottom-up (BU) estimates from 1980-2016 and five top-down (TD) estimates
  from 1998 to 2016. The BU-based total emission shows a slight increase
  owing to U.S. agriculture, while no consistent trend is shown in TD
  estimates. During 2007-2016, North American N<SUB>2</SUB>O emissions
  are estimated at 1.7 (1.0-3.0) Tg N yr<SUP>-1</SUP> (BU) and 1.3
  (0.9-1.5) Tg N yr<SUP>-1</SUP> (TD). Anthropogenic emissions were twice
  as large as natural fluxes from soil and water. Direct agricultural
  and industrial activities accounted for 68% of total anthropogenic
  emissions, 71% of which was contributed by the U.S. Our estimates of
  U.S. agricultural emissions are comparable to the EPA greenhouse gas
  (GHG) inventory, which includes estimates from IPCC tier 1 (emission
  factor) and tier 3 (process-based modeling) approaches. Conversely,
  our estimated agricultural emissions for Canada and Mexico are twice
  as large as the respective national GHG inventories.

---------------------------------------------------------
Title: Stellar Coronal Magnetic Field Measurements Based on the
    Magnetic-field-induced Transition Theory
Authors: Liu, Xianyu; Chen, Yajie; Tian, Hui; Bai, Xianyong; Jin,
   Meng; Li, Wenxian; Yang, Yang; Yang, Zihao; Deng, Yuanyong
2021AGUFMSH15G2091L    Altcode:
  Measurements of the magnetic field in the stellar coronae are extremely
  difficult. Recently, it was proposed that the magnetic-field-induced
  transition (MIT) of the Fe X 257 Å line can be used to measure the
  coronal magnetic field of the Sun. We performed forward modeling with
  a series of global stellar magnetohydrodynamics models to investigate
  the possibility of extending this method to other late-type stars. We
  first synthesized the emissions of several Fe X lines for each stellar
  model, then calculated the magnetic field strengths using the intensity
  ratios of Fe X 257 Å to several other Fe X lines based on the MIT
  theory. Finally, we compared the derived field strengths with those in
  the models, and concluded that this method can be used to measure at
  least the coronal magnetic field strengths of stars with a mean surface
  magnetic flux density about one order of magnitude higher than that of
  the Sun. Our investigation suggests the need of an extreme ultraviolet
  spectrometer to perform routine measurements of the stellar coronal
  magnetic field.

---------------------------------------------------------
Title: Transient small-scale brightenings in the quiet solar corona:
    A model for campfires observed with Solar Orbiter
Authors: Chen, Yajie; Przybylski, Damien; Peter, Hardi; Tian, Hui;
   Auchère, F.; Berghmans, D.
2021A&A...656L...7C    Altcode: 2021arXiv210410940C
  Context. Recent observations by the Extreme Ultraviolet Imager (EUI) on
  board Solar Orbiter have characterized prevalent small-scale transient
  brightenings in the corona above the quiet Sun termed campfires. <BR />
  Aims: In this study we search for comparable brightenings in a numerical
  model and then investigate their relation to the magnetic field and the
  processes that drive these events. <BR /> Methods: We used the MURaM
  code to solve the 3D radiation magnetohydrodynamic equations in a box
  that stretches from the upper convection zone to the corona. The model
  self-consistently produces a supergranular network of the magnetic
  field and a hot corona above this quiet Sun. For the comparison with
  the model, we synthesized the coronal emission as seen by EUI in its
  174 Å channel, isolated the seven strongest transient brightenings,
  and investigated the changes of the magnetic field in and around these
  in detail. <BR /> Results: The transients we isolated have a lifetime of
  about 2 min and are elongated loop-like features with lengths around 1
  Mm to 4 Mm. They tend to occur at heights of about 2 Mm to 5 Mm above
  the photosphere, a bit offset from magnetic concentrations that mark
  the bright chromospheric network, and they reach temperatures of above
  1 MK. As a result, they very much resemble the larger campfires found
  in observations. In our model most events are energized by component
  reconnection between bundles of field lines that interact at coronal
  heights. In one case, we find that untwisting a highly twisted flux
  rope initiates the heating. <BR /> Conclusions: Based on our study, we
  propose that the majority of campfire events found by EUI are driven
  by component reconnection and our model suggests that this process
  significantly contributes to the heating of the corona above the quiet
  Sun. <P />Movies associated to Figs. 2, 4, 5, and A1 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202140638/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Possible Signature of Sausage Waves in Photospheric Bright
    Points
Authors: Gao, Yuhang; Li, Fuyu; Li, Bo; Cao, Wenda; Song, Yongliang;
   Tian, Hui; Guo, Mingzhe
2021SoPh..296..184G    Altcode: 2021arXiv211211756G
  Sausage waves have been frequently reported in solar magnetic structures
  such as sunspots, pores, and coronal loops. However, they have not been
  unambiguously identified in photospheric bright points (BPs). Using
  high-resolution TiO image sequences obtained with the Goode Solar
  Telescope at the Big Bear Solar Observatory, we analyzed four isolated
  BPs. It was found that their area and average intensity oscillate
  for several cycles in an in-phase fashion. The oscillation periods
  range from 100 to 200 seconds. We interpreted the phase relation as a
  signature of sausage waves, particularly slow waves, after discussing
  sausage-wave theory and the opacity effect.

---------------------------------------------------------
Title: Campfires observed by EUI: What have we learned so far?
Authors: Berghmans, David; Auchere, F.; Zhukov, Andrei; Mierla,
   Marilena; Chen, Yajie; Peter, Hardi; Panesar, Navdeep; Chitta, Lakshmi
   Pradeep; Antolin, Patrick; Aznar Cuadrado, Regina; Tian, Hui; Hou,
   Zhenyong; Podladchikova, Olena
2021AGUFMSH21A..02B    Altcode:
  Since its very first light images of the corona, the EUI/HRIEUV
  telescope onboard Solar Orbiter has observed small localised
  brightenings in the Quiet Sun. These small localised brightenings,
  have become known as campfires, and are observed with length scales
  between 400 km and 4000 km and durations between 10 sec and 200
  sec. The smallest and weakest of these HRIEUV brightenings have
  not been previously observed. Simultaneous observations from the
  EUI High-resolution Lyman- telescope (HRILYA) do not show localised
  brightening events, but the locations of the HRIEUV events clearly
  correspond to the chromospheric network. Comparisons with simultaneous
  AIA images shows that most events can also be identified in the
  17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although
  they appear weaker and blurred. Some of the larger campfires have
  the appearance of small interacting loops with the brightening
  expanding from the contact point of the loops. Our differential
  emission measure (DEM) analysis indicated coronal temperatures. We
  determined the height for a few of these campfires to be between 1
  and 5 Mm above the photosphere. We interpret these events as a new
  extension to the flare-microflare-nanoflare family. Given their low
  height, the EUI campfires could stand as a new element of the fine
  structure of the transition region-low corona, that is, as apexes
  of small-scale loops that undergo internal heating all the way up to
  coronal temperatures. 3D MHD simulations with the MURaM code revealed
  brightenings that are in many ways similar to the campfires by EUI. The
  brightenings in the simulations suggest that campfires are triggered by
  component reconnection inside flux bundles rather than flux emergence
  or cancellation. Nevertheless, some of the observed campfires can
  be clearly linked to flux cancellation events and, intriguingly,
  are preceded by an erupting cool plasma structure. Analysis of the
  dynamics of campfires revealed that some have the appearance of coronal
  microjets, the smallest coronal jets observed in the quiet Sun. The
  HRIEUV images also reveal transient jets on a somewhat bigger scale
  with repeated outflows on the order of 100 km s1. In this paper we
  will provide an overview of the campfire related phenomena that EUI
  has observed and discuss the possible relevance for coronal heating.

---------------------------------------------------------
Title: Forward Modeling of Solar Coronal Magnetic Field Measurements
    Based on a Magnetic-field-induced Transition in Fe X
Authors: Chen, Yajie; Li, Wenxian; Tian, Hui; Chen, Feng; Bai,
   Xianyong; Yang, Yang; Yang, Zihao; Liu, Xianyu; Deng, Yuanyong
2021AGUFMSH12C..06C    Altcode:
  It was recently proposed that the intensity ratios of several extreme
  ultraviolet spectral lines from the Fe X ion can be used to measure
  the solar coronal magnetic field based on the magnetic-field-induced
  transition (MIT) theory. To verify the suitability of this method,
  we performed forward modeling with a three-dimensional radiation
  magnetohydrodynamic model of a solar active region. Intensities of
  several spectral lines from Fe X were synthesized from the model. Based
  on the MIT theory, intensity ratios of the MIT line Fe x 257 A to
  several other Fe X lines were used to derive the magnetic field
  strengths, which were then compared with the field strengths in the
  model. We also developed a new method to simultaneously estimate the
  coronal density and temperature from the Fe X 174/175 and 184/345
  A line ratios. Using these estimates, we demonstrated that the MIT
  technique can provide reasonably accurate measurements of the coronal
  magnetic field in both on-disk and off-limb solar observations. Our
  investigation suggests that a spectrometer that can simultaneously
  observe the Fe X 174, 175, 184, 257, and 345 A lines and allow an
  accurate radiometric calibration for these lines is highly desired to
  achieve reliable measurements of the coronal magnetic field. We have
  also evaluated the impact of the uncertainty in the Fe X 3p4 3d 4D5/2
  and 4D7/2 energy difference on the magnetic field measurements.

---------------------------------------------------------
Title: Magnetohydrodynamic Waves in Open Coronal Structures
Authors: Banerjee, D.; Krishna Prasad, S.; Pant, V.; McLaughlin, J. A.;
   Antolin, P.; Magyar, N.; Ofman, L.; Tian, H.; Van Doorsselaere, T.;
   De Moortel, I.; Wang, T. J.
2021SSRv..217...76B    Altcode: 2020arXiv201208802B
  Modern observatories have revealed the ubiquitous presence of
  magnetohydrodynamic waves in the solar corona. The propagating waves
  (in contrast to the standing waves) are usually originated in the lower
  solar atmosphere which makes them particularly relevant to coronal
  heating. Furthermore, open coronal structures are believed to be the
  source regions of solar wind, therefore, the detection of MHD waves
  in these structures is also pertinent to the acceleration of solar
  wind. Besides, the advanced capabilities of the current generation
  telescopes have allowed us to extract important coronal properties
  through MHD seismology. The recent progress made in the detection,
  origin, and damping of both propagating slow magnetoacoustic waves and
  kink (Alfvénic) waves is presented in this review article especially
  in the context of open coronal structures. Where appropriate, we give
  an overview on associated theoretical modelling studies. A few of the
  important seismological applications of these waves are discussed. The
  possible role of Alfvénic waves in the acceleration of solar wind is
  also touched upon.

---------------------------------------------------------
Title: Forward Modeling of Solar Coronal Magnetic-field Measurements
    Based on a Magnetic-field-induced Transition in Fe X
Authors: Chen, Yajie; Li, Wenxian; Tian, Hui; Chen, Feng; Bai,
   Xianyong; Yang, Yang; Yang, Zihao; Liu, Xianyu; Deng, Yuanyong
2021ApJ...920..116C    Altcode: 2021arXiv210711783C
  It was recently proposed that the intensity ratios of several extreme
  ultraviolet spectral lines from Fe X ions can be used to measure the
  solar coronal magnetic field based on magnetic-field-induced transition
  (MIT) theory. To verify the suitability of this method, we performed
  forward modeling with a three-dimensional radiation magnetohydrodynamic
  model of a solar active region. Intensities of several spectral lines
  from Fe X were synthesized from the model. Based on MIT theory, the
  intensity ratios of the MIT line Fe X 257 Å to several other Fe X
  lines were used to derive magnetic-field strengths, which were then
  compared with the field strengths in the model. We also developed
  a new method to simultaneously estimate the coronal density and
  temperature from the Fe X 174/175 and 184/345 Å line ratios. Using
  these estimates, we demonstrated that the MIT technique can provide
  reasonably accurate measurements of the coronal magnetic field in both
  on-disk and off-limb solar observations. Our investigation suggests that
  a spectrometer that can simultaneously observe the Fe X 174, 175, 184,
  257, and 345 Å lines and allow an accurate radiometric calibration
  for these lines is highly desired to achieve reliable measurements of
  the coronal magnetic field. We have also evaluated the impact of the
  uncertainty in the Fe x 3p<SUP>4</SUP> 3d <SUP>4</SUP>D<SUB>5/2</SUB>
  and <SUP>4</SUP>D<SUB>7/2</SUB> energy difference on the magnetic-field
  measurements.

---------------------------------------------------------
Title: Non-thermal Electron Energization During the Impulsive Phase
    of an X9.3 Flare Revealed by Insight-HXMT
Authors: Zhang, P.; Wang, W.; Su, Y.; Song, L. M.; Li, C. K.; Zhou,
   D. K.; Zhang, S. N.; Tian, H.; Liu, S. M.; Zhao, H. S.; Zhang, S.
2021ApJ...918...42Z    Altcode: 2021arXiv210609506Z
  The X9.3 flare SOL20170906T11:55 was observed by the CsI detector aboard
  the first Chinese X-ray observatory Hard X-ray Modulation telescope
  (Insight-HXMT). Using the wavelets method, we report 22 s quasiperiodic
  pulsations during the impulsive phase. The spectra from 100 keV to 800
  keV show the evolution with the gamma-ray flux of a power-law photon
  index from ~1.8 before the peak, ~2.0 around the flare peak, to ~1.8
  again. The gyrosynchrotron microwave spectral analysis reveals a 36"6
  ± 0"6 radius gyrosynchrotron source with mean transverse magnetic
  field around 608.2 Gauss. The penetrated ≥10 keV non-thermal electron
  density is about 10<SUP>6.7</SUP> cm<SUP>-3</SUP> at peak time. The
  magnetic field strength followed the evolution of high-frequency radio
  flux. Further gyrosynchrotron source modeling analysis implies that
  there exists a quite steady gyrosynchrotron source, and the non-thermal
  electron density and transverse magnetic field evolution are similar to
  higher-frequency light curves. The temporal spectral analysis reveals
  that those non-thermal electrons are accelerated by repeated magnetic
  reconnection, likely from a lower corona source.

---------------------------------------------------------
Title: Measurements of the Magnetic Field Strengths at the Bases of
    Stellar Coronae Using the Magnetic-field-induced Transition Theory
Authors: Chen, Yajie; Liu, Xianyu; Tian, Hui; Bai, Xianyong; Jin,
   Meng; Li, Wenxian; Yang, Yang; Yang, Zihao; Deng, Yuanyong
2021ApJ...918L..13C    Altcode: 2021arXiv210808155C
  Measurements of the magnetic field in the stellar coronae are extremely
  difficult. Recently, it was proposed that the magnetic-field-induced
  transition (MIT) of the Fe X 257 Å line can be used to measure the
  coronal magnetic field of the Sun. We performed forward modeling with
  a series of global stellar magnetohydrodynamics models to investigate
  the possibility of extending this method to other late-type stars. We
  first synthesized the emissions of several Fe X lines for each stellar
  model, then calculated the magnetic field strengths using the intensity
  ratios of Fe X 257 Å to several other Fe X lines based on the MIT
  theory. Finally, we compared the derived field strengths with those
  in the models, and concluded that this method can be used to measure
  at least the magnetic field strengths at the coronal bases of stars
  with a mean surface magnetic flux density about one order of magnitude
  higher than that of the Sun. Our investigation suggests the need for
  an extreme ultraviolet spectrometer to perform routine measurements
  of the stellar coronal magnetic field.

---------------------------------------------------------
Title: Coronal Microjets in Quiet-Sun Regions Observed with the
    Extreme Ultraviolet Imager on Board the Solar Orbiter
Authors: Hou, Zhenyong; Tian, Hui; Berghmans, David; Chen, Hechao;
   Teriaca, Luca; Schühle, Udo; Gao, Yuhang; Chen, Yajie; He, Jiansen;
   Wang, Linghua; Bai, Xianyong
2021ApJ...918L..20H    Altcode: 2021arXiv210808718H
  We report the smallest coronal jets ever observed in the quiet Sun with
  recent high-resolution observations from the High Resolution Telescopes
  (HRI<SUB>EUV</SUB> and HRI<SUB>Lyα</SUB>) of the Extreme Ultraviolet
  Imager on board the Solar Orbiter (SO). In the HRI<SUB>EUV</SUB>
  (174 Å) images, these microjets usually appear as nearly collimated
  structures with brightenings at their footpoints. Their average
  lifetime, projected speed, width, and maximum length are 4.6 minutes,
  62 km s<SUP>-1</SUP>, 1.0 Mm, and 7.7 Mm, respectively. Inverted-Y
  shaped structures and moving blobs can be identified in some events. A
  subset of these events also reveal signatures in the HRI<SUB>Lyα</SUB>
  (H I Lyα at 1216 Å) images and the extreme ultraviolet images
  taken by the Atmospheric Imaging Assembly (AIA) on board the Solar
  Dynamics Observatory (SDO). Our differential emission-measure (EM)
  analysis suggests a multithermal nature and an average density of ~1.4
  × 10<SUP>9</SUP> cm<SUP>-3</SUP> for these microjets. Their thermal
  and kinetic energies were estimated to be ~3.9 × 10<SUP>24</SUP> erg
  and ~2.9 × 10<SUP>23</SUP> erg, respectively, which are of the same
  order of the released energy predicted by the nanoflare theory. Most
  events appear to be located at the edges of network lanes and magnetic
  flux concentrations, suggesting that these coronal microjets are likely
  generated by magnetic reconnection between small-scale magnetic loops
  and the adjacent network field.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Stellar groups in Taurus field
    from Gaia DR2 &amp; LAMOST (Liu+, 2021)
Authors: Liu, J.; Fang, M.; Tian, H.; Liu, C.; Yang, C.; Xue, X.
2021yCat..22540020L    Altcode:
  In order to fully explore the Taurus region, we use a large searching
  area: 55°&lt;=RA&lt;=90° and 10°&lt;=DEC&lt;=35°. <P />The
  spectroscopic data used in this work are taken from the Large Sky Area
  Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5. LAMOST is
  a 4m Schmidt telescope of the National Astronomical Observatories of
  China, located at Xinglong Observing Station, China. In this work, we
  use the LAMOST DR5 data set. <P />In order to construct the spectral
  energy distribution of each source and estimate its extinction,
  we used optical photometry in the g, r, i, z, and y bands from
  Pan-STARRS (Cat. II/349) and G, G<SUB>BP</SUB>, and G<SUB>RP</SUB>
  bands from Gaia DR2 (Cat. I/345), near-infrared photometry in the J,
  H, and K<SUB>S</SUB> bands from the Two-Micron All Sky Survey (2MASS;
  see Cat. II/246), and near- and mid-infrared photometry in the W1
  (3.4um), W2 (4.6um), W3 (12um), and W4 (22um) bands from the WISE
  (see Cat. II/311) all-sky survey. <P />(2 data files).

---------------------------------------------------------
Title: Flare-induced decay-less transverse oscillations in solar
    coronal loops
Authors: Mandal, Sudip; Tian, Hui; Peter, Hardi
2021A&A...652L...3M    Altcode: 2021arXiv210702247M
  Evidence of flare-induced, large-amplitude, decay-less transverse
  oscillations is presented. A system of multithermal coronal loops,
  as observed with the Atmospheric Imaging Assembly (AIA), exhibit
  decay-less transverse oscillations after a flare erupts nearby one
  of the loop footpoints. Measured oscillation periods lie between 4.2
  min and 6.9 min wherein the displacement amplitudes range from 0.17
  Mm to 1.16 Mm. A motion-magnification technique has been employed
  to detect the preflare decay-less oscillations. These oscillations
  have similar periods (between 3.7 min and 5.0 min) similar to the
  previous ones, but their amplitudes (0.04 Mm to 0.12 Mm) are found
  to be significantly smaller. No phase difference is found among
  oscillating threads of a loop when observed through a particular AIA
  channel or when their multichannel signatures are compared. These
  features suggest that the occurrence of a flare in this case neither
  changed the nature of these oscillations (decaying versus decay-less),
  nor the oscillation periods. The only effect the flare has is to
  increase the oscillation amplitudes. <P />Movie is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141542/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Statistical investigation on the formation of sunspot light
    bridges
Authors: Li, Fu-Yu; Chen, Yu-Hao; Song, Yong-Liang; Hou, Zhen-Yong;
   Tian, Hui
2021RAA....21..144L    Altcode:
  Light bridges (LBs) are bright lanes that divide one sunspot umbra
  into two or more parts. Though frequently observed in sunspots,
  their formation mechanisms have rarely been studied and thus are not
  well understood. Here we present results from the first statistical
  investigation on the formation of LBs. Using observations with
  the Helioseismic and Magnetic Imager on board the Solar Dynamics
  Observatory, we identified 144 LBs within 71 active regions (ARs) over
  the whole year of 2014. The formation processes of these LBs can be
  categorized into three groups: penumbral intrusion (type-A), sunspot
  merging (type-B) and umbral-dot emergence (type-C). The numbers of
  events in these three categories are 74, 57 and 13, respectively. The
  duration of the LB formation process is mostly less than 40 hours,
  with an average of ~20 hours. Most LBs have a maximum length of less
  than 20″. For type-A LBs, we found a positive correlation between
  the LB length and the duration of the LB formation process, suggesting
  a similar speed of penumbral intrusion in different sunspots.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Ages of field stars from white
    dwarf comp. in Gaia (Qiu+, 2021)
Authors: Qiu, D.; Tian, H. -J.; Wang, X. -D.; Nie, J. -L.; von Hippel,
   T.; Liu, G. -C.; Fouesneau, M.; Rix, H. -W.
2021yCat..22530058Q    Altcode:
  In this work, we select 9589 MS-WD and 307 WD-WD candidate binaries
  from the catalog released by Tian+ (2020, J/ApJS/246/4), which is a
  catalog of 807611 binaries, by searching from Gaia DR2 in a range of
  distance &lt;4.0kpc and the projected separation s&lt;1.0pc. According
  to the contamination rates, we selected 4050 MS-WD binaries with
  contamination rates &lt;20%. See Section 2. <P />We use an open-source
  software suite, BASE-9 (von Hippel+ 2014arXiv1411.3786V), to constrain
  the ages, ZAMS mass, A<SUB>V</SUB>, and distance modulus for the 4050
  MS-WD candidate binaries. See Section 3. <P />We build a catalog that
  includes the ages and other parameters (see Table 2) of the 3551 field
  MS components. We also provide a catalog that includes the ages and
  other parameters of the 3551 MS-WD and 236 WD-WD binaries (see Table
  4). <P />(2 data files).

---------------------------------------------------------
Title: Formation of Solar Quiescent Coronal Loops through Magnetic
    Reconnection in an Emerging Active Region
Authors: Hou, Zhenyong; Tian, Hui; Chen, Hechao; Zhu, Xiaoshuai; Huang,
   Zhenghua; Bai, Xianyong; He, Jiansen; Song, Yongliang; Xia, Lidong
2021ApJ...915...39H    Altcode: 2021arXiv210503199H
  Coronal loops are the building blocks of solar active regions. However,
  their formation mechanism remains poorly understood. Here we present
  direct observational evidence for the formation of coronal loops
  through magnetic reconnection as new magnetic fluxes emerge into the
  solar atmosphere. Extreme-ultraviolet observations by the Atmospheric
  Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO)
  clearly show the newly formed loops following magnetic reconnection
  within a plasma sheet. Formation of the loops is also seen in the Hα
  line-core images taken by the New Vacuum Solar Telescope. Observations
  from the Helioseismic and Magnetic Imager on board SDO show that a
  positive-polarity flux concentration moves toward a negative-polarity
  one with a speed of ~0.4 km s<SUP>-1</SUP> before the formation of
  coronal loops. During the loop formation process, we found signatures
  of flux cancellation and subsequent enhancement of the transverse
  field between the two polarities. The three-dimensional magnetic
  field structure reconstructed through a magnetohydrostatic model
  shows field lines consistent with the loops in AIA images. Numerous
  bright blobs with an average width of 1.37 Mm appear intermittently
  in the plasma sheet and move upward with a projected velocity of ~114
  km s<SUP>-1</SUP>. The temperature, emission measure, and density of
  these blobs are about 3 MK, 2.0 × 10<SUP>28</SUP> cm<SUP>-5</SUP>, and
  1.2 × 10<SUP>10</SUP> cm<SUP>-3</SUP>, respectively. A power spectral
  analysis of these blobs indicates that the observed reconnection is
  likely not dominated by a turbulent process. We have also identified
  flows with a velocity of 20-50 km s<SUP>-1</SUP> toward the footpoints
  of the newly formed coronal loops.

---------------------------------------------------------
Title: The Instability Strip of RRab Stars From LAMOST-Gaia Data
Authors: Luo, C.; Liu, C.; Zhang, X.; Chen, X.; Sun, W.; Zhang, X.;
   Li, Y.; Zhang, C.; Tian, H.; Deng, L.
2021ASPC..529..147L    Altcode:
  We compile 995 RRab samples from various literature and cross-match
  them with LAMOST to identify the boundaries of instability strip (IS)
  at red and blue edges and to associate them with metallicity. We find
  a significant gap at [Fe/H]=-0.5 dex, which separates the RRab stars
  into metal-poor and metal-rich groups. For the metal-poor group, the IS
  moves toward cooler T<SUB>eff</SUB> with declining [Fe/H]. The slopes,
  dT<SUB>eff</SUB>/d[Fe/H], are 192±19 K/dex and 354±51 K/dex for
  red and blue edges, respectively. For the metal-rich group, the blue
  edge of IS moves toward hotter T<SUB>eff</SUB> with declining [Fe/H],
  while the red edge is nearly independent on [Fe/H]. A similar trend
  is also confirmed in T<SUB>eff</SUB>-luminosity diagram. By comparing
  with various theoretical models of RRab stars, we find the correlation
  between IS and metallicity is not consistent with the theoretical model.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Sgr stream K- &amp; M-giants and
    BHB stars (Yang+, 2019)
Authors: Yang, C.; Xue, X. -X.; Li, J.; Liu, C.; Zhang, Bo; Rix,
   H. -W.; Zhang, L.; Zhao, G.; Tian, H.; Zhong, J.; Xing, Q.; Wu, Y.;
   Li, C.; Carlin, J. L.; Chang, J.
2021yCat..18860154Y    Altcode:
  The Sgr stream sample consists of K-giants, M-giants, and blue
  horizontal branch stars (BHBs). The K-giants are from Sloan Extension
  for Galactic Understanding and Exploration 2 (SEGUE-2; Yanny+,
  2009, J/AJ/137/4377) and the fifth data release of Large Sky Area
  Multi-Object Fibre Spectroscopic Telescope (LAMOST DR5; see V/164),
  and their distances were estimated by Bayesian method Xue+ (2014,
  J/ApJ/784/170). The M-giants are picked up from LAMOST DR5 through
  a 2MASS+WISE photometric selection criteria. The distances were
  calculated through the (J-K)<SUB>0</SUB> color-distance relation Li+
  (2016, J/ApJ/823/59), Li+ (2019, J/ApJ/874/138), and Zhong+ (2019,
  J/ApJS/244/8). The BHBs are chosen from SDSS by color and Balmer line
  cuts, and their distances were easy to estimate because of the nearly
  constant absolute magnitude of BHB stars (Xue+ 2011, J/ApJ/738/79). <P
  />(2 data files).

---------------------------------------------------------
Title: Mapping the global magnetic field in the solar corona through
    magnetoseismology
Authors: Yang, Zihao; Bethge, Christian; Tian, Hui; Tomczyk, Steven;
   Morton, Richard; Del Zanna, Giulio; McIntosh, Scott; Karak, Bidya
   Binay; Gibson, Sarah; Samanta, Tanmoy; He, Jiansen; Chen, Yajie;
   Wang, Linghua; Bai, Xianyong
2021EGUGA..23..642Y    Altcode:
  Magnetoseismology, a technique of magnetic field diagnostics based
  on observations of magnetohydrodynamic (MHD) waves, has been widely
  used to estimate the field strengths of oscillating structures in
  the solar corona. However, previously magnetoseismology was mostly
  applied to occasionally occurring oscillation events, providing
  an estimate of only the average field strength or one-dimensional
  distribution of field strength along an oscillating structure. This
  restriction could be eliminated if we apply magnetoseismology to the
  pervasive propagating transverse MHD waves discovered with the Coronal
  Multi-channel Polarimeter (CoMP). Using several CoMP observations of
  the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
  the plasma density and wave phase speed in the corona, which allow us
  to map both the strength and direction of the coronal magnetic field
  in the plane of sky. We also examined distributions of the electron
  density and magnetic field strength, and compared their variations
  with height in the quiet Sun and active regions. Such measurements
  could provide critical information to advance our understanding of the
  Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

---------------------------------------------------------
Title: Transient small-scale brightenings in the quiet Sun corona:
    a model for "campfires" observed with Solar Orbiter
Authors: Chen, Yajie; Przybylski, Damien; Peter, Hardi; Tian, Hui
2021EGUGA..23.5061C    Altcode:
  Recent observations by the Extreme Ultraviolet Imager (EUI)
  onboard Solar Orbiter have revealed prevalent small-scale transient
  brightenings in the quiet solar corona termed campfires. To understand
  the generation mechanism of these coronal brightenings, we constructed
  a self- consistent and time-dependent quiet-Sun model extending from
  the upper convection zone to the lower corona using a realistic 3D
  radiation MHD simulation. From the model we have synthesized the coronal
  emission in the EUI 174 Å passband. We identified several transient
  coronal brightenings similar to those in EUI observations. The size
  and lifetime of these coronal brightenings are 2-4 Mm and ∼2 min,
  respectively. These brightenings are located at a height of 2-4 Mm
  above the photosphere, and the surrounding plasma is often heated
  above 1 MK. These findings are consistent with the observational
  characterisation of the campfires. Through a comparison of the magnetic
  field structures before and after the occurrence of brightenings, we
  conclude that these coronal brightenings are generated by component
  magnetic reconnection between interacting bundles of field lines or
  the relaxation of highly twisted flux ropes. Occurring in the coronal
  part of the atmosphere, these events show no measurable signature
  in the photosphere. These transient coronal brightenings may play an
  important role in heating of the local coronal plasma.

---------------------------------------------------------
Title: Formation of solar coronal loops through magnetic reconnection
    in an emerging active region
Authors: Hou, Zhenyong; Tian, Hui; Chen, Hechao; Zhu, Xiaoshuai; He,
   Jiansen; Bai, Xianyong; Huang, Zhenghua; Xia, Lidong
2021EGUGA..23.1013H    Altcode:
  Coronal loops are building blocks of solar active regions
  (ARs). However, their formation is not well understood. Here we
  present direct observational evidence for the formation of coronal loops
  through magnetic reconnection as new magnetic fluxes emerge to the solar
  atmosphere. Observations in the EUV passbands of SDO/AIA clearly show
  the newly formed loops following magnetic reconnection within a vertical
  current sheet. Formation of the loops is also seen in the Hα images
  taken by NVST. The SDO/HMI observations show that a positive-polarity
  flux concentration moves toward a negative-polarity one with a speed of
  ~0.5 km s-1 before the apparent formation of coronal loops. During the
  formation of coronal loops, we found signatures of flux cancellation
  and subsequent enhancement of the transverse field between the two
  polarities. We have reconstructed the three-dimensional magnetic field
  structure through a magnetohydrostatic model, which shows field lines
  consistent with the loops in AIA images. Numerous bright blobs with a
  width of ~1.5 Mm appear intermittently in the current sheet and move
  upward with apparent velocities of ~80 km s-1. We have also identified
  plasma blobs moving to the footpoints of the newly formed large loops,
  with apparent velocities ranging from 30 to 50 km s-1. A differential
  emission measure analysis shows that the temperature, emission measure
  and density of the bright blobs are 2.5-3.5 MK, 1.1-2.3×1028 cm-5 and
  8.9-12.9×109 cm-3, respectively. Power spectral analysis of these
  blobs indicates that the magnetic reconnection is inconsistent with
  the turbulent reconnection scenario.

---------------------------------------------------------
Title: Upflows in the Upper Solar Atmosphere
Authors: Tian, Hui; Harra, Louise; Baker, Deborah; Brooks, David H.;
   Xia, Lidong
2021SoPh..296...47T    Altcode: 2021arXiv210202429T
  Spectroscopic observations at extreme- and far-ultraviolet wavelengths
  have revealed systematic upflows in the solar transition region and
  corona. These upflows are best seen in the network structures of
  the quiet Sun and coronal holes, boundaries of active regions, and
  dimming regions associated with coronal mass ejections. They have been
  intensively studied in the past two decades because they are likely to
  be closely related to the formation of the solar wind and heating of the
  upper solar atmosphere. We present an overview of the characteristics
  of these upflows, introduce their possible formation mechanisms, and
  discuss their potential roles in the mass and energy transport in the
  solar atmosphere. Although past investigations have greatly improved
  our understanding of these upflows, they have left us with several
  outstanding questions and unresolved issues that should be addressed
  in the future. New observations from the Solar Orbiter mission, the
  Daniel K. Inouye Solar Telescope, and the Parker Solar Probe will
  likely provide critical information to advance our understanding of
  the generation, propagation, and energization of these upflows.

---------------------------------------------------------
Title: In Situ Detection of the Solar Eruption: Lay a Finger on
    the Sun
Authors: Lin, Jun; Huang, Shanjie; Li, Yan; Chong, Xiaoyu; Zhang,
   Shenyi; Li, Mingtao; Zhang, Yiteng; Zhou, Bin; Ouyang, Gaoxiang; Xiang,
   Lei; Dong, Liang; Ji, Haisheng; Tian, Hui; Song, Hongqiang; Liu, Yu;
   Jin, Zhenyu; Feng, Jing; Zhang, Hongbo; Zhang, Xianguo; Zhang, Weijie;
   Huang, Min; Lü, Qunbo; Deng, Lei; Fu, Huishan; Cheng, Xin; Wang, Min
2021ChJSS..41..183L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Small-scale Bright Blobs Ejected from a Sunspot Light Bridge
Authors: Li, Fuyu; Chen, Yajie; Hou, Yijun; Tian, Hui; Bai, Xianyong;
   Song, Yongliang
2021ApJ...908..201L    Altcode: 2021arXiv210213545L
  Light bridges (LBs) are bright lanes that divide an umbra into multiple
  parts in some sunspots. Persistent oscillatory bright fronts at a
  temperature of ∼10<SUP>5</SUP> K are commonly observed above LBs in
  the 1400/1330 Špassbands of the Interface Region Imaging Spectrograph
  (IRIS). Based on IRIS observations, we report small-scale bright blobs
  ejected from the oscillating bright front above a light bridge. Some of
  these blobs reveal a clear acceleration, whereas the others do not. The
  average speed of these blobs projected onto the plane of sky is 71.7
  ± 14.7 km s<SUP>-1</SUP>, with an initial acceleration of 1.9 ± 1.3
  km s<SUP>-2</SUP>. These blobs normally reach a projected distance of
  3-7 Mm from their origin sites. They have an average projected area of
  0.57 ± 0.37 Mm<SUP>2</SUP>. The blobs were also detected in multiple
  extreme-ultraviolet passbands of the Atmospheric Imaging Assembly on
  board the Solar Dynamics Observatory, but not in the Hα images taken
  by the New Vacuum Solar Telescope. The typical temperature and electron
  density of these blobs are around ${10}^{5.47}$ K and ${10}^{9.7}$
  cm<SUP>-3</SUP>, respectively. The estimated kinetic and thermal
  energies are on the order of ${10}^{22.8}$ erg and ${10}^{23.3}$
  erg, respectively. These small-scale blobs appear to show three
  different types of formation processes. They are possibly triggered
  by induced reconnection or release of enhanced magnetic tension due
  to interaction of adjacent shocks, local magnetic reconnection between
  emerging magnetic bipoles on the light bridge and surrounding unipolar
  umbral fields, and plasma acceleration or instability caused by upward
  shocks, respectively.

---------------------------------------------------------
Title: VizieR Online Data Catalog: LAMOST-Kepler/K2 survey (LK-MRS)
    first year obs. (Zong+, 2020)
Authors: Zong, W.; Fu, J. -N.; De Cat, P.; Wang, J.; Shi, J.; Luo, A.;
   Zhang, H.; Frasca, A.; Molenda-Zakowicz, J.; Gray, R. O.; Corbally,
   C. J.; Catanzaro, G.; Cang, T.; Wang, J.; Chen, J.; Hou, Y.; Liu,
   J.; Niu, H.; Pan, Y.; Tian, H.; Yan, H.; Zhang, Y.; Zuo, H.
2021yCat..22510015Z    Altcode:
  Phase II of the Large Sky Area Multi-Object Fibre Spectroscopic
  Telescope (LAMOST)-Kepler/K2 survey (LK-MRS), initiated in 2018,
  aims at collecting medium-resolution spectra (R~7500; hereafter MRS)
  for more than 50000 stars with multiple visits (~60 epochs) over a
  period of 5yr (2018 September to 2023 June). We selected 20 footprints
  distributed across the Kepler field and six K2 campaigns, with each
  plate containing a number of stars ranging from ~2000 to ~3000. During
  the first year of observations, the LK-MRS has already visited 13
  plates 223 times over 40 individual nights, and collected ~280000 and
  ~369000 high-quality spectra in the blue and red wavelength ranges,
  respectively. The atmospheric parameters and radial velocities for
  ~259000 spectra of 21053 targets were successfully calculated by the
  LAMOST stellar parameter pipeline. The internal uncertainties for the
  effective temperature, surface gravity, metallicity, and radial velocity
  are found to be 100K, 0.15dex, 0.09dex, and 1.00km/s, respectively, when
  derived from a medium-resolution LAMOST spectrum with a signal-to-noise
  ratio (S/N) in the g band of 10. All of the uncertainties decrease as
  S/N increases, but they stabilize for S/N&gt;100. We found 14997, 20091,
  and 1514 stars in common with the targets from the LAMOST low-resolution
  survey (LRS), Gaia, and the Apache Point Observatory Galactic Evolution
  Experiment (APOGEE), respectively, corresponding to fractions of ~70%,
  ~95%, and ~7.2%. In general, the parameters derived from LK-MRS spectra
  are consistent with those obtained from the LRS and APOGEE spectra,
  but the scatter increases as the surface gravity decreases when
  comparing with the measurements from APOGEE. A large discrepancy is
  found with the Gaia values of the effective temperature. Comparisons
  of the radial velocities of LK-MRS to Gaia and LK-MRS to APOGEE nearly
  follow a Gaussian distribution with means of μ~1.10 and 0.73km/s,
  respectively. We expect that the results from the LK-MRS spectra will
  shed new light on binary stars, asteroseismology, stellar activity,
  and other research fields. <P />(1 data file).

---------------------------------------------------------
Title: A magnetic reconnection model for hot explosions in the cool
    atmosphere of the Sun
Authors: Ni, Lei; Chen, Yajie; Peter, Hardi; Tian, Hui; Lin, Jun
2021A&A...646A..88N    Altcode: 2020arXiv201107692N
  Context. Ultraviolet (UV) bursts and Ellerman bombs (EBs) are
  transient brightenings observed in the low solar atmospheres of
  emerging flux regions. Magnetic reconnection is believed to be the
  main mechanism leading to formation of the two activities, which are
  usually formed far apart from each other. However, observations also
  led to the discovery of co-spatial and co-temporal EBs and UV bursts,
  and their formation mechanisms are still not clear. The multi-thermal
  components in these events, which span a large temperature range,
  challenge our understanding of magnetic reconnection and heating
  mechanisms in the partially ionized lower solar atmosphere. <BR />
  Aims: We studied magnetic reconnection between the emerging magnetic
  flux and back ground magnetic fields in the partially ionized and
  highly stratificated low solar atmosphere. We aim to explain the
  multi-thermal characteristics of UV bursts, and to find out whether
  EBs and UV bursts can be generated in the same reconnection process
  and how they are related with each other. We also aim to unearth the
  important small-scale physics in these events. <BR /> Methods: We used
  the single-fluid magnetohydrodynamic (MHD) code NIRVANA to perform
  simulations. The background magnetic fields and emerging fields at the
  solar surface are reasonably strong. The initial plasma parameters are
  based on the C7 atmosphere model. We simulated cases with different
  resolutions, and included the effects of ambipolar diffusion, radiative
  cooling, and heat conduction. We analyzed the current density, plasma
  density, temperature, and velocity distributions in the main current
  sheet region, and synthesized the Si IV emission spectrum. <BR />
  Results: After the current sheet with dense photosphere plasma emerges
  and reaches 0.5 Mm above the solar surface, plasmoid instability
  appears. The plasmoids collide and coalesce with each other, which
  causes the plasmas with different densities and temperatures to be mixed
  up in the turbulent reconnection region. Therefore, the hot plasmas
  corresponding to the UV emissions and colder plasmas corresponding to
  the emissions from other wavelengths can move together and occur at
  about the same height. In the meantime, the hot turbulent structures
  concentrate above 0.4 Mm, whereas the cool plasmas extend to much
  lower heights to the bottom of the current sheet. These phenomena
  are consistent with published observations in which UV bursts have a
  tendency to be located at greater heights close to corresponding EBs
  and all the EBs have partial overlap with corresponding UV bursts
  in space. The synthesized Si IV line profiles are similar to that
  observed in UV bursts; the enhanced wing of the line profiles can
  extend to about 100 km s<SUP>-1</SUP>. The differences are significant
  among the numerical results with different resolutions, indicating
  that the realistic magnetic diffusivity is crucial to revealing the
  fine structures and realistic plasmas heating in these reconnection
  events. Our results also show that the reconnection heating contributed
  by ambipolar diffusion in the low chromosphere around the temperature
  minimum region is not efficient.

---------------------------------------------------------
Title: Plasma heating induced by tadpole-like downflows in the
    flaring solar corona
Authors: Samanta, T.; Tian, H.; Chen, B.; Reeves, K. K.; Cheung,
   M. C. M.; Vourlidas, A.; Banerjee, D.
2021Innov...200083S    Altcode: 2021arXiv210314257S
  As one of the most spectacular energy release events in the solar
  system, solar flares are generally powered by magnetic reconnection in
  the solar corona. As a result of the re-arrangement of magnetic field
  topology after the reconnection process, a series of new loop-like
  magnetic structures are often formed and are known as flare loops. A
  hot diffuse region, consisting of around 5-10 MK plasma, is also
  observed above the loops and is called a supra-arcade fan. Often,
  dark, tadpole-like structures are seen to descend through the bright
  supra-arcade fans. It remains unclear what role these so-called
  supra-arcade downflows (SADs) play in heating the flaring coronal
  plasma. Here we show a unique flare observation, where many SADs collide
  with the flare loops and strongly heat the loops to a temperature
  of 10-20 MK. Several of these interactions generate clear signatures
  of quasi-periodic enhancement in the full-Sun-integrated soft X-ray
  emission, providing an alternative interpretation for quasi-periodic
  pulsations that are commonly observed during solar and stellar flares.

---------------------------------------------------------
Title: VizieR Online Data Catalog: LAMOST K giants in Galactic halo
    substructures (Yang+, 2019)
Authors: Yang, C.; Xue, X. -X.; Li, J.; Zhang, L.; Liu, C.; Zhao,
   G.; Chang, J.; Tian, H.; Li, C.
2021yCat..18800065Y    Altcode:
  LAMOST DR5 combining with Gaia DR2 enables us to construct a large
  sample of 13554 halo K giants with distances up to 100kpc, radial
  velocities, metallicities, and proper motions (see Section 2). <P
  />Finally, we find 43 friends-of-friends (FoF) groups (1867 group
  members), in which 25 groups belong to five known substructures: Sgr
  Stream (13 groups), Monoceros Ring (4 groups), Virgo Overdensity (4
  groups), Hercules-Aquila Cloud (3 groups), and Orphan Stream (1 group);
  and 18 remaining groups are likely related to unknown substructures. See
  Section 5. <P />(3 data files).

---------------------------------------------------------
Title: VizieR Online Data Catalog: The extended Gaia-PS1-SDSS (GPS1+)
    proper motion catalog (Tian+, 2020)
Authors: Tian, H. -J.; Xu, Y.; Liu, C.; Rix, H. -W.; Sesar, B.;
   Goldman, B.
2021yCat.1351....0T    Altcode:
  We still use the four basic imaging surveys, i.e., Gaia, PS1 (II/349),
  SDSS, and 2MASS, to build the GPS1+ catalog. Unlike GPS1 (I/343),
  GPS1+ will be based on the Gaia DR2 (I/345), but the other three
  astrometric data sets remain the same as those used in GPS1, i.e.,
  the same data version and treatment. <P />(1 data file).

---------------------------------------------------------
Title: Microwave diagnostics of magnetic field strengths in solar
    flaring loops
Authors: Zhu, Rui; Tan, BaoLin; Su, YingNa; Tian, Hui; Xu, Yu; Chen,
   XingYao; Song, YongLiang; Tan, GuangYu
2021ScChE..64..169Z    Altcode: 2020arXiv200615014Z
  We have performed microwave diagnostics of the magnetic field
  strengths in solar flare loops based on the theory of gyrosynchrotron
  emission. From Nobeyama Radioheliograph observations of three flare
  events at 17 and 34 GHz, we obtained the degree of circular polarization
  and the spectral index of microwave flux density, which were then used
  to map the magnetic field strengths in post-flare loops. Our results
  show that the magnetic field strength typically decreases from ~800 G
  near the loop footpoints to ~100 G at a height of 10--25 Mm. Comparison
  of our results with magnetic field modeling using a flux rope insertion
  method is also discussed. Our study demonstrates the potential of
  microwave imaging observations, even at only two frequencies, in
  diagnosing the coronal magnetic field of flaring regions.

---------------------------------------------------------
Title: Quiet-time Solar Wind Suprathermal Electrons of Different
    Solar Origins
Authors: Yang, L.; Wang, L.; Zhao, L.; Tao, J.; Li, G.;
   Wimmer-Schweingruber, R. F.; He, J.; Tian, H.; Bale, S. D.
2020AGUFMSH008..07Y    Altcode:
  The energy spectrum of solar wind strahl, halo, and superhalo electrons
  likely carries crucial information on their possible origin and
  acceleration at the Sun. Here we statistically investigate the energy
  spectrum of solar wind strahl/ halo electrons at ∼ 0.1- 1.5 keV and
  superhalo electrons at ∼ 20- 200 keV measured by Wind/ 3D Plasma
  and Energetic Particle during quiet times from 1998 to 2014, according
  to the types of their Potential Field Source Surface- mapped coronal
  source regions ( CSRs) . We adopt the classifi cation scheme developed
  by Zhao et al. to categorize the CSRs into four types: active region
  ( AR) , quiet Sun ( QS) , coronal hole ( CH) , and helmet-streamer
  associated region ( HS) . We fi nd that for the quiet-time strahl,
  the AR and HS ( QS and CH) correspond to a smaller ( larger) kappa
  index κ <SUB>strahl</SUB> with the most frequent value of 7- 8.5
  (8.5- 10) and a larger ( smaller) n<SUB>strahl</SUB> with the most
  frequent value of 0.013- 0.026 cm<SUP>− 3 </SUP>( 0.006- 0.0013
  cm<SUP>− 3 </SUP>) . For the quiet-time halo, κ <SUB>halo</SUB>
  behaves similarly to κ <SUB>strahl </SUB> , but n<SUB>halo</SUB>
  appears similar among the four CSR types. For the superhalo, the AR
  ( QS) corresponds to a larger ( smaller) power-law index β with the
  most frequent value of 2.2- 2.4 ( 1.8- 2.0) , while the HS and CH have
  a β not different from either the AR or QS; n<SUB>sup</SUB> appears
  similar, with the most frequent value of 3x10<SUP>− 8 </SUP>- 3x
  10<SUP>− </SUP><SUP>7</SUP> cm<SUP>− 3 </SUP> , among the four
  CSR types. These results suggest that the strahl ( superhalo) from
  the hotter CSRs tends to be more ( less) effi ciently accelerated.

---------------------------------------------------------
Title: The White Dwarf Binary Pathways Survey. V. The Gaia White Dwarf
    Plus AFGK Binary Sample and the Identification of 23 Close Binaries
Authors: Ren, J. -J.; Raddi, R.; Rebassa-Mansergas, A.; Hernandez,
   M. S.; Parsons, S. G.; Irawati, P.; Rittipruk, P.; Schreiber, M. R.;
   Gänsicke, B. T.; Torres, S.; Wang, H. -J.; Zhang, J. -B.; Zhao, Y.;
   Zhou, Y. -T.; Han, Z. -W.; Wang, B.; Liu, C.; Liu, X. -W.; Wang, Y.;
   Zheng, J.; Wang, J. -F.; Zhao, F.; Cui, K. -M.; Shi, J. -R.; Tian, H.
2020ApJ...905...38R    Altcode: 2020arXiv201002885R
  Close white dwarf binaries consisting of a white dwarf and an A-, F-,
  G-, or K-type main-sequence star, henceforth close WD+AFGK binaries,
  are ideal systems to understand the nature of type Ia supernovae
  progenitors and to test binary evolution models. In this work we
  identify 775 WD+AFGK candidates from TGAS (The Tycho-Gaia Astrometric
  Solution) and Gaia Data Release 2 (DR2), a well-defined sample of
  stars with available parallaxes, and we measure radial velocities
  (RVs) for 275 of them with the aim of identifying close binaries. The
  RVs have been measured from high-resolution spectra obtained at the
  Xinglong 2.16 m Telescope and the San Pedro Mártir 2.12 m Telescope
  and/or from available LAMOST DR6 (low-resolution) and RAVE DR5
  (medium-resolution) spectra. We identify 23 WD+AFGK systems displaying
  more than 3σ RV variation among 151 systems for which the measured
  values are obtained from different nights. Our WD+AFGK binary sample
  contains both AFGK dwarfs and giants, with a giant fraction ∼43%. The
  close binary fractions we determine for the WD+AFGK dwarf and giant
  samples are ≃24% and ≃15%, respectively. We also determine the
  stellar parameters (i.e., effective temperature, surface gravity,
  metallicity, mass, and radius) of the AFGK companions with available
  high-resolution spectra. The stellar parameter distributions of the
  AFGK companions that are members of close and wide binary candidates
  do not show statistically significant differences.

---------------------------------------------------------
Title: Coronal Heating by MHD Waves
Authors: Van Doorsselaere, Tom; Srivastava, Abhishek K.; Antolin,
   Patrick; Magyar, Norbert; Vasheghani Farahani, Soheil; Tian, Hui;
   Kolotkov, Dmitrii; Ofman, Leon; Guo, Mingzhe; Arregui, Iñigo; De
   Moortel, Ineke; Pascoe, David
2020SSRv..216..140V    Altcode: 2020arXiv201201371V
  The heating of the solar chromosphere and corona to the observed high
  temperatures, imply the presence of ongoing heating that balances
  the strong radiative and thermal conduction losses expected in the
  solar atmosphere. It has been theorized for decades that the required
  heating mechanisms of the chromospheric and coronal parts of the active
  regions, quiet-Sun, and coronal holes are associated with the solar
  magnetic fields. However, the exact physical process that transport
  and dissipate the magnetic energy which ultimately leads to the solar
  plasma heating are not yet fully understood. The current understanding
  of coronal heating relies on two main mechanism: reconnection and MHD
  waves that may have various degrees of importance in different coronal
  regions. In this review we focus on recent advances in our understanding
  of MHD wave heating mechanisms. First, we focus on giving an overview
  of observational results, where we show that different wave modes have
  been discovered in the corona in the last decade, many of which are
  associated with a significant energy flux, either generated in situ
  or pumped from the lower solar atmosphere. Afterwards, we summarise
  the recent findings of numerical modelling of waves, motivated by the
  observational results. Despite the advances, only 3D MHD models with
  Alfvén wave heating in an unstructured corona can explain the observed
  coronal temperatures compatible with the quiet Sun, while 3D MHD wave
  heating models including cross-field density structuring are not yet
  able to account for the heating of coronal loops in active regions to
  their observed temperature.

---------------------------------------------------------
Title: Solar Energetic Electron Events Associated with Hard X-ray
    Flares
Authors: Wang, W.; Wang, L.; Krucker, S.; Mason, G. M.; Bucik, R.;
   Tian, H.; He, J.; Su, Y.; Bale, S.
2020AGUFMSH045..05W    Altcode:
  We presented a comparison survey of 16 solar energetic electron (SEE)
  events measured by WIND/3DP with associated hard X-ray (HXR) flares
  measured by RHESSI with good count statistics, from 2002 February to
  2016 December. Among the 16 good cases, all show a double-power-law
  shape with a downward break at ~ 68keV in the electron peak flux versus
  energy spectrum at ~ 5-200keV; All cases show a clear single-power-law
  in the HXR peak flux versus energy spectrum, and a single-power-law in
  the flux versus energy spectrum of HXR-producing electrons derived via
  bremsstrahlung mechanisms. For SEEs, their acceleration site at the
  Sun should occur high (at a heliocentric altitude of ≧1.3 R<SUB>s
  </SUB>(the average solar radius)), to remain a power-law spectrum
  extending down to ~ 5 keV during their anti-sunward escape into the
  interplanetary medium (IPM). For 14 out of 16 cases, the spectral
  index above the energy break of SEEs observed at 1AU basically agreed
  with the derived spectral index of HXR-producing electrons. However,
  the SEE spectral index below the energy break is all smaller than the
  HXR-producing electron spectral index. These results suggest that SEEs
  and HXR-producing electrons share a common origin and an additional
  acceleration could exist between the SEE source and the flare region. In
  addition, for cases with <SUP>3</SUP>He/<SUP>4</SUP>He&gt;0.01, the
  observed <SUP>3</SUP>He/<SUP>4</SUP>He shows a correlation with the
  spectral index above the energy break of SEEs, indicating a possible
  relation of the <SUP>3</SUP>He-rich ion acceleration at high corona
  with SEEs.

---------------------------------------------------------
Title: Exploring the Perturbed Milky Way Disk and the Substructures
    of the Outer Disk
Authors: Xu, Y.; Liu, C.; Tian, H.; Newberg, H. J.; Laporte, C. F. P.;
   Zhang, B.; Wang, H. F.; Fu, X.; Li, J.; Deng, L. C.
2020ApJ...905....6X    Altcode: 2020arXiv201014096X
  The recent discovery of a spiral feature in the Z - V<SUB>Z</SUB>
  phase plane in the solar neighborhood implies that the galactic disk
  has been remarkably affected by a dwarf galaxy passing through it
  some hundreds of millions of years ago. Using 429,500 Large Sky Area
  Multi-Object Fibre Spectroscopic Telescope K giants stars, we show that
  the spiral feature exists not only in the solar vicinity but it also
  extends to about 15 kpc from the Galactic center and then disappears
  beyond this radius. Moreover, we find that when the spiral features
  in a plot of V<SUB>φ</SUB> as a function of position in the Z -
  V<SUB>Z</SUB> plane at various galactocentric radii are remapped to
  the R - Z plane, the spiral can explain well the observed asymmetric
  velocity substructures. This is evidence that the phase spiral features
  are the same as the bulk motions found in previous work as well as
  this work. Test particle simulations and N-body simulations show that
  an encounter with a dwarf galaxy a few hundred million years ago will
  induce a perturbation in the galactic disk. In addition, we find that
  the last impact of Sgr dSph can also contribute to the flare. As a
  consequence of the encounter, the distribution function of disk stars at
  a large range of radii is imprinted by the gravitational perturbation.

---------------------------------------------------------
Title: Untangling the global coronal magnetic field with
    multiwavelength observations
Authors: Gibson, S. E.; Malanushenko, A.; de Toma, G.; Tomczyk, S.;
   Reeves, K.; Tian, H.; Yang, Z.; Chen, B.; Fleishman, G.; Gary, D.;
   Nita, G.; Pillet, V. M.; White, S.; Bąk-Stęślicka, U.; Dalmasse,
   K.; Kucera, T.; Rachmeler, L. A.; Raouafi, N. E.; Zhao, J.
2020arXiv201209992G    Altcode:
  Magnetism defines the complex and dynamic solar corona. Coronal
  mass ejections (CMEs) are thought to be caused by stresses, twists,
  and tangles in coronal magnetic fields that build up energy and
  ultimately erupt, hurling plasma into interplanetary space. Even the
  ever-present solar wind possesses a three-dimensional morphology shaped
  by the global coronal magnetic field, forming geoeffective corotating
  interaction regions. CME evolution and the structure of the solar
  wind depend intimately on the coronal magnetic field, so comprehensive
  observations of the global magnetothermal atmosphere are crucial both
  for scientific progress and space weather predictions. Although some
  advances have been made in measuring coronal magnetic fields locally,
  synoptic measurements of the global coronal magnetic field are not yet
  available. We conclude that a key goal for 2050 should be comprehensive,
  ongoing 3D synoptic maps of the global coronal magnetic field. This will
  require the construction of new telescopes, ground and space-based,
  to obtain complementary, multiwavelength observations sensitive
  to the coronal magnetic field. It will also require development of
  inversion frameworks capable of incorporating multi-wavelength data,
  and forward analysis tools and simulation testbeds to prioritize and
  establish observational requirements on the proposed telescopes.

---------------------------------------------------------
Title: Generation of solar spicules and subsequent atmospheric heating
Authors: Chen, YaJie; Samanta, Tanmoy; Tian, Hui
2020ScChE..63.2467C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Mapping the magnetic field in the solar corona through
    magnetoseismology
Authors: Yang, ZiHao; Tian, Hui; Tomczyk, Steven; Morton, Richard;
   Bai, XianYong; Samanta, Tanmoy; Chen, YaJie
2020ScChE..63.2357Y    Altcode: 2020arXiv200803146Y
  Magnetoseismology, a technique of magnetic field diagnostics based
  on observations of magnetohydrodynamic (MHD) waves, has been widely
  used to estimate the field strengths of oscillating structures in
  the solar corona. However, previously magnetoseismology was mostly
  applied to occasionally occurring oscillation events, providing
  an estimate of only the average field strength or one-dimensional
  distribution of field strength along an oscillating structure. This
  restriction could be eliminated if we apply magnetoseismology to the
  pervasive propagating transverse MHD waves discovered with the Coronal
  Multi-channel Polarimeter (CoMP). Using several CoMP observations of
  the Fe xiii 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of
  the plasma density and wave phase speed in the corona, which allow us
  to map both the strength and direction of the coronal magnetic field
  in the plane of sky. We also examined distributions of the electron
  density and magnetic field strength, and compared their variations
  with height in the quiet Sun and active regions. Such measurements
  could provide critical information to advance our understanding of the
  Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

---------------------------------------------------------
Title: VizieR Online Data Catalog: The ZTF catalog of periodic
    variable stars (Chen+, 2020)
Authors: Chen, X.; Wang, S.; Deng, L.; de Grijs, R.; Yang, M.; Tian, H.
2020yCat..22490018C    Altcode:
  The Zwicky Transient Facility (ZTF) is a 48-inch Schmidt telescope at
  the Palomar Observatory with a 47deg<SUP>2</SUP> field of view. ZTF
  DR2 contains data acquired between 2018 March and 2019 June, covering
  a time span of around 470 days. The photometry is provided in the g
  and r bands, with a uniform exposure time of 30s per observation. <P
  />ZTF DR2 includes more than 1 billion stars, about half of which have
  &gt;20 epochs of observations. For the majority of stars located in the
  northern Galactic plane, ZTF contains ~150 epochs of observations. <P
  />(4 data files).

---------------------------------------------------------
Title: Global maps of the magnetic field in the solar corona
Authors: Yang, Zihao; Bethge, Christian; Tian, Hui; Tomczyk, Steven;
   Morton, Richard; Del Zanna, Giulio; McIntosh, Scott W.; Karak, Bidya
   Binay; Gibson, Sarah; Samanta, Tanmoy; He, Jiansen; Chen, Yajie;
   Wang, Linghua
2020Sci...369..694Y    Altcode: 2020arXiv200803136Y
  Understanding many physical processes in the solar atmosphere requires
  determination of the magnetic field in each atmospheric layer. However,
  direct measurements of the magnetic field in the Sun’s corona are
  difficult to obtain. Using observations with the Coronal Multi-channel
  Polarimeter, we have determined the spatial distribution of the
  plasma density in the corona and the phase speed of the prevailing
  transverse magnetohydrodynamic waves within the plasma. We combined
  these measurements to map the plane-of-sky component of the global
  coronal magnetic field. The derived field strengths in the corona,
  from 1.05 to 1.35 solar radii, are mostly 1 to 4 gauss. Our results
  demonstrate the capability of imaging spectroscopy in coronal magnetic
  field diagnostics.

---------------------------------------------------------
Title: Spectroscopic observations of the upper solar atmosphere
Authors: Tian, H.
2020SPD....5120001T    Altcode:
  Our understanding of the solar transition region and corona largely
  relies on spectroscopic observations. Spectroscopy allows us to measure
  key parameters such as plasma density, temperature, velocity, elemental
  abundances and magnetic field, thus enabling us to quantitatively study
  the mass and energy transport processes in the solar atmosphere. Since
  2006, Hinode/EIS has been obtaining high-quality EUV spectra in active
  regions, providing critical information to advance our understanding
  of different types of coronal dynamics such as active region outflows,
  CME-induced dimmings and persistent/decayless oscillations. Since 2013,
  the simultaneous imaging and spectroscopic observations with IRIS
  have uncovered a wide variety of fine structures and fast dynamics in
  the transition region, both in the quiet Sun and above sunspots. In
  addition, recent observations of the ground-based CoMP instrument have
  demonstrated the capability of imaging spectroscopy in coronal magnetic
  field diagnostics. With upcoming observations from Solar Orbiter/SPICE,
  EUVST and UCoMP, spectroscopy will continue to be an important tool
  for investigation of the magnetism and plasma dynamics in the upper
  solar atmosphere.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Gaia and LAMOST DR4 M giant
    members of Sgr stream (Li+, 2019)
Authors: Li, J.; Liu, C.; Xue, X.; Zhong, J.; Weiss, J.; Carlin,
   J. L.; Tian, H.
2020yCat..18740138L    Altcode:
  In this paper, we map the 6D phase space of M giants from the
  Sagittarius (Sgr) stream in LAMOST using LAMOST DR4 (V/153) radial
  velocities combined with Gaia DR2 (I/345) proper motions and ALLWISE
  (II/328) photometry. <P />(1 data file).

---------------------------------------------------------
Title: Quiet-time Solar Wind Suprathermal Electrons of Different
    Solar Origins
Authors: Yang, Liu; Wang, Linghua; Zhao, Liang; Tao, Jiawei; Li,
   Gang; Wimmer-Schweingruber, Robert F.; He, Jiansen; Tian, Hui; Bale,
   Stuart D.
2020ApJ...896L...5Y    Altcode:
  The energy spectrum of solar wind strahl, halo, and superhalo electrons
  likely carries crucial information on their possible origin and
  acceleration at the Sun. Here we statistically investigate the energy
  spectrum of solar wind strahl/halo electrons at ∼0.1-1.5 keV and
  superhalo electrons at ∼20-200 keV measured by Wind/3D Plasma and
  Energetic Particle during quiet times from 1998 to 2014, according to
  the types of their Potential Field Source Surface-mapped coronal source
  regions (CSRs). We adopt the classification scheme developed by Zhao et
  al. to categorize the CSRs into four types: active region (AR), quiet
  Sun (QS), coronal hole (CH), and helmet-streamer associated region
  (HS). We find that for the quiet-time strahl, the AR and HS (QS and
  CH) correspond to a smaller (larger) kappa index κ<SUB>strahl</SUB>
  with the most frequent value of 7-8.5 (8.5-10) and a larger (smaller)
  n<SUB>strahl</SUB> with the most frequent value of 0.013-0.026
  cm<SUP>-3</SUP> (0.006-0.0013 cm<SUP>-3</SUP>). For the quiet-time
  halo, κ<SUB>halo</SUB> behaves similarly to κ<SUB>strahl</SUB>, but
  n<SUB>halo</SUB> appears similar among the four CSR types. For the
  superhalo, the AR (QS) corresponds to a larger (smaller) power-law
  index β with the most frequent value of 2.2-2.4 (1.8-2.0), while
  the HS and CH have a β not different from either the AR or QS;
  n<SUB>sup</SUB> appears similar, with the most frequent value of 3
  × 10<SUP>-8</SUP>-3 × 10<SUP>-7</SUP> cm<SUP>-3</SUP>, among the
  four CSR types. These results suggest that the strahl (superhalo)
  from the hotter CSRs tends to be more (less) efficiently accelerated.

---------------------------------------------------------
Title: A White-light Flare Powered by Magnetic Reconnection in the
    Lower Solar Atmosphere
Authors: Song, Yongliang; Tian, Hui; Zhu, Xiaoshuai; Chen, Yajie;
   Zhang, Mei; Zhang, Jingwen
2020ApJ...893L..13S    Altcode: 2020arXiv200311747S
  White-light flares (WLFs), first observed in 1859, refer to a
  type of solar flare showing an obvious enhancement of the visible
  continuum emission. This type of enhancement often occurs in most
  energetic flares, and is usually interpreted as a consequence of
  efficient heating in the lower solar atmosphere through nonthermal
  electrons propagating downward from the energy release site in the
  corona. However, this coronal-reconnection model has difficulty
  in explaining the recently discovered small WLFs. Here we report a
  C2.3 WLF, which is associated with several observational phenomena:
  a fast decrease in opposite-polarity photospheric magnetic fluxes,
  the disappearance of two adjacent pores, significant heating of the
  lower chromosphere, a negligible increase of the hard X-ray flux, and an
  associated U-shaped magnetic field configuration. All these suggest that
  this WLF is powered by magnetic reconnection in the lower part of the
  solar atmosphere rather than by reconnection higher up in the corona.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Catalog of ultrawide binary stars
    from Gaia DR2 (Tian+, 2020)
Authors: Tian, H. -J.; El-Badry, K.; Rix, H. -W.; Gould, A.
2020yCat..22460004T    Altcode:
  Also available on the FTP, the file "All_candidates.fits" is
  the original catalog in FITS format. "WBs<SUB>Disklike.csv",
  "WBs</SUB>Intermediate.csv" and "WBs_Halolike.csv" are
  the threee subsets in original CSV format for disk-like
  (v<SUB>{perp},tot</SUB>&lt;=40km/s), intermediate
  (v<SUB>{perp},tot</SUB>=40-85km/s), and halo-like
  (v<SUB>{perp},tot</SUB>&gt;=85km/s) binaries, respectively. <P />(1
  data file).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Ages &amp; masses for GPS1 WD-MS
    binary systems (Fouesneau+, 2019)
Authors: Fouesneau, M.; Rix, H. -W.; von Hippel, T.; Hogg, D. W.;
   Tian, H.
2020yCat..18700009F    Altcode:
  Observational tests of stellar and Galactic chemical evolution call
  for the joint knowledge of a star's physical parameters, detailed
  element abundances, and precise age. For cool main-sequence (MS) stars
  the abundances of many elements can be measured from spectroscopy,
  but ages are very hard to determine. The situation is different if
  the MS star has a white dwarf (WD) companion and a known distance, as
  the age of such a binary system can then be determined precisely from
  the photometric properties of the cooling WD. As a pilot study for
  obtaining precise age determinations of field MS stars, we identify
  nearly 100 candidates for such wide binary systems: a faint WD whose
  Gaia-PS1-SDSS (GPS1) proper motion (Tian+ 2017, I/343) matches that of
  a brighter MS star in Gaia/TGAS (Gaia Collaboration 2016, I/337) with
  a good parallax (σ<SUB>{rho}</SUB>/{rho}=&lt;0.05). We model the WD's
  multi-band photometry with the BASE-9 code using this precise distance
  (assumed to be common for the pair) and infer ages for each binary
  system. The resulting age estimates are precise to =&lt;10% (=&lt;20%)
  for 42 (67) MS-WD systems. Our analysis more than doubles the number of
  MS-WD systems with precise distances known to date, and it boosts the
  number of such systems with precise age determination by an order of
  magnitude. With the advent of the Gaia DR2 (Gaia Collaboration, 2018,
  I/345) data, this approach will be applicable to a far larger sample,
  providing ages for many MS stars (that can yield detailed abundances
  for over 20 elements), especially in the age range of 2-8Gyr, where
  there are only few known star clusters. <P />(1 data file).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Radial velocity measurements in
    LAMOST-II (Wang+, 2019)
Authors: Wang, R.; Luo, A. -L.; Chen, J. -J.; Bai, Z. -R.; Chen,
   L.; Chen, X. -F.; Dong, S. -B.; Du, B.; Fu, J. -N.; Han, Z. -W.; Hou,
   J. -L.; Hou, Y. -H.; Hou, W.; Jiang, D. -K.; Kong, X.; Li, L. -F.; Liu,
   C.; Liu, J. -M.; Qin, L.; Shi, J. -R.; Tian, H.; Wu, H.; Wu, C. -J.;
   Xie, J. -W.; Zhang, H. -T.; Zhang, S.; Zhao, G.; Zhao, Y. -H.; Zhong,
   J.; Zong, W. -K.; Zuo, F.
2020yCat..22440027W    Altcode:
  The test observation for the LAMOST medium-resolution mode (MRS;
  R=7500) began on 2017 September 1, and a total of 1,594,956 spectra
  (each has two bands) of stars with S/Ns higher than 10 was collected
  until 2017 December 31 (in LAMOST phase two; LAMOST-II). <P />LAMOST
  is a telescope possessing an effective aperture of 4m and 5° fields
  of view, which is located at the Xinglong Observatory, Hebei Province,
  China. <P />(1 data file).

---------------------------------------------------------
Title: Case Study of Solar Wind Suprathermal Electron Acceleration
    at the Earth's Bow Shock
Authors: Liu, Zixuan; Wang, Linghua; Shi, Quanqi; Oka, Mitsuo; Yang,
   Liu; Wimmer-Schweingruber, Robert F.; He, Jiansen; Tian, Hui; Bale,
   Stuart D.
2020ApJ...889L...2L    Altcode:
  We present a case study of the in situ acceleration of solar wind
  suprathermal electrons at the two quasi-perpendicular-bow-shock
  crossings on 2015 November 4, combining the Wind 3D Plasma and
  Energetic Particle measurements of ambient solar wind suprathermal
  electrons and Magnetospheric Multiscale mission measurements of shocked
  suprathermal electrons. In both cases, the omnidirectional differential
  fluxes of shocked suprathermal electrons in the downstream exhibit
  a double-power-law energy spectrum with a spectral index of ∼3 at
  energies below a downward break ɛ<SUB>brk</SUB> near 40 keV and index
  of ∼6 at energies above, different from the unshocked suprathermal
  electrons observed in the ambient solar wind. At energies below
  (above) ɛ<SUB>brk</SUB>, the observed electron flux ratio between the
  downstream and ambient solar wind, J<SUB>D</SUB>/J<SUB>A</SUB>, peaks
  near 90° PA (becomes roughly isotropic). Electrons at ɛ<SUB>brk</SUB>
  have an average electron gyrodiameter (across bow shock) comparable
  to the shock thickness. These suggest that the bow-shock acceleration
  of suprathermal electrons is likely dominated by the shock drift
  acceleration mechanism. For electrons at energies below (above)
  ɛ<SUB>brk</SUB>, their estimated drift time appears to be roughly
  energy independent (decrease with energy), leading to the formation
  of a double-power-law spectrum substantially steepening at a break
  that's determined by the shock thickness.

---------------------------------------------------------
Title: Super Metal-rich Stars in the LAMOST Survey: A Test on Radial
    Migration
Authors: Chen, Y. Q.; Zhao, G.; Zhao, J. K.; Liang, X. L.; Wu, Y. Q.;
   Jia, Y. P.; Tian, H.; Liu, J. M.
2019AJ....158..249C    Altcode:
  Super metal-rich stars with [Fe/H] &gt; 0.4 are selected from
  LAMOST DR6, and two groups, the blue and the red, are found in the
  T <SUB>eff</SUB> versus logg diagram with a temperature gap between
  them. In combination with Gaia DR2, stellar positions, velocities,
  and orbits are calculated, and spatial distributions, kinematical
  properties, and orbital parameters are compared between the two
  groups. The blue group shows mainly thin-disk kinematics and spans a
  wide R range of 6-12 kpc, while the red group has both the thin-disk
  and the thick-disk kinematics with a narrower range of R = 6-10 kpc. The
  kinematical and orbital parameters of stars in the blue group indicate
  that they could belong to the young population with age less than 1
  Gyr, rather than blue stragglers of the old population. The orbital
  parameters, R <SUB> p </SUB>, R <SUB> a </SUB>, and R <SUB> g </SUB>,
  of the red group with the thick-disk kinematics are smaller than those
  with the thin-disk kinematics. The distributions of birth radius and
  migration distance indicate that radial migration is a favorable origin
  for the red group, especially those with the thick-disk kinematics,
  but not for the blue group. The relative magnitude of radial migration
  is of 51% for the whole sample and of 64% for the red group only. The
  corotation radial migration caused by the bars and spiral arms at
  resonances is the most likely mechanism for explaining these properties
  of SMR stars in this work.

---------------------------------------------------------
Title: On the Observations of Rapid Forced Reconnection in the
    Solar Corona
Authors: Srivastava, A. K.; Mishra, S. K.; Jelínek, P.; Samanta,
   Tanmoy; Tian, Hui; Pant, Vaibhav; Kayshap, P.; Banerjee, Dipankar;
   Doyle, J. G.; Dwivedi, B. N.
2019ApJ...887..137S    Altcode: 2019arXiv190107971S
  Using multiwavelength imaging observations from the Atmospheric Imaging
  Assembly on board the Solar Dynamics Observatory on 2012 May 3, we
  present a novel physical scenario for the formation of a temporary
  X-point in the solar corona, where plasma dynamics are forced externally
  by a moving prominence. Natural diffusion was not predominant; however,
  a prominence driven inflow occurred first, forming a thin current sheet,
  thereafter enabling a forced magnetic reconnection at a considerably
  high rate. Observations in relation to the numerical model reveal that
  forced reconnection may rapidly and efficiently occur at higher rates
  in the solar corona. This physical process may also heat the corona
  locally even without establishing a significant and self-consistent
  diffusion region. Using a parametric numerical study, we demonstrate
  that the implementation of the external driver increases the rate
  of the reconnection even when the resistivity required for creating
  normal diffusion region decreases at the X-point. We conjecture that
  the appropriate external forcing can bring the oppositely directed
  field lines into the temporarily created diffusion region first via the
  plasma inflows as seen in the observations. The reconnection and related
  plasma outflows may occur thereafter at considerably larger rates.

---------------------------------------------------------
Title: Generation of solar spicules and subsequent atmospheric heating
Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi;
   Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu;
   Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie
2019Sci...366..890S    Altcode: 2020arXiv200602571S
  Spicules are rapidly evolving fine-scale jets of magnetized plasma in
  the solar chromosphere. It remains unclear how these prevalent jets
  originate from the solar surface and what role they play in heating
  the solar atmosphere. Using the Goode Solar Telescope at the Big Bear
  Solar Observatory, we observed spicules emerging within minutes of the
  appearance of opposite-polarity magnetic flux around dominant-polarity
  magnetic field concentrations. Data from the Solar Dynamics Observatory
  showed subsequent heating of the adjacent corona. The dynamic
  interaction of magnetic fields (likely due to magnetic reconnection)
  in the partially ionized lower solar atmosphere appears to generate
  these spicules and heat the upper solar atmosphere.

---------------------------------------------------------
Title: Properties of Radial Velocities Measurement Based on LAMOST-II
    Medium-resolution Spectroscopic Observations
Authors: Wang, R.; Luo, A. -L.; Chen, J. -J.; Bai, Z. -R.; Chen,
   L.; Chen, X. -F.; Dong, S. -B.; Du, B.; Fu, J. -N.; Han, Z. -W.; Hou,
   J. -L.; Hou, Y. -H.; Hou, W.; Jiang, D. -K.; Kong, X.; Li, L. -F.; Liu,
   C.; Liu, J. -M.; Qin, L.; Shi, J. -R.; Tian, H.; Wu, H.; Wu, C. -J.;
   Xie, J. -W.; Zhang, H. -T.; Zhang, S.; Zhao, G.; Zhao, Y. -H.; Zhong,
   J.; Zong, W. -K.; Zuo, F.
2019ApJS..244...27W    Altcode: 2019arXiv190804773W
  The radial velocity (RV) is a basic physical quantity that can be
  determined through the Doppler shift of the spectrum of a star. The
  precision of the RV measurement depends on the resolution of the
  spectrum we used and the accuracy of wavelength calibration. In this
  work, radial velocities of the Large Sky Area Multi-Object Fibre
  Spectroscopic Telescope-II (LAMOST-II) medium-resolution (R ∼ 7500)
  spectra are measured for 1,594,956 spectra (each spectrum has two
  wavebands) through matching with templates. A set of RV standard
  stars are used to recalibrate the zero point of the measurement,
  and some reference sets with RVs derived from medium-/high-resolution
  observations are used to evaluate the accuracy of the measurement. By
  comparing with reference sets, the accuracy of our measurement
  can get 0.0277 km s<SUP>-1</SUP> with respect to radial velocities
  of standard stars. The intrinsic precision is estimated with the
  multiple observations of single stars, which can be achieved to 1.36 km
  s<SUP>-1</SUP>, 1.08 km s<SUP>-1</SUP>, and 0.91 km s<SUP>-1</SUP> for
  the spectra at signal-to-noise levels of 10, 20, and 50, respectively.

---------------------------------------------------------
Title: Solar ultraviolet bursts in a coordinated observation of IRIS,
    Hinode and SDO
Authors: Chen, YaJie; Tian, Hui; Zhu, XiaoShuai; Samanta, Tanmoy;
   Wang, LingHua; He, JianSen
2019ScChE..62.1555C    Altcode: 2019arXiv190204226C
  Solar ultraviolet (UV) bursts are small-scale compact brightenings in
  transition region images. The spectral profiles of transition region
  lines in these bursts are significantly enhanced and broadened,
  often with chromospheric absorption lines such as Ni~{\sc{ii}}
  1335.203 and 1393.330 Å superimposed. We investigate the properties
  of several UV bursts using a coordinated observation of the Interface
  Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory (SDO),
  and \textit{Hinode} on 2015 February 7. We have identified 12 UV
  bursts, and 11 of them reveal small blueshifts of the Ni~{\sc{ii}}
  absorption lines. However, the Ni~{\sc{ii}} lines in one UV burst
  exhibit obvious redshifts of $\sim$20 km s$^{-1}$, which appear to
  be related to the cold plasma downflows observed in the IRIS slit-jaw
  images. We also examine the three-dimensional magnetic field topology
  using a magnetohydrostatic model, and find that some UV bursts are
  associated with magnetic null points or bald patches. In addition, we
  find that these UV bursts reveal no obvious coronal signatures from
  the observations of the Atmospheric Imaging Assembly (AIA) on board
  SDO and the EUV Imaging Spectrometer (EIS) on board \textit{Hinode}.

---------------------------------------------------------
Title: Modeling Mg II h, k and Triplet Lines at Solar Flare Ribbons
Authors: Zhu, Yingjie; Kowalski, Adam F.; Tian, Hui; Uitenbroek, Han;
   Carlsson, Mats; Allred, Joel C.
2019ApJ...879...19Z    Altcode: 2019arXiv190412285Z
  Observations from the Interface Region Imaging Spectrograph often
  reveal significantly broadened and non-reversed profiles of the Mg II
  h, k and triplet lines at flare ribbons. To understand the formation
  of these optically thick Mg II lines, we perform plane-parallel
  radiative hydrodynamics modeling with the RADYN code, and then
  recalculate the Mg II line profiles from RADYN atmosphere snapshots
  using the radiative transfer code RH. We find that the current RH
  code significantly underestimates the Mg II h and k Stark widths. By
  implementing semiclassical perturbation approximation results of
  quadratic Stark broadening from the STARK-B database in the RH code,
  the Stark broadenings are found to be one order of magnitude larger
  than those calculated from the current RH code. However, the improved
  Stark widths are still too small, and another factor of 30 has to be
  multiplied to reproduce the significantly broadened lines and adjacent
  continuum seen in observations. Nonthermal electrons, magnetic fields,
  three-dimensional effects, or electron density effects may account
  for this factor. Without modifying the RADYN atmosphere, we have also
  reproduced non-reversed Mg II h and k profiles, which appear when the
  electron beam energy flux is decreasing. These profiles are formed at
  an electron density of ∼8 × 10<SUP>14</SUP> cm<SUP>-3</SUP> and a
  temperature of ∼1.4 × 10<SUP>4</SUP> K, where the source function
  slightly deviates from the Planck function. Our investigation also
  demonstrates that at flare ribbons the triplet lines are formed in the
  upper chromosphere, close to the formation heights of the h and k lines.

---------------------------------------------------------
Title: The Galactic spiral structure as revealed by O- and early
    B-type stars
Authors: Chen, B. -Q.; Huang, Y.; Hou, L. -G.; Tian, H.; Li, G. -X.;
   Yuan, H. -B.; Wang, H. -F.; Wang, C.; Tian, Z. -J.; Liu, X. -W.
2019MNRAS.487.1400C    Altcode: 2019arXiv190505542B; 2019MNRAS.tmp.1307C
  We investigate the morphology and kinematics of the Galactic spiral
  structure based on a new sample of O- and early B-type stars. We
  select 6858 highly confident OB star candidates from the combined
  data of the VST Photometric H α Survey Data Release 2 (VPHAS+ DR2)
  and the Gaia Data Release 2 (Gaia DR2). Together with the O-B2 stars
  from the literature, we build a sample consisting of 14 880 O- and
  early B-type stars, all with Gaia parallax uncertainties smaller
  than 20 per cent. The new sample, hitherto the largest one of O- and
  early B-type stars with robust distance and proper motion estimates,
  covers the Galactic plane of distances up to 6 kpc from the Sun. The
  sample allows us to examine the morphology of the Scutum, Sagittarius,
  Local, and Perseus Arms in great detail. The spiral structure of the
  Milky Way as traced by O- and early B-type stars shows flocculent
  patterns. Accurate structure parameters, as well as the means and
  dispersions of the vertical velocity distributions of the individual
  spiral arms are presented.

---------------------------------------------------------
Title: Evidence for Vortex Shedding in the Sun's Hot Corona
Authors: Samanta, Tanmoy; Tian, Hui; Nakariakov, Valery M.
2019PhRvL.123c5102S    Altcode: 2019arXiv190708930S
  Vortex shedding is an oscillating flow that is commonly observed
  in fluids due to the presence of a blunt body in a flowing
  medium. Numerical simulations have shown that the phenomenon of
  vortex shedding could also develop in the magnetohydrodynamic (MHD)
  domain. The dimensionless Strouhal number, the ratio of the blunt body
  diameter to the product of the period of vortex shedding and the speed
  of a flowing medium, is a robust indicator for vortex shedding, and,
  generally of the order of 0.2 for a wide range of Reynolds number. Using
  an observation from the Atmospheric Imaging Assembly on board the
  Solar Dynamics Observatory, we report a wavelike or oscillating plasma
  flow propagating upward against the Sun's gravitational force. A newly
  formed shrinking loop in the postflare region possibly generates the
  oscillation of the upflow in the wake of the hot and dense loop through
  vortex shedding. The computed Strouhal number is consistent with the
  prediction from previous MHD simulations. Our observation suggests
  the possibility of vortex shedding in the solar corona.

---------------------------------------------------------
Title: In situmeasurements of the solar eruption
Authors: Lin, Jun; Wang, Min; Tian, Hui; Song, Hongqiang; Fu, Huishan;
   Huang, Min; Lv, Qunbo; Zhang, Weijie; Zhang, Xianguo; Zhang, Kunyi;
   Li, Mingtao Zhang, Yiteng; Jin, Zhenyu; Chen, Dong; Yin, Zengshan;
   Deng, Lei; Mao, Yufeng; Li, Yan; Mei, Zhixing; Ye, Jing
2019SSPMA..49e9607L    Altcode: 2019SSPMA..49e9607J
  No abstract at ADS

---------------------------------------------------------
Title: Flame-like Ellerman Bombs and Their Connection to Solar
    Ultraviolet Bursts
Authors: Chen, Yajie; Tian, Hui; Peter, Hardi; Samanta, Tanmoy;
   Yurchyshyn, Vasyl; Wang, Haimin; Cao, Wenda; Wang, Linghua; He, Jiansen
2019ApJ...875L..30C    Altcode: 2019arXiv190301981C
  Ellerman bombs (EBs) are small-scale intense brightenings in Hα
  wing images, which are generally believed to be signatures of
  magnetic reconnection around the temperature minimum region of the
  solar atmosphere. They have a flame-like morphology when observed
  near the solar limb. Recent observations from the Interface Region
  Imaging Spectrograph (IRIS) reveal another type of small-scale
  reconnection event called an ultraviolet (UV) burst, in the lower solar
  atmosphere. Though previous observations have shown a clear coincidence
  between the occurrence of some UV bursts and EBs, the exact relationship
  between these two phenomena is still debated. We investigate the spatial
  and temporal relationship between flame-like EBs and UV bursts using
  joint near-limb observations between the 1.6 m Goode Solar Telescope
  (GST) and IRIS. In total, 161 EBs have been identified from the GST
  observations, and ∼20 of them reveal signatures of UV bursts in
  the IRIS images. Interestingly, we find that these UV bursts have a
  tendency to appear at the upper parts of their associated flame-like
  EBs. The intensity variations of most EB-related UV bursts and their
  corresponding EBs match well. Our results suggest that some of these
  UV bursts and EBs likely form at different heights during a common
  reconnection process.

---------------------------------------------------------
Title: Electron Acceleration by ICME-driven Shocks at 1 au
Authors: Yang, Liu; Wang, Linghua; Li, Gang; Wimmer-Schweingruber,
   Robert F.; He, Jiansen; Tu, Chuanyi; Tian, Hui; Bale, Stuart D.
2019ApJ...875..104Y    Altcode:
  We present a comprehensive study of in situ electron acceleration
  during 74 shocks driven by interplanetary coronal mass ejections
  (ICMEs) with good suprathermal electron observations by the Wind
  3DP instrument at 1 au from 1995 through 2014. Among the selected 59
  quasi-perpendicular (15 quasi-parallel) shock cases, ∼86% (∼60%),
  ∼62% (∼36%), and ∼17% (∼7%) show significant electron flux
  enhancements of J <SUB> D </SUB>/J <SUB> A </SUB> &gt; 1.5 across
  the shock, respectively at 0.43, 1.95, and 40 keV, where J <SUB> D
  </SUB> and J <SUB> A </SUB> are the electron flux in the shock’s
  downstream and the preceding ambient solar wind. For significantly
  shocked suprathermal electrons, the differential flux J <SUB> D </SUB>
  positively correlates most with the magnetosonic Mach number M <SUB>
  s </SUB>, while the flux enhancement J <SUB> D </SUB>/J <SUB> A </SUB>
  positively correlates most with the magnetic compression ratio r <SUB>
  B </SUB>, among the shock parameters. Both J <SUB> D </SUB> and J <SUB>
  A </SUB> generally fit well to a double-power-law spectrum at ∼0.4-100
  keV, J ∝ E <SUP>-β </SUP>, with an index of β <SUB>1</SUB> ∼ 2-6
  below a break energy of E <SUB>br</SUB> (which is typically ∼2 keV)
  and an index of β <SUB>2</SUB> ∼ 2.0-3.2 at energies above. {β
  }<SUB>1</SUB><SUP>D</SUP> is similar to {β }<SUB>1</SUB><SUP>A</SUP>
  in all the shock cases, while {β }<SUB>2</SUB><SUP>D</SUP> is similar
  to (larger than) {β }<SUB>2</SUB><SUP>A</SUP> in ∼60% (∼40%) of the
  shock cases with significant electron enhancements. Furthermore, J <SUB>
  D </SUB>/J <SUB> A </SUB> mostly peaks in the directions perpendicular
  to the interplanetary magnetic field at ∼0.4-50 keV. These
  results suggest that both quasi-parallel and quasi-perpendicular
  shocks accelerate electrons in situ at 1 au mainly via shock drift
  acceleration, with an acceleration efficiency probably affected by
  the induced electric field at the shock surface.

---------------------------------------------------------
Title: Classification of large-scale stellar spectra based on deep
    convolutional neural network
Authors: Liu, W.; Zhu, M.; Dai, C.; He, D. Y.; Yao, Jiawen; Tian,
   H. F.; Wang, B. Y.; Wu, K.; Zhan, Y.; Chen, B. -Q.; Luo, A. -Li;
   Wang, R.; Cao, Y.; Yu, X. C.
2019MNRAS.483.4774L    Altcode: 2018MNRAS.tmp.2885L
  Classification of stellar spectra from voluminous spectra is a
  very important and challenging task. In order to better classify
  stellar spectra, inspired by the principle of deep convolutional
  neural network (CNN), we propose a supervised algorithm for stellar
  spectra classification based on 1-D stellar spectra convolutional
  neural network (1-D SSCNN). In 1-D SSCNN, we modify the traditional
  2-D convolutional neural network into 1-D network to adapt to the
  spectral classification. On the basis of using convolution algorithm,
  the spectral features are extracted and used for classification. We
  firstly use the stellar spectra data to train a 1-D SSCNN to obtain
  a well-trained model, and then we apply the well-trained model to
  classify the unknown spectra. To evaluate the performance of the
  proposed algorithms, we apply 1-D SSCNN to classify three spectral
  types: F-type spectra, G-type spectra and K-type spectra and ten
  subclasses of K-type spectra: A0-type, A5-type, F0-type, F5-type,
  G0-type, G5-type, K0-type, K5-type, M0-type and M5-type spectra from
  Sloan Digital Sky Survey (SDSS). Our 1-D SSCNN algorithm obtain higher
  classification accuracy compared with Support Vector Machine (SVM),
  Random Forest (RF) and Artificial neural network (ANN).

---------------------------------------------------------
Title: Investigating the Transition Region Explosive Events and
    Their Relationship to Network Jets
Authors: Chen, Yajie; Tian, Hui; Huang, Zhenghua; Peter, Hardi;
   Samanta, Tanmoy
2019ApJ...873...79C    Altcode: 2019arXiv190111215C
  Recent imaging observations with the Interface Region Imaging
  Spectrograph (IRIS) have revealed prevalent intermittent jets with
  apparent speeds of 80-250 km s<SUP>-1</SUP> from the network lanes
  in the solar transition region (TR). Additionally, spectroscopic
  observations of the TR lines have revealed the frequent presence of
  highly non-Gaussian line profiles with enhanced emission at the line
  wings, often referred to as explosive events (EEs). Using simultaneous
  imaging and spectroscopic observations from IRIS, we investigate
  the relationship between EEs and network jets. We first identify
  EEs from the Si IV 1393.755 Å line profiles in our observations,
  then examine related features in the 1330 Å slit-jaw images. Our
  analysis suggests that EEs with double peaks or enhancements in both
  wings appear to be located at either the footpoints of network jets or
  transient compact brightenings. These EEs are most likely produced by
  magnetic reconnection. We also find that EEs with enhancements only
  at the blue wing are mainly located on network jets, away from the
  footpoints. These EEs clearly result from the superposition of the
  high-speed network jets on the TR background. In addition, EEs showing
  enhancement only at the red wing of the line are often located around
  the jet footpoints, which is possibly caused by the superposition of
  reconnection downflows on the background emission. Moreover, we find
  some network jets that are not associated with any detectable EEs. Our
  analysis suggests that some EEs are related to the birth or propagation
  of network jets, and that others are not connected to network jets.

---------------------------------------------------------
Title: COronal Magnetism and Plasma ASsembled Scopes(COMPASS)
Authors: Qu, Zhongquan; Li, Hui; Zhong, Yue; Liang, Yu; Song, Zhiming;
   Zhang, Haiying; Zhang, Hongxin; Chen, Yao; Tian, Hui; Cheng, Xin;
   Xia, Lidong; Li, Bo; Chen, Bo; Yan, Xiaoli; Liu, Rui; Shen, Chenglong;
   Feng, Li; Hou, Junfeng; Li, Hao; Li, Zheng; Li, Shaoying
2019SSPMA..49e9606Q    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar Ultraviolet Bursts
Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.;
   Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal
   J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria
   S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark
   C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr
2018SSRv..214..120Y    Altcode: 2018arXiv180505850Y
  The term "ultraviolet (UV) burst" is introduced to describe small,
  intense, transient brightenings in ultraviolet images of solar active
  regions. We inventorize their properties and provide a definition
  based on image sequences in transition-region lines. Coronal signatures
  are rare, and most bursts are associated with small-scale, canceling
  opposite-polarity fields in the photosphere that occur in emerging flux
  regions, moving magnetic features in sunspot moats, and sunspot light
  bridges. We also compare UV bursts with similar transition-region
  phenomena found previously in solar ultraviolet spectrometry and
  with similar phenomena at optical wavelengths, in particular Ellerman
  bombs. Akin to the latter, UV bursts are probably small-scale magnetic
  reconnection events occurring in the low atmosphere, at photospheric
  and/or chromospheric heights. Their intense emission in lines with
  optically thin formation gives unique diagnostic opportunities
  for studying the physics of magnetic reconnection in the low solar
  atmosphere. This paper is a review report from an International Space
  Science Institute team that met in 2016-2017.

---------------------------------------------------------
Title: Investigation of White-light Emission in Circular-ribbon Flares
Authors: Song, Yongliang; Tian, Hui
2018ApJ...867..159S    Altcode: 2018arXiv181002958S
  Using observations by the Solar Dynamics Observatory from 2010 June to
  2017 December, we have performed the first statistical investigation of
  circular-ribbon flares (CFs) and examined the white-light emission in
  them. We find 90 CFs occurring in 36 active regions (ARs), including
  eight X-class, 34 M-class, and 48 C- and B-class flares. The occurrence
  rate of white-light flares (WLFs) is 100% (8/8) for X-class CFs,
  ∼62% (21/34) for M-class CFs, and ∼8% (4/48) for C- and B-class
  CFs. Sometimes we observe several CFs in a single AR, and nearly
  all of them are WLFs. Compared to normal CFs, those with white-light
  enhancement tend to have a shorter duration, smaller size, stronger
  electric current and more complicated magnetic field. We find that for
  X-class WLFs, the white-light enhancement is positively correlated
  with the flare class, implying that it is largely determined by the
  amount of released energy. However, there is no such correlation for M-
  and C-class WLFs, suggesting that other factors such as the timescale,
  spatial scale, and magnetic field complexity may play important roles
  in the generation of white-light emission if the released energy is
  not high enough.

---------------------------------------------------------
Title: Dark Structures in Sunspot Light Bridges
Authors: Zhang, Jingwen; Tian, Hui; Solanki, Sami K.; Wang, Haimin;
   Peter, Hardi; Ahn, Kwangsu; Xu, Yan; Zhu, Yingjie; Cao, Wenda; He,
   Jiansen; Wang, Linghua
2018ApJ...865...29Z    Altcode: 2018arXiv180900146Z
  We present unprecedented high-resolution TiO images and Fe I 1565
  nm spectropolarimetric data of two light bridges taken by the 1.6
  m Goode Solar Telescope at Big Bear Solar Observatory. In the first
  light bridge (LB1), we find striking knot-like dark structures within
  the central dark lane. Many dark knots show migration away from the
  penumbra along the light bridge. The sizes, intensity depressions,
  and apparent speeds of their proper motion along the light bridges of
  33 dark knots identified from the TiO images are mainly in the ranges
  of 80 ∼ 200 km, 30% ∼ 50%, and 0.3 ∼ 1.2 km s<SUP>-1</SUP>,
  respectively. In the second light bridge (LB2), a faint central dark
  lane and striking transverse intergranular lanes were observed. These
  intergranular lanes have sizes and intensity depressions comparable
  to those of the dark knots in LB1 and also migrate away from the
  penumbra at similar speeds. Our observations reveal that LB2 is made
  up of a chain of evolving convection cells, as indicated by patches of
  blueshift surrounded by narrow lanes of redshift. The central dark lane
  generally corresponds to blueshifts, supporting the previous suggestion
  of central dark lanes being the top parts of convection upflows. In
  contrast, the intergranular lanes are associated with redshifts and
  located at two sides of each convection cell. The magnetic fields are
  stronger in intergranular lanes than in the central dark lane. These
  results suggest that these intergranular lanes are manifestations of
  convergent convective downflows in the light bridge. We also provide
  evidence that the dark knots observed in LB1 may have a similar origin.

---------------------------------------------------------
Title: Two Solar Tornadoes Observed with the Interface Region
    Imaging Spectrograph
Authors: Yang, Zihao; Peter, Hardi; Su, Yang; Samanta, Tanmoy; Zhang,
   Jingwen; Tian, Hui; Chen, Yajie
2018cosp...42E3746Y    Altcode:
  The barbs or legs of some prominences show an apparent motion of
  rotation, which are often termed solar tornadoes. It is under debate
  whether the apparent motion is a real rotating motion, or caused by
  oscillations or counter-streaming flows. We present analysis results
  from spectroscopic observations of two tornadoes by the Interface
  Region Imaging Spectrograph. Each tornado was observed for more than 2.5
  hours. Doppler velocities are derived through a single Gaussian fit to
  the Mg II k 2796Å and Si IV 1393Å line profiles. We find coherent and
  stable red and blue shifts adjacent to each other across the tornado
  axes, which appears to favor the interpretation of these tornadoes
  as rotating cool plasmas with temperatures of 10^4 K-10^5 K. This
  interpretation is further supported by simultaneous observations of the
  Atmospheric Imaging Assembly on board the Solar Dynamics Observatory,
  which reveal periodic motions of dark structures in the tornadoes. Our
  results demonstrate that spectroscopic observations can provide key
  information to disentangle different physical processes in solar
  prominences.

---------------------------------------------------------
Title: Turbulence and Heating in the Flank and Wake Regions of a
    Coronal Mass Ejection
Authors: He, Jiansen; Song, Hong-Qiang; Tomczyk, Steven; Wang, Linghua;
   Tian, Hui; Fan, Siteng; Zhang, Lei; Yan, Limei
2018cosp...42E1404H    Altcode:
  As a coronal mass ejection (CME) passes, the flank and wake regions are
  typically strongly disturbed. Various instruments, including the Large
  Angle and Spectroscopic Coronagraph (LASCO), the Atmospheric Imaging
  Assembly (AIA), and the Coronal Multi-channel Polarimeter (CoMP),
  observed a CME close to the east limb on 26 October 2013.A hot (∼10
  MK) rising blob was detected on the east limb, with an initial ejection
  flow speed of ∼330 km/s. The magnetic structures on both sides and
  in the wake of the CME were strongly distorted, showing initiation
  of turbulent motions with Doppler-shift oscillations enhanced from
  ∼ ±3 km/s to ∼ ±15 km/s and effective thermal velocities from
  ∼30 km/s to ∼60 km/s, according to the CoMP observations at the
  Fe XIII line. The CoMP Doppler-shift maps suggest that the turbulence
  behaved differently at various heights; it showed clear wave-like
  torsional oscillations at lower altitudes, which are interpreted as the
  anti-phase oscillation of an alternating red/blue Doppler shift across
  the strands at the flank. The turbulence seems to appear differently in
  the channels of different temperatures. Its turnover time was ∼1000
  seconds for the Fe 171 Å channel, while it was ∼500 seconds for the
  Fe 193 Å channel. Mainly horizontal swaying rotations were observed in
  the Fe 171 Å channel, while more vertical vortices were seen in the
  Fe 193 Å channel. The differential-emission-measure profiles in the
  flank and wake regions have two components that evolve differently:
  the cool component decreased over time, evidently indicating a
  drop-out of cool materials due to ejection, while the hot component
  increased dramatically,probably because of the heating process, which
  is suspected to be a result of magnetic reconnection and turbulence
  dissipation. These results suggest a new turbulence-heating scenario
  of the solar corona and solar wind.

---------------------------------------------------------
Title: Diagnosing the magnetic field structure of a coronal cavity
    observed during the 2017 total solar eclipse
Authors: Chen, Yajie; Su, Yingna; Tian, Hui; Qu, Zhongquan; Deng,
   Linhua; Jibben, Patricia
2018cosp...42E.607C    Altcode:
  We present an investigation of a coronal cavity observed above the
  western limb in the coronal red line Fe X 637.4 nm using a telescope
  of Peking University and in the green line Fe XIV 530.3 nm using a
  telescope of Yunnan Observatories, Chinese Academy of Sciences during
  the total solar eclipse on 2017 August 21. A series of magnetic
  field models are constructed based on the magnetograms taken by
  the Helioseismic and Magnetic Imager onboard the Solar Dynamics
  Observatory (SDO) one week before the eclipse. The model field lines
  are then compared with coronal structures seen in images taken by
  the Atmospheric Imaging Assembly on board SDO and in our coronal red
  line images. The best-fit model consists of a flux rope with a twist
  angle of 3.1pi, which is consistent with the most probable value
  of the total twist angle of interplanetary flux ropes observed at 1
  AU. Linear polarization of the Fe XIII 1074.7 nm line calculated from
  this model shows a “lagomorphic" signature that is also observed by the
  Coronal Multichannel Polarimeter of the High Altitude Observatory. We
  also find a ring-shaped structure in the line-of-sight velocity of
  Fe XIII 1074.7 nm, which implies hot plasma flows along a helical
  magnetic field structure, in the cavity. These results suggest that
  the magnetic structure of the cavity is a highly twisted flux rope,
  which may erupt eventually. The temperature structure of the cavity
  has also been investigated using the intensity ratio of Fe XIII 1074.7
  nm and Fe X 637.4 nm.

---------------------------------------------------------
Title: Diagnosing Flare Dynamics Through the fe XXI 1354.08Å Line
Authors: Tian, Hui
2018cosp...42E3385T    Altcode:
  The Fe XXI 1354.08 line is the only strong emission line formed above
  10 MK in the spectral range of IRIS. It has been demonstrated to be very
  useful in diagnosing flare dynamics. For instance, the completeevolution
  of chromospheric evaporation has been well observed and it appears
  to correlate with the energy deposition rate in many flares, which
  provides critical constraint to models of chromosphericevaporation. With
  the Fe XXI line we have even observed multi-episode chromospheric
  evaporations in a flare. The Fe XXI line has also been successful in
  observing reconnection outflows, revealing important insight into the
  flare reconnection process. Moreover, global MHD oscillations have
  been detected in flare loops, both in the intensity and Doppler shift
  of the Fe XXI line, allowing more accurate mode identification that
  is crucial for coronal seismology.

---------------------------------------------------------
Title: Observations of white-light flares in NOAA active region 11515:
    high occurrence rate and relationship with magnetic transients
Authors: Song, Y. L.; Tian, H.; Zhang, M.; Ding, M. D.
2018A&A...613A..69S    Altcode: 2018arXiv180104371S
  <BR /> Aims: There are two goals in this study. One is to investigate
  how frequently white-light flares (WLFs) occur in a flare-productive
  active region (NOAA active region 11515). The other is to investigate
  the relationship between WLFs and magnetic transients (MTs). <BR />
  Methods: We used the high-cadence (45 s) full-disk continuum filtergrams
  and line-of-sight magnetograms taken by the Helioseismic and Magnetic
  Imager (HMI) on board the Solar Dynamics Observatory (SDO) to identify
  WLFs and MTs, respectively. Images taken by the Atmospheric Imaging
  Assembly (AIA) on board SDO were also used to show the flare morphology
  in the upper atmosphere. <BR /> Results: We found at least 20 WLFs out
  of a total of 70 flares above C class (28.6%) in NOAA active region
  11515 during its passage across the solar disk (E45°-W45°). Each of
  these WLFs occurred in a small region, with a short duration of about 5
  min. The enhancement of the white-light continuum intensity is usually
  small, with an average enhancement of 8.1%. The 20 WLFs we observed
  were found along an unusual configuration of the magnetic field that
  was characterized by a narrow ribbon of negative field. Furthermore,
  the WLFs were found to be accompanied by MTs, with radical changes
  in magnetic field strength (or even a sign reversal) observed during
  the flare. In contrast, there is no obvious signature of MTs in the 50
  flares without white-light enhancements. <BR /> Conclusions: Our results
  suggest that WLFs occur much more frequently than previously thought,
  with most WLFs being fairly weak enhancements. This may explain why WLFs
  are reported rarely. Our observations also suggest that MTs and WLFs are
  closely related and appear cospatial and cotemporal, when considering
  HMI data. A greater enhancement of WL emission is often accompanied by a
  greater change in the line-of-sight component of the unsigned magnetic
  field. Considering the close relationship between MTs and WLFs, many
  previously reported flares with MTs may be WLFs. <P />The movie is
  available at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Statistical Investigation of Supersonic Downflows in the
    Transition Region above Sunspots
Authors: Samanta, Tanmoy; Tian, Hui; Prasad Choudhary, Debi
2018ApJ...859..158S    Altcode: 2018arXiv180405054S
  Downflows at supersonic speeds have been observed in the transition
  region (TR) above sunspots for more than three decades. These downflows
  are often seen in different TR spectral lines above sunspots. We
  have performed a statistical investigation of these downflows using
  a large sample that was missing previously. The Interface Region
  Imaging Spectrograph (IRIS) has provided a wealth of observational
  data of sunspots at high spatial and spectral resolutions in the
  past few years. We have identified 60 data sets obtained with IRIS
  raster scans. Using an automated code, we identified the locations
  of strong downflows within these sunspots. We found that around
  80% of our sample shows supersonic downflows in the Si IV 1403 Å
  line. These downflows mostly appear in the penumbral regions, though
  some of them are found in the umbrae. We also found that almost half of
  these downflows show signatures in chromospheric lines. Furthermore,
  a detailed spectral analysis was performed by selecting a small
  spectral window containing the O IV 1400/1401 Å and Si IV 1403 Å
  lines. Six Gaussian functions were simultaneously fitted to these
  three spectral lines and their satellite lines associated with the
  supersonic downflows. We calculated the intensity, Doppler velocity,
  and line width for these lines. Using the O IV 1400/1401 Å line ratio,
  we find that the downflow components are around one order of magnitude
  less dense than the regular components. Results from our statistical
  analysis suggest that these downflows may originate from the corona
  and that they are independent of the background TR plasma.

---------------------------------------------------------
Title: Multi-episode Chromospheric Evaporation Observed in a Solar
    Flare
Authors: Tian, H.; Chen, N. -H.
2018ApJ...856...34T    Altcode: 2018arXiv180104370T
  With observations of the Interface Region Imaging Spectrograph (IRIS),
  we study chromospheric heating and evaporation during an M1.6 flare
  SOL2015-03-12T11:50. At the flare ribbons, the Mg II 2791.59 Å line
  shows quasi-periodic short-duration red-wing enhancement, which is
  likely related to repetitive chromospheric condensation as a result of
  episodic heating. On the contrary, the Si IV 1402.77 Å line reveals
  a persistent red-wing asymmetry in both the impulsive and decay
  phases, suggesting that this line responds to both cooling downflows
  and chromospheric condensation. The first two episodes of red-wing
  enhancement occurred around 11:42 UT and 11:45 UT, when two moving
  brightenings indicative of heating fronts crossed the IRIS slit. The
  greatly enhanced red wings of the Si IV and Mg II lines at these
  occasions are accompanied by an obvious increase in the line intensities
  and the HXR flux, suggesting two episodes of energy injection into
  the lower atmosphere in the form of nonthermal electrons. The Mg II
  k/h ratio has a small value of ∼1.2 at the ribbons and decreases
  to ∼1.1 at these two occasions. Correspondingly, the Fe XXI 1354
  Å line reveals two episodes of chromospheric evaporation, which is
  characterized as a smooth decrease of the blueshift from ∼300 km
  s<SUP>-1</SUP> to nearly zero within ∼3 minutes. The Fe XXI 1354 Å
  line is entirely blueshifted in the first episode, while it appears to
  contain a nearly stationary component and a blueshifted component in
  the second episode. Additional episodes of blueshifted Fe XXI emission
  are found around the northern ribbon in the decay phase, though no
  obvious response is detected in the Si IV and Mg II emission. We have
  also examined the Fe XXI emission at the flare loop top and identified
  a secondary component with a ∼200 km s<SUP>-1</SUP> redshift, which
  possibly results from the downward moving reconnection outflow. Our
  analysis also yields a rest wavelength of 1354.0878 ± 0.0072 Å for
  this Fe XXI line.

---------------------------------------------------------
Title: Diagnosing the Magnetic Field Structure of a Coronal Cavity
    Observed during the 2017 Total Solar Eclipse
Authors: Chen, Yajie; Tian, Hui; Su, Yingna; Qu, Zhongquan; Deng,
   Linhua; Jibben, Patricia R.; Yang, Zihao; Zhang, Jingwen; Samanta,
   Tanmoy; He, Jiansen; Wang, Linghua; Zhu, Yingjie; Zhong, Yue; Liang, Yu
2018ApJ...856...21C    Altcode: 2018arXiv180204432C
  We present an investigation of a coronal cavity observed above the
  western limb in the coronal red line Fe X 6374 Å using a telescope of
  Peking University and in the green line Fe XIV 5303 Å using a telescope
  of Yunnan Observatories, Chinese Academy of Sciences, during the total
  solar eclipse on 2017 August 21. A series of magnetic field models is
  constructed based on the magnetograms taken by the Helioseismic and
  Magnetic Imager on board the Solar Dynamics Observatory (SDO) one week
  before the eclipse. The model field lines are then compared with coronal
  structures seen in images taken by the Atmospheric Imaging Assembly
  on board SDO and in our coronal red line images. The best-fit model
  consists of a flux rope with a twist angle of 3.1π, which is consistent
  with the most probable value of the total twist angle of interplanetary
  flux ropes observed at 1 au. Linear polarization of the Fe XIII 10747
  Å line calculated from this model shows a “lagomorphic” signature
  that is also observed by the Coronal Multichannel Polarimeter of the
  High Altitude Observatory. We also find a ring-shaped structure in the
  line-of-sight velocity of Fe XIII 10747 Å, which implies hot plasma
  flows along a helical magnetic field structure, in the cavity. These
  results suggest that the magnetic structure of the cavity is a highly
  twisted flux rope, which may erupt eventually. The temperature structure
  of the cavity has also been investigated using the intensity ratio of
  Fe XIII 10747 Å and Fe X 6374 Å.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Gaia-PS1-SDSS (GPS1) proper motion
    catalog (Tian+, 2017)
Authors: Tian, H. -J.; Gupta, P.; Sesar, B.; Rix, H. -W.; Martin,
   N. F.; Liu, C.; Goldman, B.; Platais, I.; Kudritzki, R. -P.; Waters,
   C. Z.
2018yCat.1343....0T    Altcode:
  In order to construct proper motions, we analyze and model catalog
  positions from four different imaging surveys, as discussed below. Gaia
  DR1 is based on observations collected between 2014 July 25 and 2015
  September 16. PS1 observations were collected between 2010 and 2014. The
  SDSS DR9 data used here were obtained in the years between 2000 and
  2008. The images from 2MASS were taken between 1997 and 2001. <P />(1
  data file).

---------------------------------------------------------
Title: Two-stage Energy Release Process of a Confined Flare with
    Double HXR Peaks
Authors: Ning, Hao; Chen, Yao; Wu, Zhao; Su, Yang; Tian, Hui; Li,
   Gang; Du, Guohui; Song, Hongqiang
2018ApJ...854..178N    Altcode: 2018arXiv180106641N
  A complete understanding of the onset and subsequent evolution of
  confined flares has not been achieved. Earlier studies mainly analyzed
  disk events so as to reveal their magnetic topology and the cause of
  confinement. In this study, taking advantage of a tandem of instruments
  working at different wavelengths of X-rays, EUVs, and microwaves,
  we present dynamic details about a confined flare observed on the
  northwestern limb of the solar disk on 2016 July 24. The entire
  dynamic evolutionary process starting from its onset is consistent
  with a loop-loop interaction scenario. The X-ray profiles manifest an
  intriguing double-peak feature. From the spectral fitting, it has been
  found that the first peak is nonthermally dominated, while the second
  peak is mostly multithermal with a hot (∼10 MK) and a super-hot
  (∼30 MK) component. This double-peak feature is unique in that the
  two peaks are clearly separated by 4 minutes, and the second peak
  reaches up to 25-50 keV in addition, at energy bands above 3 keV,
  the X-ray fluxes decline significantly between the two peaks. This,
  together with other available imaging and spectral data, manifest a
  two-stage energy release process. A comprehensive analysis is carried
  out to investigate the nature of this two-stage process. We conclude
  that the second stage with the hot and super-hot sources mainly involves
  direct heating through a loop-loop reconnection at a relatively high
  altitude in the corona. The uniqueness of the event characteristics
  and the complete dataset make the study a nice addition to present
  literature on solar flares.

---------------------------------------------------------
Title: Observations of a White-light Flare Associated with a Filament
    Eruption
Authors: Song, Y. L.; Guo, Y.; Tian, H.; Zhu, X. S.; Zhang, M.; Zhu,
   Y. J.
2018ApJ...854...64S    Altcode: 2018arXiv180104408S
  We present observations of an M5.7 white-light flare (WLF) associated
  with a small filament eruption in NOAA active region 11476 on 2012
  May 10. During this flare, a circular flare ribbon appeared in the
  east and a remote brightening occurred in the northwest of the active
  region. Multi-wavelength data are employed to analyze the WLF, including
  white light (WL), ultraviolet, extreme ultraviolet, hard X-ray (HXR),
  and microwave. A close spatial and temporal relationship between the WL,
  HXR, and microwave emissions is found in this WLF. However, the peak
  time of the WL emission lagged that of the HXR and microwave emissions
  by about 1-2 minutes. Such a result tends to support the backwarming
  mechanism for the WL emission. Interestingly, the enhanced WL emission
  occurred at the two footpoints of the filament. Through forced and
  potential field extrapolations, we find that the 3D magnetic field in
  the flare region has a fan-spine feature and that a flux rope lies
  under the dome-like field structure. We describe the entire process
  of flare evolution into several steps, each one producing the sequent
  brightening below the filament, the circular flare ribbons, and the
  WL enhancement, respectively. We suggest that a reconnection between
  the magnetic field of the filament and the overlying magnetic field
  or reconnection within the flux rope leads to the WL enhancement.

---------------------------------------------------------
Title: Magnetic Braids in Eruptions of a Spiral Structure in the
    Solar Atmosphere
Authors: Huang, Zhenghua; Xia, Lidong; Nelson, Chris J.; Liu, Jiajia;
   Wiegelmann, Thomas; Tian, Hui; Klimchuk, James A.; Chen, Yao; Li, Bo
2018ApJ...854...80H    Altcode: 2018arXiv180105967H
  We report on high-resolution imaging and spectral observations of
  eruptions of a spiral structure in the transition region, which
  were taken with the Interface Region Imaging Spectrograph, and the
  Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic
  Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The eruption
  coincided with the appearance of two series of jets, with velocities
  comparable to the Alfvén speeds in their footpoints. Several pieces of
  evidence of magnetic braiding in the eruption are revealed, including
  localized bright knots, multiple well-separated jet threads, transition
  region explosive events, and the fact that all three of these are
  falling into the same locations within the eruptive structures. Through
  analysis of the extrapolated 3D magnetic field in the region, we found
  that the eruptive spiral structure corresponded well to locations
  of twisted magnetic flux tubes with varying curl values along their
  lengths. The eruption occurred where strong parallel currents,
  high squashing factors, and large twist numbers were obtained. The
  electron number density of the eruptive structure is found to be ∼3 ×
  10<SUP>12</SUP> cm<SUP>-3</SUP>, indicating that a significant amount
  of mass could be pumped into the corona by the jets. Following the
  eruption, the extrapolations revealed a set of seemingly relaxed loops,
  which were visible in the AIA 94 Å channel, indicating temperatures
  of around 6.3 MK. With these observations, we suggest that magnetic
  braiding could be part of the mechanisms explaining the formation of
  solar eruption and the mass and energy supplement to the corona.

---------------------------------------------------------
Title: Frequently Occurring Reconnection Jets from Sunspot Light
    Bridges
Authors: Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Solanki, Sami
   K.; Young, Peter R.; Ni, Lei; Cao, Wenda; Ji, Kaifan; Zhu, Yingjie;
   Zhang, Jingwen; Samanta, Tanmoy; Song, Yongliang; He, Jiansen; Wang,
   Linghua; Chen, Yajie
2018ApJ...854...92T    Altcode: 2018arXiv180106802T
  Solid evidence of magnetic reconnection is rarely reported within
  sunspots, the darkest regions with the strongest magnetic fields
  and lowest temperatures in the solar atmosphere. Using the world’s
  largest solar telescope, the 1.6 m Goode Solar Telescope, we detect
  prevalent reconnection through frequently occurring fine-scale jets
  in the Hα line wings at light bridges, the bright lanes that may
  divide the dark sunspot core into multiple parts. Many jets have an
  inverted Y-shape, shown by models to be typical of reconnection in a
  unipolar field environment. Simultaneous spectral imaging data from
  the Interface Region Imaging Spectrograph show that the reconnection
  drives bidirectional flows up to 200 km s<SUP>-1</SUP>, and that the
  weakly ionized plasma is heated by at least an order of magnitude up
  to ∼80,000 K. Such highly dynamic reconnection jets and efficient
  heating should be properly accounted for in future modeling efforts
  of sunspots. Our observations also reveal that the surge-like activity
  previously reported above light bridges in some chromospheric passbands
  such as the Hα core has two components: the ever-present short surges
  likely to be related to the upward leakage of magnetoacoustic waves
  from the photosphere, and the occasionally occurring long and fast
  surges that are obviously caused by the intermittent reconnection jets.

---------------------------------------------------------
Title: Magnetic Reconnection at the Earliest Stage of Solar Flux
    Emergence
Authors: Tian, Hui; Zhu, Xiaoshuai; Peter, Hardi; Zhao, Jie; Samanta,
   Tanmoy; Chen, Yajie
2018ApJ...854..174T    Altcode: 2018arXiv180106785T
  On 2016 September 20, the Interface Region Imaging Spectrograph observed
  an active region during its earliest emerging phase for almost 7 hr. The
  Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory
  observed continuous emergence of small-scale magnetic bipoles with
  a rate of ∼10<SUP>16</SUP> Mx s<SUP>-1</SUP>. The emergence of
  magnetic fluxes and interactions between different polarities lead to
  the frequent occurrence of ultraviolet (UV) bursts, which exhibit as
  intense transient brightenings in the 1400 Å images. In the meantime,
  discrete small patches with the same magnetic polarity tend to move
  together and merge, leading to the enhancement of the magnetic fields
  and thus the formation of pores (small sunspots) at some locations. The
  spectra of these UV bursts are characterized by the superposition of
  several chromospheric absorption lines on the greatly broadened profiles
  of some emission lines formed at typical transition region temperatures,
  suggesting heating of the local materials to a few tens of thousands of
  kelvin in the lower atmosphere by magnetic reconnection. Some bursts
  reveal blue- and redshifts of ∼100 km s<SUP>-1</SUP> at neighboring
  pixels, indicating the spatially resolved bidirectional reconnection
  outflows. Many such bursts appear to be associated with the cancellation
  of magnetic fluxes with a rate of the order of ∼10<SUP>15</SUP> Mx
  s<SUP>-1</SUP>. We also investigate the three-dimensional magnetic
  field topology through a magnetohydrostatic model and find that a
  small fraction of the bursts are associated with bald patches (magnetic
  dips). Finally, we find that almost all bursts are located in regions
  of large squashing factor at the height of ∼1 Mm, reinforcing our
  conclusion that these bursts are produced through reconnection in the
  lower atmosphere.

---------------------------------------------------------
Title: Two Solar Tornadoes Observed with the Interface Region
    Imaging Spectrograph
Authors: Yang, Zihao; Tian, Hui; Peter, Hardi; Su, Yang; Samanta,
   Tanmoy; Zhang, Jingwen; Chen, Yajie
2018ApJ...852...79Y    Altcode: 2017arXiv171108968Y
  The barbs or legs of some prominences show an apparent motion of
  rotation, which are often termed solar tornadoes. It is under debate
  whether the apparent motion is a real rotating motion, or caused by
  oscillations or counter-streaming flows. We present analysis results
  from spectroscopic observations of two tornadoes by the Interface
  Region Imaging Spectrograph. Each tornado was observed for more than
  2.5 hr. Doppler velocities are derived through a single Gaussian fit to
  the Mg II k 2796 Å and Si IV 1393 Å line profiles. We find coherent
  and stable redshifts and blueshifts adjacent to each other across
  the tornado axes, which appears to favor the interpretation of these
  tornadoes as rotating cool plasmas with temperatures of 10<SUP>4</SUP>
  K-10<SUP>5</SUP> K. This interpretation is further supported by
  simultaneous observations of the Atmospheric Imaging Assembly on
  board the Solar Dynamics Observatory, which reveal periodic motions
  of dark structures in the tornadoes. Our results demonstrate that
  spectroscopic observations can provide key information to disentangle
  different physical processes in solar prominences.

---------------------------------------------------------
Title: Turbulence and Heating in the Flank and Wake Regions of a
    Coronal Mass Ejection
Authors: Fan, Siteng; He, Jiansen; Yan, Limei; Tomczyk, Steven; Tian,
   Hui; Song, Hongqiang; Wang, Linghua; Zhang, Lei
2018SoPh..293....6F    Altcode:
  As a coronal mass ejection (CME) passes, the flank and wake regions are
  typically strongly disturbed. Various instruments, including the Large
  Angle and Spectroscopic Coronagraph (LASCO), the Atmospheric Imaging
  Assembly (AIA), and the Coronal Multi-channel Polarimeter (CoMP),
  observed a CME close to the east limb on 26 October 2013. A hot (≈10
  MK) rising blob was detected on the east limb, with an initial ejection
  flow speed of ≈330 kms−<SUP>1</SUP>. The magnetic structures
  on both sides and in the wake of the CME were strongly distorted,
  showing initiation of turbulent motions with Doppler-shift oscillations
  enhanced from ≈±3 kms−<SUP>1</SUP> to ≈±15 kms−<SUP>1</SUP>
  and effective thermal velocities from ≈30 kms−<SUP>1</SUP> to ≈60
  kms−<SUP>1</SUP>, according to the CoMP observations at the Fe XIII
  line. The CoMP Doppler-shift maps suggest that the turbulence behaved
  differently at various heights; it showed clear wave-like torsional
  oscillations at lower altitudes, which are interpreted as the antiphase
  oscillation of an alternating red/blue Doppler shift across the strands
  at the flank. The turbulence seems to appear differently in the channels
  of different temperatures. Its turnover time was ≈1000 seconds for
  the Fe 171 Å channel, while it was ≈500 seconds for the Fe 193 Å
  channel. Mainly horizontal swaying rotations were observed in the Fe
  171 Å channel, while more vertical vortices were seen in the Fe 193
  Å channel. The differential-emission-measure profiles in the flank
  and wake regions have two components that evolve differently: the
  cool component decreased over time, evidently indicating a drop-out
  of cool materials due to ejection, while the hot component increased
  dramatically, probably because of the heating process, which is
  suspected to be a result of magnetic reconnection and turbulence
  dissipation. These results suggest a new turbulence-heating scenario
  of the solar corona and solar wind.

---------------------------------------------------------
Title: The Strongest Acceleration of &gt;40 keV Electrons by
    ICME-driven Shocks at 1 au
Authors: Yang, Liu; Wang, Linghua; Li, Gang; Wimmer-Schweingruber,
   Robert F.; He, Jiansen; Tu, Chuanyi; Tian, Hui; Bale, Stuart D.
2018ApJ...853...89Y    Altcode:
  We present two case studies of the in-situ electron acceleration
  during the 2000 February 11 shock and the 2004 July 22 shock, with
  the strongest electron flux enhancement at 40 keV across the shock,
  among all the quasi-perpendicular and quasi-parallel ICME-driven
  shocks observed by the WIND 3DP instrument from 1995 through 2014 at
  1 au. We find that for this quasi-perpendicular (quasi-parallel) shock
  on 2000 February 11 (2004 July 22), the shocked electron differential
  fluxes at ∼0.4-50 keV in the downstream generally fit well to a
  double-power-law spectrum, J ∼ E <SUP>-β </SUP>, with an index of β
  ∼ 3.15 (4.0) at energies below a break at ∼3 keV (∼1 keV) and β
  ∼ 2.65 (2.6) at energies above. For both shock events, the downstream
  electron spectral indices appear to be similar for all pitch angles,
  which are significantly larger than the index prediction by diffusive
  shock acceleration. In addition, the downstream electron pitch-angle
  distributions show the anisotropic beams in the anti-sunward-traveling
  direction, while the ratio of the downstream over ambient fluxes appears
  to peak near 90° pitch angles, at all energies of ∼0.4-50 keV. These
  results suggest that in both shocks, shock drift acceleration likely
  plays an important role in accelerating electrons in situ at 1 au. Such
  ICME-driven shocks could contribute to the formation of solar wind
  halo electrons at energies ≲2 keV, as well as the production of solar
  wind superhalo electrons at energies ≳2 keV in interplanetary space.

---------------------------------------------------------
Title: A Study on Sunward-propagating Alfvénic Fluctuations with
    a Power-law Spectrum (SAFP) Observed by the WIND Spacecraft
Authors: Wang, X.; Wu, H.; Tu, C. Y.; Wang, L.; He, J.; Tian, H.
2017AGUFMSH33B2773W    Altcode:
  Sunward-propagating Alfvénic fluctuations with a power-law spectrum
  (SAFP) have been recently reported to be a significant physical
  phenomenon in the solar wind. However, some characteristics of these
  SAFPs are still unknown. Here we develop a new method for identifying
  SAFPs. In this method, we can identify all SAFPs with any value of θRB
  (angle between the global magnetic field and the radial direction). We
  find 508 SAFPs using the WIND spacecraft observation from 1995 to
  2014. We also find that SAFP occurs more frequently when θRB equals
  90°. The spectral index with an average -1.77 changes continuously
  from -2.18 for the parallel to -1.71 for the perpendicular. SAFPs
  occur more at the maximum and tend to be observed in the slow solar
  wind especially at solar minimum. We also apply the new method to
  identify anti-sunward-propagating Alfvénic fluctuations with a
  power-law spectrum (AFP) for comparison. The number of SAFPs is much
  less than AFPs, and the cases with local bending account for about
  half of all observed cases. SAFPs have a preference for negative σc
  and ASFs for positive. The statistical results demonstrate that SAFP
  has a steeper and weaker power spectrum and present a weaker power
  anisotropy than that of AFP. These new results may reveal new insight
  into the physical mechanism of the SAFP generation.

---------------------------------------------------------
Title: Solar Wind  0.1-1 keV Electrons in the Corotating Interaction
    Regions
Authors: Wang, L.; Tao, J.; Li, G.; Wimmer-Schweingruber, R. F.;
   Jian, L. K.; He, J.; Tu, C.; Tian, H.; Bale, S. D.
2017AGUFMSH34A..03W    Altcode:
  Here we present a statistical study of the 0.1-1 keV suprathermal
  electrons in the undisturbed and compressed slow/fast solar wind, for
  the 71 corotating interaction regions (CIRs) with good measurements
  from the WIND 3DP and MFI instruments from 1995 to 1997. For each of
  these CIRs, we separate the strahl and halo electrons based on their
  different behaviors in pitch angle distributions in the undisturbed and
  compressed solar wind. We fit both the strahl and halo energy spectra
  to a kappa function with an index κ index and effective temperature
  Teff, and calculate the pitch-angle width at half-maximum (PAHM) of
  the strahl population. We also integrate the electron measurements
  between 0.1 and 1.0 keV to obtain the number density n and average
  energy Eavg for the strahl and halo populations. We find that for
  both the strahl and halo populations within and around these CIRs,
  the fitted κ index strongly correlates with Teff, similar to the
  quiet-time solar wind (Tao et al., ApJ, 2016). The number density of
  both the strahl and halo shows a strong positive correlation with the
  electron core temperature. The strahl number density ns is correlated
  with the magnitude of interplanetary magnetic field, and the strahl
  PAHM width is anti-correlated with the solar wind speed. These results
  suggest that the origin of strahl electrons from the solar corona is
  likely related to the electron core temperature and magnetic field
  strength, while the production of halo electrons in the interplanetary
  medium could depend on the solar wind velocity.

---------------------------------------------------------
Title: A Study on Sunward Propagating Alfvénic Fluctuations With
    a Power Law Spectrum Observed by the Wind Spacecraft
Authors: Wu, Honghong; Wang, Xin; Tu, Chuanyi; Wang, Linghua; He,
   Jiansen; Tian, Hui
2017JGRA..122.9768W    Altcode:
  Sunward propagating Alfvénic fluctuations with a power law spectrum
  (SAFP) have been recently observed in the upstream region of the
  Earth's bow shock. However, some physical properties of these
  fluctuations such as anisotropy remain unclear. Here we develop a
  new method for identifying SAFPs, and present for the first time
  the anisotropy of SAFPs power and spectral index. In this method,
  the propagation direction determination of SAFPs does not rely on a
  radial magnetic geometry but the pitch angle distribution of strahl
  electron outflow. Therefore, the SAFPs with any value of θ<SUB>RB</SUB>
  (angle between the global mean magnetic field and the Sun-to-Earth
  radial direction) can be identified, so that enables the study of
  the spectral anisotropy. We find 508 SAFPs using the Wind spacecraft
  measurements from 1995 to 2014. We show that the SAFP has an averaged
  spectral index of -1.77 ± 0.28 and the index changes continuously
  from -2.18 ± 0.21 when θ<SUB>RB</SUB>=0°-10° to -1.71 ± 0.03 when
  θ<SUB>RB</SUB>=80°-90°. These SAFPs are observed more frequently
  in the slow solar wind especially at solar minimum. We also select
  antisunward propagating Alfvénic fluctuations with a power law spectrum
  using the same method for comparison. The results indicate that the
  power spectrum of SAFP is steeper, and the spectral intensity as well as
  the power anisotropy of SAFP is weaker. These new findings may provide
  information on the generation of turbulence in the upstream region.

---------------------------------------------------------
Title: Probing the solar transition region: current status and
    future perspectives
Authors: Tian, Hui
2017RAA....17..110T    Altcode:
  The solar transition region (TR) is the temperature regime from
  roughly 0.02 MK to 0.8 MK in the solar atmosphere. It is the transition
  layer from the collisional and partially ionized chromosphere to the
  collisionless and fully ionized corona. The TR plays an important role
  in the mass and energy transport in both the quiet solar atmosphere and
  solar eruptions. Most of the TR emission lines fall into the spectral
  range of far ultraviolet and extreme ultraviolet (∼ 400 Å-1600
  Å). Imaging and spectroscopic observations in this spectral range are
  the most important ways to obtain information about the physics of the
  TR. Static solar atmosphere models predict a very thin TR. However,
  recent high-resolution observations indicate that the TR is highly
  dynamic and inhomogeneous. I will summarize some major findings about
  the TR made through imaging and spectroscopic observations in the
  past 20 years. These existing observations have demonstrated that the
  TR may be the key to understanding coronal heating and origin of the
  solar wind. Future exploration of the solar TR may need to focus on
  the upper TR, since the plasma in this temperature regime (0.1 MK-0.8
  MK) has not been routinely imaged before. High-resolution imaging and
  spectroscopic observations of the upper TR will not only allow us to
  track the mass and energy from the lower atmosphere to the corona,
  but also help us to understand the initiation and heating mechanisms
  of coronal mass ejections and solar flares.

---------------------------------------------------------
Title: Multi-label Learning for Detection of CME-Associated Phenomena
Authors: Yang, Y. H.; Tian, H. M.; Peng, B.; Li, T. R.; Xie, Z. X.
2017SoPh..292..131Y    Altcode:
  Coronal mass ejections (CMEs) are considered as one of the driving
  sources of space weather. They are usually associated with many physical
  phenomena, e.g. flares, coronal dimmings, and sigmoids. To detect these
  phenomena, traditional supervised-learning methods assumed that at most
  one event occurred in a CME; therefore each CME instance is associated
  with a single label and the phenomenon is processed in isolation. This
  simplifying assumption does not fit well, as CMEs might have multiple
  events simultaneously. We propose to detect multiple CME-associated
  events by multi-label learning methods. With the data available
  from the Atmospheric Imaging Assembly (AIA) and the Large Angle and
  Spectrometric Coronagraph (LASCO), texture features representing the
  events are extracted from all of the associated and not-associated CMEs
  and converted into feature vectors for multi-label learning use. Then
  a function is learned to predict the proper label sets for CMEs,
  such that eight events, i.e. coronal dimming, coronal hole, coronal
  jet, coronal wave, filament, filament eruption, flare, and sigmoid,
  are detected explicitly. To test the proposed detection algorithm, we
  adopt the four-fold cross-validation strategy on a set of 551 labeled
  CMEs from AIA. Experimental results demonstrate the good performance
  of the multi-label classification methods in terms of test error.

---------------------------------------------------------
Title: Searching for a termination shock in a well-observed limb flare
Authors: Reeves, Kathy; Chen, Bin; White, Stephen; Tian, Hui
2017shin.confE..66R    Altcode:
  We examine a well-observed flare that occurred on the limb of the Sun
  on March 7, 2015 in order to find possible signatures of a termination
  shock due to outflows from reconnecting magnetic fields. Images
  of this flare from Hinode/XRT and the SDO/AIA 131 bandpass show a
  cusp-shaped morphology. The IRIS slit was positioned in the region of
  the current sheet, above the flare loops. Fe XXI is detected in the
  IRIS spectra with an average Doppler velocity of about 20 km/s. The
  non-thermal widths in IRIS decrease steadily from 23:00 UT on the 7th
  until 00:20 UT the next day, but there is no strong evidence that the
  slit crossed a termination shock. Data from Nobeyama Radioheliograph
  (NoRH) is primarily due to thermal free-free emission based on the
  examination of NoRH images at 17 GHz and 34 GHz, and RHESSI data shows
  a thermal looptop source at 6-10 keV. The lack of non-thermal emission
  in this data implies that there is no shock region that accelerates
  particles. However, neither of these instruments were observing during
  the impulsive phase of the flare, which peaked at about 22:25 UT. We
  also investigate the temperature structure of the flare using XRT and
  AIA data, and do not find any evidence for a termination shock.

---------------------------------------------------------
Title: Surge-like Oscillations above Sunspot Light Bridges Driven
    by Magnetoacoustic Shocks
Authors: Zhang, Jingwen; Tian, Hui; He, Jiansen; Wang, Linghua
2017ApJ...838....2Z    Altcode: 2017arXiv170208585Z
  High-resolution observations of the solar chromosphere and transition
  region often reveal surge-like oscillatory activities above sunspot
  light bridges (LBs). These oscillations are often interpreted
  as intermittent plasma jets produced by quasi-periodic magnetic
  reconnection. We have analyzed the oscillations above an LB in a sunspot
  using data taken by the Interface Region Imaging Spectrograph. The
  chromospheric 2796 Å images show surge-like activities above the
  entire LB at any time, forming an oscillating wall. Within the wall
  we often see that the core of the Mg II k 2796.35 Å line first
  experiences a large blueshift, and then gradually decreases to zero
  shift before increasing to a redshift of comparable magnitude. Such a
  behavior suggests that the oscillations are highly nonlinear and likely
  related to shocks. In the 1400 Å passband, which samples emission
  mainly from the Si IV ion, the most prominent feature is a bright
  oscillatory front ahead of the surges. We find a positive correlation
  between the acceleration and maximum velocity of the moving front,
  which is consistent with numerical simulations of upward propagating
  slow-mode shock waves. The Si IV 1402.77 Å line profile is generally
  enhanced and broadened in the bright front, which might be caused
  by turbulence generated through compression or by the shocks. These
  results, together with the fact that the oscillation period stays
  almost unchanged over a long duration, lead us to propose that the
  surge-like oscillations above LBs are caused by shocked p-mode waves
  leaked from the underlying photosphere.

---------------------------------------------------------
Title: Dynamics of Subarcsecond Bright Dots in the Transition Region
    above Sunspots and Their Relation to Penumbral Micro-jets
Authors: Samanta, Tanmoy; Tian, Hui; Banerjee, Dipankar; Schanche,
   Nicole
2017ApJ...835L..19S    Altcode: 2017arXiv170102531S
  Recent high-resolution observations have revealed that subarcsecond
  bright dots (BDs) with sub-minute lifetimes appear ubiquitously
  in the transition region (TR) above sunspot penumbra. The presence
  of penumbral micro-jets (PMJs) in the chromosphere was previously
  reported. It was proposed that both the PMJs and BDs are formed due
  to a magnetic reconnection process and may play an important role
  in heating of the penumbra. Using simultaneous observations of the
  chromosphere from the Solar Optical Telescope (SOT) on board Hinode and
  observations of the TR from the Interface Region Imaging Spectrograph,
  we study the dynamics of BDs and their relation to PMJs. We find two
  types of BDs, one that is related to PMJs, and another that does not
  show any visible dynamics in the SOT Ca II H images. From a statistical
  analysis we show that these two types have different properties. The
  BDs that are related to PMJs always appear at the top of the PMJs,
  the vast majority of which show inward motion and originate before
  the generation of the PMJs. These results may indicate that the
  reconnection occurs at the lower coronal/TR height and initiates PMJs
  at the chromosphere. This formation mechanism is in contrast with the
  formation of PMJs by reconnection in the (upper) photosphere between
  differently inclined fields.

---------------------------------------------------------
Title: Observations of the solar corona during the total solar
    eclipse on 21 August 2017
Authors: Tian, Hui; Qu, ZhongQuan; Chen, YaJie; Deng, LinHua; Huang,
   ZhengHua; Li, Hao; Zhong, Yue; Liang, Yu; Zhang, JingWen; Zhang,
   YiGong; Lun, BaoLi; Cheng, XiangMing; Yan, XiaoLi; Xue, ZhiKe; Xin,
   YuXin; Song, ZhiMing; Zhu, YingJie; Samanta, Tanmoy
2017E&PP....1...68T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Signatures of Reconnection Observed in a Candle-Flame Solar
    Flare at the Limb
Authors: Reeves, K.; Chen, B.; White, S. M.; Schanche, N.; Tian, H.
2016AGUFMSH31B2565R    Altcode:
  We examine a well-observed flare that occurred on the limb of the Sun
  on March 7, 2015 in order to find possible signatures of a termination
  shock due to outflows from reconnecting magnetic fields. Images of this
  flare from Hinode/XRT and the SDO/AIA 131 bandpass show a cusp-shaped
  morphology. The IRIS slit was positioned in the region of the current
  sheet, above the flare loops. Fe XXI is detected in the IRIS spectra
  with an average Doppler velocity of about 20 km/s. The non-thermal
  widths in IRIS decrease steadily from 23:00 UT on the 7th until 00:20
  UT the next day. This decrease correlates well with the microwave
  radio flux observed by the Nobeyama Radioheliograph (NoRH), which is
  primarily due to thermal free-free emission based on the examination
  of NoRH images at 17 GHz and 34 GHz. Temperatures of the loop-top
  source derived from RHESSI and XRT also show a steady decrease during
  this time. We measure downflow velocities in the cusp region in the
  AIA 131 A bandpass, and find that from 22-23 UT the flows are about
  300-400 km/s, and they slow down to about 100 km/s after 23 UT. This
  work supported by NASA Grant NNX15AJ93G.

---------------------------------------------------------
Title: The anisotropy of sunward-propagating Alfvénic fluctuations
    with power-law spectra observed by Wind spacecraft
Authors: Wu, H.; Wang, X.; Tu, C.; Wang, L.; He, J.; Tian, H.;
   Marsch, E.
2016AGUFMSH41A2515W    Altcode:
  Sunward-propagating Alfvén fluctuations with power-law spectra
  (UPAFs) were reported to be the clue on understanding nonlinear inverse
  cascade. Here we present for the first time the spectral anisotropy of
  UPAFs with respect to the global mean magnetic field direction using
  Wind spacecraft measurements within 20 years from 1995 to 2005. It is
  found that the spectral anisotropy of UPAFs is different from that
  of the anti-sunward-propagating Alfvén fluctuations (DPAFs). By
  determining the propagation direction of the fluctuations straightly
  by strahl electron outflow rather than the measured magnetic field
  data, we find 1190 UPAFs and 37663 DPAFs. UPAFs spectrum has an
  average spectral index of -2.14 when θRB is close to 0° and -1.77
  when θRB is close to 90°, while for DPAFs they are -2.00 and -1.64,
  respectively. The power of UPAFs shows no obvious anisotropy, although
  DPAFs do have larger power at larger θRB. Here we also present the
  first probable picture for illustrating inverse cascade in the solar
  wind. Those results reveal that UPAFs could help us interpret the
  physical process as a new objective.

---------------------------------------------------------
Title: Multi-wavelength Study of Transition Region Penumbral
    Subarcsecond Bright Dots Using IRIS and NST
Authors: Deng, Na; Yurchyshyn, Vasyl; Tian, Hui; Kleint, Lucia; Liu,
   Chang; Xu, Yan; Wang, Haimin
2016ApJ...829..103D    Altcode: 2016arXiv160700306D
  Using high-resolution transition region (TR) observations taken by
  the Interface Region Imaging Spectrograph (IRIS) mission, Tian et
  al. revealed numerous short-lived subarcsecond bright dots (BDs)
  above sunspots (mostly located in the penumbrae), which indicate yet
  unexplained small-scale energy releases. Moreover, whether or not
  these subarcsecond TR brightenings have any signature in the lower
  atmosphere and how they are formed are still not fully resolved. This
  paper presents a multi-wavelength study of the TR penumbral BDs using a
  coordinated observation of a near disk center sunspot with IRIS and the
  1.6 m New Solar Telescope (NST) at the Big Bear Solar Observatory. NST
  provides high-resolution chromospheric and photospheric observations
  with narrowband Hα imaging spectroscopy and broadband TiO images,
  respectively, complementary to IRIS TR observations. A total of 2692
  TR penumbral BDs are identified from a 37 minute time series of IRIS
  1400 Å slit-jaw images. Their locations tend to be associated more
  with downflowing and darker fibrils in the chromosphere, and weakly
  associated with bright penumbral features in the photosphere. However,
  temporal evolution analyses of the BDs show that there is no consistent
  and convincing brightening response in the chromosphere. These results
  are compatible with a formation mechanism of the TR penumbral BDs
  by falling plasma from coronal heights along more vertical and dense
  magnetic loops. The BDs may also be produced by small-scale impulsive
  magnetic reconnection taking place sufficiently high in the atmosphere
  that has no energy release in the chromosphere.

---------------------------------------------------------
Title: VizieR Online Data Catalog: WISE and 2MASS photometry of M
    giant stars (Li+, 2016)
Authors: Li, J.; Smith, M. C.; Zhong, J.; Hou, J.; Carlin, J. L.;
   Newberg, H. J.; Liu, C.; Chen, L.; Li, L.; Shao, Z.; Small, E.;
   Tian, H.
2016yCat..18230059L    Altcode:
  We cross-matched our LAMOST spectroscopically confirmed sample of M
  giants, M dwarfs, and QSOs (see section 2) to the ALLWISE Source Catalog
  in the NASA/IPAC Infrared Science Archive, using a search radius of
  3". We also applied some cuts detailed in section 3. <P />(1 data file).

---------------------------------------------------------
Title: The Stellar Age-T <SUB>eff</SUB>-Kinematical Asymmetry in
    the Solar Neighborhood from LAMOST
Authors: Tian, H. J.; Liu, C.; Carlin, J. L.; Zhao, Y. H.; Chen, X. L.
2016IAUS..317..354T    Altcode:
  With the velocity de-projection technique, we derived the averaged 3
  dimensional local velocity distribution using only the line-of-sight
  velocity for the 200,000 FGK type main-sequence stars from the LAMOST
  DR1 data. Taking the effective temperature as a proxy for age, we
  investigate the variation of the velocity distribution as a function of
  T <SUB>eff</SUB> and disk height within 100 &lt; |z| &lt; 500 pc. Using
  the mean velocities of the cool stars, we derive the solar motion of
  (U <SUB>⊙</SUB>, V <SUB>⊙</SUB>, W <SUB>⊙</SUB>)=(9.58+/-2.39,
  10.52+/-1.96, 7.01+/-1.67) kms<SUP>-1</SUP> with respect to the
  local standard of rest (LSR). Moreover, we find that the stars with T
  <SUB>eff</SUB> &gt; 6000 K show a net asymmetric motion of &lt;U&gt;~2
  kms<SUP>-1</SUP> and &lt;W&gt;~3 kms<SUP>-1</SUP> compared to the
  stars with T <SUB>eff</SUB> &lt; 6000 K. And their azimuthal velocity
  increases when |z| increases. The asymmetric motion in the warmer
  stars is likely because they are too young and not completely relaxed.

---------------------------------------------------------
Title: Source of Quasi-Periodic Brightenings of Solar Coronal Bright
Points: Waves or Repeated Reconnections
Authors: Samanta, Tanmoy; Tian, Hui; Banerjee, Dipankar
2016cosp...41E1696S    Altcode:
  Coronal bright points (BPs) are small-scale luminous features seen
  in the solar corona. Quasi-periodic brightenings are frequently
  observed in the BPs and are generally linked with underlying magnetic
  flux changes. We study the dynamics of a BP seen in the coronal hole
  using the Atmospheric Imaging Assembly images, the Helioseismic and
  Magnetic Imager magnetogram on board the Solar Dynamics Observatory,
  and spectroscopic data from the newly launched Interface Region
  Imaging Spectrograph (IRIS). The detailed analysis shows that the
  BP evolves throughout our observing period along with changes in
  underlying photospheric magnetic flux and shows periodic brightenings
  in different EUV and far-UV images. With the highest possible spectral
  and spatial resolution of IRIS, we attempted to identify the sources
  of these oscillations. IRIS sit-and-stare observation provided a
  unique opportunity to study the time evolution of one footpoint of
  the BP as the slit position crossed it. We noticed enhanced line
  profile asymmetry, enhanced line width, intensity enhancements, and
  large deviation from the average Doppler shift in the line profiles at
  specific instances, which indicate the presence of sudden flows along
  the line-of-sight direction. We propose that transition region explosive
  events originating from small-scale reconnections and the reconnection
  outflows are affecting the line profiles. The correlation between
  all these parameters is consistent with the repetitive reconnection
  scenario and could explain the quasi-periodic nature of the brightening.

---------------------------------------------------------
Title: Are IRIS Bombs Connected to Ellerman Bombs?
Authors: Tian, Hui; Xu, Zhi; He, Jiansen; Madsen, Chad
2016ApJ...824...96T    Altcode: 2016arXiv160405423T
  Recent observations by the Interface Region Imaging Spectrograph
  (IRIS) have revealed pockets of hot gas (∼2-8 × 10<SUP>4</SUP> K)
  potentially resulting from magnetic reconnection in the partially
  ionized lower solar atmosphere (IRIS bombs; IBs). Using joint
  observations between IRIS and the Chinese New Vacuum Solar Telescope,
  we have identified 10 IBs. We find that 3 are unambiguously and 3
  others are possibly connected to Ellerman bombs (EBs), which show
  intense brightening of the extended {{{H}}}<SUB>α </SUB> wings without
  leaving an obvious signature in the {{{H}}}<SUB>α </SUB> core. These
  bombs generally reveal the following distinct properties: (1) the O
  IV 1401.156 Å and 1399.774 Å lines are absent or very weak; (2) the
  Mn I 2795.640 Å line manifests as an absorption feature superimposed
  on the greatly enhanced Mg II k line wing; (3) the Mg II k and h lines
  show intense brightening in the wings and no dramatic enhancement in the
  cores; (4) chromospheric absorption lines such as Ni II 1393.330 Å and
  1335.203 Å are very strong; and (5) the 1700 Å images obtained with
  the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory
  reveal intense and compact brightenings. These properties support the
  formation of these bombs in the photosphere, demonstrating that EBs
  can be heated much more efficiently than previously thought. We also
  demonstrate that the Mg II k and h lines can be used to investigate EBs
  similarly to {{{H}}}<SUB>α </SUB>, which opens a promising new window
  for EB studies. The remaining four IBs obviously have no connection
  to EBs and they do not have the properties mentioned above, suggesting
  a higher formation layer, possibly in the chromosphere.

---------------------------------------------------------
Title: Global Sausage Oscillation of Solar Flare Loops Detected by
    the Interface Region Imaging Spectrograph
Authors: Tian, Hui; Young, Peter R.; Reeves, Katharine K.; Wang,
   Tongjiang; Antolin, Patrick; Chen, Bin; He, Jiansen
2016ApJ...823L..16T    Altcode: 2016arXiv160501963T
  An observation from the Interface Region Imaging Spectrograph
  reveals coherent oscillations in the loops of an M1.6 flare on 2015
  March 12. Both the intensity and Doppler shift of Fe xxi 1354.08 Å
  show clear oscillations with a period of ∼25 s. Remarkably similar
  oscillations were also detected in the soft X-ray flux recorded by
  the Geostationary Operational Environmental Satellites (GOES). With
  an estimated phase speed of ∼2420 km s<SUP>-1</SUP> and a derived
  electron density of at least 5.4 × 10<SUP>10</SUP> cm<SUP>-3</SUP>,
  the observed short-period oscillation is most likely the global
  fast sausage mode of a hot flare loop. We find a phase shift of
  ∼π/2 (1/4 period) between the Doppler shift oscillation and the
  intensity/GOES oscillations, which is consistent with a recent forward
  modeling study of the sausage mode. The observed oscillation requires
  a density contrast between the flare loop and coronal background of a
  factor ≥42. The estimated phase speed of the global mode provides a
  lower limit of the Alfvén speed outside the flare loop. We also find
  an increase of the oscillation period, which might be caused by the
  separation of the loop footpoints with time.

---------------------------------------------------------
Title: Multi-wavelength Study of Transition Region Penumbral
    Bright Dots Using Interface Region Imaging Spectrograph and New
    Solar Telescope
Authors: Deng, Na; Yurchyshyn, Vasyl B.; Tian, Hui; Kleint, Lucia;
   Liu, Chang; Xu, Yan; Wang, Haimin
2016SPD....47.0101D    Altcode:
  Using high-resolution transition region (TR) observations taken by
  the Interface Region Imaging Spectrograph (IRIS) mission, Tian et
  al. (2014b) revealed numerous short-lived sub-arcsecond bright dots
  above sunspots (mostly located in the penumbrae), which indicate yet
  unexplained small-scale energy releases. Moreover, whether these TR
  brightenings have any signature in the lower atmosphere and how they
  are formed are still not fully resolved. This paper presents a study of
  these bright dots using a coordinated observation of a near disk-center
  sunspot with IRIS and the 1.6 m New Solar Telescope (NST) at the Big
  Bear Solar Observatory. NST provides high-resolution chromospheric
  and photospheric observations with narrow-band H-alpha imaging
  spectroscopy and broad-band TiO images, respectively, complementary
  to IRIS TR observations. A total of 2692 TR penumbral bright dots
  are identified from a 37-minute time series of IRIS 1400 A slitjaw
  images. Their locations tend to be associated more with downflowing and
  darker fibrils in the chromosphere, and weakly associated with bright
  penumbral features in the photosphere. However, temporal evolution
  analyses of the dots show that there is no consistent and convincing
  brightening response in the chromosphere. These results are compatible
  with a formation mechanism of the TR penumbral bright dots by falling
  plasma from coronal heights along more vertical and dense magnetic
  loops. The dots may also be produced by small-scale impulsive magnetic
  reconnection taking place sufficiently high in the atmosphere that
  has no energy release in the chromosphere.Acknowledgement: This work
  is mainly supported by NASA grants NNX14AC12G, NNX13AF76G and by NSF
  grant AGS 1408703.

---------------------------------------------------------
Title: Erratum: "Modeling the Chromosphere of a Sunspot and the
    Quiet Sun" <A href="/abs/2015ApJ...811...87A">(2015, ApJ, 811, 87)</A>
Authors: Avrett, E.; Tian, H.; Landi, E.; Curdt, W.; Wuelser, J. -P.
2016ApJ...821...70A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Statistical Study of Network Jets Observed in the Solar
Transition Region: a Comparison Between Coronal Holes and Quiet-Sun
    Regions
Authors: Narang, Nancy; Arbacher, Rebecca T.; Tian, Hui; Banerjee,
   Dipankar; Cranmer, Steven R.; DeLuca, Ed E.; McKillop, Sean
2016SoPh..291.1129N    Altcode: 2016arXiv160406295N; 2016SoPh..tmp...56N
  Recent IRIS observations have revealed a prevalence of intermittent
  small-scale jets with apparent speeds of 80 -250 kms−<SUP>1</SUP>,
  emanating from small-scale bright regions inside network boundaries
  of coronal holes. We find that these network jets appear not only in
  coronal holes but also in quiet-sun regions. Using IRIS 1330 Å (C
  II) slit-jaw images, we extracted several parameters of these network
  jets, e.g. apparent speed, length, lifetime, and increase in foot-point
  brightness. Using several observations, we find that some properties of
  the jets are very similar, but others are obviously different between
  the quiet Sun and coronal holes. For example, our study shows that
  the coronal-hole jets appear to be faster and longer than those in
  the quiet Sun. This can be directly attributed to a difference in the
  magnetic configuration of the two regions, with open magnetic field
  lines rooted in coronal holes and magnetic loops often present in
  the quiet Sun. We also detected compact bright loops that are most
  likely transition region loops and are mostly located in quiet-Sun
  regions. These small loop-like regions are generally devoid of network
  jets. In spite of different magnetic structures in the coronal hole and
  quiet Sun in the transition region, there appears to be no substantial
  difference for the increase in footpoint brightness of the jets, which
  suggests that the generation mechanism of these network jets is very
  likely the same in both regions.

---------------------------------------------------------
Title: The Enhancement of BAO in the SDSS MGS
Authors: Tian, H. J.; Neyrinck, M. C.; Budavári, T.; Szalay, A. S.
2016IAUS..319..145T    Altcode:
  We show that redshift-space distortions of galaxy correlations have a
  strong effect on correlation functions with the signature of the Baryon
  Acoustic Oscillations (BAO). Near the line of sight, the features become
  sharper as a result of redshift-space distortions. We analyze the SDSS
  DR7 main-galaxy sample (MGS), splitting the sample into slices 2.5 deg
  on the sky in various rotations. Measuring 2D correlation functions
  in each slice, we do see a sharp bump along the line of sight. Using
  Mexican-hat wavelets, we localize it to (110 +/- 10) h - 1 Mpc and
  estimate its significance at about 4σ.

---------------------------------------------------------
Title: Observations of Small-scale IRIS Bombs (Reconnection Events)
    in an Evolving Active Region
Authors: Madsen, C. A.; Tian, H.; DeLuca, E. E.
2015AGUFMSH31B2414M    Altcode:
  We present the first Interface Region Imaging Spectrograph (IRIS)
  observations of small-scale bombs evolving with their host active
  region. Bombs appear most clearly in the IRIS 1330 Å and 1400 Å
  slit-jaw images as small (~1 arcsec), compact, intense brightenings at
  transition region temperatures. Their NUV/FUV emission spectra exhibit
  dramatic line splitting and strong absorption features indicative of
  bidirectional flows from magnetic reconnection embedded deep within the
  cool lower solar atmosphere. The bombs may contribute significantly
  to the heating of the solar atmosphere in active regions; however,
  it's unclear how prevalent the bombs are throughout the lifetime of an
  active region. Using a semi-automated detection method, we locate bombs
  within AR 11850 over the course of four observations from 06:00 UT on
  September 25, 2013 until 11:30 UT the next day. The active region is
  first observed in an emerging phase and rapidly grows into a mature
  active region with well-developed sunspots. The bomb occurrence rate
  drops dramatically as the active region fully emerges. We also find
  that the bombs fall into two distinct populations: one appears largely
  during active region emergence and contains a majority of the bombs,
  while the other population is present regardless of active region
  age. The first population of bombs is typically found embedded in the
  low-lying loops prominent in the young active region. Furthermore,
  we use Solar Dynamics Observatory/Helioseismic and Magnetic Imager
  (SDO/HMI) line-of-sight magnetograms to show that the bombs associated
  with the first population occur at the boundaries between the upward
  and downward flux of small, isolated bipolar regions. These regions
  dissipate as the active region emerges and reconfigures its magnetic
  field into two large network patches of upward and downward flux with a
  clear inversion line. The second, smaller population of bombs usually
  occurs far from the active region loop structures in the plage and
  sunspot penumbrae. They are associated with the boundaries between
  strong upward or downward flux and regions where the magnetic field
  is perpendicular to the line of sight.

---------------------------------------------------------
Title: Temporal Evolution of Chromospheric Evaporation: Case
    Studies of the M1.1 Flare on 2014 September 6 and X1.6 Flare on 2014
    September 10
Authors: Tian, Hui; Young, Peter R.; Reeves, Katharine K.; Chen, Bin;
   Liu, Wei; McKillop, Sean
2015ApJ...811..139T    Altcode: 2015arXiv150502736T
  With observations from the Interface Region Imaging Spectrograph, we
  track the complete evolution of ∼11 MK evaporation flows in an M1.1
  flare on 2014 September 6 and an X1.6 flare on 2014 September 10. These
  hot flows, as indicated by the blueshifted Fe xxi 1354.08 Å line,
  evolve smoothly with a velocity decreasing exponentially from ∼200
  km s<SUP>-1</SUP> to almost stationary within a few minutes. We find a
  good correlation between the flow velocity and energy deposition rate
  as represented by the hard X-ray flux observed with the Reuven Ramaty
  High Energy Solar Spectroscopic Imager, or time derivative of the soft
  X-ray flux observed with the Geostationary Operational Environmental
  Satellites and the HINODE X-ray Telescope, which is in general agreement
  with models of nonthermal electron heating. The maximum blueshift of
  Fe xxi appears approximately at the same time as or slightly after
  the impulsive enhancement of the ultraviolet continuum and the Mg ii
  2798.8 Å line emission, demonstrating that the evaporation flow is
  closely related to heating of the lower chromosphere. Finally, while
  the hot Fe xxi 1354.08 Å line is entirely blueshifted with no obvious
  rest component, cool chromospheric and transition region lines like
  Si iv 1402.77 Å are often not entirely redshifted but just reveal an
  obvious red wing enhancement at the ribbons, suggesting that the speed
  of chromospheric condensation might be larger than previously thought.

---------------------------------------------------------
Title: Modeling the Chromosphere of a Sunspot and the Quiet Sun
Authors: Avrett, E.; Tian, H.; Landi, E.; Curdt, W.; Wülser, J. -P.
2015ApJ...811...87A    Altcode:
  Semiempirical atmospheric modeling attempts to match an observed
  spectrum by finding the temperature distribution and other physical
  parameters along the line of sight through the emitting region such
  that the calculated spectrum agrees with the observed one. In this
  paper we take the observed spectrum of a sunspot and the quiet Sun
  in the EUV wavelength range 668-1475 Å from the 2001 SUMER atlas
  of Curdt et al. to determine models of the two atmospheric regions,
  extending from the photosphere through the overlying chromosphere into
  the transition region. We solve the coupled statistical equilibrium
  and optically thick radiative transfer equations for a set of 32 atoms
  and ions. The atoms that are part of molecules are treated separately,
  and are excluded from the atomic abundances and atomic opacities. We
  compare the Mg ii k line profile observations from the Interface
  Region Imaging Spectrograph with the profiles calculated from the two
  models. The calculated profiles for the sunspot are substantially
  lower than the observed ones, based on the SUMER models. The only
  way we have found to raise the calculated Mg ii lines to agree with
  the observations is to introduce illumination of the sunspot from the
  surrounding active region.

---------------------------------------------------------
Title: Self-Absorption in the Solar Transition Region
Authors: Yan, Limei; Peter, Hardi; He, Jiansen; Tian, Hui; Xia,
   Lidong; Wang, Linghua; Tu, Chuanyi; Zhang, Lei; Chen, Feng; Barczynski,
   Krzysztof
2015ApJ...811...48Y    Altcode: 2015arXiv150105706Y
  Transient brightenings in the transition region of the Sun have
  been studied for decades and are usually related to magnetic
  reconnection. Recently, absorption features due to chromospheric
  lines have been identified in transition region emission lines raising
  the question of the thermal stratification during such reconnection
  events. We analyze data from the Interface Region Imaging Spectrograph
  in an emerging active region. Here the spectral profiles show clear
  self-absorption features in the transition region lines of Si iv. While
  some indications existed that opacity effects might play some role
  in strong transition region lines, self-absorption has not been
  observed before. We show why previous instruments could not observe
  such self-absorption features, and discuss some implications of this
  observation for the corresponding structure of reconnection events in
  the atmosphere. Based on this we speculate that a range of phenomena,
  such as explosive events, blinkers or Ellerman bombs, are just different
  aspects of the same reconnection event occurring at different heights
  in the atmosphere.

---------------------------------------------------------
Title: Direct Observations of Magnetic Reconnection Outflow and CME
    Triggering in a Small Erupting Solar Prominence
Authors: Reeves, Katharine K.; McCauley, Patrick I.; Tian, Hui
2015ApJ...807....7R    Altcode: 2015arXiv150507307R
  We examine a small prominence eruption that occurred on 2014 May 1 at
  01:35 UT and was observed by the Interface Region Imaging Spectrometer
  (IRIS) and the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics
  Observatory. Pre- and post-eruption images were taken by the X-ray
  Telescope (XRT) on Hinode. Pre-eruption, a dome-like structure exists
  above the prominence, as demarcated by coronal rain. As the eruption
  progresses, we find evidence for reconnection between the prominence
  magnetic field and the overlying field. Fast flows are seen in AIA
  and IRIS, indicating reconnection outflows. Plane-of-sky flows of
  300 km s<SUP>-1</SUP> are observed in the AIA 171 A channel along a
  potentially reconnected field line. IRIS detects intermittent fast
  line of sight flows of 200 km s<SUP>-1</SUP> coincident with the
  AIA flows. Differential emission measure calculations show heating
  at the origin of the fast flows. Post-eruption XRT images show hot
  loops probably due to reconfiguration of magnetic fields during the
  eruption and subsequent heating of plasma in these loops. Although
  there is evidence for reconnection above the prominence during the
  eruption, high spatial resolution images from IRIS reveal potential
  reconnection sites below the prominence. A height-time analysis of the
  erupting prominence shows a slow initial rise with a velocity of 0.4 km
  s<SUP>-1</SUP> followed by a rapid acceleration with a final velocity
  of 250 km s<SUP>-1</SUP>. Brightenings in IRIS during the transition
  between these two phases indicate the eruption trigger for the fast
  part of the eruption is likely a tether-cutting mechanism rather than
  a break-out mechanism.

---------------------------------------------------------
Title: Quasi-periodic Oscillation of a Coronal Bright Point
Authors: Samanta, Tanmoy; Banerjee, Dipankar; Tian, Hui
2015ApJ...806..172S    Altcode: 2015arXiv150500587S
  Coronal bright points (BPs) are small-scale luminous features seen
  in the solar corona. Quasi-periodic brightenings are frequently
  observed in the BPs and are generally linked with underlying magnetic
  flux changes. We study the dynamics of a BP seen in the coronal hole
  using the Atmospheric Imaging Assembly images, the Helioseismic and
  Magnetic Imager magnetogram on board the Solar Dynamics Observatory,
  and spectroscopic data from the newly launched Interface Region
  Imaging Spectrograph (IRIS). The detailed analysis shows that the
  BP evolves throughout our observing period along with changes in
  underlying photospheric magnetic flux and shows periodic brightenings
  in different EUV and far-UV images. With the highest possible spectral
  and spatial resolution of IRIS, we attempted to identify the sources
  of these oscillations. IRIS sit-and-stare observation provided a
  unique opportunity to study the time evolution of one footpoint of
  the BP as the slit position crossed it. We noticed enhanced line
  profile asymmetry, enhanced line width, intensity enhancements, and
  large deviation from the average Doppler shift in the line profiles at
  specific instances, which indicate the presence of sudden flows along
  the line-of-sight direction. We propose that transition region explosive
  events originating from small-scale reconnections and the reconnection
  outflows are affecting the line profiles. The correlation between
  all these parameters is consistent with the repetitive reconnection
  scenario and could explain the quasi-periodic nature of the brightening.

---------------------------------------------------------
Title: Internetwork Chromospheric Bright Grains Observed With IRIS
    and SST
Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson,
   Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt,
   Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan;
   Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean;
   Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli,
   Sarah; Kankelborg, Charles
2015ApJ...803...44M    Altcode: 2015arXiv150203490M
  The Interface Region Imaging Spectrograph (IRIS) reveals small-scale
  rapid brightenings in the form of bright grains all over coronal holes
  and the quiet Sun. These bright grains are seen with the IRIS 1330,
  1400, and 2796 Å slit-jaw filters. We combine coordinated observations
  with IRIS and from the ground with the Swedish 1 m Solar Telescope
  (SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H
  3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å,
  Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps
  in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.}
  33), temporal, and spectral resolution. We conclude that the IRIS
  slit-jaw grains are the counterpart of so-called acoustic grains,
  i.e., resulting from chromospheric acoustic waves in a non-magnetic
  environment. We compare slit-jaw images (SJIs) with spectra from the
  IRIS spectrograph. We conclude that the grain intensity in the 2796
  Å slit-jaw filter comes from both the Mg ii k core and wings. The
  signal in the C ii and Si iv lines is too weak to explain the presence
  of grains in the 1300 and 1400 Å SJIs and we conclude that the grain
  signal in these passbands comes mostly from the continuum. Although
  weak, the characteristic shock signatures of acoustic grains can often
  be detected in IRIS C ii spectra. For some grains, a spectral signature
  can be found in IRIS Si iv. This suggests that upward propagating
  acoustic waves sometimes reach all the way up to the transition region.

---------------------------------------------------------
Title: The role of turbulence in coronal heating and solar wind
    expansion
Authors: Cranmer, S. R.; Asgari-Targhi, M.; Miralles, M. P.; Raymond,
   J. C.; Strachan, L.; Tian, H.; Woolsey, L. N.
2015RSPTA.37340148C    Altcode: 2014arXiv1412.2307C
  Plasma in the Sun's hot corona expands into the heliosphere as a
  supersonic and highly magnetized solar wind. This paper provides an
  overview of our current understanding of how the corona is heated and
  how the solar wind is accelerated. Recent models of magnetohydrodynamic
  turbulence have progressed to the point of successfully predicting
  many observed properties of this complex, multi-scale system. However,
  it is not clear whether the heating in open-field regions comes mainly
  from the dissipation of turbulent fluctuations that are launched from
  the solar surface, or whether the chaotic "magnetic carpet" in the
  low corona energizes the system via magnetic reconnection. To help
  pin down the physics, we also review some key observational results
  from ultraviolet spectroscopy of the collisionless outer corona.

---------------------------------------------------------
Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode
    and Magnetic Modeling With Data-Driven Simulations
Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.;
   Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner,
   P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint,
   L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.;
   Carlsson, M.; Hansteen, V.
2015ApJ...801...83C    Altcode: 2015arXiv150101593C
  We report on observations of recurrent jets by instruments on board
  the Interface Region Imaging Spectrograph, Solar Dynamics Observatory
  (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21,
  recurrent coronal jets were observed to emanate from NOAA Active Region
  11793. Far-ultraviolet spectra probing plasma at transition region
  temperatures show evidence of oppositely directed flows with components
  reaching Doppler velocities of ±100 km s<SUP>-1</SUP>. Raster Doppler
  maps using a Si iv transition region line show all four jets to have
  helical motion of the same sense. Simultaneous observations of the
  region by SDO and Hinode show that the jets emanate from a source
  region comprising a pore embedded in the interior of a supergranule. The
  parasitic pore has opposite polarity flux compared to the surrounding
  network field. This leads to a spine-fan magnetic topology in the
  coronal field that is amenable to jet formation. Time-dependent
  data-driven simulations are used to investigate the underlying drivers
  for the jets. These numerical experiments show that the emergence of
  current-carrying magnetic field in the vicinity of the pore supplies
  the magnetic twist needed for recurrent helical jet formation.

---------------------------------------------------------
Title: The 2014 March 29 X-flare: Subarcsecond Resolution Observations
    of Fe XXI λ1354.1
Authors: Young, Peter R.; Tian, Hui; Jaeggli, Sarah
2015ApJ...799..218Y    Altcode: 2014arXiv1409.8603Y
  The Interface Region Imaging Spectrometer (IRIS) is the first solar
  instrument to observe ~10 MK plasma at subarcsecond spatial resolution
  through imaging spectroscopy of the Fe XXI λ1354.1 forbidden line. IRIS
  observations of the X1 class flare that occurred on 2014 March 29 at
  17:48 UT reveal Fe XXI emission from both the flare ribbons and the
  post-flare loop arcade. Fe XXI appears at all of the chromospheric
  ribbon sites, although typically with a delay of one raster (75 s) and
  sometimes offset by up to 1”. 100-200 km s<SUP>-1</SUP> blue-shifts
  are found at the brightest ribbons, suggesting hot plasma upflow into
  the corona. The Fe XXI ribbon emission is compact with a spatial
  extent of &lt;2”, and can extend beyond the chromospheric ribbon
  locations. Examples are found of both decreasing and increasing
  blue-shift in the direction away from the ribbon locations, and
  blue-shifts were present for at least six minutes after the flare
  peak. The post-flare loop arcade, seen in Atmospheric Imaging Assembly
  131 Å filtergram images that are dominated by Fe XXI, exhibited
  bright loop-tops with an asymmetric intensity distribution. The sizes
  of the loop-tops are resolved by IRIS at &gt;=1”, and line widths
  in the loop-tops are not broader than in the loop-legs suggesting the
  loop-tops are not sites of enhanced turbulence. Line-of-sight speeds
  in the loop arcade are typically &lt;10 km s<SUP>-1</SUP>, and mean
  non-thermal motions fall from 43 km s<SUP>-1</SUP> at the flare peak
  to 26 km s<SUP>-1</SUP> six minutes later. If the average velocity
  in the loop arcade is assumed to be at rest, then it implies a new
  reference wavelength for the Fe XXI line of 1354.106 ± 0.023 Å.

---------------------------------------------------------
Title: Observations of Umbral Flashes and Running Sunspot Waves with
    the Interface Region Imaging Spectrograph
Authors: Madsen, Chad A.; Tian, Hui; DeLuca, Edward E.
2015ApJ...800..129M    Altcode:
  We present simultaneous, high-resolution, multi-temperature observations
  of running waves and umbral flashes in a sunspot with the Interface
  Region Imaging Spectrograph. We analyze intensity variations in
  slit-jaw images to investigate the relationship between running
  waves in the 1400 Å (Si IV/transition region) passband and umbral
  flashes in the 2796 Å (Mg II/chromosphere) passband. Using global
  wavelet analysis, we find that the dominant wave periods increase
  from approximately 150 s near the sunspot center to about 300 s in
  the penumbra in both passbands. This coincides extremely well with
  the radially increasing inclination of magnetic field lines observed
  with Solar Dynamics Observatory/Helioseismic and Magnetic Imager,
  suggesting that the waves are propagating vertically along the inclined
  field lines. Furthermore, apparent horizontal velocities for running
  waves decrease from about 12 km s<SUP>-1</SUP> in the umbra to about
  4 km s<SUP>-1</SUP> in the penumbra which is predicted by the same
  inclined field geometry. Finally, we find that umbral flashes lead
  running waves in both the spatial and temporal domains. The former
  result is attributable to the inclined field geometry; however, the
  geometry does not predict the radially increasing time lag which is
  likely due to the opacity difference between the emission lines that
  dominate the two passbands. These results suggest that running waves
  and umbral flashes both originate from photospheric p-mode oscillations
  and are manifestations of upward-propagating slow magnetoacoustic modes
  at different altitudes and temperatures. The apparent trans-sunspot
  propagation of running waves is not real but rather an image of these
  upward-propagating modes traveling along field lines of radially
  increasing inclination.

---------------------------------------------------------
Title: Comparing High-speed Transition Region Jets in Coronal Holes
    and Quiet Sun Regions
Authors: Tate Arbacher, Rebecca; Tian, Hui; Cranmer, Steven R.
2015AAS...22513705T    Altcode:
  The complicated energy transfer and plasma motion in the transition
  region, between the photosphere and the corona, may play a significant
  role in the formation and acceleration of the solar wind. New
  observations from the Interface Region Imaging Spectrograph (IRIS)
  have revealed unprecedented levels of detail in this less-studied
  region. Coronal holes in particular are a likely source of solar
  wind material, though the formation and acceleration mechanisms of
  the fast solar wind are still largely unknown. In our previous work,
  we have reported the prevalence of small-scale high-speed (~80-250
  km/s) jets with transition region temperatures from the network
  structures of coronal holes. Here we undertake a comparative study
  of these short-lived episodic network jets in a coronal hole region
  and a quiet sun region using IRIS sit-and-stare slit-jaw imaging in
  the 1330 Angstrom (C II) passband. The pointing coordinates, exposure
  time, observing cadence, and field of view of both observations are all
  identical. Our preliminary study suggests that the speeds and lengths
  of the network jets may differ between quiet sun and coronal hole
  regions. The quiet sun region exhibits many compact bright regions with
  sizes of 5-10 arcseconds which produce very few jets. The jets that do
  exist tend to propagate at much slower speeds over smaller distances
  than their coronal hole counterparts. Comparatively, in the coronal
  hole, such compact regions are almost absent and all network patches
  are permeated by the intermittent high-reaching jets. Such a difference
  suggests that magnetic loops are much smaller in the coronal hole and
  the network jets are produced at low heights. The recurrence frequency
  seems to be higher in the coronal hole region, with many of the isolated
  quiet sun region jets demonstrating curved trajectories.This work is
  supported under contract 8100002705 from Lockheed-Martin to SAO and
  by the NSF-REU solar physics program at SAO, grant number AGS-1263241.

---------------------------------------------------------
Title: Comparing High-speed Transition Region Jets in Coronal Holes
    and Quiet Sun Regions
Authors: Arbacher, R. T.; Tian, H.; Cranmer, S. R.
2014AGUFMSH51C4181A    Altcode:
  The complicated energy transfer and plasma motion in the transition
  region, between the photosphere and the corona, may play a significant
  role in the formation and acceleration of the solar wind. New
  observations from the Interface Region Imaging Spectrograph (IRIS)
  have revealed unprecedented levels of detail in this less-studied
  region. Coronal holes in particular are a likely source of solar
  wind material, though the formation and acceleration mechanisms of
  the fast solar wind are still largely unknown. In our previous work,
  we have reported the prevalence of small-scale high-speed (~80-250
  km/s) jets with transition region temperatures from the network
  structures of coronal holes. Here we undertake a comparative study
  of these short-lived episodic network jets in a coronal hole region
  and a quiet sun region using IRIS sit-and-stare slit-jaw imaging in
  the 1330 Angstrom (C II) passband. The pointing coordinates, exposure
  time, observing cadence, and field of view of both observations are
  all identical. Our preliminary study suggests that the speeds and
  lengths of the network jets may differ between quiet sun and coronal
  hole regions. The quiet sun region exhibits many compact bright regions
  with sizes of 5-10 arcseconds which produce very few jets. The jets
  that do exist tend to propagate at much slower speeds over smaller
  distances than their coronal hole counterparts. Comparatively, in the
  coronal hole, such compact regions are almost absent and all network
  patches are permeated by the intermittent high-reaching jets. Such
  a difference suggests that magnetic loops are much smaller in the
  coronal hole and the network jets are produced at low heights. The
  recurrence frequency seems to be higher in the coronal hole region,
  with many of the isolated quiet sun region jets demonstrating curved
  trajectories. This work is supported under contract 8100002705 from
  Lockheed-Martin to SAO and by the NSF-REU solar physics program at SAO,
  grant number AGS-1263241.

---------------------------------------------------------
Title: IRIS Observations of Magnetic Reconnection and Chromospheric
    Evaporation in a Solar Flare
Authors: Tian, H.; Li, G.; Reeves, K.; Raymond, J. C.; Guo, F.
2014AGUFMSH23A4145T    Altcode:
  NASA's IRIS mission has observed signatures of the Fe XXI 1354 line
  in tens of solar flares. In many of them, large blue shifts were
  identified, supporting the scenario of chromospheric evaporation in
  postflare loops. In the standard CSHKP flare model, the postflare
  loops are a natual consequence of magnetic reconnection occurring at
  the flare site. The CSHKP model also predicts downflow (and upflow)
  plasma having a speed close to the Alfven speed. Yet, to date there
  were no observations of fast moving downflow plasma in flares. Here, we
  report the first detection of large red shift (~200 km/s along line of
  sight) of the Fe XXI line with IRIS. Combined imaging and spectroscopic
  observations of IRIS, together with SDO/AIA and RHESSI observations,
  reveal that the redshifted Fe XXI feature co-located with the loop-top
  hard X-Ray source and above the retracting loops. We intepret this large
  redshift as signature of downward moving reconnection outflow/retracting
  loops. Possible flux rope eruption and reconnection inflows are
  also observed. Furthermore, we found that the entire Fe XXI line is
  blueshifted by ~250 km/s at the loop footpoints. Cool lines of Si IV,
  O IV, C II and Mg II all show obvious redshift at the same locations,
  consistent with the scenario of chromospheric evaporation. The map of
  electron temperature reconstructed from SDO/AIA observations shows
  that the locations of ~10MK temperature generally coincide with the
  observed Fe XXI feature very well. Hard X-rays up to ~100keV were found
  from RHESSI observations, indicating an efficient electron acceleration
  process in this event.

---------------------------------------------------------
Title: Imaging and Spectroscopic Observations of Magnetic Reconnection
    and Chromospheric Evaporation in a Solar Flare
Authors: Tian, Hui; Li, Gang; Reeves, Katharine K.; Raymond, John C.;
   Guo, Fan; Liu, Wei; Chen, Bin; Murphy, Nicholas A.
2014ApJ...797L..14T    Altcode: 2014arXiv1411.2301T
  Magnetic reconnection is believed to be the dominant energy release
  mechanism in solar flares. The standard flare model predicts both
  downward and upward outflow plasmas with speeds close to the coronal
  Alfvén speed. Yet, spectroscopic observations of such outflows,
  especially the downflows, are extremely rare. With observations of
  the newly launched Interface Region Imaging Spectrograph (IRIS), we
  report the detection of a greatly redshifted (~125 km s<SUP>-1</SUP>
  along the line of sight) Fe XXI 1354.08 Å emission line with a ~100 km
  s<SUP>-1</SUP> nonthermal width at the reconnection site of a flare. The
  redshifted Fe XXI feature coincides spatially with the loop-top
  X-ray source observed by RHESSI. We interpret this large redshift as
  the signature of downward-moving reconnection outflow/hot retracting
  loops. Imaging observations from both IRIS and the Atmospheric Imaging
  Assembly (AIA) on board the Solar Dynamics Observatory also reveal
  the eruption and reconnection processes. Fast downward-propagating
  blobs along these loops are also found from cool emission lines (e.g.,
  Si IV, O IV, C II, Mg II) and images of AIA and IRIS. Furthermore,
  the entire Fe XXI line is blueshifted by ~260 km s<SUP>-1</SUP> at
  the loop footpoints, where the cool lines mentioned above all exhibit
  obvious redshift, a result that is consistent with the scenario of
  chromospheric evaporation induced by downward-propagating nonthermal
  electrons from the reconnection site.

---------------------------------------------------------
Title: Prevalence of Micro-Jets from the Network Structures of the
    Solar Transition Region and Chromosphere
Authors: DeLuca, E. E.; Tian, H.; Cranmer, S. R.; Reeves, K.; Miralles,
   M. P.; McCauley, P.; McKillop, S.
2014AGUFMSH51C4180D    Altcode:
  IRIS observations in the 1330Å, 1400Å and 2796Å passbands have
  revealed numerous small-scale jet-like features with speeds of ~80-250
  km/s from the chromospheric network. These network jets occur in
  both the quiet Sun and coronal holes. Their widths are often ~300
  km or less. Many of these jets show up as elongated features with
  enhanced line width in maps obtained with transition region (TR)
  lines, suggesting that these jets reach at least TR temperatures and
  they constitute an important element of TR structures. The ubiquitous
  presence of these high-reaching (often &gt;10 Mm) jets also suggests
  that they may play a crucial role in the mass and energy budgets
  of the corona and solar wind. The generation of these jets in the
  network and the accompanying Alfven waves is also consistent with
  the "magnetic furnace model" of solar wind proposed by Axford &amp;
  McKenzie (1992). The large speeds (greater than sound speed) suggest
  that the Lorentz force (perhaps related to reconnection) must play
  an important role in the generation and propagation of the network
  jets. We believe that many network jets are the on-disk counterparts
  and TR manifestation of type-II spicules.

---------------------------------------------------------
Title: Hot explosions in the cool atmosphere of the Sun
Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.;
   De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
   Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint,
   L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.;
   Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.
2014Sci...346C.315P    Altcode: 2014arXiv1410.5842P
  The solar atmosphere was traditionally represented with a simple
  one-dimensional model. Over the past few decades, this paradigm shifted
  for the chromosphere and corona that constitute the outer atmosphere,
  which is now considered a dynamic structured envelope. Recent
  observations by the Interface Region Imaging Spectrograph (IRIS) reveal
  that it is difficult to determine what is up and down, even in the cool
  6000-kelvin photosphere just above the solar surface: This region hosts
  pockets of hot plasma transiently heated to almost 100,000 kelvin. The
  energy to heat and accelerate the plasma requires a considerable
  fraction of the energy from flares, the largest solar disruptions. These
  IRIS observations not only confirm that the photosphere is more complex
  than conventionally thought, but also provide insight into the energy
  conversion in the process of magnetic reconnection.

---------------------------------------------------------
Title: The unresolved fine structure resolved: IRIS observations of
    the solar transition region
Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title,
   A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira,
   T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
   S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
   Martínez-Sykora, J.
2014Sci...346E.315H    Altcode: 2014arXiv1412.3611H
  The heating of the outer solar atmospheric layers, i.e., the transition
  region and corona, to high temperatures is a long-standing problem
  in solar (and stellar) physics. Solutions have been hampered by an
  incomplete understanding of the magnetically controlled structure of
  these regions. The high spatial and temporal resolution observations
  with the Interface Region Imaging Spectrograph (IRIS) at the solar
  limb reveal a plethora of short, low-lying loops or loop segments
  at transition-region temperatures that vary rapidly, on the time
  scales of minutes. We argue that the existence of these loops solves
  a long-standing observational mystery. At the same time, based on
  comparison with numerical models, this detection sheds light on a
  critical piece of the coronal heating puzzle.

---------------------------------------------------------
Title: Evidence of nonthermal particles in coronal loops heated
    impulsively by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale,
   F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.;
   Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.;
   Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
   Kleint, L.; Kankelborg, C.; Jaeggli, S.
2014Sci...346B.315T    Altcode: 2014arXiv1410.6130T
  The physical processes causing energy exchange between the Sun’s
  hot corona and its cool lower atmosphere remain poorly understood. The
  chromosphere and transition region (TR) form an interface region between
  the surface and the corona that is highly sensitive to the coronal
  heating mechanism. High-resolution observations with the Interface
  Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to
  60 seconds) of intensity and velocity on small spatial scales (≲500
  kilometers) at the footpoints of hot and dynamic coronal loops. The
  observations are consistent with numerical simulations of heating by
  beams of nonthermal electrons, which are generated in small impulsive
  (≲30 seconds) heating events called “coronal nanoflares.” The
  accelerated electrons deposit a sizable fraction of their energy
  (≲10<SUP>25 </SUP>erg) in the chromosphere and TR. Our analysis
  provides tight constraints on the properties of such electron beams
  and new diagnostics for their presence in the nonflaring corona.

---------------------------------------------------------
Title: Prevalence of small-scale jets from the networks of the solar
    transition region and chromosphere
Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.;
   Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves,
   K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber,
   M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
   Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli,
   S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
2014Sci...346A.315T    Altcode: 2014arXiv1410.6143T
  As the interface between the Sun’s photosphere and corona, the
  chromosphere and transition region play a key role in the formation and
  acceleration of the solar wind. Observations from the Interface Region
  Imaging Spectrograph reveal the prevalence of intermittent small-scale
  jets with speeds of 80 to 250 kilometers per second from the narrow
  bright network lanes of this interface region. These jets have lifetimes
  of 20 to 80 seconds and widths of ≤300 kilometers. They originate from
  small-scale bright regions, often preceded by footpoint brightenings
  and accompanied by transverse waves with amplitudes of ~20 kilometers
  per second. Many jets reach temperatures of at least ~10<SUP>5</SUP>
  kelvin and constitute an important element of the transition region
  structures. They are likely an intermittent but persistent source of
  mass and energy for the solar wind.

---------------------------------------------------------
Title: On the prevalence of small-scale twist in the solar
    chromosphere and transition region
Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.;
   Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen,
   J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser,
   J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
   S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
   Martinez-Sykora, J.
2014Sci...346D.315D    Altcode: 2014arXiv1410.6862D
  The solar chromosphere and transition region (TR) form an interface
  between the Sun’s surface and its hot outer atmosphere. There,
  most of the nonthermal energy that powers the solar atmosphere
  is transformed into heat, although the detailed mechanism remains
  elusive. High-resolution (0.33-arc second) observations with NASA’s
  Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere
  and TR that are replete with twist or torsional motions on sub-arc
  second scales, occurring in active regions, quiet Sun regions, and
  coronal holes alike. We coordinated observations with the Swedish
  1-meter Solar Telescope (SST) to quantify these twisting motions and
  their association with rapid heating to at least TR temperatures. This
  view of the interface region provides insight into what heats the low
  solar atmosphere.

---------------------------------------------------------
Title: Open questions on prominences from coordinated observations
    by IRIS, Hinode, SDO/AIA, THEMIS, and the Meudon/MSDP
Authors: Schmieder, B.; Tian, H.; Kucera, T.; López Ariste, A.;
   Mein, N.; Mein, P.; Dalmasse, K.; Golub, L.
2014A&A...569A..85S    Altcode: 2014arXiv1407.3171S
  Context. A large prominence was observed by multiple instruments on the
  ground and in space during an international campaign on September 24,
  2013, for three hours (12:12 UT -15:12 UT). Instruments used in the
  campaign included the newly launched (June 2013) Interface Region
  Imaging Spectrograph (IRIS), THEMIS (Tenerife), the Hinode Solar
  Optical Telescope (SOT), the Solar Dynamic Observatory's Atmospheric
  Imaging Assembly (SDO/AIA), and the Multichannel Subtractive Double
  Pass spectrograph (MSDP) in the Meudon Solar Tower. The movies obtained
  in 304 Å with the EUV imager SDO/AIA, and in Ca II line by SOT show
  the dynamic nature of the prominence. <BR /> Aims: The aim of this
  work is to study the dynamics of the prominence fine structures in
  multiple wavelengths to understand their formation. <BR /> Methods:
  The spectrographs IRIS and MSDP provided line profiles with a high
  cadence in Mg II h (2803.5 Å) and k (2796.4 Å) lines along four
  slit positions (IRIS), and in Hα in a 2D field of view (MSDP). The
  spectropolarimetry of THEMIS (Tenerife) allowed us to derive the
  magnetic field of the prominence using the He D<SUB>3</SUB> line
  depolarization (Hanle effect combined with the Zeeman effect). <BR />
  Results: The magnetic field is found to be globally horizontal with
  a relatively weak field strength (8-15 Gauss). On the other hand,
  the Ca II movie reveals turbulent-like motion that is not organized in
  specific parts of the prominence. We tested the addition of a turbulent
  magnetic component. This model is compatible with the polarimetric
  observations at those places where the plasma turbulence peaks. On the
  other hand, the Mg II line profiles show multiple peaks well separated
  in wavelength. This is interpreted by the existence of small threads
  along the line of sight with a large dispersion of discrete values of
  Doppler shifts, from 5 km s<SUP>-1</SUP> (a quasi-steady component) to
  60-80 km s<SUP>-1</SUP>. Each peak corresponds to a Gaussian profile,
  and not to a reversed profile as was expected by the present non-LTE
  radiative transfer modeling. This is a very surprising behavior for
  the Mg II line observed in prominences. <BR /> Conclusions: Turbulent
  fields on top of the macroscopic horizontal component of the magnetic
  field supporting the prominence give rise to the complex dynamics of
  the plasma. The plasma with the high velocities (70 km s<SUP>-1</SUP> to
  100 km s<SUP>-1</SUP> if we take into account the transverse velocities)
  may correspond to condensation of plasma along more or less horizontal
  threads of the arch-shape structure visible in 304 Å. The steady
  flows (5 km s<SUP>-1</SUP>) would correspond to a more quiescent plasma
  (cool and prominence-corona transition region) of the prominence packed
  into dips in horizontal magnetic field lines. The very weak secondary
  peaks in the Mg II profiles may reflect the turbulent nature of parts
  of the prominence. <P />Movies are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201423922/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: An Interface Region Imaging Spectrograph First View on Solar
    Spicules
Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen,
   V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt,
   N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.;
   McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli,
   S.; Kankelborg, C.
2014ApJ...792L..15P    Altcode: 2014arXiv1407.6360P
  Solar spicules have eluded modelers and observers for decades. Since
  the discovery of the more energetic type II, spicules have become
  a heated topic but their contribution to the energy balance of the
  low solar atmosphere remains unknown. Here we give a first glimpse of
  what quiet-Sun spicules look like when observed with NASA's recently
  launched Interface Region Imaging Spectrograph (IRIS). Using IRIS
  spectra and filtergrams that sample the chromosphere and transition
  region, we compare the properties and evolution of spicules as
  observed in a coordinated campaign with Hinode and the Atmospheric
  Imaging Assembly. Our IRIS observations allow us to follow the thermal
  evolution of type II spicules and finally confirm that the fading
  of Ca II H spicules appears to be caused by rapid heating to higher
  temperatures. The IRIS spicules do not fade but continue evolving,
  reaching higher and falling back down after 500-800 s. Ca II H type
  II spicules are thus the initial stages of violent and hotter events
  that mostly remain invisible in Ca II H filtergrams. These events
  have very different properties from type I spicules, which show lower
  velocities and no fading from chromospheric passbands. The IRIS spectra
  of spicules show the same signature as their proposed disk counterparts,
  reinforcing earlier work. Spectroheliograms from spectral rasters also
  confirm that quiet-Sun spicules originate in bushes from the magnetic
  network. Our results suggest that type II spicules are indeed the
  site of vigorous heating (to at least transition region temperatures)
  along extensive parts of the upward moving spicular plasma.

---------------------------------------------------------
Title: Observations of Subarcsecond Bright Dots in the Transition
    Region above Sunspots with the Interface Region Imaging Spectrograph
Authors: Tian, H.; Kleint, L.; Peter, H.; Weber, M.; Testa, P.;
   DeLuca, E.; Golub, L.; Schanche, N.
2014ApJ...790L..29T    Altcode: 2014arXiv1407.1060T
  Observations with the Interface Region Imaging Spectrograph (IRIS)
  have revealed numerous sub-arcsecond bright dots in the transition
  region above sunspots. These bright dots are seen in the 1400 Å and
  1330 Å slit-jaw images. They are clearly present in all sunspots we
  investigated, mostly in the penumbrae, but also occasionally in some
  umbrae and light bridges. The bright dots in the penumbrae typically
  appear slightly elongated, with the two dimensions being 300-600 km and
  250-450 km, respectively. The long sides of these dots are often nearly
  parallel to the bright filamentary structures in the penumbrae but
  sometimes clearly deviate from the radial direction. Their lifetimes
  are mostly less than one minute, although some dots last for a few
  minutes or even longer. Their intensities are often a few times stronger
  than the intensities of the surrounding environment in the slit-jaw
  images. About half of the bright dots show apparent movement with
  speeds of ~10-40 km s<SUP>-1</SUP> in the radial direction. Spectra of
  a few bright dots were obtained and the Si IV 1402.77 Å line profiles
  in these dots are significantly broadened. The line intensity can be
  enhanced by one to two orders of magnitude. Some relatively bright
  and long-lasting dots are also observed in several passbands of the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory,
  and they appear to be located at the bases of loop-like structures. Many
  of these bright dots are likely associated with small-scale energy
  release events at the transition region footpoints of magnetic loops.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
   Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
   C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
   C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
   D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
   Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
   R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
   Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
   Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
   Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
   W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
   Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
   Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
   Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
   M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
   K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
   J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
   Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
2014SoPh..289.2733D    Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
  The Interface Region Imaging Spectrograph (IRIS) small explorer
  spacecraft provides simultaneous spectra and images of the photosphere,
  chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
  spatial resolution, two-second temporal resolution, and 1 km
  s<SUP>−1</SUP> velocity resolution over a field-of-view of up to
  175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
  orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
  19-cm UV telescope that feeds a slit-based dual-bandpass imaging
  spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
  1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
  formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
  transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
  images in four different passbands (C II 1330, Si IV 1400, Mg II k
  2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
  rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
  of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
  emission from plasma at temperatures between 5000 K and 10 MK and will
  advance our understanding of the flow of mass and energy through an
  interface region, formed by the chromosphere and transition region,
  between the photosphere and corona. This highly structured and dynamic
  region not only acts as the conduit of all mass and energy feeding
  into the corona and solar wind, it also requires an order of magnitude
  more energy to heat than the corona and solar wind combined. The
  IRIS investigation includes a strong numerical modeling component
  based on advanced radiative-MHD codes to facilitate interpretation of
  observations of this complex region. Approximately eight Gbytes of data
  (after compression) are acquired by IRIS each day and made available
  for unrestricted use within a few days of the observation.

---------------------------------------------------------
Title: Detection of Supersonic Downflows and Associated Heating
    Events in the Transition Region above Sunspots
Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.;
   De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.;
   McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen,
   J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.;
   Kankelborg, C.
2014ApJ...789L..42K    Altcode: 2014arXiv1406.6816K
  Interface Region Imaging Spectrograph data allow us to study the solar
  transition region (TR) with an unprecedented spatial resolution of
  0.”33. On 2013 August 30, we observed bursts of high Doppler shifts
  suggesting strong supersonic downflows of up to 200 km s<SUP>-1</SUP>
  and weaker, slightly slower upflows in the spectral lines Mg II h
  and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated
  with brightenings in the slitjaw images (SJIs). The bursty behavior
  lasts throughout the 2 hr observation, with average burst durations
  of about 20 s. The locations of these short-lived events appear to
  be the umbral and penumbral footpoints of EUV loops. Fast apparent
  downflows are observed along these loops in the SJIs and in the
  Atmospheric Imaging Assembly, suggesting that the loops are thermally
  unstable. We interpret the observations as cool material falling
  from coronal heights, and especially coronal rain produced along the
  thermally unstable loops, which leads to an increase of intensity
  at the loop footpoints, probably indicating an increase of density
  and temperature in the TR. The rain speeds are on the higher end of
  previously reported speeds for this phenomenon, and possibly higher
  than the free-fall velocity along the loops. On other observing days,
  similar bright dots are sometimes aligned into ribbons, resembling
  small flare ribbons. These observations provide a first insight into
  small-scale heating events in sunspots in the TR.

---------------------------------------------------------
Title: Persistent Doppler Shift Oscillations Observed with Hinode/EIS
in the Solar CoronA: Spectroscopic Signatures of Alfvénic Waves
    and Recurring Upflows
Authors: Tian, Hui
2014shin.confE.152T    Altcode:
  Using data obtained by the EUV Imaging Spectrometer on board Hinode,
  we have performed a survey of obvious and persistent (without
  significant damping) Doppler shift oscillations in the corona. We
  have found mainly two types of oscillations from February to April
  in 2007. One type is found at loop footpoint regions, with a dominant
  period around 10 minutes. They are characterized by coherent behavior
  of all line parameters (line intensity, Doppler shift, line width,
  and profile asymmetry), and apparent blueshift and blueward asymmetry
  throughout almost the entire duration. Such oscillations are likely to
  be signatures of quasi-periodic upflows (small-scale jets, or coronal
  counterpart of type-II spicules), which may play an important role
  in the supply of mass and energy to the hot corona. The other type of
  oscillation is usually associated with the upper part of loops. They are
  most clearly seen in the Doppler shift of coronal lines with formation
  temperatures between one and two million degrees. The global wavelets
  of these oscillations usually peak sharply around a period in the range
  of three to six minutes. No obvious profile asymmetry is found and
  the variation of the line width is typically very small. The intensity
  variation is often less than 2%. These oscillations are more likely to
  be signatures of kink/Alfvéen waves rather than flows. In a few cases,
  there seems to be a ?/2 phase shift between the intensity and Doppler
  shift oscillations, which may suggest the presence of slow-mode standing
  waves according to wave theories. However, we demonstrate that such a
  phase shift could also be produced by loops moving into and out of a
  spatial pixel as a result of Alfvénic oscillations. In this scenario,
  the intensity oscillations associated with Alfvénic waves are caused by
  loop displacement rather than density change. These coronal waves may be
  used to investigate properties of the coronal plasma and magnetic field.

---------------------------------------------------------
Title: IRIS observations of sunspot oscillations
Authors: Tian, Hui
2014shin.confE.151T    Altcode:
  We present the first results of sunspot oscillations from observations
  by the Interface Region Imaging Spectrograph. The strongly nonlinear
  oscillation is identified in both the slit-jaw images and the
  spectra of several emission lines formed in the transition region and
  chromosphere. We first apply a single Gaussian fit to the profiles
  of the MgII 2796.35 Å, CII 1335.71 Å, and Si IV 1393.76 Å lines
  in the sunspot. The intensity change is ∼30%. The Doppler shift
  oscillation reveals a sawtooth pattern with an amplitude of ∼10
  km -1 in Si iv. The Si iv oscillation lags those of CII and MgII by
  ∼6 and ∼25 s, respectively. The line width suddenly increases
  as the Doppler shift changes from redshift to blueshift. However,
  we demonstrate that this increase is caused by the superposition of
  two emission components. We then perform detailed analysis of the
  line profiles at a few selected locations on the slit. The temporal
  evolution of the line core is dominated by the following behavior:
  a rapid excursion to the blue side, accompanied by an intensity
  increase, followed by a linear decrease of the velocity to the red
  side. The maximum intensity slightly lags the maximum blueshift in Si
  IV, whereas the intensity enhancement slightly precedes the maximum
  blueshift in MgII. We find a positive correlation between the maximum
  velocity and deceleration, a result that is consistent with numerical
  simulations of upward propagating magnetoacoustic shock waves.

---------------------------------------------------------
Title: Analyzing an IRIS Blowout jet via Magnetofrictional Simulation
Authors: Savcheva, Antonia; Tian, Hui; Meyer, Karen
2014AAS...22432310S    Altcode:
  The imaging spectrograph, IRIS, offers unprecedented spatial and
  temporal resolution of small-scale phenomena, which allows the
  study of their spectral properties in the chromosphere and transition
  region. This study present IRIS observations of a blowout coronal jet,
  demonstrating the ability of IRIS to detect reconnection effects in
  the low atmosphere in the available suite of spectral lines. We present
  Doppler velocity and non-thermal width (NTW) maps of the jet and their
  evolution in time. We interpret the results using MHD simulations of
  jets. In addition, we present a data-driven magnetofrictional simulation
  of the same jet and match the magnetic and current structure of the
  jet to the observed NTW maps. We infer the height of the null point
  and the extent of the region showing reconnection effects. We discuss
  the implications of understanding reconnection effects in conjunction
  with NTW maps.

---------------------------------------------------------
Title: IRIS observations of the transition region above sunspots:
    oscillations and moving penumbral dots
Authors: Tian, Hui; DeLuca, Ed; Weber, Mark A.; McKillop, Sean;
   Reeves, Kathy; Kleint, Lucia; Martinez-Sykora, Juan; De Pontieu,
   Bart; Carlsson, Mats
2014AAS...22431306T    Altcode:
  NASA's IRIS mission is providing high-cadence and high-resolution
  observations of the solar transition region and chromosphere. We
  present results from IRIS observation of the transition region above
  sunspots. The major findings can be summarized as following: (1) The C
  II and Mg II line profiles are almost Gaussian in the sunspot umbra and
  clearly exhibit a deep reversal at the line center in the plage region,
  suggesting a greatly reduced opacity in the sunspot atmosphere. (2)
  Strongly nonlinear sunspot oscillations can be clearly identified
  in not only the slit jaw images of 2796Å, 1400Å and 1330Å, but
  also in spectra of the bright Mg II, C II and Si IV lines. The Si
  iv oscillation lags those of C ii and Mg ii by 3 and 12 seconds,
  respectively. The temporal evolution of the line core is dominated by
  the following behavior: a rapid excursion to the blue side, accompanied
  by an intensity increase, followed by a linear decrease of the velocity
  to the red side. The maximum intensity slightly lags the maximum blue
  shift in Si iv , whereas the intensity enhancement slightly precedes the
  maximum blue shift in Mg ii . We find a positive correlation between
  the maximum velocity and deceleration. These results are consistent
  with numerical simulations of upward propagating magneto-acoustic
  shock waves. We also demonstrate that the strongly nonlinear line
  width oscillation, reported both previously and here, is spurious. (3)
  Many small-scale bright dots are present in the penumbral filaments and
  light bridges in SJI 1330Å and 1400Å images obtained in high-cadence
  observations. They are usually smaller than 1" and often just a couple
  of pixels wide. Some bright dots show apparent movement with a speed of
  20-60 km/s(either outward or inward). The lifetime of these penumbral
  dots is mostly less than 1 min. The most obvious feature of the Si IV
  profiles in the bright dots is the enhanced line width. Besides that,
  the profile looks normal and no obvious fast flows are detected. The
  bright dots in the light bridges even show oscillation patterns. It's
  not clear whether these oscillations are triggered by the umbral
  oscillations or not.

---------------------------------------------------------
Title: High-resolution Observations of the Shock Wave Behavior for
    Sunspot Oscillations with the Interface Region Imaging Spectrograph
Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu,
   B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.;
   Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.;
   Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
   Kankelborg, C.; Jaeggli, S.; McIntosh, S. W.
2014ApJ...786..137T    Altcode: 2014arXiv1404.6291T
  We present the first results of sunspot oscillations from observations
  by the Interface Region Imaging Spectrograph. The strongly nonlinear
  oscillation is identified in both the slit-jaw images and the
  spectra of several emission lines formed in the transition region and
  chromosphere. We first apply a single Gaussian fit to the profiles of
  the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the
  sunspot. The intensity change is ~30%. The Doppler shift oscillation
  reveals a sawtooth pattern with an amplitude of ~10 km s<SUP>-1</SUP>
  in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and
  ~12 s, respectively. The line width suddenly increases as the Doppler
  shift changes from redshift to blueshift. However, we demonstrate
  that this increase is caused by the superposition of two emission
  components. We then perform detailed analysis of the line profiles at
  a few selected locations on the slit. The temporal evolution of the
  line core is dominated by the following behavior: a rapid excursion
  to the blue side, accompanied by an intensity increase, followed by a
  linear decrease of the velocity to the red side. The maximum intensity
  slightly lags the maximum blueshift in Si IV, whereas the intensity
  enhancement slightly precedes the maximum blueshift in Mg II. We find
  a positive correlation between the maximum velocity and deceleration,
  a result that is consistent with numerical simulations of upward
  propagating magnetoacoustic shock waves.

---------------------------------------------------------
Title: Dynamics of a prominence observed in Mg II lines by IRIS
Authors: Schmieder, Brigitte; Mein, Pierre; Dalmasse, Kévin; Tian,
   Hui; Kucera, Therese; Lopez-Ariste, Arturo
2014cosp...40E2927S    Altcode:
  In September 2013 several prominences were observed with the IRIS
  spectrograph during a 60 day-long international program. We will present
  one set of observations obtained using multiple instruments on September
  24. SDO/AIA and IRIS slit jaws provided images of the prominence
  corresponding to different physical conditions of the transition
  region between the cool plasma and the corona. The vector magnetic
  field was derived from THEMIS (Tenerife) observations using the He D3
  depolarisation due to the magnetic field. The inversion code (CPA) takes
  into account the Hanle and the Zeeman effects. Movies from SDO/AIA in
  304 A and Hinode/SOT in Ca II show the dynamics of the fine structures
  in the plane of the sky. From Mg II and Si IV line spectra observed by
  IRIS and H-alpha observed by the Multi-channel subtractive spectrograph
  (MSDP) in the Meudon solar tower we derived the Dopplershifts of the
  fine structures. The profiles of the Mg II lines are narrow (FHWM =0.15
  A) and not reversed, contrary to the predictions of the theoretical
  models (Paletou et al 1993). We could resolve the velocity of several
  structures along the LOS with Dopplershifts as high as 60 km/s.

---------------------------------------------------------
Title: Observations of Coronal Mass Ejections with the Coronal
    Multichannel Polarimeter
Authors: Tian, H.; Tomczyk, S.; McIntosh, S. W.; Bethge, C.; de Toma,
   G.; Gibson, S.
2013SoPh..288..637T    Altcode: 2013arXiv1303.4647T
  The Coronal Multichannel Polarimeter (CoMP) measures not only the
  polarization of coronal emission, but also the full radiance profiles of
  coronal emission lines. For the first time, CoMP observations provide
  high-cadence image sequences of the coronal line intensity, Doppler
  shift, and line width simultaneously over a large field of view. By
  studying the Doppler shift and line width we may explore more of the
  physical processes of the initiation and propagation of coronal mass
  ejections (CMEs). Here we identify a list of CMEs observed by CoMP
  and present the first results of these observations. Our preliminary
  analysis shows that CMEs are usually associated with greatly increased
  Doppler shift and enhanced line width. These new observations provide
  not only valuable information to constrain CME models and probe
  various processes during the initial propagation of CMEs in the low
  corona, but also offer a possible cost-effective and low-risk means
  of space-weather monitoring.

---------------------------------------------------------
Title: The Evolving Magnetic Scales of the Outer Solar Atmosphere
    and Their Potential Impact on Heliospheric Turbulence
Authors: McIntosh, Scott W.; Bethge, Christian; Threlfall, James;
   De Moortel, Ineke; Leamon, Robert J.; Tian, Hui
2013arXiv1311.2538M    Altcode:
  The presence of turbulent phenomena in the outer solar atmosphere
  is a given. However, because we are reduced to remotely sensing the
  atmosphere of a star with instruments of limited spatial and/or spectral
  resolution, we can only infer the physical progression from macroscopic
  to microscopic phenomena. Even so, we know that many, if not all,
  of the turbulent phenomena that pervade interplanetary space have
  physical origins at the Sun and so in this brief article we consider
  some recent measurements which point to sustained potential source(s)
  of heliospheric turbulence in the magnetic and thermal domains. In
  particular, we look at the scales of magnetism that are imprinted on
  the outer solar atmosphere by the relentless magneto-convection of the
  solar interior and combine state-of-the-art observations from the Solar
  Dynamics Observatory (SDO) and the Coronal Multi-channel Polarimeter
  (CoMP) which are beginning to hint at the origins of the wave/plasma
  interplay prevalent closer to the Earth. While linking these disparate
  scales of observation and understanding of their connection is near
  to impossible, it is clear that the constant evolution of subsurface
  magnetism on a host of scales guides and governs the flow of mass
  and energy at the smallest scales. In the near future significant
  progress in this area will be made by linking observations from high
  resolution platforms like the Interface Region Imaging Spectrograph
  (IRIS) and Advanced Technology Solar Telescope (ATST) with full-disk
  synoptic observations such as those presented herein.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Galactic extinction from SDSS
    BHB stars (Tian+, 2014)
Authors: Tian, H. J.; Liu, C.; Hu, J. Y.; Xu, Y.; Chen, X. L.
2013yCat..35610142T    Altcode: 2013yCat..35619142T
  File table3 contains the SDSS colors of the 94 template BHB stars
  and their coordinates and the errors of colors. The 94 BHB stars are
  selected from 7 globular clusters. <P />(2 data files).

---------------------------------------------------------
Title: Temperature dependence of ultraviolet line parameters in
    network and internetwork regions of the quiet Sun and coronal holes
Authors: Wang, X.; McIntosh, S. W.; Curdt, W.; Tian, H.; Peter, H.;
   Xia, L. -D.
2013A&A...557A.126W    Altcode:
  <BR /> Aims: We study the temperature dependence of the average Doppler
  shift and the non-thermal line width in network and internetwork
  regions for both the quiet Sun (QS) and the coronal hole (CH), by
  using observations of the Solar Ultraviolet Measurements of Emitted
  Radiation instrument onboard the Solar and Heliospheric Observatory
  spacecraft. <BR /> Methods: We obtain the average Doppler shift and
  non-thermal line width in the network regions of QS, internetwork
  regions of QS, network regions of CH, and internetwork regions of CH by
  applying a single-Gaussian fit to the line profiles averaged in each
  of the four regions. The formation temperatures of the lines we use
  cover the range from 10<SUP>4</SUP> to 1.2 × 10<SUP>6</SUP> K. Two
  simple scenarios are proposed to explain the temperature dependence of
  the line parameters in the network regions. In one of the scenarios,
  the spectral line consists of three components: a rapid, weak upflow
  generated in the lower atmosphere, a nearly static background, and
  a slow cooling downflow. In the other scenario, there are just two
  components, which include a bright core component and a faint wide tail
  one. <BR /> Results: An enhancement of the Doppler shift magnitude
  and the non-thermal line width in network regions compared to the
  internetwork regions is reported. We also report that most transition
  region lines are less redshifted (by 0-8 km s<SUP>-1</SUP>) and broader
  (by 0-5 km s<SUP>-1</SUP>) in CH compared to the counterparts of QS. In
  internetwork regions, the difference in the Doppler shifts between the
  coronal hole and the QS is slightly smaller, especially for the lines
  with formation temperatures lower than 2 × 10<SUP>5</SUP> K. And the
  two simple scenarios can reproduce the variation in the line parameters
  with the temperature very well. <BR /> Conclusions: Our results suggest
  that the physical processes in network and internetwork regions are
  different and that one needs to separate network and internetwork when
  discussing dynamics and physical properties of the solar atmosphere. The
  agreement between the results of the observation and our scenarios
  suggests that the temperature dependence of Doppler shifts and line
  widths might be caused by the different relative contributions of the
  three components at different temperatures. The results may shed new
  light on our understanding of the complex chromosphere-corona mass
  cycle. However, the existing observational results do not allow us to
  distinguish between the two scenarios. At this stage, a high-resolution
  instrument Interface Region Imaging Spectrograph is highly desirable.

---------------------------------------------------------
Title: A Detailed Comparison between the Observed and Synthesized
    Properties of a Simulated Type II Spicule
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Leenaarts, Jorrit;
   Pereira, Tiago M. D.; Carlsson, Mats; Hansteen, Viggo; Stern, Julie
   V.; Tian, Hui; McIntosh, Scott W.; Rouppe van der Voort, Luc
2013ApJ...771...66M    Altcode: 2013arXiv1305.2397M
  We have performed a three-dimensional radiative MHD simulation of the
  solar atmosphere. This simulation shows a jet-like feature that shows
  similarities to the type II spicules observed for the first time with
  Hinode's Solar Optical Telescope. Rapid blueshifted events (RBEs) on the
  solar disk are associated with these spicules. Observational results
  suggest they may contribute significantly in supplying the corona
  with hot plasma. We perform a detailed comparison of the properties
  of the simulated jet with those of type II spicules (observed with
  Hinode) and RBEs (with ground-based instruments). We analyze a wide
  variety of synthetic emission and absorption lines from the simulations
  including chromospheric (Ca II 8542 Å, Ca II H, and Hα) to transition
  region and coronal temperatures (10,000 K to several million K). We
  compare their synthetic intensities, line profiles, Doppler shifts,
  line widths, and asymmetries with observations from Hinode/SOT and
  EIS, SOHO/SUMER, the Swedish 1 m Solar Telescope, and SDO/AIA. Many
  properties of the synthetic observables resemble the observations,
  and we describe in detail the physical processes that lead to these
  observables. Detailed analysis of the synthetic observables provides
  insight into how observations should be analyzed to derive information
  about physical variables in such a dynamic event. For example, we
  find that line-of-sight superposition in the optically thin atmosphere
  requires the combination of Doppler shifts and spectral line asymmetry
  to determine the velocity in the jet. In our simulated type II spicule,
  the lifetime of the asymmetry of the transition region lines is shorter
  than that of the coronal lines. Other properties differ from the
  observations, especially in the chromospheric lines. The mass density
  of the part of the spicule with a chromospheric temperature is too low
  to produce significant opacity in chromospheric lines. The synthetic
  Ca II 8542 Å and Hα profiles therefore do not show signal resembling
  RBEs. These and other discrepancies are described in detail, and we
  discuss which mechanisms and physical processes may need to be included
  in the MHD simulations to mimic the thermodynamic processes of the
  chromosphere and corona, in particular to reproduce type II spicules.

---------------------------------------------------------
Title: A Statistical Study on the Reconnection in Boundary Layers
    of Small-scale Magnetic Flux Tubes in Solar Winds
Authors: Qi, Yu; Yao, Shuo; He, Jian-sen; Tian, Hui; Tu, Chuan-yi
2013ChA&A..37..163Q    Altcode:
  With the data from WIND satellite in 1995—2005, the small-scale
  magnetic flux tubes determined with two methods, i.e., the artificial
  recognition and program selection respectively, are compared. It is
  found that there are magnetic reconnections in the boundary layers
  of 41% small-scale magnetic flux tubes determined with the program
  selection method, which is similar to the re- sult of small-scale
  magnetic flux tubes determined with the method of artificial
  recognition. The features of magnetic reconnections, such as the
  magnetic shear angle, magnetic field strength, and duration of the
  dissipation region of recon- nection at the small-scale flux tubes'
  boundaries determined from both methods have the same statistical
  tendency. This shows that there is no essential differ- ence in the
  properties of reconnections in the boundary layers of the small-scale
  magnetic flux tubes determined with the two methods. Hence the data
  yielded by both methods can be used as the samples for statistically
  studying the events of reconnection in the front and back boundary
  layers of small-scale flux ropes. There are totally 71 magnetic
  reconnection events selected in this paper. Our statistical result shows
  that in 50 events (70%) the decrease of magnetic field strength in the
  dissipation region of reconnection is larger than 20%, and in 47 events
  (66%) the magnetic shear angle is larger than 90 degrees. These indicate
  that the magnetic reconnections in boundaries of the small-scale
  magnetic flux tubes are more likely to be anti-parallel. The statistics
  has been performed sep- arately in the reconnections of the front
  and back boundary layers of small-scale magnetic flux tubes. The
  results show that the features of reconnections in the front and back
  boundaries are similar to each other, which is different from the
  various properties in the front and back boundaries of the magnetic
  clouds, and this means that the expansion in the large-scale magnetic
  flux tubes, such as magnetic clouds, does not happen in the small-scale
  magnetic flux tubes.

---------------------------------------------------------
Title: Global oscillations and small scale dynamics of a filament
Authors: Tian, Hui; Ofman, Leon; Wang, Tongjiang
2013enss.confE.104T    Altcode:
  Using AIA data, we observed global oscillatory motions along the axis
  of a filament with detailed small scale dynamics. The global oscillation
  lasted for more than two days before the eruption of the filament. Both
  magnetic tension and gravity are likely to be involved in the global
  oscillation, as predicted by theoretical models. A closer look of the
  detailed dynamics within the filament suggests that torsional motions
  around the prominence axis are also present. Torsional motions around
  the two legs of the filament resemble the so-called "solar tornadoes"
  observed at limb by AIA. Variable counter-streaming flows in the
  prominence body were detected as well before the filament eruption. The
  HMI magnetic field data and multi-line diagnostics are used to
  investigate possible mechanisms responsible for the different types
  of oscillations and flows before the eventual eruption of the filament.

---------------------------------------------------------
Title: Formation of a hot plasma blob: observations of AIA, CoMP
    and MK4
Authors: Tian, Hui; Gibson, Sarah
2013enss.confE.107T    Altcode:
  Using AIA observations, we found that a hot blob of plasma formed as
  a trans-equatorial loop system rose and opened up. The hot blob was
  most clearly seen in the AIA 94 passband and not obvious in any other
  passbands. A cusp-like structure quickly developed below the hot blob
  when the blob left the FOV of AIA 1.5 hours after its formation. This
  event was also observed by the CoMP and MK4 instruments in Mauna Loa
  Solar Observatory. The CoMP observation reveals a clear "bunny ear"
  pattern suggestive of a magnetic flux rope around the AIA blob. The
  hot blob observed by AIA seems to coincide with the region of enhanced
  linear polarization between the two dark ears. A comparison between
  these observations with MHD simulations of flux rope eruption suggest
  that the hot blob might be the lower part of, or just below, the
  erupted flux rope. In the MK4 data we see a clear three-part CME
  propagating outward.

---------------------------------------------------------
Title: Persistent Doppler Shift Oscillations Observed with Hinode/EIS
in the Solar Corona: Spectroscopic Signatures of Alfvénic Waves
    and Recurring Upflows
Authors: Tian, Hui; McIntosh, Scott W.; Wang, Tongjiang; Ofman, Leon;
   De Pontieu, Bart; Innes, Davina E.; Peter, Hardi
2012ApJ...759..144T    Altcode: 2012arXiv1209.5286T
  Using data obtained by the EUV Imaging Spectrometer on board Hinode,
  we have performed a survey of obvious and persistent (without
  significant damping) Doppler shift oscillations in the corona. We
  have found mainly two types of oscillations from February to April
  in 2007. One type is found at loop footpoint regions, with a dominant
  period around 10 minutes. They are characterized by coherent behavior
  of all line parameters (line intensity, Doppler shift, line width,
  and profile asymmetry), and apparent blueshift and blueward asymmetry
  throughout almost the entire duration. Such oscillations are likely to
  be signatures of quasi-periodic upflows (small-scale jets, or coronal
  counterpart of type-II spicules), which may play an important role
  in the supply of mass and energy to the hot corona. The other type of
  oscillation is usually associated with the upper part of loops. They are
  most clearly seen in the Doppler shift of coronal lines with formation
  temperatures between one and two million degrees. The global wavelets
  of these oscillations usually peak sharply around a period in the range
  of three to six minutes. No obvious profile asymmetry is found and
  the variation of the line width is typically very small. The intensity
  variation is often less than 2%. These oscillations are more likely to
  be signatures of kink/Alfvén waves rather than flows. In a few cases,
  there seems to be a π/2 phase shift between the intensity and Doppler
  shift oscillations, which may suggest the presence of slow-mode standing
  waves according to wave theories. However, we demonstrate that such a
  phase shift could also be produced by loops moving into and out of a
  spatial pixel as a result of Alfvénic oscillations. In this scenario,
  the intensity oscillations associated with Alfvénic waves are caused by
  loop displacement rather than density change. These coronal waves may be
  used to investigate properties of the coronal plasma and magnetic field.

---------------------------------------------------------
Title: Explosive Events: Swirling Transition Region Jets
Authors: Curdt, W.; Tian, H.; Kamio, S.
2012SoPh..280..417C    Altcode: 2012SoPh..tmp...24C; 2012arXiv1201.3199C
  In this paper, we extend our earlier work to provide additional evidence
  for an alternative scenario to explain the nature of events called
  `explosive events'. The bidirected, fast Doppler motion of explosive
  events observed spectroscopically in the transition region emission is
  classically interpreted as a pair of bidirectional jets moving upward
  and downward from a reconnection site. We discuss the problems of this
  model. In our previous work, we focused basically on the discrepancy of
  fast Doppler motion without detectable motion in the image plane. We
  now suggest an alternative scenario for the explosive events, based
  on our observations of spectral line tilts and bifurcated structure
  in some events. Both features are indicative of rotational motion
  in narrow structures. We explain the bifurcation as the result of
  rotation of hollow cylindrical structures and demonstrate that this
  kind of sheath model can also be applied to explain the nature of the
  puzzling `explosive events'. We find that the spectral tilt, the lack
  of apparent motion, the bifurcation, and a rapidly growing number
  of direct observations support an alternative scenario of linear,
  spicular-sized jets with a strong spinning motion.

---------------------------------------------------------
Title: Collimation of laser-driven energetic protons in a capillary
Authors: Chen, D. -P.; Yin, Y.; Ge, Z. -Y.; Xu, H.; Zhuo, H. -B.;
   Ma, Y. -Y.; Shao, F. -Q.; Tian, C. -L.; Tian
2012JPlPh..78..333C    Altcode:
  Energetic divergent proton beams can be generated in the interaction
  of ultra-intense laser pulses with solid-density foil targets via
  target normal sheath acceleration (TNSA). In this paper, a scheme
  using a capillary to reduce the proton beam divergence is proposed. By
  two-dimensional particle-in-cell (PIC) simulations, it is shown that
  strong transverse electric and magnetic fields rapidly grow at the
  inner surface of the capillary when the laser-driven hot electrons
  propagate through the target and into the capillary. The spontaneous
  magnetic field collimates the electron flow, and the ions dragged from
  the capillary wall by hot electrons neutralize the negative charge and
  thus restrain the transverse extension of the sheath field set up by
  electrons. The proton beam divergence, which is mainly determined by
  the accelerating sheath field, is therefore reduced by the transverse
  limitation of the sheath field in the capillary.

---------------------------------------------------------
Title: Explosive events - swirling transition region jets
Authors: Curdt, Werner; Kamio, Suguru; Tian, Hui; Teriaca, Luca
2012cosp...39..381C    Altcode: 2012cosp.meet..381C
  The bi-directed, fast Doppler motion of explosive events observed
  spectroscopically in the transition region emission is classically
  interpreted as a pair of jets moving upward and downward from a
  reconnection site. We discuss the problems of such a model and provide
  evidence for an alternative scenario to explain the nature of so-called
  'explosive events'. The discrepancy of fast Doppler motion without
  detectable motion in the image plane is an old, unsolved problem. We
  now provide the spectral tilt and the jet bifurcation as additional
  arguments. Both features are indicative of rotational motion in narrow
  structures. We interpret the bifurcation as the result of rotation of
  hollow cylindrical structures and demonstrate that such a sheath model
  can also be applied to explain the nature of the puzzling 'explosive
  events'. We find that the spectral tilt, the lack of apparent motion,
  the bifurcation, and a rapidly growing number of direct observations
  support an alternative scenario of linear, spicular-sized jets with
  a strong spinning motion.

---------------------------------------------------------
Title: Temperature Dependence of UV Line Parameters in Network and
    Internetwork Regions of the Quiet Sun and Coronal holes
Authors: Wang, Xin; McIntosh, Scott W.; Tian, Hui
2012shin.confE...7W    Altcode:
  By using observations of SUMER on board the SOHO spacecraft, we study
  the temperature dependence of the Doppler shift, non-thermal width in
  network and internetwork regions for both the quiet Sun (QS) and the
  coronal hole (CH). In network regions, most of the transition region
  (TR) line profiles are more red shifted (by 0-5km/s) and narrower (by
  1-6km/s) in QS than in CH. Our results suggest that the mass cycle
  between the chromosphere and corona mainly occurs in the network
  and one needs to separate network and internetwork when discussing
  thermal and dynamic properties of the solar atmosphere. In addition, a
  three-component toy model is built to explain the temperature dependence
  of the line parameters, which includes a rapid, weak upflow generated
  in the lower atmosphere, a nearly static background, and a slow cooling
  downflow. The agreement between the results of the observation and our
  model suggests that the temperature dependence of Doppler shifts and
  line widths might be caused by the different relative contributions of
  the three components at different temperatures and will shed a new light
  on our understanding of the complex chromosphere-coronal mass cycle.

---------------------------------------------------------
Title: Two components of the coronal emission revealed by both
    spectroscopic and imaging observations
Authors: Tian, Hui; McIntosh, Scott W.; De Pontieu, Bart
2012shin.confE...1T    Altcode:
  Boundaries of active regions have been suggested to be possible sources
  of the slow solar wind. X-ray and EUV imaging observations often reveal
  high-speed ( 100 km/s) quasi-periodic propagating disturbances (PDs)
  along the fan-like structures at edges of active regions. Meanwhile EUV
  spectroscopic observations of active region boundaries usually reveal
  a blue shift of the order of 20 km/s and no periodicity. We think that
  the key to solve these discrepancies is the asymmetry of the emission
  line profile. The ubiquitous presence of blueward asymmetries of EUV
  emission line profiles suggests at least two emission components:
  a primary component accounting for the background coronal emission
  and a weak secondary component associated with high-speed ( 100 km/s)
  upflows. Through jointed imaging and spectroscopic observations, we have
  demonstrated that the PDs are responsible for the secondary component
  of line profiles and suggested that they may be an efficient means to
  provide heated mass into the corona and solar wind. The intermittent
  nature of these high-speed outflows (fine-scale jets) suggests that
  the mass supply to the corona and solar wind is episodic rather than
  continuous. Similar spectroscopic signatures have also been found in
  CME-induced dimming regions, suggesting possible solar wind streams from
  dimming regions. Unresolved problems include the production mechanism
  of these high-speed outflows and the connection between these outflows
  to the interplanetary space.

---------------------------------------------------------
Title: New insight into CME processes revealed by CoMP observations
Authors: Tian, Hui; McIntosh, Scott W.; Bethge, Christian; Tomczyk,
   Steve; Sitongia, Leonard E.
2012shin.confE..11T    Altcode:
  CoMP measures not only the polarization of coronal emission, but also
  measures the full radiance profiles of coronal emission lines. For the
  first time, CoMP observations provide high-cadence image sequences
  of the coronal intensity, Doppler shift, line width and linear
  polarization simultaneously. These measurements may help us explore
  more of the physical processes at the onset of solar eruptions such
  as CMEs and flares. They should also provide important constraints to
  models of solar eruptions. Our preliminary analysis shows that CMEs are
  usually associated with greatly increased Doppler shift and enhanced
  line width. The linear polarization in CMEs measured by CoMP has also
  been investigated.

---------------------------------------------------------
Title: What can we Learn about Solar Coronal Mass Ejections,
    Coronal Dimmings, and Extreme-Ultraviolet Jets Through Spectroscopic
    Observations?
Authors: Tian, Hui; McIntosh, Scott W.; Xia, L. -D.; He, J. -S.;
   Wang, X.
2012shin.confE..10T    Altcode:
  Solar eruptions, particularly coronal mass ejections (CMEs) and
  extreme-ultraviolet (EUV) jets, have rarely been investigated with
  spectroscopic observations. We analyze several data sets obtained by
  the EUV Imaging Spectrometer onboard Hinode and find various types of
  flows during CMEs and jet eruptions. We found weak high-speed ( 100
  km/s) outflows in CME induced dimming regions, temperature-dependent
  outflows (speed increases with temperature) immediately outside the
  dimming region, and strong high-speed ( 200 km/s) outflows associated
  with the CME ejecta and EUV jets. We have made plasma diagnostics
  (density, temperature, mass) for the dimming regions and CME/jet
  ejecta. Our results suggest that spectroscopic observations can provide
  useful information on the kinematics and plasma properties of solar
  mass eruptions.

---------------------------------------------------------
Title: Erratum: "Pulsed Alfvén Waves in the Solar Wind" <A
    href="/abs/2011ApJ...737L..35G">(2011, ApJ, 737, l35)</A>
Authors: Gosling, J. T.; Tian, H.; Phan, T. D.
2012ApJ...751L..22G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Recent Results from the Coronal Multi-Channel Polarimeter
Authors: Tomczyk, Steven; Bethge, C.; Gibson, S. E.; McIntosh, S. W.;
   Rachmeler, L. A.; Tian, H.
2012AAS...22031001T    Altcode:
  The Coronal Multi-Channel Polarimeter (CoMP) instrument is a
  ground-based filter/polarimeter which can image the solar corona at
  wavelengths around the emission lines of FeXIII at 1074.7 and 1079.8
  nm and the chromospheric emission line of HeI at 1083.0 nm. The
  instrument consists of a 20-cm aperture coronagraph followed by a
  Stokes polarimeter and a Lyot birefringent filter with a passband
  of 0.14 nm width. Both the polarimeter and filter employ liquid
  crystals for rapid electro-optical tuning. This instrument measures
  the line-of-sight strength of the coronal magnetic field through the
  Zeeman effect and the plane-of-sky direction of the magnetic field via
  resonance scattering. The line-of-sight velocity can also be determined
  from the Doppler shift. The CoMP has obtained daily observations from
  the Mauna Loa Solar Observatory for almost one year. We will present
  recent measurements of the polarization signatures seen with the
  CoMP and a comparison with models that allow us to constrain coronal
  structure. We also will present observations of coronal waves taken
  with the CoMP and discuss their implications for the heating of the
  solar corona and the acceleration of the solar wind.

---------------------------------------------------------
Title: Hinode/EIS Line Profile Asymmetries and Their Relationship with
    the Distribution of SDO/AIA Propagating Coronal Disturbance Velocities
Authors: Sechler, M.; McIntosh, S. W.; Tian, H.; De Pontieu, B.
2012ASPC..455..361S    Altcode: 2012arXiv1201.5028S
  Using joint observations from Hinode/EIS and the Atmospheric Imaging
  Array (AIA) on the Solar Dynamics Observatory (SDO) we explore the
  asymmetry of coronal EUV line profiles. We find that asymmetries exist
  in all of the spectral lines studied, and not just the hottest lines
  as has been recently reported in the literature. Those asymmetries
  indicate that the velocities of the second emission component are
  relatively consistent across temperature and consistent with the
  apparent speed at which material is being inserted from the lower
  atmosphere that is visible in the SDO/AIA images as propagating coronal
  disturbances. Further, the observed asymmetries are of similar magnitude
  (a few percent) and width (determined from the RB analysis) across the
  temperature space sampled and in the small region studied. Clearly,
  there are two components of emission in the locations where the
  asymmetries are identified in the RB analysis, their characteristics
  are consistent with those determined from the SDO/AIA data. There is
  no evidence from our analysis that this second component is broader
  than the main component of the line.

---------------------------------------------------------
Title: Two Components of the Coronal Emission Revealed by Both
    Spectroscopic and Imaging Observations
Authors: Tian, H.; McIntosh, S. W.; De Pontieu, B.
2012ASPC..456...97T    Altcode:
  X-ray and EUV imaging observations often reveal quasi-periodic
  propagating disturbances along the fan-like structures at edges of
  active regions. These disturbances have historically been interpreted
  as being signatures of slow-mode magnetoacoustic waves propagating
  into the corona. Recent spectroscopic observations have revealed
  the ubiquitous presence of blueward asymmetries of EUV emission line
  profiles. Such asymmetries suggest that there are at least two emission
  components: a primary component accounting for the background emission
  and a secondary component associated with high-speed upflows. Thus, a
  single Gaussian fit can not reflect the real physics here. Through joint
  imaging and spectroscopic observations, we find a clear association
  of the secondary component with the upward propagating disturbances
  and conclude that they are more likely to be real plasma outflows
  (small-scale recurring jets) rather than slow waves. These outflows
  may result from impulsive heating processes in the lower transition
  region or chromosphere and could be an efficient means to provide hot
  plasma into the corona and possibly also solar wind.

---------------------------------------------------------
Title: On the Doppler Velocity of Emission Line Profiles Formed in
    the "Coronal Contraflow" that Is the Chromosphere-Corona Mass Cycle
Authors: McIntosh, Scott W.; Tian, Hui; Sechler, Marybeth; De Pontieu,
   Bart
2012ApJ...749...60M    Altcode: 2012arXiv1202.1248M
  This analysis begins to explore the complex chromosphere-corona mass
  cycle using a blend of imaging and spectroscopic diagnostics. Single
  Gaussian fits (SGFs) to hot emission line profiles (formed above 1 MK)
  at the base of coronal loop structures indicate material blueshifts
  of 5-10 km s<SUP>-1</SUP>, while cool emission line profiles (formed
  below 1 MK) yield redshifts of a similar magnitude—indicating, to
  zeroth order, that a temperature-dependent bifurcating flow exists
  on coronal structures. Image sequences of the same region reveal
  weakly emitting upward propagating disturbances in both hot and cool
  emission with apparent speeds of 50-150 km s<SUP>-1</SUP>. Spectroscopic
  observations indicate that these propagating disturbances produce a weak
  emission component in the blue wing at commensurate speed, but that they
  contribute only a few percent to the (ensemble) emission line profile
  in a single spatio-temporal resolution element. Subsequent analysis of
  imaging data shows material "draining" slowly (~10 km s<SUP>-1</SUP>)
  out of the corona, but only in the cooler passbands. We interpret
  the draining as the return flow of coronal material at the end of
  the complex chromosphere-corona mass cycle. Further, we suggest that
  the efficient radiative cooling of the draining material produces a
  significant contribution to the red wing of cool emission lines that is
  ultimately responsible for their systematic redshift as derived from an
  SGF when compared to those formed in hotter (conductively dominated)
  domains. The presence of counterstreaming flows complicates the line
  profiles, their interpretation, and asymmetry diagnoses, but allows
  a different physical picture of the lower corona to develop.

---------------------------------------------------------
Title: What can We Learn about Solar Coronal Mass Ejections,
    Coronal Dimmings, and Extreme-ultraviolet Jets through Spectroscopic
    Observations?
Authors: Tian, Hui; McIntosh, Scott W.; Xia, Lidong; He, Jiansen;
   Wang, Xin
2012ApJ...748..106T    Altcode: 2012arXiv1201.2204T
  Solar eruptions, particularly coronal mass ejections (CMEs) and
  extreme-ultraviolet (EUV) jets, have rarely been investigated with
  spectroscopic observations. We analyze several data sets obtained
  by the EUV Imaging Spectrometer on board Hinode and find various
  types of flows during CMEs and jet eruptions. CME-induced dimming
  regions are found to be characterized by significant blueshift and
  enhanced line width by using a single Gaussian fit, while a red-blue
  (RB) asymmetry analysis and an RB-guided double Gaussian fit of
  the coronal line profiles indicate that these are likely caused by
  the superposition of a strong background emission component and a
  relatively weak (~10%), high-speed (~100 km s<SUP>-1</SUP>) upflow
  component. This finding suggests that the outflow velocity in the
  dimming region is probably of the order of 100 km s<SUP>-1</SUP>, not
  ~20 km s<SUP>-1</SUP> as reported previously. These weak, high-speed
  outflows may provide a significant amount of mass to refill the corona
  after the eruption of CMEs, and part of them may experience further
  acceleration and eventually become solar wind streams that can serve
  as an additional momentum source of the associated CMEs. Density and
  temperature diagnostics of the dimming region suggest that dimming
  is primarily an effect of density decrease rather than temperature
  change. The mass losses in dimming regions as estimated from different
  methods are roughly consistent with each other, and they are 20%-60%
  of the masses of the associated CMEs. With the guide of RB asymmetry
  analysis, we also find several temperature-dependent outflows (speed
  increases with temperature) immediately outside the (deepest) dimming
  region. These outflows may be evaporation flows that are caused by
  the enhanced thermal conduction or nonthermal electron beams along
  reconnecting field lines, or induced by the interaction between the
  opened field lines in the dimming region and the closed loops in
  the surrounding plage region. In an erupted CME loop and an EUV jet,
  profiles of emission lines formed at coronal and transition region
  temperatures are found to exhibit two well-separated components, an
  almost stationary component accounting for the background emission and
  a highly blueshifted (~200 km s<SUP>-1</SUP>) component representing
  emission from the erupting material. The two components can easily
  be decomposed through a double Gaussian fit, and we can diagnose the
  electron density, temperature, and mass of the ejecta. Combining the
  speed of the blueshifted component and the projected speed of the
  erupting material derived from simultaneous imaging observations,
  we can calculate the real speed of the ejecta.

---------------------------------------------------------
Title: Spectroscopic observations of coronal mass ejections, coronal
    dimming and EUV jets
Authors: Tian, Hui; McIntosh, Scott W.
2012decs.confE..10T    Altcode:
  Solar eruptions, particularly coronal mass ejections (CMEs) and
  extreme-ultraviolet (EUV) jets, have rarely been investigated with
  spectroscopic observations. We analyze several data sets obtained by
  the EUV Imaging Spectrometer onboard Hinode and find various types of
  flows during CMEs and jet eruptions. CME-induced dimming regions are
  found to be characterized by significant blueshift and enhanced line
  width by using a single Gaussian fit. While a red-blue (RB) asymmetry
  analysis and a RB-guided double Gaussian fit of the coronal line
  profiles indicate that these are likely caused by the superposition
  of a strong background emission component and a relatively weak ( 10%)
  high-speed ( 100 km s-1) upflow component. This finding suggests that
  the outflow velocity in the dimming region is probably of the order
  of 100 km s-1, not 20 km s-1 as reported previously. Density and
  temperature diagnostics of the dimming region suggest that dimming
  is primarily an effect of density decrease rather than temperature
  change. The mass losses in dimming regions as estimated from different
  methods are roughly consistent with each other and they are 20%-60%
  of the masses of the associated CMEs. With the guide of RB asymmetry
  analysis, we also find several temperature-dependent outflows (speed
  increases with temperature) immediately outside the (deepest) dimming
  region. These outflows may be evaporation flows which are caused by
  the enhanced thermal conduction or nonthermal electron beams along
  reconnecting field lines, or induced by the interaction between the
  opened field lines in the dimming region and the closed loops in
  the surrounding plage region. In an erupted CME loop and an EUV jet,
  profiles of emission lines formed at coronal and transition region
  temperatures are found to exhibit two well-separated components, an
  almost stationary component accounting for the background emission
  and a highly blueshifted ( 200 km s-1) component representing
  emission from the erupting material. The two components can easily
  be decomposed through a double Gaussian fit and we can diagnose the
  electron density, temperature and mass of the ejecta. Combining the
  speed of the blueshifted component and the projected speed of the
  erupting material derived from simultaneous imaging observations,
  we can calculate the real speed of the ejecta.

---------------------------------------------------------
Title: Temperature dependence of EUV line parameters in network and
    internetwork regions for quiet Sun and coronal hole
Authors: Wang, Xin; McIntosh, Scott W.; Tian, Hui
2012decs.confE.107W    Altcode:
  By using SUMER observations, we study the temperature dependence
  of the intensity contrast, Doppler shift, non-thermal width and
  profile asymmetry in network and internetwork regions for both the
  quiet Sun (QS) and coronal holes (CHs). In network regions, most of
  the transition region (TR) line profiles are more red shifted (by
  0-5km/s) and narrower (by 1-6km/s) in QS than in CH. In the network,
  the RB asymmetries of all the selected TR and coronal line profiles
  are smaller (more blueward) in CH than in QS. While in the interwork
  region the difference disappears. In addition, we also systematically
  investigate differential emission measures (DEM) and electron densities
  and found different behavior in network and internetwork regions by
  using joint observations of SUMER and EIS. Our results suggest that
  the mass cycle between the chromosphere and corona mainly occurs in
  the network and one needs to separate network and internetwork when
  discussing thermal and dynamic properties of the solar atmosphere.

---------------------------------------------------------
Title: The mass cycle between the chromosphere and the corona/solar
    wind
Authors: Tian, Hui
2012decs.confE...9T    Altcode:
  The plasma is not static but flows almost everywhere above the
  chromosphere. EUV and FUV spectroscopy reveals a lot of information
  of these mass flows, and thus enhances our understanding of coronal
  heating and solar wind origin. Through a single Gaussian fit to
  line profiles, emission lines formed in the transition region (TR)
  are usually found to exhibit ubiquitous redshifts. While coronal
  lines show predominant blueshifts in coronal holes (CHs), quiet-Sun
  (QS) network boundaries and active region (AR) edges. However, careful
  scrutiny of the line profiles indicates that they are obviously enhanced
  in the blue wings, suggesting the presence of a secondary high-speed
  upflow component besides the primary component. Meanwhile, imaging
  observations of HINODE/SOT and SDO/AIA clearly reveal ubiquitous
  episodic high-speed outflows in the form of type-II chromospheric
  spicules and propagating coronal disturbances (PDs). It has been
  suggested that the secondary component is associated with the type-II
  spicules and PDs, although further detailed investigations are needed
  to reach a solid conclusion. Moreover, recent AIA observations reveal
  slow downflows in cool passbands, which may represent the cooling
  of the previously heated plasma and should be embedded in TR line
  profiles. These heating upflows and cooling downflows are natural
  results of the mass cycling between the chromosphere and corona/solar
  wind, and their different relative intensities at different temperatures
  are likely to be responsible for the well-known temperature dependence
  of TR Doppler shift. So far various double Gaussian fit algorithms and
  red-blue asymmetry analysis techniques have been applied to coronal
  line profiles to derive parameters of the upflow component. However, an
  unambiguous decomposition of different components are still not possible
  by using data acquired by current spectrographs. The IRIS instrument,
  with a very small instrumental width and high spectral, temporal and
  spatial resolutions, might be able to unambiguously decompose different
  emission components in this continuous mass cycling process.

---------------------------------------------------------
Title: Searching for the stellar streams.
Authors: Tian, H.; Jiang, B. -W.
2012PABei..30...64T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Does the Kinetic Alfven Wave or Oblique Whistler Wave dominate
    the Dissipation Range of Solar Wind Turbulence?
Authors: He, J.; Marsch, E.; Tu, C.; Wang, X.; Yao, S.; Tian, H.
2011AGUFMSH42B..04H    Altcode:
  Presently, there is an intense debate on which oblique wave mode is,
  besides the parallel Alfven-cyclotron wave, responsible for further
  energy cascading or damping in the dissipation range of solar wind
  turbulence. From numerical simulation and dimensional analysis, the
  power spectra in the dissipation range with a power law like k^(-7/3)
  can be reproduced based on either the kinetic Alfven wave or whistler
  wave. Here, we aim to show which one may be dominant in reality on
  the basis of solar wind measurements by STEREO satellite. We extract
  small-scale magnetic fluctuations in the dissipation range from
  the time series by employing the wavelet decomposition method. We
  then study two parameters (magnetic compressibility and magnetic
  polarization) of the small-scale magnetic fluctuations in such time
  intervals where the direction of the local mean magnetic field is nearly
  orthogonal to the direction of the solar wind velocity. We find that
  the magnetic compressibility in the dissipation range is less than
  0.25, which is much smaller than the magnetic compressibility (~1.0)
  of quasi-perpendicular whistler waves, but closer to the value of
  kinetic Alfven waves. Moreover, we find that the small-scale magnetic
  fluctuations seems to be elliptically polarized in the plane normal
  to the solar wind velocity direction, and the major axis of the
  polarization ellipse is perpendicular to local mean magnetic field
  direction. This kind of observed magnetic polarization is consistent
  with the characteristics of kinetic Alfven waves. Therefore, we may
  conclude that, in the fast solar wind streams we have looked at,
  oblique kinetic Alfven waves do exist and may play a role in the
  dissipation range and for turbulence cascading and damping.

---------------------------------------------------------
Title: Pulsed Alfvén Waves in the Solar Wind
Authors: Gosling, J. T.; Tian, H.; Phan, T.
2011AGUFMSH11C..08G    Altcode:
  Using 3-s plasma and magnetic field data from the Wind spacecraft
  located in the solar wind well upstream from Earth, we report
  observations of isolated, pulse-like Alfvénic disturbances in the solar
  wind. These isolated events are characterized by roughly plane-polarized
  rotations in the solar wind magnetic field and velocity vectors away
  from the directions of the underlying field and velocity and then
  back again. They pass over Wind on time scales ranging from seconds to
  several minutes. These isolated, pulsed Alfvén waves are pervasive; we
  have identified 175 such events over the full range of solar wind speeds
  (320 - 550 km/s) observed in a randomly chosen 10-day interval. The
  large majority of these events are propagating away from the Sun in the
  solar wind rest frame. Maximum field rotations in the interval studied
  ranged from 6 to 109 degrees. Similar to most Alfvénic-fluctuations in
  the solar wind at 1 AU, the observed changes in velocity are typically
  less than that predicted for pure Alfvén waves (Alfvénicity ranged
  from 0.28 to 0.93). Most of the events are associated with small
  enhancements or depressions in magnetic field strength and small
  changes in proton number density and/or temperature. The pulse-like and
  roughly symmetric nature of the magnetic field and velocity rotations
  in these events suggests that these Alfvénic disturbances are not
  evolving when observed. They thus appear to be, and probably are,
  solitary waves. It is presently uncertain how these waves originate,
  although they may evolve out of Alfvénic turbulence.

---------------------------------------------------------
Title: Two Components of the Coronal Emission Revealed by
    Extreme-Ultraviolet Spectroscopic Observations
Authors: Tian, H.; Mcintosh, S. W.; De Pontieu, B.; Martinez-Sykora,
   J.; Wang, X.; Sechler, M.
2011AGUFMSH33A2027T    Altcode:
  Recent spectroscopic observations have revealed the ubiquitous presence
  of blueward asymmetries of emission lines formed in the solar corona
  and transition region. These asymmetries are most prominent in loop
  footpoint regions, where a clear correlation of the asymmetry with the
  Doppler shift and line width determined from the single-Gaussian fit
  is found. Such asymmetries suggest at least two emission components: a
  primary component accounting for the background emission and a secondary
  component associated with high-speed upflows. The latter has been
  proposed to play a vital role in the coronal heating process and there
  is no agreement on its properties. Here we slightly modify the initially
  developed technique of red-blue (RB) asymmetry analysis and apply it to
  both artificial spectra and spectra observed by the Extreme-ultraviolet
  Imaging Spectrometer on board Hinode, and demonstrate that the secondary
  component usually contributes a few percent of the total emission, has
  a velocity ranging from 50 to 150 km/s, and a Gaussian width comparable
  to that of the primary one in loop footpoint regions. The results of
  the RB asymmetry analysis are then used to guide a double-Gaussian fit
  and we find that the obtained properties of the secondary component
  are generally consistent with those obtained from the RB asymmetry
  analysis. Through a comparison of the location, relative intensity,
  and velocity distribution of the blueward secondary component with
  the properties of the upward propagating disturbances revealed in
  simultaneous images from the Atmospheric Imaging Assembly on board
  the Solar Dynamics Observatory, we find a clear association of the
  secondary component with the propagating disturbances.

---------------------------------------------------------
Title: Two Components of the Solar Coronal Emission Revealed by
    Extreme-ultraviolet Spectroscopic Observations
Authors: Tian, Hui; McIntosh, Scott W.; De Pontieu, Bart;
   Martínez-Sykora, Juan; Sechler, Marybeth; Wang, Xin
2011ApJ...738...18T    Altcode: 2011arXiv1106.1141T
  Recent spectroscopic observations have revealed the ubiquitous presence
  of blueward asymmetries of emission lines formed in the solar corona
  and transition region. These asymmetries are most prominent in loop
  footpoint regions, where a clear correlation of the asymmetry with the
  Doppler shift and line width determined from the single-Gaussian fit
  is found. Such asymmetries suggest at least two emission components: a
  primary component accounting for the background emission and a secondary
  component associated with high-speed upflows. The latter has been
  proposed to play a vital role in the coronal heating process and there
  is no agreement on its properties. Here we slightly modify the initially
  developed technique of red-blue (RB) asymmetry analysis and apply it to
  both artificial spectra and spectra observed by the Extreme-ultraviolet
  Imaging Spectrometer on board Hinode, and demonstrate that the secondary
  component usually contributes a few percent of the total emission,
  and has a velocity ranging from 50 to 150 km s<SUP>-1</SUP> and a
  Gaussian width comparable to that of the primary one in loop footpoint
  regions. The results of the RB asymmetry analysis are then used to
  guide a double-Gaussian fit and we find that the obtained properties of
  the secondary component are generally consistent with those obtained
  from the RB asymmetry analysis. Through a comparison of the location,
  relative intensity, and velocity distribution of the blueward secondary
  component with the properties of the upward propagating disturbances
  revealed in simultaneous images from the Atmospheric Imaging Assembly
  on board the Solar Dynamics Observatory, we find a clear association
  of the secondary component with the propagating disturbances.

---------------------------------------------------------
Title: Pulsed Alfvén Waves in the Solar Wind
Authors: Gosling, J. T.; Tian, H.; Phan, T. D.
2011ApJ...737L..35G    Altcode:
  Using 3 s plasma and magnetic field data from the Wind spacecraft
  located in the solar wind well upstream from Earth, we report
  observations of isolated, pulse-like Alfvénic disturbances in the solar
  wind. These isolated events are characterized by roughly plane-polarized
  rotations in the solar wind magnetic field and velocity vectors away
  from the directions of the underlying field and velocity and then
  back again. They pass over Wind on timescales ranging from seconds to
  several minutes. These isolated, pulsed Alfvén waves are pervasive;
  we have identified 175 such events over the full range of solar wind
  speeds (320-550 km s<SUP>-1</SUP>) observed in a randomly chosen 10
  day interval. The large majority of these events are propagating away
  from the Sun in the solar wind rest frame. Maximum field rotations
  in the interval studied ranged from 6° to 109°. Similar to most
  Alfvénic fluctuations in the solar wind at 1 AU, the observed changes
  in velocity are typically less than that predicted for pure Alfvén
  waves (Alfvénicity ranged from 0.28 to 0.93). Most of the events
  are associated with small enhancements or depressions in magnetic
  field strength and small changes in proton number density and/or
  temperature. The pulse-like and roughly symmetric nature of the
  magnetic field and velocity rotations in these events suggests that
  these Alfvénic disturbances are not evolving when observed. They
  thus appear to be, and probably are, solitary waves. It is presently
  uncertain how these waves originate, although they may evolve out of
  Alfvénic turbulence.

---------------------------------------------------------
Title: Observation of High-speed Outflow on Plume-like
    Structures of the Quiet Sun and Coronal Holes with Solar Dynamics
    Observatory/Atmospheric Imaging Assembly
Authors: Tian, Hui; McIntosh, Scott W.; Habbal, Shadia Rifai; He,
   Jiansen
2011ApJ...736..130T    Altcode: 2011arXiv1105.3119T
  Observations from the Atmospheric Imaging Assembly onboard the Solar
  Dynamics Observatory reveal ubiquitous episodic outflows (jets)
  with an average speed around 120 km s<SUP>-1</SUP> at temperatures
  often exceeding a million degree in plume-like structures, rooted in
  magnetized regions of the quiet solar atmosphere. These outflows are not
  restricted to the well-known plumes visible in polar coronal holes, but
  are also present in plume-like structures originating from equatorial
  coronal holes and quiet-Sun (QS) regions. Outflows are also visible
  in the "inter-plume" regions throughout the atmosphere. Furthermore,
  the structures traced out by these flows in both plume and inter-plume
  regions continually exhibit transverse (Alfvénic) motion. Our finding
  suggests that high-speed outflows originate mainly from the magnetic
  network of the QS and coronal holes (CHs), and that the plume flows
  observed are highlighted by the denser plasma contained therein. These
  outflows might be an efficient means to provide heated mass into the
  corona and serve as an important source of mass supply to the solar
  wind. We demonstrate that the QS plume flows can sometimes significantly
  contaminate the spectroscopic observations of the adjacent CHs—greatly
  affecting the Doppler shifts observed, thus potentially impacting
  significant investigations of such regions.

---------------------------------------------------------
Title: Spectroscopic evidence for helicity in explosive events
Authors: Curdt, W.; Tian, H.
2011A&A...532L...9C    Altcode: 2011arXiv1107.1969C
  <BR /> Aims: We report spectroscopic observations in support of a novel
  view of transition region explosive events, observations that lend
  empirical evidence that at least in some cases explosive events may
  be nothing else but spinning narrow spicule-like structures. <BR />
  Methods: Our spectra of textbook explosive events with simultaneous
  Doppler flow of a red and a blue component are extreme cases of high
  spectroscopic velocities that lack apparent motion, to be expected
  if interpreted as a pair of collimated, linearly moving jets. The
  awareness of this conflict led us to the alternative interpretation of
  redshift and blueshift as a spinning motion of a small plasma volume. In
  contrast to the bidirectional jet scenario, a small volume of spinning
  plasma would be fully compatible with the observation of flows without
  detectable apparent motion. We suspect that these small volumes could
  be spicule-like structures and try to find evidence for this. We show
  observations of helical motion in macrospicules and argue that these
  features - if scaled down to a radius comparable to the slit size of
  a spectrometer - should have a spectroscopic signature similar to that
  observed in explosive events, which is admittedly not easily detectable
  by imagers. Despite of this difficulty, evidence of helicity in spicules
  has been reported in the literature. This led us to the new insight that
  the same narrow spinning structures may be the drivers in both cases,
  structures that imagers observe as spicules and that in spectrometers
  cross the slit and are seen as explosive events. <BR /> Results:
  We arrive at a concept that supports the idea that explosive events
  and spicules are different manifestations of the same helicity-driven
  scenario. In contrast to the conventional view of explosive events as
  linear bidirectional jets that are triggered by a reconnection event
  in the transition region, this new interpretation is compatible with
  the observational results. Consequently, in this case a photospheric
  or subphotospheric trigger has to be assumed. <BR /> Conclusions:
  We suggest that explosive events/spicules are to be compared to the
  unwinding of a loaded torsional spring.

---------------------------------------------------------
Title: Observation of High-speed Outflow on Plume-like Structures
    of the Quiet Sun and Coronal Holes with SDO/AIA
Authors: Tian, Hui; McIntosh, Scott W.; Habbal, Shadia Rifal; He,
   Jiansen
2011shin.confE.161T    Altcode:
  Observations from the Atmospheric Imaging Assembly (AIA) onboard the
  Solar Dynamics Observatory (SDO) reveal ubiquitous episodic outflows
  (jets) with an average speed around 120 km s-1 at temperatures
  often exceeding a million degree in plume-like structures, rooted in
  magnetized regions of the quiet solar atmosphere. These outflows are not
  restricted to the well-known plumes visible in polar coronal holes, but
  are also present in plume-like structures originating from equatorial
  coronal holes and quiet-Sun regions. Outflows are also visible in
  the "interplume" regions throughout the atmosphere. Furthermore, the
  structures traced out by these flows in both plume and inter-plume
  regions continually exhibit transverse (Alfvéenic) motion. Our finding
  suggests that high-speed outflows originate mainly from the magnetic
  network of the quiet Sun and coronal holes, and that the plume flows
  observed are highlighted by the denser plasma contained therein. These
  outflows might be an efficient means to provide heated mass into the
  corona and serve as an important source of mass supply to the solar
  wind. We demonstrate that the quiet-Sun plume flows can sometimes
  significantly contaminate the spectroscopic observations of the adjacent
  coronal holes - greatly affecting the Doppler shifts observed, thus
  potentially impacting significant investigations of such regions.

---------------------------------------------------------
Title: Hydrogen Lyα and Lyβ Radiances and Profiles in Polar
    Colornal Holes
Authors: Tian, Hui; Teriaca, Luca; Curdt, Werner; Vial, Jean-Claude
2011shin.confE.166T    Altcode:
  The hydrogen Lyα plays a dominant role in the radiative energy
  transport in the lower transition region, and is important for
  the studies of transition-region structure as well as solar wind
  origin. We investigate the Lyα profiles obtained by the Solar
  Ultraviolet Measurement of Emitted Radiation spectrograph on the
  Solar and Heliospheric Observatory spacecraft in coronal holes and
  the quiet Sun. In a subset of these observations, the Hi Lyβ, Si III,
  and Ovi lines were also (quasi-)simultaneously recorded. We find that
  the distances between the two peaks of Lyα profiles are larger in
  coronal holes than in the quiet Sun, indicating a larger opacity in
  coronal holes. This difference might result from the different magnetic
  structures or the different radiation fields in the two regions. Most
  of the Lyβ profiles in the coronal hole have a stronger blue peak,
  in contrast to those in quiet-Sun regions while in both regions the
  Lyα profiles are stronger in the blue peak. Although the asymmetries
  are likely to be produced by differential flows in the solar atmosphere,
  their detailed formation processes are still unclear. The radiance ratio
  between Lyα and Lyβ decreases toward the limb in the coronal hole,
  which might be due to the different opacity of the two lines. We also
  find that the radiance distributions of the four lines are set by a
  combined effect of limb brightening and the different emission level
  between coronal holes and the quiet Sun.

---------------------------------------------------------
Title: Two-dimensional correlation functions for density and magnetic
    field fluctuations in magnetosheath turbulence measured by the
    Cluster spacecraft
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Zong, Q. -G.; Yao, S.;
   Tian, H.
2011JGRA..116.6207H    Altcode:
  Knowledge of multidimensional correlation functions is crucial for
  understanding the anisotropy of turbulence. The two-dimensional (2-D)
  spatial correlation functions (SCFs) obtained in previous studies
  of space plasma turbulence were restricted to large-length scales
  and covered a limited angular domain of the two-point separation
  vector with respect to the mean magnetic field. Here we aim to
  derive 2-D SCFs with smaller-length scale and nearly full angular
  distribution for the fluctuations of the number density and magnetic
  field in magnetosheath turbulence. We use the Cluster four-spacecraft
  measurements of the fluctuations with respect to a temporally and
  spatially varying background magnetic field to construct the 2-D
  SCFs. We find that the correlation function of the density fluctuations
  shows a pattern similar to that of the magnetic field fluctuations,
  both of which appear to be composed of two populations, whereby the
  major population extends along the coordinate parallel to mean magnetic
  field (S<SUB>$\parallel$</SUB>) and the minor one deviates toward the
  perpendicular coordinate (S<SUB>$\perp$</SUB>). This pattern of 2-D SCFs
  implies that the energy of magnetosheath turbulence seems to cascade,
  in the inertial range close to the ion scale, mostly transverse to the
  background magnetic field and meanwhile partly along the field (i.e.,
  k<SUB>$\perp$</SUB> $\gg$ k<SUB>$\parallel$</SUB>).

---------------------------------------------------------
Title: Possible Evidence of Alfvén-cyclotron Waves in the Angle
    Distribution of Magnetic Helicity of Solar Wind Turbulence
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Yao, Shuo; Tian, Hui
2011ApJ...731...85H    Altcode:
  The fluctuating magnetic helicity is considered an important parameter
  in diagnosing the characteristic modes of solar wind turbulence. Among
  them is the Alfvén-cyclotron wave, which is probably responsible for
  the solar wind plasma heating, but has not yet been identified from
  the magnetic helicity of solar wind turbulence. Here, we present the
  possible signatures of Alfvén-cyclotron waves in the distribution
  of magnetic helicity as a function of θ<SUB>VB</SUB>, which is
  the angle between the solar wind velocity and local mean magnetic
  field. We use magnetic field data from the STEREO spacecraft to
  calculate the θ<SUB>VB</SUB> distribution of the normalized reduced
  fluctuating magnetic helicity σ<SUB>m</SUB>. We find a dominant
  negative σ<SUB>m</SUB> for 1 s &lt; p &lt; 4 s (p is time period)
  and for θ<SUB>VB</SUB> &lt; 30° in the solar wind outward magnetic
  sector, and a dominant positive σ<SUB>m</SUB> for 0.4 s &lt; p
  &lt; 4 s and for θ<SUB>VB</SUB>&gt;150° in the solar wind inward
  magnetic sector. These features of σ<SUB>m</SUB> appearing around the
  Doppler-shifted ion-cyclotron frequencies may be consistent with the
  existence of Alfvén-cyclotron waves among the outward propagating
  fluctuations. Moreover, right-handed polarized waves at larger
  propagation angles, which might be kinetic Alfvén waves or whistler
  waves, have also been identified on the basis of the σ<SUB>m</SUB>
  features in the angular range 40° &lt; θ<SUB>VB</SUB> &lt; 140°. Our
  findings suggest that Alfvén-cyclotron waves (together with other
  wave modes) play a prominent role in turbulence cascading and plasma
  heating of the solar wind.

---------------------------------------------------------
Title: The Spectroscopic Signature of Quasi-periodic Upflows in
    Active Region Timeseries
Authors: Tian, Hui; McIntosh, Scott W.; De Pontieu, Bart
2011ApJ...727L..37T    Altcode: 2010arXiv1012.5112T
  Quasi-periodic propagating disturbances are frequently observed in
  coronal intensity image sequences. These disturbances have historically
  been interpreted as being the signature of slow-mode magnetoacoustic
  waves propagating into the corona. The detailed analysis of Hinode EUV
  Imaging Spectrometer (EIS) timeseries observations of an active region
  (known to contain propagating disturbances) shows strongly correlated,
  quasi-periodic, oscillations in intensity, Doppler shift, and line
  width. No frequency doubling is visible in the latter. The enhancements
  in the moments of the line profile are generally accompanied by a faint,
  quasi-periodically occurring, excess emission at ~100 km s<SUP>-1</SUP>
  in the blue wing of coronal emission lines. The correspondence of
  quasi-periodic excess wing emission and the moments of the line profile
  indicates that repetitive high-velocity upflows are responsible for
  the oscillatory behavior observed. Furthermore, we show that the same
  quasi-periodic upflows can be directly identified in a simultaneous
  image sequence obtained by the Hinode X-Ray Telescope. These results
  are consistent with the recent assertion of De Pontieu &amp; McIntosh
  that the wave interpretation of the data is not unique. Indeed, given
  that several instances are seen to propagate along the direction of
  the EIS slit that clearly shows in-phase, quasi-periodic variations of
  intensity, velocity, width (without frequency doubling), and blue wing
  enhanced emission, this data set would appear to provide a compelling
  example that upflows are more likely to be the main cause of the
  quasi-periodicities observed here, as such correspondences are hard
  to reconcile in the wave paradigm.

---------------------------------------------------------
Title: Redshift-space Enhancement of Line-of-sight Baryon Acoustic
    Oscillations in the Sloan Digital Sky Survey Main-galaxy Sample
Authors: Tian, H. J.; Neyrinck, Mark C.; Budavári, Tamás; Szalay,
   Alexander S.
2011ApJ...728...34T    Altcode: 2010arXiv1011.2481T
  We show that redshift-space distortions of galaxy correlations have
  a strong effect on correlation functions with distinct, localized
  features, like the signature of the baryon acoustic oscillations
  (BAO). Near the line of sight, the features become sharper as a result
  of redshift-space distortions. We demonstrate this effect by measuring
  the correlation function in Gaussian simulations and the Millennium
  simulation. We also analyze the SDSS DR7 main-galaxy sample, splitting
  the sample into slices 2fdg5 on the sky in various rotations. Measuring
  two-dimensional correlation functions in each slice, we do see a sharp
  bump along the line of sight. Using Mexican-hat wavelets, we localize
  it to (110 ± 10) h <SUP>-1</SUP> Mpc. Averaging only along the line of
  sight, we estimate its significance at a particular wavelet scale and
  location at 2.2σ. In a flat angular weighting in the (π, r<SUB>p</SUB>
  ) coordinate system, the noise level is suppressed, pushing the bump's
  significance to 4σ. We estimate that there is about a 0.2% chance of
  getting such a signal anywhere in the vicinity of the BAO scale from
  a power spectrum lacking a BAO feature. However, these estimates of
  the significances make some use of idealized Gaussian simulations,
  and thus are likely a bit optimistic.

---------------------------------------------------------
Title: The coronal convection
Authors: Curdt, W.; Tian, H.; Marsch, E.
2011CEAB...35..187C    Altcode: 2011arXiv1101.2365C
  We study the hydrogen Lyman emission in various solar features -- now
  including Ly-α observations free from geocoronal absorption -- and
  investigate statistically the imprint of flows and of the magnetic field
  on the line profile and radiance distribution. As a new result, we found
  that in Ly-α rasters locations with higher opacity cluster in the cell
  interior, while the network has a trend to flatter profiles. Even deeper
  self reversals and larger peak distances were found in coronal hole
  spectra. We also compare simultaneous Ly-α and Ly-β profiles. There
  is an obvious correspondence between asymmetry and redshift for both
  lines, but, most surprisingly, the asymmetries of Ly-α and Ly-β
  are opposite. We conclude that in both cases downflows determine
  the line profile, in case of Ly-α by absorption and in the case of
  Ly-β by emission. Our results show that the magnetically structured
  atmosphere plays a dominating role in the line formation and indicate
  the presence of a persisting downflow at both footpoints of closed
  loops. We claim that this is the manifestation of a fundamental mass
  transportation process, which Foukal back in 1978 introduced as the
  'coronal convection'.

---------------------------------------------------------
Title: Quasi-periodic outflows observed by the X-Ray Telescope
    onboard Hinode in the boundary of an active region
Authors: Guo, Li-Jia; Tian, Hui; He, Jian-Sen
2010RAA....10.1307G    Altcode: 2010arXiv1006.5258G
  Persistent outflows have recently been detected at the boundaries
  of some active regions. Although these outflows are suggested to be
  possible sources of the slow solar wind, the nature of these outflows
  is poorly understood. Through an analysis of an image sequence
  obtained by the X-Ray Telescope onboard the Hinode spacecraft, we
  found that quasi-periodic outflows are present in the boundary of an
  active region. The flows are observed to occur intermittently, often
  with a period of 5-10 min. The projected flow speed can reach more
  than 200 km s<SUP>-1</SUP>, while its distribution peaks around 50 km
  s<SUP>-1</SUP>. This sporadic high-speed outflow may play an important
  role in the mass loading process of the slow solar wind. Our results
  may imply that the outflow of the slow solar wind in the boundary of
  the active region is intermittent and quasi-periodic in nature.

---------------------------------------------------------
Title: Existence of Alfvén-cyclotron waves in solar wind turbulence
    as identified from the angular distribution of magnetic helicity
Authors: He, J.; Marsch, E.; Tu, C.; Yao, S.; Tian, H.
2010AGUFMSH43D..07H    Altcode:
  The fluctuating magnetic helicity is a helpful mean for diagnosing
  the wave characteristics in solar wind turbulence. However, the
  signature of the Alfvén-cyclotron wave has not yet been revealed
  from magnetic helicity, due to the limitations of the methods used
  previously. We propose a new method to study the magnetic helicity,
  σ_m, which is now considered as a function not only of the frequency
  (f) but also the angle (Θ_VB) between the solar wind velocity
  and local mean magnetic field B_0. We apply this method to STEREO
  measurements of solar wind turbulence in both the magnetic-field
  outward sectors and inward sectors. As a result, we find the following
  remarkable features of the σ_m distributions. In outward sectors,
  σ_m&lt;0 for f∈[0.1,1.0]Hz and Θ_VB&lt;30, and σ_m&gt;0 for
  f∈[0.1,1.0]Hz and 30&lt;Θ_VB&lt;150. In inward sectors, σ_m&gt;0
  for f∈[0.1,1.0]Hz and Θ_VB&gt;150, and σ_m&lt;0 for f∈[0.1,1.0]Hz
  and 30&lt;Θ_VB&lt;150. These new findings indicate the existence of
  Alfvén-cyclotron waves propagating quasi-parallel or anti-parallel
  to B_0, besides the possible existence of kinetic-Alfvén or whistler
  waves propagating obliquely to B_0. Therefore, we suggest that the
  Alfvén-cyclotron wave, together with other wave modes, plays a crucial
  role in turbulence cascading and heating of the solar wind.

---------------------------------------------------------
Title: Signatures of transition region explosive events in hydrogen
    Ly-beta profiles
Authors: Xia, L.; Zhang, M.; Tian, H.; Chen, Y.
2010AGUFMSH11B1646X    Altcode:
  Transition-region (TR) explosive events (EEs) are small-scale
  dynamic phenomena often observed in the far and extreme ultraviolet
  (FUV/EUV) spectral lines formed in the solar transition region. In this
  contribution, we investigate the relationship between the peak emission
  of hydrogen Ly-beta profiles and the emission of C II (103.7nm) and
  O VI (103.2nm) lines to search for signatures of explosive events in
  Ly-beta profiles. Two rasters made by the SUMER (Solar Ultraviolet
  Measurements of Emitted Radiation) instrument on board SOHO in a
  quiet-Sun region and an equatorial coronal hole were selected for our
  study. Explosive events were identified from profiles of C II and O
  VI, respectively. We compared Ly-beta profiles during EEs with those
  averaged in the entire quiet-Sun and coronal-hole regions. We find that
  the central part of Ly-beta profiles reverses more and the distance of
  the two peaks becomes larger during EEs, both in the coronal hole and
  in the quiet Sun. The average Ly-beta profile of the EEs detected by
  C II has an obviously stronger blue peak. During EEs, there is a clear
  correlation between the increased peak emission of Ly-beta profiles and
  the enhanced wing emission of the C II and O VI lines. The correlation
  is more pronounced for the Ly-beta peaks and C II wings, and less
  significant for the Ly-beta blue peak and O VI blue wing. We also
  find that the Ly-beta profiles are more reversed in the coronal hole
  than in the quiet Sun. We suggest that the jets produced by EEs emit
  Doppler-shifted Ly-beta photons, causing enhanced emission at positions
  of the peaks of Ly-beta profiles. The more-reversed Ly-beta profiles
  confirm the presence of a higher opacity in the coronal hole than in
  the quiet Sun. The finding that EEs modify the Ly-beta line profile
  in QS and CHs implies that one should be careful in the modeling and
  interpretation of relevant observational data.

---------------------------------------------------------
Title: Signatures of transition region explosive events in hydrogen
    Lyβ profiles
Authors: Zhang, M.; Xia, L. -D.; Tian, H.; Chen, Y.
2010A&A...520A..37Z    Altcode: 2010arXiv1006.2509Z
  <BR /> Aims: We search for signatures of transition region explosive
  events (EEs) in hydrogen Lyβ profiles. The relationship between the
  peak emission of Lyβ profiles and the wing emission of C ii and
  O vi during EEs is investigated. <BR /> Methods: Two rasters made
  by the SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
  instrument onboard SOHO in a quiet-Sun region and an equatorial
  coronal hole were selected for our study. Transition-region explosive
  events were identified from profiles of C ii 1037 Å and O vi 1032
  Å, respectively. We compared Lyβ profiles during EEs with those
  averaged in the entire quiet-Sun and coronal-hole regions. <BR />
  Results: We find that the central part of Lyβ profiles reverses more
  and the distance of the two peaks becomes larger during EEs, both in
  the coronal hole and in the quiet Sun. The average Lyβ profile of the
  EEs detected by C ii has an obviously stronger blue peak. During EEs,
  there is a clear correlation between the increased peak emission of Lyβ
  profiles and the enhanced wing emission of the C ii and O vi lines. The
  correlation is more pronounced for the Lyβ peaks and C ii wings,
  and less significant for the Lyβ blue peak and O vi blue wing. We
  also find that the Lyβ profiles are more reversed in the coronal
  hole than in the quiet Sun. <BR /> Conclusions: We suggest that the
  jets produced by EEs emit the Doppler-shifted Lyβ photons, causing
  enhanced emission at positions of the peaks of Lyβ profiles. The
  more-reversed Lyβ profiles confirm the presence of higher opacity in
  the coronal hole than in the quiet Sun. The finding that EEs modify
  the Lyβ line profile in QS and CHs implies that one should be careful
  in the modeling and interpretation of relevant observational data.

---------------------------------------------------------
Title: Horizontal supergranule-scale motions inferred from TRACE
    ultraviolet observations of the chromosphere
Authors: Tian, H.; Potts, H. E.; Marsch, E.; Attie, R.; He, J. -S.
2010A&A...519A..58T    Altcode: 2010arXiv1006.0321T
  <BR /> Aims: We study horizontal supergranule-scale motions
  revealed by TRACE observation of the chromospheric emission, and
  investigate the coupling between the chromosphere and the underlying
  photosphere. <BR /> Methods: A highly efficient feature-tracking
  technique called balltracking has been applied for the first time to
  the image sequences obtained by TRACE (transition region and coronal
  explorer) in the passband of white light and the three ultraviolet
  passbands centered at 1700 Å, 1600 Å, and 1550 Å. The resulting
  velocity fields have been spatially smoothed and temporally averaged
  in order to reveal horizontal supergranule-scale motions that may
  exist at the emission heights of these passbands. <BR /> Results:
  We find indeed a high correlation between the horizontal velocities
  derived in the white-light and ultraviolet passbands. The horizontal
  velocities derived from the chromospheric and photospheric emission
  are comparable in magnitude. <BR /> Conclusions: The horizontal
  motions derived in the UV passbands might indicate the existence of
  a supergranule-scale magneto-convection in the chromosphere, which
  may shed new light on the study of mass and energy supply to the
  corona and solar wind at the height of the chromosphere. However, it
  is also possible that the apparent motions reflect the chromospheric
  brightness evolution as produced by acoustic shocks which might be
  modulated by the photospheric granular motions in their excitation
  process, or advected partly by the supergranule-scale flow towards
  the network while propagating upward from the photosphere. To reach a
  firm conclusion, it is necessary to investigate the role of granular
  motions in the excitation of shocks through numerical modeling, and
  future high-cadence chromospheric magnetograms must be scrutinized.

---------------------------------------------------------
Title: Magnetic and spectroscopic properties of supergranular-scale
    coronal jets and erupting loops in a polar coronal hole
Authors: He, J. -S.; Marsch, E.; Curdt, W.; Tian, H.; Tu, C. -Y.;
   Xia, L. -D.; Kamio, S.
2010A&A...519A..49H    Altcode:
  Context. Coronal jets and mass ejections associated with erupting loops
  are two distinct and frequently observed types of transient upflows
  of plasma in coronal holes (CHs). But the magnetic and spectroscopic
  properties of these events at the supergranular scale are not well
  known. <BR /> Aims: Here we aim at studying in a polar hole the plasma
  and field characteristics of coronal jets and erupting loops of a
  supergranular size, for which we use observations from XRT, EIS and SOT
  on Hinode as well as EUVI on STEREO. <BR /> Methods: The open magnetic
  field structures related to the coronal jets are obtained by magnetic
  field extrapolation into the corona from SOT magnetograms. Furthermore,
  we use the EIS observations to analyze ultraviolet line intensities
  and Doppler shifts in association with the erupting loops. <BR />
  Results: We find that the coronal jet plasma is indeed ejected along
  open field lines, thus confirming the conjecture of jet formation in
  an open magnetic environment. The magnetic evolution at the jet base
  is investigated, and the results indicate that the interaction between
  two flux tubes of opposite magnetic polarities as well as the squeezing
  of several tubes with identical polarities might be responsible for
  the jet initiation. We reveal for the first time the spectroscopic
  signatures of a supergranular-size erupting loop at its early stage,
  which consists of three steps. The first step is the onset, which is
  featured by a sudden brightening of one footpoint, as well as by the
  occurrence of blueshifts along almost its entire path. The second step
  is the initial expansion of the closed loop, which is estimated to move
  upward at a speed of about 20 km s<SUP>-1</SUP>, as derived from the
  line-of-sight (LOS) blueshift and the loop enlargement projected onto
  the plane of the sky. In the third step, the loop's bright footpoint
  is apparently diminishing its intensity and enhancing its blueshift,
  which indicates that plasma upflow from the leg is filling the expanding
  loop volume. <BR /> Conclusions: From our results we conclude that
  in polar CHs, where the steady fast solar wind is known to emanate,
  there are also at least two possible ways of causing transient plasma
  outflows at supergranular scale. One is related to coronal jets
  guided by open field lines, the other to the eruption of closed loops,
  which is triggered by magnetic reconnection at their footpoints. <P
  />3 movies (for Figs. 2-4) are only available in electronic form at
  <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Signatures of Magnetic Reconnection at Boundaries of
    Interplanetary Small-scale Magnetic Flux Ropes
Authors: Tian, Hui; Yao, Shuo; Zong, Qiugang; He, Jiansen; Qi, Yu
2010ApJ...720..454T    Altcode: 2010arXiv1007.2247T
  The interaction between interplanetary small-scale magnetic flux ropes
  and the magnetic field in the ambient solar wind is an important topic
  in the understanding of the evolution of magnetic structures in the
  heliosphere. Through a survey of 125 previously reported small flux
  ropes from 1995 to 2005, we find that 44 of them reveal clear signatures
  of Alfvénic fluctuations and thus classify them as Alfvén wave trains
  rather than flux ropes. Signatures of magnetic reconnection, generally
  including a plasma jet of ~30 km s<SUP>-1</SUP> within a magnetic field
  rotational region, are clearly present at boundaries of about 42% of
  the flux ropes and 14% of the wave trains. The reconnection exhausts
  are often observed to show a local increase in the proton temperature,
  density, and plasma beta. About 66% of the reconnection events at
  flux rope boundaries are associated with a magnetic field shear angle
  larger than 90° and 73% of them reveal a decrease of 20% or more in
  the magnetic field magnitude, suggesting a dominance of anti-parallel
  reconnection at flux rope boundaries. The occurrence rate of magnetic
  reconnection at flux rope boundaries through the years 1995-2005 is also
  investigated and we find that it is relatively low around the solar
  maximum and much higher when approaching solar minima. The average
  magnetic field depression and shear angle for reconnection events at
  flux rope boundaries also reveal a similar trend from 1995 to 2005. Our
  results demonstrate for the first time that boundaries of a substantial
  fraction of small-scale flux ropes have properties similar to those
  of magnetic clouds, in the sense that both of them exhibit signatures
  of magnetic reconnection. The observed reconnection signatures could
  be related either to the formation of small flux ropes or to the
  interaction between flux ropes and the interplanetary magnetic fields.

---------------------------------------------------------
Title: The evolution of the \vec{z} distribution of normal neutron
    stars in the Galaxy
Authors: Wei, Y. -C.; Zhang, C. -M.; Zhao, Y. -H.; Peng, Q. -H.; Wu,
   X. -J.; Wang, J.; Pan, Y. -Y.; Yin, H. -X.; Yan, Y.; Yan, T. -S.;
   Tian, H. -J.; Esamdin, A.; Luo, A. L.; Cai, Y.; Taani, A.
2010AN....331..817W    Altcode:
  Under the two initial 1-D one parameter velocity distribution forms
  (one is normal, the other is exponential), the z direction scale
  height evolution of normal neutron stars in the Galaxy is studied by
  numerical simulation. We do statistics for the cases at different time
  segments, also do statistics for the cumulative cases made of each
  time segment. The results show in the cumulative cases the evolution
  curves of the scale heights are smoother than in the each time segment,
  i.e., the cumulation improve the signal-to-noise ratio. Certainly the
  evolution cases are different at different Galactic disk locations,
  which also have very large difference from the average cases in the
  whole disk. In the initial stages of z evolution of normal neutron
  stars, after the beginning transient states, the cumulative scale
  heights increase linearly with time, and the cumulative scale height
  increasing rates have linear relationship with the initial velocity
  distribution parameters, which have larger fluctuation in the vicinity
  of the Sun than in the whole disk. We utilize the linear relationship of
  the cumulative scale height increasing rates vs. the initial velocity
  distribution parameters in the vicinity of the Sun to make comparison
  with the observation near the Sun. The results show if there is no
  magnetic decay, then the deserved initial velocity parameters are
  obvious lower than the present well known results from some authors;
  whereas if introducing magnetic decay, for the 1-D normal case we
  can make consistence among concerning results using magnetic decay
  time values which are supported by some authors, while for the 1-D
  exponential case the results show the lackness of young pulsar samples
  in the larger z in the vicinity of the Sun.

---------------------------------------------------------
Title: Hydrogen Lyman Emission through the Solar Cycle
Authors: Curdt, W.; Tian, H.
2010ASPC..428...81C    Altcode: 2010arXiv1002.3551C
  We present observations and results of radiance and irradiance
  studies completed by SOHO/SUMER during the past solar cycle. We
  find that the cycle variation in Ly-α irradiance as observed by,
  e.g., UARS/SOLSTICE cannot be explained by quiet Sun radiance data,
  and conclude that the explanation must be related to differences in
  the Ly-α radiance of various solar features and changes in their
  fractional distribution over the solar cycle. Consequently, we studied
  the emission of the hydrogen Ly-α line in various solar features—for
  the first time observed by SUMER on disk in full resolution—to
  investigate the imprint of the magnetic field on line profile and
  radiance distribution. We also compare quasi-simultaneous Ly-α and
  Ly-β line profiles. Such high-resolution observations—not hampered
  by geocoronal absorption—have never been completed before.

---------------------------------------------------------
Title: Intermittent outflows at the edge of an active region -
    a possible source of the solar wind?
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Guo, L. -J.; Tian, H.
2010A&A...516A..14H    Altcode:
  Context. It has already been established that the solar wind may
  originate at the edges of active regions (ARs), but the key questions
  of how frequently these outflows occur, and at which height the
  nascent solar wind originates have not yet been addressed. <BR />
  Aims: We study the occurrence rate of these intermittent outflows,
  the related plasma activities beneath in the low solar atmosphere,
  and the interplanetary counterparts of the nascent solar wind
  outflow. <BR /> Methods: We use the observations from XRT/Hinode
  and TRACE to study the outflow patterns. The occurrence frequency of
  the intermittent outflow is estimated by counting the occurrences of
  propagating intensity enhancements in height-time diagrams. We adopt
  observations of SOT/Hinode and EIS/Hinode to investigate the phenomena
  in the chromosphere associated with the coronal outflows. The ACE
  plasma and field in-situ measurements near Earth are used to study
  the interplanetary manifestations. <BR /> Results: We find that in
  one elongated coronal emission structure, referred to as strand,
  the plasma flows outward intermittently, about every 20 min. The flow
  speed sometimes exceeds 200 km s<SUP>-1</SUP>, which is indicative of
  rapid acceleration, and thus exceeds the coronal sound speed at low
  altitudes. The inferred flow speed of the soft-X-ray-emitting plasma
  component seems a little higher than that of the Fe ix/x-emitting plasma
  component. Chromospheric jets are found to occur at the root of the
  strand. Upflows in the chromosphere are also confirmed by blue-shifts of
  the He ii line. The heliospheric plasma counterpart close to the Earth
  is found to be an intermediate-speed solar wind stream. The AR edge may
  also deliver some plasmas to a fraction of the fast solar wind stream,
  most of which emanate from the neighboring CH. <BR /> Conclusions:
  The possible origin of the nascent solar wind in the chromosphere,
  the observed excessive outflow speed of over 200 km s<SUP>-1</SUP> in
  the lower corona, and the corresponding intermediate-speed solar wind
  stream in interplanetary space are all linked in our case study. These
  phenomena from the low solar atmosphere to the heliosphere near Earth in
  combination shed new light on the solar wind formation process. These
  observational results will constrain future modeling of the solar
  winds originating close to an AR.

---------------------------------------------------------
Title: Solar Transition Region in the Quiet Sun and Active Regions
Authors: Tian, H.; Curdt, W.; He, J. -S.
2010aogs...21..277T    Altcode: 2009arXiv0912.0345T
  The solar transition region (TR), in which above the photosphere the
  temperature increases rapidly and the density drops dramatically,
  is believed to play an important role in coronal heating and solar
  wind acceleration. Longlasting upflows are present in the upper TR
  and interpreted as signatures of mass supply to large coronal loops
  in the quiet Sun. Coronal bright points (BPs) are local heating
  phenomena and we found a different Doppler-shift pattern at TR and
  coronal temperatures in one BP, which might be related to the twisted
  loop system. The dominant energy loss in the lower TR is the Ly-α
  emission. It has been found that most Ly-α radiance profiles are
  stronger in the blue peak, an asymmetry opposite to higher order Lyman
  lines. This asymmetry is stronger when the downflow in the middle TR
  is stronger, indicating that the TR flows play an important role in
  the line formation process. The peak separation of Ly-α is found to be
  larger in coronal holes than in the quiet Sun, reflecting the different
  magnetic structures and radiation fields between the two regions. The
  Lyman line profiles are found to be not reversed in sunspot plume and
  umbra regions, while they are obviously reversed in the surrounding
  plage region. At TR temperatures, the densities of the sunspot plume
  and umbra are a factor of 10 lower than of the plage, indicating that
  the sunspot plasma emitting at TR temperatures is higher and possibly
  more extended in height above sunspots than above the plage region.

---------------------------------------------------------
Title: New views on the emission and structure of the solar transition
    region
Authors: Tian, Hui; Marsch, Eckart; Tu, Chuanyi; Curdt, Werner;
   He, Jiansen
2010PhDT.......178T    Altcode: 2010arXiv1004.3017T
  The Sun is the only star that we can spatially resolve and it can
  be regarded as a fundamental plasma laboratory of astrophysics. The
  solar transition region (TR), the layer between the solar chromosphere
  and corona, plays an important role in solar wind origin and coronal
  heating. Recent high-resolution observations made by SOHO, TRACE,
  and Hinode indicate that the TR is highly nonuniform and magnetically
  structured. Through a combination of spectroscopic observations and
  magnetic field extrapolations, the TR magnetic structures and plasma
  properties have been found to be different in coronal holes and in the
  quiet Sun. In active regions, the TR density and temperature structures
  also differ in sunspots and the surrounding plage regions. Although
  the TR is believed to be a dynamic layer, quasi-steady flows lasting
  from several hours to several days are often present in the quiet
  Sun, coronal holes, and active regions, indicating some kind of
  plasma circulation/convection in the TR and corona. The emission of
  hydrogen Lyman lines, which originates from the lower TR, has also
  been intensively investigated in the recent past. Observations show
  clearly that the flows and dynamics in the middle and upper TR can
  greatly modify the Lyman line profiles.

---------------------------------------------------------
Title: Upward and downward propagation of transverse waves due to
    small-scale magnetic reconnection in the chromosphere
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Tian, H.
2010AIPC.1216...32H    Altcode:
  We aim at studying the connections between the propagation
  of transverse waves on spicules and the small-scale magnetic
  reconnections at the feet of the spicules. The observed transverse
  wave may be interpreted as an Alfvén wave or a kink wave. We use the
  observations from SOT/Hinode in the Ca II H line to study the spicule
  dynamics above the reconnection sites. We found in three cases that
  the transverse oscillations were excited by magnetic reconnection,
  and steepened while propagating upwardly. In case-1, the steepening
  oscillations were attenuated at greater heights in association with
  the extension of the spicule plasma. In case-2, the transverse wave
  seems to be initiated by a footpoint jump of the spicule trace in the
  photosphere. The transverse wave in case-3 was found to be reflected,
  and then to propagate downward. These results reveal the wave dynamics
  in the low solar atmosphere, and provide observational evidence that is
  useful for the modeling of coronal heating and solar wind acceleration,
  involving wave generation by magnetic reconnection in the chromosphere.

---------------------------------------------------------
Title: Upflows in the upper transition region of the quiet Sun
Authors: Tian, H.; Tu, C. -Y.; Marsch, E.; He, J. -S.; Zhou, C.;
   Zhao, L.
2010AIPC.1216...36T    Altcode: 2009arXiv0911.1833T
  We investigate the physical meaning of the prominent blue shifts of
  Ne VIII, which is observed to be associated with quiet-Sun network
  junctions (boundary intersections), through data analyses combining
  force-free-field extrapolations with EUV spectroscopic observations. For
  a middle-latitude region, we reconstruct the magnetic funnel structure
  in a sub-region showing faint emission in EIT-Fe 195. This funnel
  appears to consist of several smaller funnels that originate from
  network lanes, expand with height and finally merge into a single
  wide open-field region. However, the large blue shifts of Ne VIII are
  generally not associated with open fields, but seem to be associated
  with the legs of closed magnetic loops. Moreover, in most cases
  significant upflows are found in both of the funnel-shaped loop
  legs. These quasi-steady upflows are regarded as signatures of
  mass supply to the coronal loops rather than the solar wind. Our
  observational result also reveals that in many cases the upflows in
  the upper transition region (TR) and the downflows in the middle TR
  are not fully cospatial. Based on these new observational results, we
  suggest different TR structures in coronal holes and in the quiet Sun.

---------------------------------------------------------
Title: Reconfiguration of the coronal magnetic field by means of
    reconnection driven by photospheric magnetic flux convergence
Authors: He, J. -S.; Marsch, E.; Tu, C. -Y.; Tian, H.; Guo, L. -J.
2010A&A...510A..40H    Altcode:
  Context. Magnetic reconnection is commonly believed to be responsible
  for flare-like events and plasma ejections in the solar atmosphere,
  but the field-line reconfiguration observed in association with magnetic
  reconnection has rarely been observed before. <BR /> Aims: We attempt to
  reconstruct the configuration of the magnetic field during a magnetic
  reconnection event, estimate the reconnection rate, and analyze the
  resulting X-ray burst and plasma ejection. <BR /> Methods: We use the
  local-correlation-tracking (LCT) method to track the convergence of
  magnetic fields with opposite polarities using photospheric observations
  from SOT/Hinode. The magnetic field lines are then extrapolated from
  the tracked footpoint positions into the corona, and the changes in
  field-line connections are marked. We estimate the reconnection rate
  by calculating the convective electric field in the photosphere, which
  is normalized to the product of the plasma jet speed and the coronal
  magnetic field strength inside the inflow region. The observed X-ray
  burst and plasma ejection are analysed with data from XRT/Hinode and
  TRACE, respectively. <BR /> Results: We find that in this reconnection
  event the two sets of approaching closed loops were reconfigured to
  a set of superimposed large-scale closed loops and another set of
  small-scale closed loops. Enhanced soft X-ray emission was seen to
  rapidly fill the reconnected loop after the micro-flare occurred at
  the reconnection site. Plasma was ejected from that site with a speed
  between 27 and 40 km s<SUP>-1</SUP>. The reconnection rate is estimated
  to range between 0.03 and 0.09. <BR /> Conclusions: Our work presents
  a study of the magnetic field reconfiguration owing to magnetic
  reconnection driven by flux convergence in the photosphere. This
  observation of the magnetic structure change is helpful for future
  diagnosis of magnetic reconnection. The results obtained for the
  reconnection rate, the X-ray emission burst, and the plasma ejection
  provides new observational evidence, and places constraints on future
  theoretical study of magnetic reconnection in the Sun.

---------------------------------------------------------
Title: The SUMER Ly-α line profile in quiescent prominences
Authors: Curdt, W.; Tian, H.; Teriaca, L.; Schühle, U.
2010A&A...511L...4C    Altcode: 2010arXiv1002.1197C
  <BR /> Aims: As the result of a novel observing technique, we publish
  for the first time SoHO-SUMER observations of the true spectral line
  profile of hydrogen Lyman-α in quiescent prominences. Because SoHO is
  not in Earth orbit, our high-quality data set is free of geocoronal
  absorption. We studied the line profile to complement earlier
  observations of the higher Lyman lines and to substantiate recent
  model predictions. <BR /> Methods: We applied the reduced-aperture
  observing mode to two prominence targets and did a statistical
  analysis of the line profiles in both data sets. In particular, we
  investigated the shape of the profile, the radiance distribution, and
  the line shape-to-radiance interrelation. We also compared Ly-α data
  to co-temporal λ 1206 Si iii data. <BR /> Results: We find that the
  average profile of Ly-α has a blue-peak dominance and is reversed
  more if the line-of-sight is perpendicular to the field lines. The
  contrast of Ly-α prominence emission rasters is very low, and the
  radiance distribution differs from the log-normal distribution of the
  disk. Features in the Si iii line are not always co-spatial with Ly-α
  emission. <BR /> Conclusions: Our empirical results support recent
  multi-thread models, which predict that asymmetries and depths of the
  self-reversal depend on the orientation of the prominence axis relative
  to the line-of-sight.

---------------------------------------------------------
Title: The coronal convection
Authors: Curdt, Werner; Tian, Hui; Marsch, Eckart
2010cosp...38.2927C    Altcode: 2010cosp.meet.2927C
  We studied with SUMER the hydrogen Lyman emission in various solar
  features -now including Ly-α observations -and investigated the
  imprints that coronal flows and the solar magnetic field have on the
  line profile and radiance distribution. As a new result, we found
  that in Ly-α raster maps the locations with higher line opacity
  (evident by strong self-absorption dips) cluster in the cell interior
  of the magnetic network, while the lines from the network lanes tend
  to reveal flatter profiles. Even deeper self reversals and larger
  peak separations were found in coronal hole spectra. We also compared
  the quasi-simultaneously obtained Ly-α and Ly-β profiles and found
  an obvious correspondence between asymmetry and redshift for both
  lines, but, most surprisingly, the asymmetries of Ly-α and Ly-β are
  opposite. We conclude that in both cases downflows determine the line
  profile, in the case of Ly-α by absorption and in the case of Ly-β
  by emission. Our results, which are further supported by recent Hinode
  data, show that the magnetic structure of the solar atmosphere plays
  a dominant role in the line formation, and indicate the prevalence of
  persistent downflows at both footpoints of closed loops. We suggest
  all this to be the manifestation of a continuous mass-transportation
  process, which Foukal back in 1978 introduced as 'coronal convection'.

---------------------------------------------------------
Title: Upward propagation and subsequent steepening of transverse
    waves launched by small-scale magnetic reconnection in the
    chromosphere
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui
2010cosp...38.1805H    Altcode: 2010cosp.meet.1805H
  SOT observations of chromospheric spicules have revealed that
  Alfven-like transverse oscilla-tions on the spicules are prevalent
  in the chromosphere. But the propagation features, e.g., the phase
  speed and the propagation direction, have not been derived directly
  from observations. It is still not clear how these transverse waves
  are generated. Here we aim at identifying the propagation feature of
  the transverse wave, studying its ampli-tude evolution as well as its
  generation by magnetic reconnection underneath. The phase speed is
  estimated to range between 20 and 150 km/s, based on time lags between
  different transverse oscillation profiles at various heights along the
  dynamic spicule. The transverse fluctuation is found to originate at
  the cusp of an inverted Y-shaped emission structure, where apparently
  magnetic reconnection occurred. The transverse wave steepened with
  height probably due to density rarefaction in the stratified atmosphere,
  and evolved into a nonlinear state with a large relative disturbance,
  yielding a relative velocity-amplitude (dV/Vph) of 0.21 at 5.5 Mm. The
  nonlinear transverse wave seems to be damped in velocity amplitude
  beyond 5.5 Mm, with the transverse-fluctuation energy possibly being
  converted to the longitudinal-motion energy. We also estimate the
  energy flux density carried by the transverse wave, and find it is
  still sufficient, in spite of possible attenuation in the transition
  region, for heating the quiet corona or driving the solar wind. In
  another case, we find that upward propagation (launched by magnetic
  recon-nection) is subsequently followed by clear downward propagation,
  which may indicate possible wave reflection at some height in the
  transition region. Our findings shed new light on future modelling
  of coronal heating and solar wind acceleration, involving magnetic
  reconnection in the chromosphere. References: [1]. He, J.-S., Marsch,
  E., Tu, C.-Y., Tian, H., Excitation of kink waves due to small-scale
  magnetic reconnection in the chromosphere? ApJL, 705, L217-L222,
  2009. [2]. He, J.-S., Marsch, E., Tu, C.-Y., Tian, H., Upward and
  downward propagation of transverse waves due to small-scale magnetic
  reconnection in the chromospehre, SolarWind-12, in press.

---------------------------------------------------------
Title: Characteristics of the Expansion of Magnetic Funnels in Solar
    Quiet Regions
Authors: Tan, Bo; Tian, Hui; He, Jian-sen
2010ChA&A..34...40T    Altcode: 2010ChA&A..34...40B
  Via the potential field extrapolation of the observed photospheric
  magnetic field, the structure of the photospheric magnetic fields
  above solar quiet regions is renewed. As revealed by the result,
  below 20 Mm the open magnetic lines exhibit many obvious small funnel
  structures. These funnels expand with height and at the height of about
  20 Mm they combine into large funnel structures. By a systematic study
  of the tendency of change of the cross section areas of funnels, it
  is discovered that the cross section areas of funnels in solar quiet
  regions expand approximately linearly. The velocity of expansion of
  magnetic funnels at rather low altitudes (&lt; 20 Mm) is larger than
  that at high altitudes (&gt; 20 Mm). This phenomenon has important
  significance for the two-dimensional numerical simulations of the
  origin of solar wind and the mass flow in magnetic loops. At the same
  time it is found that the number of closed magnetic lines decreases
  in the form of exponential function.

---------------------------------------------------------
Title: Reconstruction of reconnecting magnetic field in both solar
    corona and geo-magnetosphere and its application to reconnection
    diagnosis
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Zong, Qiugang;
   Tian, Hui; Guo, Lijia
2010cosp...38.1942H    Altcode: 2010cosp.meet.1942H
  Magnetic reconnection is a critical process of energy transfer in the
  solar-terrestrial plasma. The related 3-D magnetic field geometry
  and its temporal reconfiguration are important for reconnection
  diagnosis. For example, we can estimate how fast the coronal
  magnetic field is reconnected, based on temporal variation of the
  reconnecting field lines, and we can learn about the micro-physics
  in the reconnection region with the help of 3-D reconstruction of the
  magnetic field in geo-space. For a solar micro-flare event, we study
  the evolution of magnetic field lines, which are ex-trapolated from
  dynamic footpoints showing convergence motions. We find that the two
  sets of approaching closed loops were reconfigured to form a joint set
  of superimposed large-scale closed loops and another set of small-scale
  closed loops. We estimate the reconnection rate in two ways. One way
  is to calculate the convective electric field in the photosphere,
  which is normalized to the product of the plasma jet speed and the
  coronal magnetic field strength inside the inflow region. Another
  way is to directly calculate the reconnection rate based on Vin/VA,
  where Vin is the motion of the convex segments on the reconnecting
  field lines. The reconnection rate is estimated to range between 0.03
  and 0.09. This is the first work illustrat-ing the reconfiguration
  of the magnetic field geometry, owing to reconnection driven by flux
  convergence in the photosphere. For a magnetic reconnection event in
  the geo-magnetotail, we reconstruct the 3D magnetic field structure
  containing a pair of nulls with a novel method based on Cluster
  4-spacecraft measurements. We study the electron dynamics near one
  null of the pair, and propose a new scenario of micro-physics in the
  null region. In this scenario, electrons are temporarily trapped in the
  central reconnection region, accelerated possibly by parallel electric
  field and electron pressure gradient, and reflected from the magnetic
  cusp mirrors leading to the bi-directional energetic electron beams,
  which may excite the high-frequency electrostatic waves. Here, we
  have demonstrated that reconstruction of the real-time magnetic field
  structure is quite helpful for magnetic reconnection diagnosis, e.g.,
  estimation of the reconnection rate and analysis of the micro-physics in
  the inner reconnection region. References: [1]. He, J.-S., Marsch, E.,
  Tu, C.-Y., Tian, H., Guo, L.-J., Reconfiguration of the coronal magnetic
  field by means of reconnection driven by photospheric magnetic flux
  convergence, AA, 510, A40, 2010. [2]. He, J.-S., Zong, Q.-G., Deng,
  X.-H., Tu, C.-Y., et al., Electron trapping around a magnetic null,
  Geophys. Res. Lett., 35, L14104, 2008.

---------------------------------------------------------
Title: Solar wind origins in coronal holes and in the quiet Sun
Authors: He, J. -S.; Tu, C. -Y.; Tian, H.; Marsch, E.
2010AdSpR..45..303H    Altcode:
  Coronal hole (CH) and the quiet Sun (QS) are considered to account
  for sources of fast and slow solar wind streams, respectively. The
  differences between the solar wind streams flowing out from the CH
  and the QS are thought to be related with different plasma generation
  and acceleration mechanisms in the respective source regions. Here we
  review recent studies on the solar wind origin in the CH and the QS,
  compare the possible flow geometries and magnetic structures in these
  two kinds of solar regions, and summarize the physics associated with
  two different origin scenarios.

---------------------------------------------------------
Title: New views on the emission and structure of the solar transition
    region
Authors: Tian, Hui; Marsch, Eckart; Tu, Chuanyi; Curdt, Werner;
   He, Jiansen
2010NewAR..54...13T    Altcode:
  The Sun is the only star that we can spatially resolve and it can
  be regarded as a fundamental plasma laboratory of astrophysics. The
  solar transition region (TR), the layer between the solar chromosphere
  and corona, plays an important role in solar wind origin and coronal
  heating. Recent high-resolution observations made by SOHO, TRACE,
  and Hinode indicate that the TR is highly nonuniform and magnetically
  structured. Through a combination of spectroscopic observations and
  magnetic field extrapolations, the TR magnetic structures and plasma
  properties have been found to be different in coronal holes and in the
  quiet Sun. In active regions, the TR density and temperature structures
  also differ in sunspots and the surrounding plage regions. Although
  the TR is believed to be a dynamic layer, quasi-steady flows lasting
  from several hours to several days are often present in the quiet
  Sun, coronal holes, and active regions, indicating some kind of
  plasma circulation/convection in the TR and corona. The emission of
  hydrogen Lyman lines, which originates from the lower TR, has also
  been intensively investigated in the recent past. Observations show
  clearly that the flows and dynamics in the middle and upper TR can
  greatly modify the Lyman line profiles.

---------------------------------------------------------
Title: The Nascent Fast Solar Wind Observed by the EUV Imaging
    Spectrometer on Board Hinode
Authors: Tian, Hui; Tu, Chuanyi; Marsch, Eckart; He, Jiansen; Kamio,
   Suguru
2010ApJ...709L..88T    Altcode: 2009arXiv0912.4316T
  The origin of the solar wind is one of the most important unresolved
  problems in space and solar physics. We report here the first
  spectroscopic signatures of the nascent fast solar wind on the basis
  of observations made by the EUV Imaging Spectrometer on Hinode in a
  polar coronal hole in which patches of blueshift are clearly present on
  Dopplergrams of coronal emission lines with a formation temperature of
  lg(T/K)&gt;5.8. The corresponding upflow is associated with open field
  lines in the coronal hole and seems to start in the solar transition
  region and becomes more prominent with increasing temperature. This
  temperature-dependent plasma outflow is interpreted as evidence of the
  nascent fast solar wind in the polar coronal hole. The patches with
  significant upflows are still isolated in the upper transition region
  but merge in the corona, in agreement with the scenario of solar wind
  outflow being guided by expanding magnetic funnels.

---------------------------------------------------------
Title: A new view of solar wind origin near active regions and in
    polar coronal holes on the basis of Hinode observations
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui; Guo,
   Lijia; Curdt, Werner; Xia, Lidong; Kamio, Suguru
2010cosp...38.2938H    Altcode: 2010cosp.meet.2938H
  The possibility of full-range solar observations from Hinode with high
  temporal and spatial resolution motivated us to revisit the solar wind
  origin in the solar atmosphere. For the solar wind origin near active
  regions, we reveal activity in the chromosphere to be responsible for
  the coronal outflow at the AR edge; meanwhile we also succeeded in
  finding the related solar wind stream in the heliosphere. Chromospheric
  spicule-like jets are found to occur intermittently, and to flow
  in similar direction than the intermittent coronal outflows. EIS
  observations reveal that there are blue-shifts at the edge of AR
  in both chromosphere and corona, and that the blue-shift increases
  with temperature. Therefore, we suggest that the nascent solar wind
  may probably originate in the chromosphere at the edge of ARs. The
  connection between the source regions and their respective solar
  wind streams is established through magnetic field lines, which are
  extrapolated to reach the solar ecliptic plane at 2.5 Rs. We find that
  the AR edge may be the source region of an intermediate-speed (400 km/s)
  solar wind stream. For the solar wind origin in polar coronal holes
  (CHs), we extend the blue-shift observations from the transition
  region up to the corona, investigate the magnetic characteristics
  in association with the polar coronal jets, and study in details the
  initial phase of meso-scale loop eruption in polar CHs. We find that the
  blue-shift becomes more and more dominant with increasing temperature
  from the transition region to the corona. The polar coronal jets are
  found to be elongated along the extrapolated open field lines, which
  appear in fanning-out shape. The cancellation between bipolar magnetic
  fields, or squeezing of monopolar magnetic fields, may be the driver for
  a jet launch. The meso-scale loop started its eruption with a sudden
  brightening at one footpoint, then expanded and moved upwardly with a
  speed of 20 km/s, causing the mass at the footpoint to flow outwardly
  and to fill in the expanded volume. We suggest that mass confined in
  the coronal loops may be dynamically released into the outer corona
  and even heliosphere via magnetic reconnection. References: [1]. He,
  J.-S., Marsch, E., Tu, C.-Y., Guo, L.-J., Tian, H., Intermittent
  outflows at the edge of an active region -a possible source of the
  solar wind. Submitted to AA. [2]. Tian, H., Tu, C.-Y., Marsch, E.,
  He, J.-S., Kamio, S., The nascent fast solar wind observed by the EUV
  imaging spectrometer on board Hinode, ApJ, 709, L88-L93, 2010. [3]. He,
  J.-S., Marsch, E., Curdt, W., Tu, C.-Y., Xia, L.-D., Tian, H., Kamio,
  S., Meso-scale coronal jets and erupting loops guided by magnetic
  fields in a polar coronal hole region, in preparation.

---------------------------------------------------------
Title: Semiempirical Models of the Solar Atmosphere. III. Set of
    Non-LTE Models for Far-Ultraviolet/Extreme-Ultraviolet Irradiance
    Computation
Authors: Fontenla, J. M.; Curdt, W.; Haberreiter, M.; Harder, J.;
   Tian, H.
2009ApJ...707..482F    Altcode:
  Semiempirical atmospheric models of solar surface features as observed
  at moderate resolution are useful tools for understanding the observed
  solar spectral irradiance variations. Paper I described a set of models
  constructed to reproduce the observed radiance spectrum for solar
  surface features at ~2 arcsec resolution that constitute an average
  over small-scale features such as granulation. Paper II showed that a
  revision of previous models of low-chromospheric inter-network regions
  explains the observed infrared CO lines in addition to the UV and radio
  continuum from submillimeter to centimetric wavelengths. The present
  paper (1) shows that the Ca II H and K line wing observations are
  also explained by the new quiet-Sun-composite model, (2) introduces
  new low-chromospheric models of magnetic features that follow the
  ideas in Paper II, (3) introduces new upper chromospheric structures
  for all quiet-Sun and active-region models, and (4) shows how the new
  set of models explains EUV/FUV observations of spectral radiance and
  irradiance. This paper also discusses the chromospheric radiative-loss
  estimates in each of the magnetic features. The new set of models
  provides a basis for the spectral irradiance synthesis at EUV/FUV
  wavelengths based on the features observed on the solar surface.

---------------------------------------------------------
Title: Excitation of Kink Waves Due to Small-Scale Magnetic
    Reconnection in the Chromosphere?
Authors: He, Jiansen; Marsch, Eckart; Tu, Chuanyi; Tian, Hui
2009ApJ...705L.217H    Altcode:
  The kink wave, which has often been observed in coronal loops, is
  considered as a possibly important energy source contributing to coronal
  heating. However, its generation has not yet been observed. Here, we
  report the first observation of kink-wave excitation caused by magnetic
  reconnection as inferred from Solar Optical Telescope measurements made
  in the Ca II line. We observed transverse-displacement oscillations
  on a spicule which propagated upwardly along the spicule trace and
  originated from the cusp of an inverted Y-shaped structure, where
  apparently magnetic reconnection occurred. Such transverse oscillation
  of an individual spicule is interpreted by us to be the signature
  of a kink wave that was excited by magnetic reconnection. We present
  the height variations of the velocity amplitude, δv, and the phase
  speed, C <SUB>k</SUB>, of the kink wave, starting from its source
  region. The kink wave is found to steepen with height and to evolve
  into a nonlinear state with a large relative disturbance, yielding a
  (δv/C <SUB>k</SUB>) of 0.21 at 5.5 Mm. This nonlinear kink wave seems
  to be damped in velocity amplitude beyond 5.5 Mm, which may result from
  the conversion of transverse-fluctuation energy to longitudinal-motion
  energy required to sustain the spicule. We also estimate the energy
  flux density carried by the kink wave, and in spite of its attenuation
  in the transition region conclude it to be sufficient for heating the
  quiet corona. Our findings shed new light on future modeling of coronal
  heating and solar wind acceleration involving magnetic reconnection
  in the chromosphere.

---------------------------------------------------------
Title: Upflows in Funnel-like Legs of Coronal Magnetic Loops
Authors: Tian, Hui; Marsch, Eckart; Curdt, Werner; He, Jiansen
2009ApJ...704..883T    Altcode: 2009arXiv0909.0739T
  The prominent blueshifts of Ne VIII associated with the junctions of the
  magnetic network in the quiet Sun are still not well understood. By
  comparing the coronal magnetic-field structures as obtained by a
  potential-field reconstruction with the conspicuous blueshift patches
  on the Dopplergram of Ne VIII as observed in an equatorial quiet-Sun
  region, we find that most of the regions with significant upflow are
  associated with the funnel-like legs of magnetic loops and cospatial
  with increments of the line width. These quasi-steady upflows can be
  regarded as the signatures of mass supply to coronal loops. By using the
  square root of the line intensity as a proxy for the plasma density,
  the mass flux of the upflow in each funnel can be estimated. We find
  that the mass flux is anti-correlated with the funnel's expansion factor
  as determined from the extrapolated magnetic field. One of the loop
  systems is associated with a coronal bright point, which was observed
  by several instruments and exhibited various morphologies in different
  wavelengths and viewing directions. A remarkable agreement between its
  magnetic structure and the associated EUV emission pattern was found,
  suggesting an almost potential-field nature of the coronal magnetic
  field. We also report the direct detection of a small-scale siphon flow
  by both STEREO satellites. However, this transient siphon flow occurred
  in a weak mixed-polarity-field region, which was outside the adjacent
  magnetic funnel, and thus it is perhaps not related to plasma upflow
  in the funnel. Based on these observations, we suggest that at upper
  transition region (TR) temperatures the dominant flows in quiet-Sun
  coronal loops are long-lasting upflows rather than siphon flows. We
  also discuss the implications of our results for coronal heating and
  unresolved magnetic structures.

---------------------------------------------------------
Title: Hydrogen Lyα and Lyβ Radiances and Profiles in Polar
    Coronal Holes
Authors: Tian, Hui; Teriaca, Luca; Curdt, Werner; Vial, Jean-Claude
2009ApJ...703L.152T    Altcode: 2009arXiv0909.0735T
  The hydrogen Lyα plays a dominant role in the radiative energy
  transport in the lower transition region, and is important for
  the studies of transition-region structure as well as solar wind
  origin. We investigate the Lyα profiles obtained by the Solar
  Ultraviolet Measurement of Emitted Radiation spectrograph on the
  Solar and Heliospheric Observatory spacecraft in coronal holes and the
  quiet Sun. In a subset of these observations, the H I Lyβ, Si III,
  and O VI lines were also (quasi-)simultaneously recorded. We find
  that the distances between the two peaks of Lyα profiles are larger
  in coronal holes than in the quiet Sun, indicating a larger opacity in
  coronal holes. This difference might result from the different magnetic
  structures or the different radiation fields in the two regions. Most
  of the Lyβ profiles in the coronal hole have a stronger blue peak,
  in contrast to those in quiet-Sun regions while in both regions the
  Lyα profiles are stronger in the blue peak. Although the asymmetries
  are likely to be produced by differential flows in the solar atmosphere,
  their detailed formation processes are still unclear. The radiance ratio
  between Lyα and Lyβ decreases toward the limb in the coronal hole,
  which might be due to the different opacity of the two lines. We also
  find that the radiance distributions of the four lines are set by a
  combined effect of limb brightening and the different emission level
  between coronal holes and the quiet Sun.

---------------------------------------------------------
Title: Solar transition region above sunspots
Authors: Tian, H.; Curdt, W.; Teriaca, L.; Landi, E.; Marsch, E.
2009A&A...505..307T    Altcode: 2009arXiv0906.2211T
  Aims: We study the transition region (TR) properties above sunspots and
  the surrounding plage regions, by analyzing several sunspot reference
  spectra obtained by the SUMER (Solar Ultraviolet Measurements of Emitted
  Radiation) instrument in March 1999 and November 2006. <BR />Methods:
  We compare the SUMER spectra observed in the umbra, penumbra, plage,
  and sunspot plume regions. The hydrogen Lyman line profiles averaged
  in each of the four regions are presented. For the sunspot observed
  in 2006, the electron densities, differential emission measure (DEM),
  and filling factors of the TR plasma in the four regions are also
  investigated. <BR />Results: The self-reversals of the hydrogen Lyman
  line profiles are almost absent in sunspots at different locations (at
  heliocentric angles of up to 49°) on the solar disk. In the sunspot
  plume, the Lyman lines are also not reversed, whilst the lower Lyman
  line profiles observed in the plage region are obviously reversed, a
  phenomenon found also in the normal quiet Sun. The TR densities of the
  umbra and plume are similar and one order of magnitude lower than those
  of the plage and penumbra. The DEM curve of the sunspot plume exhibits
  a peak centered at log(T / K) ~ 5.45, which exceeds the DEM of other
  regions by one to two orders of magnitude at these temperatures. We
  also find that more than 100 lines, which are very weak or not observed
  anywhere else on the Sun, are well observed by SUMER in the sunspot,
  especially in the sunspot plume. <BR />Conclusions: We suggest that the
  TR above sunspots is higher and probably more extended, and that the
  opacity of the hydrogen lines is much lower above sunspots, compared to
  the TR above plage regions. Our result indicates that the enhanced TR
  emission of the sunspot plume is probably caused by a large filling
  factor. The strongly enhanced emission at TR temperatures and the
  reduced continuum ensure that many normally weak TR lines are clearly
  distinctive in the spectra of sunspot plumes. <P />Tables 5 and 6 are
  only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Hydrogen Lyman-α and Lyman-β spectral radiance profiles in
    the quiet Sun
Authors: Tian, H.; Curdt, W.; Marsch, E.; Schühle, U.
2009A&A...504..239T    Altcode: 2009arXiv0907.1069T
  Aims: We extend earlier work by studying the line profiles of the
  hydrogen Lyman-α and Lyman-β lines in the quiet Sun. They were
  obtained quasi-simultaneously in a raster scan with a size of about
  150” × 120” near disk center. <BR />Methods: The self-reversal depths
  of the Ly-α and Ly-β profiles. we are quantified by measuring the
  maximum spectral radiances of the two horns and the minimum spectral
  radiance of the central reversal. The information on the asymmetries
  of the Ly-α and Ly-β profiles is obtained through calculating
  the 1st and 3rd-order moments of the line profiles. By comparing
  maps of self-reversal depths and the moments with radiance images
  of the Lyman lines, photospheric magnetograms, and Dopplergrams of
  two other optically thin lines, we studied the spatial distribution
  of the Ly-α and Ly-β profiles with different self-reversal depths,
  and investigated the relationship between profile asymmetries and flows
  in the solar atmosphere. <BR />Results: We find that the emissions of
  the Lyman lines tend to be more strongly absorbed in the internetwork,
  as compared to those in the network region. Almost all of the Ly-α
  profiles are self-reversed, while about 17% of the Ly-β profiles are
  not reversed. The ratio of Ly-α and Ly-β intensities seems to be
  independent of the magnetic field strength. Most Ly-α profiles are
  stronger in the blue horn, whereas most Ly-β profiles are stronger
  in the red horn. However, the opposite asymmetries of Ly-α and
  Ly-β are not correlated pixel-to-pixel. We also confirm that when
  larger transition-region downflows are present, the Ly-α and Ly-β
  profiles are more enhanced in the blue and red horns, respectively. The
  first-order moment of Ly-β, which reflects the combined effects of
  the profile asymmetry and motion of the emitting material, strongly
  correlates with the Doppler shifts of the Si iii and O vi lines, while
  this correlation is much weaker for Ly-α. Our analysis shows that both
  Ly-α and Ly-β might be more redshifted if stronger transition-region
  downflows are present. We also find that the observed average Ly-β
  profile is redshifted with respect to its rest position.

---------------------------------------------------------
Title: Thermal stability and gas generation of petroleum in the
    earth's subsurface based on kinetics modelling and field observations
Authors: Xiao, X. M.; Tian, H.; Song, Z. G.
2009GeCAS..73R1460X    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Kinetic modelling of gas generation and methane carbon isotope
    fractionation during the cracking of aromatic hydrocarbons
Authors: Tian, H.; Xiao, X. M.; Guo, L. G.; Zhu, Y. F.
2009GeCAS..73Q1330T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Upward Propagating Alfvén Wave and its Connection With
    Magnetic Reconnection in the Chromosphere as Observed by SOT
Authors: Tu, C.; He, J.; Marsch, E.; Tian, H.; Guo, L.; Yao, S.
2009AGUSMSH31B..02T    Altcode:
  We identify high-frequency Alfvén waves propagating upward in the solar
  chromosphere and transition region from observational data obtained
  by the Solar Optical Telescope (SOT) onboard Hinode. We find that in
  four cases the spicules are modulated by high-frequency (&gt;0.02~Hz)
  transverse fluctuations, which are inferred to be associated with
  Alfvén waves. They apparently propagate upward along the spicules with
  phase speeds ranging from 50 to 150~km/s. Three of these modulated
  spicules show clear wave-like shapes, with short wavelengths being
  less than 8~Mm. In our analysis we thus identified directly upward
  propagation of Alfvén waves in the solar chromosphere and transition
  region. In addition to the recently reported Alfvén waves with
  very long wavelengths and wave periods, we find here four examples
  of Alfvén waves with shorter wavelengths and periods. Moreover,
  we report observational evidence for Alfvén-wave excitation due to
  magnetic reconnection. These findings shed new light on the wave origin
  and on the coronal and solar-wind heating by waves.

---------------------------------------------------------
Title: Upward propagating high-frequency Alfvén waves as identified
    from dynamic wave-like spicules observed by SOT on Hinode
Authors: He, J. -S.; Tu, C. -Y.; Marsch, E.; Guo, L. -J.; Yao, S.;
   Tian, H.
2009A&A...497..525H    Altcode:
  Aims: We identify high-frequency Alfvén waves propagating upward in
  the solar chromosphere and transition region from observation by Solar
  Optical Telescope (SOT) onboard Hinode. <BR />Methods: The spicule shape
  is enhanced through application of a normal radial gradient filter and
  an un-sharp mask on the images taken by SOT. The displaced position
  of the spicule is at each height obtained by tracing the maximum
  intensity after image processing. The dominant wave period is obtained
  by the FFT method applied to the time variations of the displaced
  position at a certain height. The phase speed is estimated with the
  help of a cross-correlation analysis of two temporal sequences of the
  displaced positions at two heights along the spicule. <BR />Results:
  We find in four cases that the spicules are modulated by high-frequency
  (≥0.02 Hz) transverse fluctuations. Such fluctuations are suggested
  to be Alfvén waves that propagate upward along the spicules with
  phase speed ranges from 50 to 150 km s<SUP>-1</SUP>. Three of the
  modulated spicules show clear wave-like shapes with short wavelengths
  less than 8 Mm. <BR />Conclusions: Our work identified directly upward
  propagation of Alfvén waves in the solar chromosphere and transition
  region. In addition to the recently reported Alfvén waves with very
  long wavelength and wave period, we find here four examples of Alfvén
  waves with shorter wavelengths and periods. These findings shed new
  light on the wave origin and on coronal and solar-wind heating.

---------------------------------------------------------
Title: The Emission Heights of Transition Region Lines in an
    Equatorial Coronal Hole and the Surrounding Quiet Sun
Authors: Tian, Hui; Xia, Li-Dong; He, Jian-Sen; Tan, Bo; Yao, Shuo
2008ChJAA...8..732T    Altcode:
  Using the correlation between the radiance or Doppler velocity and
  the extrapolated magnetic field, we determined the emission heights
  of a set of solar transition region lines in an equatorial coronal
  hole and in the surrounding quiet Sun region. We found that for
  all of the six lower-transition-region lines, the emission height
  is about 4 5 Mm in the equatorial coronal hole, and around 2 Mm in
  the quiet Sun region. This result confirms the previous findings
  that plasma with different temperature can coexist at the same layer
  of transition region. In the quiet Sun region, the emission height
  of the upper-transition-region line Ne VIII is almost the same that
  of the lower-transition-region line, but in the coronal hole, it is
  twice as high. This difference reveals that the outflow of Ne VIII
  is a signature of solar wind in the coronal hole and is just a mass
  supply to the large loops in the quiet Sun.

---------------------------------------------------------
Title: The Ly-α profile and center-to-limb variation of the quiet Sun
Authors: Curdt, W.; Tian, H.; Teriaca, L.; Schühle, U.; Lemaire, P.
2008A&A...492L...9C    Altcode: 2008arXiv0812.1441C
  Aims: We study the emission of the hydrogen Lyman-α line in the quiet
  Sun, its center-to-limb variation, and its radiance distribution. We
  also compare quasi-simultaneous Ly-α and Ly-β line profiles. <BR
  />Methods: We used the high spectral and spatial resolution of the
  SUMER spectrometer and completed raster scans at various locations
  along the disk. For the first time, we used a method to reduce the
  incoming photon flux to a 20%-level by partly closing the aperture
  door. We also performed a quasi-simultaneous observation of both Ly-α
  and Ly-β at the Sun center in sit-and-stare mode. We infer the flow
  characteristic in the Ly-α map from variations in the calibrated λ
  1206 Si iii line centroids. <BR />Results: We present the average
  profile of Ly-α, its radiance distribution, its center-to-limb
  behaviour, and the signature of flows on the line profiles. Little
  center-to-limb variation and no limb brightening are observed in the
  profiles of the Ly-α line. In contrast to all other lines of the
  Lyman series, which have a red-horn asymmetry, Ly-α has a robust and
  - except for dark locations - dominating blue-horn asymmetry. There
  appears to be a brightness-to-asymmetry relationship. A similar
  and even clearer trend is observed in the downflow-to-asymmetry
  relationship. This important result is consistent with predictions
  from models that include flows. However, the absence of a clear
  center-to-limb variation in the profiles may be more indicative of
  an isotropic field than a mainly radial flow. <BR />Conclusions: It
  appears that the ubiquitous hydrogen behaves in a similar way to a
  filter that dampens all signatures of the line formation by processes
  in both the chromosphere and transition region.

---------------------------------------------------------
Title: The redshifted network contrast of transition region emission
Authors: Curdt, W.; Tian, H.; Dwivedi, B. N.; Marsch, E.
2008A&A...491L..13C    Altcode: 2009arXiv0901.0808C
  Aims: We study the VUV emission of the quiet Sun and the net redshift
  of transition region lines in the SUMER spectral range. We aim at
  establishing a link with atmospheric processes and interpreting the
  observed downflow as the most evident part of the prevailing global
  coronal mass transport. <BR />Methods: We rank and arrange all pixels
  of a monochromatic raster scan by radiance and define equally-sized
  bins of bright, faint, and medium-bright pixels. Comparing the bright
  pixels with the faint pixels, we determine the spectrally-resolved
  network contrast for 19 emission lines. We then compare the contrast
  centroids of these lines with the position of the line itself. We
  establish a relationship between the observed redshift of the network
  contrast with the line formation temperature. <BR />Results: We find
  that the network contrast is offset in wavelength compared to the
  emission line itself. This offset, if interpreted as redshift, peaks
  at middle transition region temperatures and is 10 times higher than
  the previously reported net redshift of transition region emission
  lines. We demonstrate that the brighter pixels are more redshifted,
  causing both a significant shift of the network contrast profile and the
  well-known net redshift. We show that this effect can be reconstructed
  from the radiance distribution. This result is compatible with loop
  models, which assume downflows near both footpoints.

---------------------------------------------------------
Title: Radiance and Doppler shift distributions across the network
    of the quiet Sun
Authors: Tian, H.; Tu, C. -Y.; Xia, L. -D.; He, J. -S.
2008A&A...489.1297T    Altcode: 2009arXiv0907.1073T
  Aims: The radiance and Doppler-shift distributions across the solar
  network provide observational constraints of two-dimensional modeling
  of transition-region emission and flows in coronal funnels. These
  distributions have not, however, been studied in detail and we attempt
  an investigation for a quiet Sun region. <BR />Methods: Two different
  methods, dispersion plots and average-profile studies, were applied to
  investigate these distributions for three EUV lines. In the dispersion
  plots, we divided the entire quiet Sun region scanned by SUMER into
  a bright and a dark part according to an image of Fe xii taken by EIT
  during the scanning; we plotted intensities and Doppler shifts in each
  bin as determined according to a filtered intensity of Si ii. We also
  studied the difference in height variations of the magnetic field as
  extrapolated from the MDI magnetogram, in and outside network, in the
  two parts. For the average-profile study, we selected 74 individual
  cases and derived the average profiles of intensities and Doppler
  shifts across the network. Cases with large values of blue shift of
  Ne viii were further studied. <BR />Results: The dispersion plots
  reveal that the intensities of Si ii and C iv increase from network
  boundary to network center in both the bright and dark parts. However,
  the intensity of Ne viii shows different trends, namely increasing
  in the bright part and decreasing in the dark part. In both parts,
  the Doppler shift of C iv increases steadily from internetwork to
  network center. The height variations in the magnetic field imply a
  more homogeneous magnetic structure at greater heights and clearly
  reflect the different magnetic structures in the two regions. The
  average-profile study reveals that the intensities of the three lines
  all decline from the network center to internetwork region. The binned
  intensities of Si ii and Ne viii have a good correlation. We also find
  that the large blue shift of Ne viii does not coincide with large red
  shift of C iv. <BR />Conclusions: Our results suggest that the network
  structure is still prominent at the layer where Ne viii is formed in
  the quiet Sun, and that the magnetic structures expand more strongly
  in the dark part than in the bright part of this quiet Sun region. Our
  results might also hint for a scenario of magnetic reconnection between
  open funnels and side loops.

---------------------------------------------------------
Title: Long-period oscillations in solar coronal bright points
Authors: Tian, H.; Xia, L. -D.; Li, S.
2008A&A...489..741T    Altcode:
  Aims: By analyzing TRACE (Transition Region and Coronal Explorer)
  data, we investigate intensity oscillations in coronal bright points
  (BPs) as well as the underlying chromosphere. <BR />Methods: A Fourier
  analysis is applied to a sequence of images observed in the 195 Å
  and 1216 Å passbands of TRACE. We produce images of Fourier power in
  three different period ranges (4-16 min, 20-40 min, 42-75 min). The
  presence of periodic oscillations are further checked by applying
  a wavelet analysis to a selected rectangular region in each of the
  three BPs. <BR />Results: We find a clear signature of oscillations
  with different periods dominating in different strands of BP loops
  in the 195 Å passband. The oscillatory power is stronger in BPs than
  in the surrounding quiet Sun. In the chromospheric 1216 Å passband,
  oscillations in these period ranges are found mainly above the magnetic
  network elements, which are not necessarily associated with the coronal
  BPs. The wavelet analyses reveal that oscillations with periods ranging
  from 8 to 64 min can last for several cycles in both the BPs and the
  underlying chromosphere. <BR />Conclusions: It is still unclear whether
  these oscillations are caused by propagating magneto-acoustic waves
  in loop systems associated with the BPs, or result from recurrent
  magnetic reconnection powering the BPs.

---------------------------------------------------------
Title: Plasma Flows Guided by Strong Magnetic Fields in the Solar
    Corona
Authors: Marsch, Eckart; Tian, Hui; Sun, Jian; Curdt, Werner;
   Wiegelmann, Thomas
2008ApJ...685.1262M    Altcode:
  In this study new results are presented regarding the relationships
  between the coronal magnetic field and the intensities and Doppler
  shifts of ultraviolet emission lines. This combination of magnetic
  field and spectroscopic data is used here to study material flows in
  association with the coronal field. We introduce the term "coronal
  circulation" to describe this flow, and to indicate that the plasma is
  not static but flows everywhere in the extended solar atmosphere. The
  blueshifts and redshifts often seen in transition region and coronal
  ultraviolet emission lines are interpreted as corresponding to upflows
  and downflows of the plasma on open (funnels) and closed (loops) coronal
  magnetic field lines, which tightly confine and strongly lead the flows
  in the low-beta plasma. Evidence for these processes exists in the
  ubiquitous redshifts mostly seen at both legs of loops on all scales,
  and the sporadic blueshifts occurring in strong funnels. Therefore,
  there is no static magnetically stratified plasma in the corona, since
  panta rhei, but rather a continuous global plasma circulation, being
  the natural perpetuation of photospheric convection which ultimately
  is the driver.

---------------------------------------------------------
Title: Network oscillations at the boundary of an equatorial
    coronal hole
Authors: Tian, H.; Xia, L. -D.
2008A&A...488..331T    Altcode: 2009arXiv0907.0818T
  Aims: We investigate intensity oscillations observed simultaneously in
  the quiet chromosphere and in the corona, above an enhanced network
  area at the boundary of an equatorial coronal hole. <BR />Methods:
  A Fourier analysis is applied to a sequence of images observed in
  the 171 Å and 1600 Å passbands of TRACE. Four interesting features
  above the magnetic network are further investigated by using a
  wavelet analysis. <BR />Results: Our results reveal that, in both
  the 171 Å and 1600 Å passbands, oscillations above the magnetic
  network show a lack of power at high frequencies (5.0-8.3 mHz), and
  a significant power at low (1.3-2.0 mHz) and intermediate frequencies
  (2.6-4.0 mHz). The global 5-min oscillation is clearly present in the
  4 analyzed features when seen in the 1600 Å passband, and is also
  found with enhanced power in feature 1 (leg of a large coronal loop)
  and feature 2 (legs of a coronal bright point loop) when seen in
  the 171 Å passband. Two features above an enhanced network element
  (feature 3 and feature 4) show repeated propagating behaviors with a
  dominant period of 10 min and 5 min, respectively. <BR />Conclusions:
  We suggest these oscillations are likely to be slow magneto-acoustic
  waves propagating along inclined magnetic field lines, from the lower
  solar atmosphere into the corona. The energy flux carried by these waves
  is estimated of the order of 40~erg~ cm<SUP>-2</SUP>~s<SUP>-1</SUP>
  for the 171 Å passband and is far lower than the energy required to
  heat the quiet corona. For the 1600 Å passband, the energy flux is
  about 1.4×10^6~erg~ cm<SUP>-2</SUP>~s<SUP>-1</SUP>, which is about
  one third of the required energy budget for the chromosphere.

---------------------------------------------------------
Title: Modeling the UV/EUV Spectrum with SRPM
Authors: Haberreiter, M.; Fontenla, J.; Curdt, W.; Tian, H.
2008ESPM...12.3.12H    Altcode:
  We present a new set of semi-empirical solar atmosphere structures
  for different features on the solar disk that is consistent with the
  latest inter- network model by Fontenla et al. (2007), which reproduces
  the CO lines in the IR as well as the UV and radio continua. The
  intensity distribution of SUMER observations is used to define a set
  of solar disk features that accounts for the observed range of upper
  chromospheric heating. Using these models the UV/EUV (as well as longer
  wavelengths) radiance spectra are computed with SRPM in full-NLTE using
  the latest available atomic data and considering 24 elements up to high
  ionization stages with a total of approximately 14000 atomic levels
  and approximately 170000 line transitions. The radiance spectra of
  the new atmosphere structures allow us to study in detail the varying
  contributions of these features to the solar spectral irradiance. The
  synthetic spectra are compared with SUMER data and EUV irradiance
  observations obtained with the EVE rocket-instrument during a recent
  rocket flight.

---------------------------------------------------------
Title: The line profile and center-to-limb variation of quiet-Sun
    Lyman-alpha emission
Authors: Curdt, W.; Tian, H.; Teriaca, L.; Schühle, U.; Lemaire, P.
2008ESPM...12.2.91C    Altcode:
  We study the emission of the hydrogen Lyman-alpha line in the quiet
  Sun, its center-to-limb variation, and its radiance distribution, which
  we also compare to the Lyman-beta line. We use the high spectral and
  spatial resolution of the SUMER spectrometer and take raster scans at
  various locations on the disk. For the first time, we have used a new
  method to reduce the incoming photon flux to a 20%-level by partly
  closing the aperture door. We also performed a quasi-simultaneous
  observation of both Ly-a and Ly-b at Sun centre in sit-and-stare
  mode. We deduce the flow characteristic in Ly-a map from variations of
  the calibrated Si III line centroids. We present the average profile
  of Ly-a, its radiance distribution, its center-to-limb behaviour,
  and the signature of flows on the line profiles. Different from all
  other lines of the Lyman series, which have a red-horn asymmetry, Ly-a
  has a robust and dominating blue-horn asymmetry. To our knowledge,
  this result is only predicted by models which include flows.

---------------------------------------------------------
Title: Cool and Hot Components of a Coronal Bright Point
Authors: Tian, H.; Curdt, W.; Marsch, E.; He, J. -S.
2008ESPM...122.113T    Altcode:
  We performed a systematic study of the Doppler shifts and electron
  densities measured in an EUV bright point (hereafter BP) observed in
  more than 10 EUV lines with formation temperatures from log(T=K) =
  4.5 to 6.3. Those parts of a BP seen in transition region and coronal
  lines are defined as its cool and hot components, respectively. We find
  that the transition from cool to hot occurs at a temperature around
  log(T=K) = 5.7. The two components of the BP reveal a totally different
  orientation and Doppler-shift pattern, which might result from a twist
  of the associated magnetic loop system. The analysis of magnetic-field
  evolution and topology seems to favour a two-stage heating process,
  in which magnetic cancelation and separator reconnection are powering,
  respectively, the cool and hot components of the BP. We also found
  that the electron densities of both components of the BP are higher
  than those of the surrounding quiet Sun, and comparable to or smaller
  than active-region densities.

---------------------------------------------------------
Title: The Redshifted Network Contrast - Signature of Coronal
    Convectio
Authors: Curdt, W.; Tian, H.; Dwivedi, B. N.; Marsch, E.
2008ESPM...12.2.92C    Altcode:
  Observations and interpretations of red- and/or blueshifted emission
  lines from cosmic objects are crucial to understanding the physical
  processes at work there. The ubiquituous net redshifts of solar
  transition region (TR) emission lines are known since the Skylab
  era. Brekke et al. and Chae et al. independently verified this result
  by analyzing the high spectral resolution observations from the
  SUMER/SoHO instrument. Both these groups found similar results for
  the quantitative dependence of the net redshift on line formation
  temperatures from 30 000 K to 1 MK. To our knowledge, however, a
  satisfactory physical explanation of the redshift is still a matter
  of debate. We present a new method to explain the TR red shift, which
  is based on the radiance-redshift relationship, and which employs the
  redshift of the network contrast as compared to the position of the
  emission line itself. In contrast to the earlier work, our indirect
  method is unique in several ways namely, <P />(i) it does not require
  a good wavelength calibration and thus avoids related problems, <P
  />(ii) it is independent of the knowledge of the exact rest wavelength,
  and <P />(iii) it intimately relies on the physical processes in the
  solar atmosphere.

---------------------------------------------------------
Title: Electron trapping around a magnetic null
Authors: He, J. -S.; Zong, Q. -G.; Deng, X. -H.; Tu, C. -Y.; Xiao,
   C. -J.; Wang, X. -G.; Ma, Z. -W.; Pu, Z. -Y.; Lucek, E.; Pedersen,
   A.; Fazakerley, A.; Cornilleau-Wehrlin, N.; Dunlop, M. W.; Tian, H.;
   Yao, S.; Tan, B.; Fu, S. -Y.; Glassmeier, K. -H.; Reme, H.; Dandouras,
   I.; Escoubet, C. P.
2008GeoRL..3514104H    Altcode:
  Magnetic reconnection is an important process in astrophysical,
  space and laboratory plasmas. The magnetic null pair structure is
  theoretically suggested to be a crucial feature of the three-dimensional
  magnetic reconnection. The physics around the null pair, however, has
  not been explored in combination with the magnetic field configuration
  deduced from in situ observations. Here, we report the identification of
  the configuration around a null pair and simultaneous electron dynamics
  near one null of the pair, observed by four Cluster spacecraft in the
  geo-magnetotail. Further, we propose a new scenario of electron dynamics
  in the null region, suggesting that electrons are temporarily trapped
  in the central reconnection region including electron diffusion region
  resulting in an electron density peak, accelerated possibly by parallel
  electric field and electron pressure gradient, and reflected from the
  magnetic cusp mirrors leading to the bi-directional energetic electron
  beams, which excite the observed high frequency electrostatic waves.

---------------------------------------------------------
Title: Cool and Hot Components of a Coronal Bright Point
Authors: Tian, Hui; Curdt, Werner; Marsch, Eckart; He, Jiansen
2008ApJ...681L.121T    Altcode: 2009arXiv0906.3005T
  We performed a systematic study of the Doppler shifts and electron
  densities measured in an EUV bright point (hereafter BP) observed in
  more than 10 EUV lines with formation temperatures from log (T/K) =
  4.5 to 6.3. Those parts of a BP seen in transition region and coronal
  lines are defined as its cool and hot components, respectively. We find
  that the transition from cool to hot occurs at a temperature around log
  (T/K) = 5.7. The two components of the BP reveal a totally different
  orientation and Doppler-shift pattern, which might result from a twist
  of the associated magnetic loop system. The analysis of magnetic field
  evolution and topology seems to favor a two-stage heating process, in
  which magnetic cancellation and separator reconnection are powering,
  respectively, the cool and hot components of the BP. We also found
  that the electron densities of both components of the BP are higher
  than those of the surrounding quiet Sun, and comparable to or smaller
  than active region densities.

---------------------------------------------------------
Title: A magnetic null geometry reconstructed from Cluster spacecraft
    observations
Authors: He, J. -S.; Tu, C. -Y.; Tian, H.; Xiao, C. -J.; Wang, X. -G.;
   Pu, Z. -Y.; Ma, Z. -W.; Dunlop, M. W.; Zhao, H.; Zhou, G. -P.; Wang,
   J. -X.; Fu, S. -Y.; Liu, Z. -X.; Zong, Q. -G.; Glassmeier, K. -H.;
   Reme, H.; Dandouras, I.; Escoubet, C. P.
2008JGRA..113.5205H    Altcode:
  This paper reports for the first time the identification of a magnetic
  structure around a magnetic null in a magnetic reconnection region
  in the magnetotail. Magnetic reconnection is one of the fundamental
  processes in astrophysical and solar-terrestrial plasmas. Though
  the concept of reconnection has been studied for many years,
  the process that really occurs has not been fully revealed by
  direct measurements. In particular, the lack of a description of
  three-dimensional (3-D) reconnecting magnetic field from observations
  makes the task more difficult. The Cluster spacecraft array provide an
  opportunity to reconstruct the 3-D magnetic reconnection structure based
  on magnetic field vectors simultaneously measured at four positions. The
  identification of this structure comes from a new method of analysis
  of in situ measurements proposed here. Applying a fitting model of 10
  spherical harmonic functions and a Harris current sheet function, plus
  a constant field, we reconstruct a 3-D magnetic field configuration
  around the magnetic null in an reconnection event observed by Cluster
  in the geo-magnetotail.

---------------------------------------------------------
Title: Sizes of transition-region structures in coronal holes and
    in the quiet Sun
Authors: Tian, H.; Marsch, E.; Tu, C. -Y.; Xia, L. -D.; He, J. -S.
2008A&A...482..267T    Altcode: 2009arXiv0906.3028T
  Aims: We study the height variations of the sizes of chromospheric and
  transition-region features in a small coronal hole and the adjacent
  quiet Sun, considering images of the intensity, Doppler shift, and
  non-thermal motion of ultraviolet emission lines as measured by SUMER
  (Solar Ultraviolet Measurements by Emitted Radiation), together with
  the magnetic field as obtained by extrapolation from photospheric
  magnetograms. <BR />Methods: In order to estimate the characteristic
  sizes of the different features present in the chromosphere and
  transition region, we have calculated the autocorrelation function
  for the images as well as the corresponding extrapolated magnetic
  field at different heights. The Half Width at Half Maximum (HWHM) of
  the autocorrelation function is considered to be the characteristic
  size of the feature shown in the corresponding image. <BR />Results:
  Our results indicate that, in both the coronal hole and quiet Sun,
  the HWHM of the intensity image is larger than that of the images of
  Doppler-shift and non-thermal width at any given altitude. The HWHM
  of the intensity image is smaller in the chromosphere than in the
  transition region, where the sizes of intensity features of lines at
  different temperatures are almost the same. But in the upper part of
  the transition region, the intensity size increases more strongly with
  temperature in the coronal hole than in the quiet Sun. We also studied
  the height variations of the HWHM of the magnetic field magnitude B
  and its component \vert B<SUB>z</SUB> \vert, and found they are equal
  to each other at a certain height below 40 Mm in the coronal hole. The
  height variations of the HWHM of \vert B<SUB>z</SUB>/B \vert seem to be
  consistent with the temperature variations of the intensity size. <BR
  />Conclusions: Our results suggest that coronal loops are much lower,
  and magnetic structures expand through the upper transition region
  and lower corona much more strongly with height in the coronal hole
  than in the quiet Sun.

---------------------------------------------------------
Title: Signature of mass supply to quiet coronal loops
Authors: Tian, H.; Tu, C. -Y.; Marsch, E.; He, J. -S.; Zhou, G. -Q.
2008A&A...478..915T    Altcode: 2009arXiv0906.3007T
  Aims:The physical implication of large blue shift of Ne viii in the
  quiet Sun region is investigated in this paper. <BR />Methods: We
  compare the significant Ne viii blue shifts, which are visible as large
  blue patches on the Doppler-shift map of a middle-latitude quiet-Sun
  region observed by SUMER, with the coronal magnetic-field structures
  as reconstructed from a simultaneous photospheric magnetogram by means
  of a force-free-field extrapolation. <BR />Results: We show for the
  first time that coronal funnels also exist in the quiet Sun. The
  region studied contains several small funnels that originate from
  network lanes, expand with height and finally merge into a single wide
  open-field region. However, the large blue shifts of the Ne viii line
  are not generally associated with funnels. A comparison between the
  projections of coronal loops onto the solar x{-}y-plane and the Ne
  viii dopplergram indicates that there are some loops that reveal large
  Ne viii blue shifts in both legs, and some loops with upflow in one
  and downflow in the other leg. <BR />Conclusions: Our results suggest
  that strong plasma outflow, which can be traced by large Ne viii blue
  shift, is not necessarily associated with the solar wind originating
  in coronal funnels but appears to be a signature of mass supply to
  coronal loops. Under the assumption that the measured Doppler shift
  of the Ne viii line represents the real outflow velocity of the neon
  ions being markers of the proton flow, we estimate the mass supply
  rate to coronal loops to be about 10<SUP>34</SUP> s<SUP>-1</SUP>.

---------------------------------------------------------
Title: Sizes and heights of magnetic structures in the solar
    transition region as observed in ultraviolet emission lines at
    different temperatures
Authors: Marsch, Eckart; Tian, Hui; Tu, Chuanyi; He, Jiansen; Zhou,
   G. -Q.; Xia, Lidong
2008cosp...37.1922M    Altcode: 2008cosp.meet.1922M
  We investigate the height variations of the sizes of transition-region
  (TR) features in a small coronal hole and the adjacent quiet Sun,
  thereby considering images of the intensity, Doppler shift, and
  non-thermal motion of ultraviolet emission lines as measured by SUMER
  (Solar Ultraviolet Measurements by Emitted Radiation), together with
  the magnetic field as obtained by extrapolation from photospheric
  magnetograms. In order to estimate the sizes of different features
  present in the upper chromosphere and TR, we have calculated the
  autocorrelation function for the images as well as the corresponding
  extrapolated magnetic field at different heights. The half width at
  half maximum of the autocorrelation function is considered as the
  characteristic size of a feature shown in the corresponding image, and
  found in the intensity image to be smaller in the upper chromosphere
  than the TR. Through a correlation analysis of the emission pattern
  with the magnetic field (network and carpet of loops), the so-called
  correlation height of the emission can be determined. A detailed
  comparison is made of the coronal magnetic field obtained by
  extrapolation with the radiances of many ultraviolet lines, which
  are emitted by ions of various elements in different ionization
  stages, corresponding to different local coronal temperatures. At
  mesoscopic scales of several megameters the regions with strong emission
  (originating from multiple small closed loops) are found to be located
  at low heights, whereas weak emissions (coming from locally open,
  i.e. far reaching fields) appear to originate at greater heights. Our
  analysis confirms the notion that plasma at different temperature can
  coexist at the same height, and that the TR is not thermally stratified
  but strongly nonuniform and magnetically structured.

---------------------------------------------------------
Title: A model of the solar wind driven by supergranular circulation
Authors: Tu, Chuanyi; Tian, Hui; He, Jiansen; Marsch, Eckart
2008cosp...37.3238T    Altcode: 2008cosp.meet.3238T
  The scenario for the origin of the solar wind driven by the
  supergranular circulation as suggested by Tu et al. (2005) is tested
  with model calculation and data analysis. This scenario assumes that the
  fast solar wind originates at heights above 5 Mm in magnetically open
  funnels in corona holes. Mass and energy are supplied to the solar wind
  through reconnection of open field lines in the funnels with closed
  loops advected by the supergranular circulation to the reconnection
  sites. To test this scenario, we developed a one-dimensional one-fluid
  model with mass flux and energy flux supplied at 5 Mm to mimic the
  result expected from field-line reconnections. The upward flow and
  the downward flow resulting from this model are shown to be consistent
  with the blueshift of Ne VIII and redshift of Si II observed by SUMMER
  on SOHO. The mass and energy supply rates required by the model are
  shown to be consistent with the mass and energy delivery rates due to
  reconnection between magnetic loops in the intra-network region and open
  magnetic funnel at the network intersections. The model calculations
  support the scenario of the solar wind being driven by supergranular
  circulation. A discussion of a possible mechanism for the solar wind
  origin in the quiet sun is also given, where the solar wind is suggested
  to start flowing outward at a height of 20 Mm, which is higher than the
  emission height of Ne VIII ( 5 Mm). We found that Ne VIII blueshifts
  can occur at both legs of some closed loops, which suggests that mass
  can be supplied upward to the corona from both footpoints. Tu, C.-Y.,
  Zhou, C., Marsch, E., Xia, L.-D., Zhao, L., Wang, J.-X., and Wilhelm,
  K., Solar wind origin in coronal funnels, Science, 308, 519, 2005.

---------------------------------------------------------
Title: Boundary layer effects above a Himalayan valley near Mount
    Everest
Authors: Sun, Fanglin; Ma, Yaoming; Li, Maoshan; Ma, Weiqiang; Tian,
   Hui; Metzger, Stefan
2007GeoRL..34.8808S    Altcode:
  Periodical Wind Profiler and Radio Acoustic Sounding System observations
  have been commenced at the Himalayas' northern slope nearby Mount
  Everest in September 2005. Primarily data sets obtained 25 km remote
  from the glacier edge are utilized for a preliminary discussion
  of planetary boundary layer circulation resembling high alpine
  mountainous regions. Substantial findings include the detection of
  two wind shears and the phenomenon of glacier wind at a distance of
  25 km from the glaciers. The latter lead to a reversed compensatory
  flow in a vertical scale of up to 2000 m above ground level, pointing
  at supra regional impact.

---------------------------------------------------------
Title: Emission heights of coronal bright points on Fe XII radiance
    map
Authors: Tian, H.; Tu, C. -Y.; He, J. -S.; Marsch, E.
2007AdSpR..39.1853T    Altcode: 2009arXiv0907.4954T
  The study of coronal bright points (BPs) is important for understanding
  coronal heating and the origin of the solar wind. Previous studies
  indicated that coronal BPs have a highly significant tendency to
  coincide with magnetic neutral lines in the photosphere. Here we further
  studied the emission heights of the BPs above the photosphere in the
  bipolar magnetic loops that are apparently associated with them. As BPs
  are seen in projection against the disk their true emission heights are
  unknown. The correlation of the BP locations on the Fe XII radiance
  map from EIT with the magnetic field features (in particular neutral
  lines) was investigated in detail. The coronal magnetic field was
  determined by an extrapolation of the photospheric field (derived from
  2-D magnetograms obtained from the Kitt Peak observatory) to different
  altitudes above the disk. It was found that most BPs sit on or near a
  photospheric neutral line, but that the emission occurs at a height
  of about 5 Mm. Some BPs, while being seen in projection, still seem
  to coincide with neutral lines, although their emission takes place
  at heights of more than 10 Mm. Such coincidences almost disappear
  for emissions above 20 Mm. We also projected the upper segments of
  the 3-D magnetic field lines above different heights, respectively,
  on to the tangent x- y plane, where x is in the east-west and y in
  the south-north direction. The shape of each BP was compared with the
  respective field-line segment nearby. This comparison suggests that
  most coronal BPs are actually located on the top of their associated
  magnetic loops. Finally, we calculated for each selected BP region the
  correlation coefficient between the Fe XII intensity enhancement and
  the horizontal component of the extrapolated magnetic field vector at
  the same x- y position in planes of different heights, respectively. We
  found that for almost all the BP regions we studied the correlation
  coefficient, with increasing height, increases to a maximal value and
  then decreases again. The height corresponding to this maximum was
  defined as the correlation height, which for most bright points was
  found to range below 20 Mm.

---------------------------------------------------------
Title: a Study on the Height of the Corona Bright Points on FeXII
    Radiance Map
Authors: Tian, H.; Tu, C. -Y.; He, J. -S.; Marsch, E.
2006cosp...36.1952T    Altcode: 2006cosp.meet.1952T
  By registering SOHO EIT FeXII -19 5 nm coronal images with Kitt Peak
  magnetograms D A Falconer et al 1998 found that the brightest features
  in the network lanes which they called network coronal bright points
  had a highly significant coincidence with magnetic network neutral lines
  They found that most bright points sit on neutral lines in the network
  magnetic flux We further studied the height information of the bright
  points on the FeXII radiance map by comparing the individual pattern
  of the coronal bright points with the distribution of the top segments
  of the loops from the 3-D magnetic field force-free extrapolated from
  the photospheric magnetogram If we assume the source regions of the
  bright points are all on the top of the loops then the height of bright
  points of FeXII radiance is between 5Mm-10Mm