explanation      blue bibcodes open ADS page with paths to full text
Author name code: huang
ADS astronomy entries on 2022-09-14
=author:"Huang, Zhenghua" 

---------------------------------------------------------
Title: An EUV Jet Driven by a Series of Transition Region Microjets
Authors: Wei, Hengyuan; Huang, Zhenghua; Fu, Hui; Xiong, Ming; Xia,
   Lidong; Zhang, Chao; Deng, Kaiwen; Li, Haiyi
2022ApJ...936...51W    Altcode: 2022arXiv220800112W
  Jets are one of the most common eruptive events in the solar atmosphere,
  and they are believed to be important in the context of coronal
  heating and solar wind acceleration. We present an observational study
  on a sequence of jets with the data acquired with the Solar Dynamics
  Observatory and the Interface Region Imaging Spectrograph. This sequence
  is peculiar in that an extreme-ultraviolet (EUV) jet, ~29″ long
  and with a dome-like base, appears to be a consequence of a series of
  transition region (TR) microjets that are a few arcsecs in length. We
  find that the occurrence of any TR microjets is always associated
  with the change of geometry of microloops at the footpoints of the
  microjets. A bundle of TR flux ropes is seen to link a TR microjet
  to the dome-like structure at the base of the EUV jet. This bundle
  rises as a response to the TR microjets, with the rising motion
  eventually triggering the EUV jet. We propose a scenario involving a
  set of magnetic reconnections, in which the series of TR microjets are
  associated with the processes to remove the constraints to the TR flux
  ropes and thus allows them to rise and trigger the EUV jet. Our study
  demonstrates that small-scale dynamics in the lower solar atmosphere
  are crucial in understanding the energy and mass connection between
  the corona and the solar lower atmosphere, even though many of them
  might not pump mass and energy to the corona directly.

---------------------------------------------------------
Title: Dynamics in the Transition Region beneath Active Region
    Upflows Viewed by IRIS
Authors: Huang, Zhenghua; Fu, Hui; Xia, Lidong; Hou, Zhenyong;
   Wang, Ziyuan
2022cosp...44.2534H    Altcode:
  Coronal upflows at the edges of active regions (ARs), which are a
  possible source of slow solar wind, have been found to connect with
  dynamics in the transition region. To infer at what scale transition
  region dynamics connect to AR upflows, we investigate the statistical
  properties of the small-scale dynamics in the transition region
  underneath the upflows at the edge of NOAA Active Region 11934. With
  observations from the Interface Region Imaging Spectrograph (IRIS),
  we found that the Si IV 1403\AA\ Doppler map consists of numerous
  blueshifted and redshifted patches mostly with sizes less than 1
  Mm$^{2}$. The blueshifted structures in the transition region tend to be
  brighter than the redshifted ones, but their nonthermal velocities have
  no significant difference. With the SWAMIS feature-tracking procedure,
  we found in IRIS slit-jaw 1400 \AA\ images that dynamic bright dots with
  an average size of about 0.3 Mm$^2$ and lifetimes of mostly less than
  200 s were spread all over the region. Most of the bright dots appear
  to be localized, without a clear signature of plasma propagation to a
  long distance on the projection plane. Surge-like motions with speeds
  of about 15 km/s could be seen in some events at the boundaries of the
  upflow region, where the magnetic field appeared to be inclined. We
  conclude that the transition region dynamics connecting to coronal
  upflows should occur in at a very fine scale, suggesting that the
  corresponding coronal upflows should also be highly structured. It
  is also plausible that the transition region dynamics might just act
  as stimulation at the coronal base, which then drives the upflows in
  the corona.

---------------------------------------------------------
Title: A coronal jet facilitated by a series of transition region
    microjets
Authors: Wei, Hengyuan; Fu, Hui; Xia, Lidong; Xiong, Ming; Huang,
   Zhenghua; Hengyua Wei, A. coronal jet facilitated by a. s.
2022cosp...44.2566W    Altcode:
  Jets are one of the most common features in the solar atmosphere,
  which are thought to be essential to understand the coronal heating and
  solar wind accelerating. They are widely observed in the photosphere,
  chromosphere and corona with scales from several Mm to hundreds of
  Mm. The observations of the magnetic field of coronal jets found that
  they are always multipolarities, and they are sometimes produced by
  reconnection between emerging bipoles and local open fields. With
  the Solar Dynamics Observation (SDO) and Interface Region Imaging
  Spectrograph (IRIS), we observe a jet event that occurred as a
  subsequence of a series of microjets in the transition region. We found
  that six micro-jets are associated with six reconnection processes
  between an open field and local micro-loops, which then allow a small
  twisted transition region magnetic loops to rise and reconnect with
  open field that produces a coronal jet. The coronal jet is multithermal,
  with enhanced emission in temperatures from log(T/K) = 5.5 to log(T/K)
  = 7.3, and the strongest response is in the temperatures from log(T/K)
  = 6.1 to log(T/K) = 6.7. We also found that the coronal jet has a
  rotating motion, which says it is similar to the coronal jet reported
  in the previous literature. Our observations show a clear example that
  how small-scale activities finally trigger a larger eruption in the
  solar atmosphere.

---------------------------------------------------------
Title: Anisotropic nonthermal motions in the transition region of
    solar active regions
Authors: Mou, Chaozhou; Peter, Hardi; Xia, Lidong; Huang, Zhenghua
2022A&A...660A...3M    Altcode:
  Context. We study the nonthermal motions in the transition region
  of active regions (ARs) using center-to-limb observations of Si
  IV 1394 Å and 1403 Å lines. <BR /> Aims: The aim of this study
  is to investigate the characteristics of nonthermal motions in the
  transition region of ARs using the center-to-limb measurement. <BR
  /> Methods: We used Interface Region Imaging Spectrograph (IRIS)
  observations of the Si IV doublet lines 1393.78 Å and 1402.77 Å from
  the transition region of ARs to analyze nonthermal motions. We compared
  our analyzed data to similar data for the quiet Sun (QS) regions. We
  derive the nonthermal width by performing a single Gaussian fitting
  on the average spectral line profiles of Si IV doublet lines. We
  carried out a statistical analysis of the nonthermal width using the
  center-to-limb measurement. <BR /> Results: We find that the nonthermal
  motions are clearly decreasing on the disk with increasing distance
  from disk center. Only close to the limb, clearly beyond μ = 0.4,
  does the nonthermal broadening increase again towards the limb. The
  decrease in the nonthermal broadening in ARs away from disk center is
  markedly different from what is seen in the QS. <BR /> Conclusions:
  We conclude that nonthermal motions are anisotropic in ARs, with the
  vertical component being greater than the horizontal one. In contrast,
  we find the situation in the QS to be consistent with the findings of
  previous studies; only opacity effects are responsible for the increase
  in the nonthermal widths towards the limb, and nonthermal motions are
  isotropic in the QS.

---------------------------------------------------------
Title: Charge States, Helium Abundance, and FIP Bias of the
    Interplanetary CMEs Classified by Flares and Hot Channels
Authors: Zhai, Huitong; Fu, Hui; Huang, Zhenghua; Xia, Lidong
2022ApJ...928..136Z    Altcode:
  Identifying the material source of coronal mass ejections (CMEs)
  is crucial for understanding the generation mechanisms of CMEs. The
  composition parameters of interplanetary coronal mass ejections (ICMEs)
  associated with different activities on the Sun may be diverse, as
  the materials come from distinct regions or are generated by different
  processes. We classified ICMEs into three types by associated activities
  on the Sun, with (T1) and without (T3) flares and hot channels, and
  only associated with flares (T2). The composition parameters of each
  type of ICMEs were analyzed. We found that all CMEs with hot channels
  are accompanied by flares, and strong flares are all associated with
  hot channels in our database. The average length of the filaments in
  T1 cases are much shorter than those in T3 cases. The average charge
  states of iron (Q <SUB>Fe</SUB>) and helium abundance (A <SUB>He</SUB>)
  for T3 ICMEs are less than 12% and 7%, respectively. The Q <SUB>Fe</SUB>
  and A <SUB>He</SUB> for T1 ICMEs present clear bimodal distributions
  with the minimum between two peaks at 12% and 7%, respectively. Nearly
  two-thirds of the hot plasma (with higher Q <SUB>Fe</SUB>) inside
  ICMEs is associated with higher A <SUB>He</SUB>. The Q <SUB>Fe</SUB>
  and A <SUB>He</SUB> are both positively correlated with the flare
  intensities. The A <SUB>He</SUB> and filament scales are not explicitly
  linked to each other. The statistical results demonstrate that the
  material contribution of the filaments to ICMEs is low and more than
  half of the hot materials inside ICMEs originate from the chromosphere
  in our database. We suggest that they are heated by the chromospheric
  evaporation process at the hot channel (flux rope) footpoint regions
  before and/or during the flaring process.

---------------------------------------------------------
Title: Statistical properties of Hα jets in the polar coronal hole
    and their implications in coronal activities
Authors: Qi, Youqian; Huang, Zhenghua; Xia, Lidong; Fu, Hui; Guo,
   Mingzhe; Hou, Zhenyong; Liu, Weixin; Sun, Mingzhe; Liu, Dayang
2022A&A...657A.118Q    Altcode: 2021arXiv211015543Q
  Context. Dynamic features such as chromospheric jets, transition
  region network jets, coronal plumes, and coronal jets are abundant
  in the network regions of polar coronal holes on the Sun. <BR />
  Aims: We investigate the relationship between chromospheric jets
  and coronal activities, such as coronal plumes and jets. <BR />
  Methods: We analyzed observations of a polar coronal hole including the
  filtergrams taken by the New Vacuum Solar Telescope at the Hα − 0.6
  Å to study the Hα jets, as well as the Atmospheric Imaging Assembly
  171 Å images to follow the evolution of coronal activities. <BR />
  Results: The Hα jets are persistent in the network regions, with
  only some regions (denoted as R1-R5) rooted in discernible coronal
  plumes. With an automated method, we identified and tracked 1320
  Hα jets in the network regions. We find that the average lifetime,
  height, and ascending speed of the Hα jets are 75.38 s, 2.67 Mm,
  65.60 km s<SUP>−1</SUP>, respectively. The Hα jets rooted in
  R1-R5 are higher and faster than those in the others. We also find
  that propagating disturbances (PDs) in coronal plumes have a close
  connection with the Hα jets. The speeds of 28 out of 29 Hα jets
  associated with PDs are ≳50 km s<SUP>−1</SUP>. In the case of a
  coronal jet, we find that the speeds in both the coronal jet and the Hα
  jet are over 150 km s<SUP>−1</SUP>, suggesting that both cool and hot
  jets can be coupled. <BR /> Conclusions: Based on our analyses, it is
  evident that more dynamic Hα jets could release their energy to the
  corona, which might be the result of a Kelvin-Helmholtz instability
  developing or that of small-scale magnetic activities. We suggest
  that chromospheric jets, transition region network jets, and ray-like
  features in the corona are coherent phenomena that serve as important
  vehicles for cycling energy and mass in the solar atmosphere. <P
  />Movies associated to Figs. 1, 5, and 7 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141401/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Concept of the solar ring mission
Authors: Zhang, Quanhao; Wang, Yuming; Ji, Haisheng; Shen, Chenglong;
   Guo, Jingnan; Huang, Zhenghua; Liu, Kai; Li, Xiaolei; Liu, Rui; Wang,
   Jingxiu; Wang, Shui; Wang, Yamin
2021AGUFMSH15A2020Z    Altcode:
  Solar wind structures have been investigated for more than 100
  years. In order to investigate the physical essence of solar wind,
  we develop a new method to 3-dimensionally reconstruct the solar wind
  structures named as CORrelation-Aided Reconstruction (CORAR), which
  is based on the images observed by satellites from different viewing
  angles. Furthermore, we use both the observational and numerical
  data to assess the optimal angle between the two spacecraft for the
  reconstruction. Base on this, we have proposed the concept of the
  next-generation observational project: the Solar Ring mission. The
  current preliminary design of the Solar Ring mission is to deploy
  three spacecraft, which are separated by about 120 degree and every
  two groups by about 120 degree. In cooperation with the satellites
  around the earth (e.g., Advanced Space-based Solar Observatory,
  ASO-S), this conguration with necessary science payloads will allow
  us to establish three unprecedented capabilities: (1) determine
  the photospheric vector magnetic eld with unambiguity, (2) provide
  360-degree maps of the Sun and the inner heliosphere routinely, and
  (3) resolve the solar wind structures at multiple scales and multiple
  longitudes. With these capabilities, the Solar Ring mission aims to
  address the origin of solar cycle, the origin of solar eruptions, the
  origin of solar wind structures and the origin of severe space weather
  events. The successful accomplishment of the mission will advance our
  understanding of the star and the space environment that hold our life
  and enhance our capability of expanding the next new territory of human.

---------------------------------------------------------
Title: Dynamics in the Transition Region beneath Active Region
    Upflows Viewed by IRIS
Authors: Huang, Zhenghua; Xia, Lidong; Fu, Hui; Hou, Zhenyong;
   Wang, Ziyuan
2021ApJ...918...33H    Altcode: 2021arXiv210701577H
  Coronal upflows at the edges of active regions (ARs), which are
  a possible source of slow solar wind, have been found to connect
  with dynamics in the transition region. To infer at what scale
  transition region dynamics connect to AR upflows, we investigate
  the statistical properties of the small-scale dynamics in the
  transition region underneath the upflows at the edge of NOAA Active
  Region 11934. With observations from the Interface Region Imaging
  Spectrograph (IRIS), we found that the Si IV 1403 Å Doppler map
  consists of numerous blueshifted and redshifted patches mostly with
  sizes less than 1 Mm<SUP>2</SUP>. The blueshifted structures in the
  transition region tend to be brighter than the redshifted ones, but
  their nonthermal velocities have no significant difference. With the
  SWAMIS feature-tracking procedure, we found in IRIS slit-jaw 1400 Å
  images that dynamic bright dots with an average size of about 0.3
  Mm<SUP>2</SUP> and lifetimes of mostly less than 200 s were spread
  all over the region. Most of the bright dots appear to be localized,
  without a clear signature of plasma propagation to a long distance on
  the projection plane. Surge-like motions with speeds of about 15 km
  s<SUP>-1</SUP> could be seen in some events at the boundaries of the
  upflow region, where the magnetic field appeared to be inclined. We
  conclude that the transition region dynamics connecting to coronal
  upflows should occur in at a very fine scale, suggesting that the
  corresponding coronal upflows should also be highly structured. It
  is also plausible that the transition region dynamics might just act
  as stimulation at the coronal base, which then drives the upflows in
  the corona.

---------------------------------------------------------
Title: Solar Ultraviolet Bursts in the Joint Footpoints of Multiple
    Transition Region Loops
Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Fu, Hui; Qi,
   Youqian; Liu, Dayang; Tang, Ning
2021Symm...13.1390H    Altcode:
  No abstract at ADS

---------------------------------------------------------
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: 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: Population of Bright Plume Threads in Solar Polar Coronal Holes
Authors: Huang, Zhenghua; Zhang, Quanhao; Xia, Lidong; Feng, Li;
   Fu, Hui; Liu, Weixin; Sun, Mingzhe; Qi, Youqian; Liu, Dayang; Zhang,
   Qingmin; Li, Bo
2021SoPh..296...22H    Altcode: 2021arXiv210103768H
  Coronal holes are well accepted to be source regions of the fast solar
  wind. As one of the common structures in coronal holes, coronal plumes
  might contribute to the origin of the nascent solar wind. To estimate
  the contribution of coronal plumes to the nascent solar wind, we make
  the first attempt to estimate their populations in the solar polar
  coronal holes. By comparing the observations viewed from two different
  angles taken by the twin satellites of STEREO and the results of Monte
  Carlo simulations, we estimate about 16 - 27 plumes rooted in an area
  of 4 ×10<SUP>4</SUP>arcsec<SUP>2</SUP> of the polar coronal holes
  near the solar minimum, which occupy about 2 - 3.4% of the area. Based
  on these values, the contribution of coronal plumes to the nascent
  solar wind has also been discussed. A further investigation indicates
  that a more precise number of coronal plumes can be worked out with
  observations from three or more viewing angles.

---------------------------------------------------------
Title: The High Helium Abundance and Charge States of the
    Interplanetary CME and Its Material Source on the Sun
Authors: Fu, Hui; Harrison, R. A.; Davies, J. A.; Xia, LiDong; Zhu,
   XiaoShuai; Li, Bo; Huang, ZhengHua; Barnes, D.
2020ApJ...900L..18F    Altcode: 2020arXiv200808816F
  Identifying the source of the material within coronal mass ejections
  (CMEs) and understanding CME onset mechanisms are fundamental issues in
  solar and space physics. Parameters relating to plasma composition,
  such as charge states and He abundance (A<SUB>He</SUB>), may be
  different for plasmas originating from differing processes or regions
  on the Sun. Thus, it is crucial to examine the relationship between
  in situ measurements of CME composition and activity on the Sun. We
  study the CME that erupted on 2014 September 10, in association with
  an X1.6 flare, by analyzing Atmospheric Imaging Assembly imaging and
  Interface Region Imaging Spectrograph (IRIS) spectroscopic observations
  and its in situ signatures detected by Wind and Advanced Composition
  Explorer. We find that during the slow expansion and intensity increase
  of the sigmoid, plasma temperatures of 9 MK, and higher, first appear
  at the footpoints of the sigmoid, associated with chromospheric
  brightening. Then the high-temperature region extends along the
  sigmoid. IRIS observations confirm that this extension is caused by
  transportation of hot plasma upflow. Our results show that chromospheric
  material can be heated to 9 MK, and above, by chromospheric evaporation
  at the sigmoid footpoints before flare onset. The heated chromospheric
  material can transport into the sigmoidal structure and supply mass
  to the CME. The aforementioned CME mass supply scenario provides a
  reasonable explanation for the detection of high charge states and
  elevated A<SUB>He</SUB> in the associated interplanetary CME. The
  observations also demonstrate that the quasi-steady evolution in the
  precursor phase is dominated by magnetic reconnection between the
  rising flux rope and the overlying magnetic field structure.

---------------------------------------------------------
Title: Concept of the solar ring mission: An overview
Authors: Wang, YuMing; Ji, HaiSheng; Wang, YaMin; Xia, LiDong; Shen,
   ChengLong; Guo, JingNan; Zhang, QuanHao; Huang, ZhengHua; Liu, Kai;
   Li, XiaoLei; Liu, Rui; Wang, JingXiu; Wang, Shui
2020ScChE..63.1699W    Altcode: 2020arXiv200312728W
  The concept of the Solar Ring mission was gradually formed from L5/L4
  mission concept, and the proposal of its pre-phase study was funded by
  the National Natural Science Foundation of China in November 2018 and
  then by the Strategic Priority Program of Chinese Academy of Sciences in
  space sciences in May 2019. Solar Ring mission will be the first attempt
  to routinely monitor and study the Sun and inner heliosphere from a full
  360-degree perspective in the ecliptic plane. The current preliminary
  design of the Solar Ring mission is to deploy six spacecraft, grouped
  in three pairs, on a sub-AU orbit around the Sun. The two spacecraft in
  each group are separated by about 30 degrees and every two groups by
  about 120 degrees. This configuration with necessary science payloads
  will allow us to establish three unprecedented capabilities: (1)
  determine the photospheric vector magnetic field with unambiguity,
  (2) provide 360-degree maps of the Sun and the inner heliosphere
  routinely, and (3) resolve the solar wind structures at multiple
  scales and multiple longitudes. With these capabilities, the Solar Ring
  mission aims to address the origin of solar cycle, the origin of solar
  eruptions, the origin of solar wind structures and the origin of severe
  space weather events. The successful accomplishment of the mission
  will advance our understanding of the star and the space environment
  that hold our life and enhance our capability of expanding the next
  new territory of human.

---------------------------------------------------------
Title: Heating at the Remote Footpoints as a Brake on Jet Flows
    along Loops in the Solar Atmosphere
Authors: Huang, Zhenghua; Zhang, Qingmin; Xia, Lidong; Li, Bo; Wu,
   Zhao; Fu, Hui
2020ApJ...897..113H    Altcode: 2020arXiv200704132H
  We report on observations of a solar jet propagating along coronal loops
  taken by the Solar Dynamics Observatory, the Interface Region Imaging
  Spectrograph, and the 1 m New Vacuum Solar Telescope. The ejecta of
  the jet consist of multithermal components and propagate with a speed
  greater than 100 km s<SUP>-1</SUP>. Brightenings are found in the
  remote footpoints of the coronal loops having compact and round shape
  in the Hα images. The emission peak of the remote brightening in the
  Atmospheric Imaging Assembly (AIA) 94 Å passband lags 60 s behind
  that in the jet base. The brightenings in the remote footpoints are
  believed to be consequences of heating by nonthermal electrons, MHD
  waves, and/or a conduction front generated by the magnetic reconnection
  processes of the jet. The heating in the remote footpoints leads to
  extension of the brightening along the loops toward the jet base, which
  is believed to be the chromospheric evaporation. This apparently acts
  as a brake on the ejecta, leading to a deceleration in the range from
  1.5 to 3 km s<SUP>-2</SUP> with an error of ∼1.0 km s<SUP>-2</SUP>
  when the chromospheric evaporation and the ejecta meet at locations
  near the loop apexes. The dynamics of this jet allows for a unique
  opportunity to diagnose the chromospheric evaporation from the remote
  footpoints, from which we deduce a velocity in the range of 330-880
  km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: Transition Region Loops in the Very Late Phase of Flux
    Emergence in IRIS Sit-and-stare Observations
Authors: Huang, Zhenghua; Li, Bo; Xia, Lidong; Shi, MiJie; Fu, Hui;
   Hou, Zhenyong
2019ApJ...887..221H    Altcode: 2019arXiv191102199H
  Loops are one of the fundamental structures that trace the geometry of
  the magnetic field in the solar atmosphere. Their evolution and dynamics
  provide a crucial proxy for studying how the magnetized structures
  are formed and heated in the solar atmosphere. Here, we report on
  spectroscopic observations of a set of transition-region loops taken
  by the Interface Region Imaging Spectrograph (IRIS) at Si IV 1394 Å
  in the sit-and-stare mode. The loops are corresponding to the flux
  emergence at its very late phase when the emerged magnetic features in
  the photosphere have fully developed. We find the transition-region
  loops are still expanding and moving upward with a velocity of a few
  kilometers per second (≲10 km s<SUP>-1</SUP>) at this stage. The
  expansion of the loops leads to interactions between the loops
  themselves and with the ambient field, which can drive magnetic
  reconnection evidenced by multiple intense brightenings, including
  transition-region explosive events and IRIS bombs in the footpoint
  region associated with the moving polarity. A set of quasi-periodic
  brightenings with a period of about 130 s is found at the loop apex,
  from which the Si IV 1394 Å profiles are significantly non-Gaussian
  with enhancements at both blue and red wings at Doppler velocities
  of about 50 km s<SUP>-1</SUP>. We suggest that the transition-region
  loops in the very late phase of flux emergence can be powered by
  heating events generated by the interactions between the expanding
  loops and the ambient fields and also by (quasi-)periodic processes,
  such as oscillation-modulated braiding reconnection.

---------------------------------------------------------
Title: Synthetic Extreme-ultraviolet Emissions Modulated by Leaky
    Fast Sausage Modes in Solar Active Region Loops
Authors: Shi, Mijie; Li, Bo; Huang, Zhenghua; Chen, Shao-Xia
2019ApJ...883..196S    Altcode: 2019arXiv190807131S
  We study the extreme-ultraviolet (EUV) emissions modulated by leaky
  fast sausage modes (FSMs) in solar active region (AR) loops and examine
  their observational signatures via spectrometers like the EUV imaging
  spectrometer (EIS). After computing fluid variables of leaky FSMs with
  magnetohydrodynamic (MHD) simulations, we forward-model the intensity
  and spectral properties of the Fe X 185 Å and Fe XII 195 Å lines
  by incorporating nonequilibrium ionization (NEI) in the computations
  of the relevant ionic fractions. The damping times derived from the
  intensity variations are then compared with the wave values, namely,
  the damping times directly found from our MHD simulations. Our results
  show that in the equilibrium ionization cases, the density variations
  and the intensity variations can be either in phase or in antiphase,
  depending on the loop temperature. NEI considerably impacts the
  intensity variations but has only marginal effects on the derived
  Doppler velocity or Doppler width. We find that the damping time
  derived from the intensity can largely reflect the wave damping time
  if the loop temperature is not drastically different from the nominal
  formation temperature of the corresponding emission line. These results
  are helpful for understanding the modulations to the EUV emissions by
  leaky FSMs and hence helpful for identifying FSMs in solar AR loops.

---------------------------------------------------------
Title: On the Relation Between Transition Region Network Jets and
    Coronal Plumes
Authors: Qi, Youqian; Huang, Zhenghua; Xia, Lidong; Li, Bo; Fu, Hui;
   Liu, Weixin; Sun, Mingzhe; Hou, Zhenyong
2019SoPh..294...92Q    Altcode: 2019arXiv190610353Q
  Both coronal plumes and network jets are rooted in network lanes. The
  relationship between the two, however, has yet to be addressed. For this
  purpose, we perform an observational analysis using images acquired
  on 2015 December 4 with the Atmospheric Imaging Assembly (AIA) 171 Å
  passband to follow the evolution of coronal plumes, the observations
  taken by the Interface Region Imaging Spectrograph (IRIS) at slit-jaw
  1330 Å to study the network jets, and the line-of-sight magnetograms
  taken by the Helioseismic and Magnetic Imager (HMI) to overview the
  photospheric magnetic features in the regions. Four regions in the
  network lanes are identified and labeled R1-R4, which are abundant
  with network jets. R1 and R2 are associated with coronal plumes that
  could be clearly seen for at least five days, while coronal plumes
  are hardly seen in R3 and R4 for at least three days. Furthermore,
  while magnetic features in all these regions are dominated by positive
  polarity, they are more compact (suggesting stronger convergence) in
  R1 and R2 than that in R3 and R4. We develop an automated method to
  identify and track the network jets in the regions. We find that the
  network jets rooted in R1 and R2 are higher and faster than those in
  R3 and R4, indicating that network regions producing stronger coronal
  plumes also tend to produce more dynamic network jets. We suggest that
  the stronger convergence in R1 and R2 might provide a condition for
  faster shocks and/or more small-scale magnetic reconnection events
  that power more dynamic network jets and coronal plumes.

---------------------------------------------------------
Title: Observations of small-scale energetic events in the solar
transition region: explosive events, UV bursts, and network jets
Authors: Huang, Zhenghua; Li, Bo; Xia, Lidong
2019STP.....5b..58H    Altcode: 2019SZF.....5b..63H; 2019arXiv190406688H
  In this paper, we review observational aspects of three common
  small-scale energetic events in the solar transition region (TR),
  namely TR explosive events, ultraviolet bursts and jets. These events
  are defined in either (both) spectral or (and) imaging data. The
  development of multiple instruments capable of observing the TR has
  allowed researchers to gain numerous insights into these phenomena in
  recent years. These events have provided a proxy to study how mass
  and energy are transported between the solar chromosphere and the
  corona. As the physical mechanisms responsible for these small-scale
  events might be similar to the mechanisms responsible for large-scale
  phenomena, such as flares and coronal mass ejections, analysis of these
  events could also help our understanding of the solar atmosphere from
  small to large scales. The observations of these small-scale energetic
  events demonstrate that the TR is extremely dynamic and is a crucial
  layer in the solar atmosphere between the chromosphere and the corona.

---------------------------------------------------------
Title: Helium abundance and speed difference between helium ions
    and protons in the solar wind from coronal holes, active regions,
    and quiet Sun
Authors: Fu, Hui; Madjarska, Maria S.; Li, Bo; Xia, Lidong; Huang,
   Zhenghua
2019EGUGA..21.3666F    Altcode:
  Two main models have been developed to explain the mechanisms of
  release, heating, and acceleration of the nascent solar wind, the
  wave-turbulence-driven (WTD) models and reconnection-loop-opening
  (RLO) models, in which the plasma release processes are fundamentally
  different. Given that the statistical observational properties of
  helium ions produced in magnetically diverse solar regions could
  provide valuable information for the solar wind modelling, we examine
  the statistical properties of the helium abundance (A_He) and the
  speed difference between helium ions and protons (v_αp) for coronal
  holes (CHs), active regions (ARs), and the quiet Sun (QS). We find
  bimodal distributions in the space of A_He and v_αp/v<SUB>A</SUB>
  (where v<SUB>A</SUB> is the local Alfven speed) for the solar wind as
  a whole. The CH windmeasurements are concentrated at higher A_He and
  v_αp/v<SUB>A</SUB> values with a smaller A_He distribution range,
  while the AR and QS wind is associated with lower A_He and v_αp/v_A,
  and a larger A_He distribution range. The magnetic diversity of the
  source regions and the physical processes related to it are possibly
  responsible for the different properties of A_He and v_αp/v_A. The
  statistical results suggest that the two solar wind generation
  mechanisms, WTD and RLO, work in parallel in all solar wind source
  regions. In CH regions WTD plays a major role, whereas the RLO mechanism
  is more important in AR and QS.

---------------------------------------------------------
Title: Synthetic Emissions of the Fe XXI 1354 Å Line from Flare
    Loops Experiencing Fundamental Fast Sausage Oscillations
Authors: Shi, Mijie; Li, Bo; Huang, Zhenghua; Chen, Shao-Xia
2019ApJ...874...87S    Altcode: 2019arXiv190206087S
  Inspired by recent IRIS observations, we forward model the response
  of the Fe XXI 1354 Å line to fundamental, standing, linear
  fast sausage modes (FSMs) in flare loops. Starting with the fluid
  parameters for an FSM in a straight tube with equilibrium parameters
  largely compatible with the IRIS measurements, we synthesize the
  line profiles by incorporating the non-Equilibrium Ionization (NEI)
  effect in the computation of the contribution function. We find that
  both the intensity and Doppler shift oscillate at the wave period
  (P). The phase difference between the two differs from the expected
  value (90°) only slightly because NEI plays only a marginal role
  in determining the ionic fraction of Fe XXI in the examined dense
  loop. The Doppler width modulations, however, posses an asymmetry in
  the first and second halves of a wave period, leading to a secondary
  periodicity at P/2 in addition to the primary one at P. This behavior
  results from the competition between the broadening due to bulk flow and
  that due to temperature variations, with the latter being stronger but
  not overwhelmingly so. These expected signatures, with the exception of
  the Doppler width, are largely consistent with the IRIS measurements,
  thereby corroborating the reported detection of a fundamental FSM. The
  forward-modeled signatures are useful for identifying fundamental
  FSMs in flare loops from measurements of the Fe XXI 1354 Å line with
  instruments similar to IRIS, even though a much higher cadence is
  required for the expected behavior in the Doppler widths to be detected.

---------------------------------------------------------
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: Non-equilibrium Ionization Effects on Extreme-ultraviolet
    Emissions Modulated by Standing Sausage Modes in Coronal Loops
Authors: Shi, Mijie; Li, Bo; Van Doorsselaere, Tom; Chen, Shao-Xia;
   Huang, Zhenghua
2019ApJ...870...99S    Altcode: 2018arXiv181108571S
  Forward-modeling the emission properties in various passbands is
  important for confidently identifying magnetohydrodynamic waves in the
  structured solar corona. We examine how non-equilibrium ionization
  (NEI) affects the extreme-ultraviolet (EUV) emissions modulated by
  standing fast sausage modes (FSMs) in coronal loops, taking the Fe
  IX 171 Å and Fe XII 193 Å emission lines as examples. Starting with
  the expressions for linear FSMs in straight cylinders, we synthesize
  the specific intensities and spectral profiles for the two spectral
  lines by incorporating the self-consistently derived ionic fractions
  in the relevant contribution functions. We find that relative to the
  case where equilibrium ionization (EI) is assumed, NEI considerably
  impacts the intensity modulations, but shows essentially no effect
  on the Doppler velocities or widths. Furthermore, NEI may affect the
  phase difference between intensity variations and those in Doppler
  widths for Fe XII 193 Å when the line of sight is oblique to the loop
  axis. While this difference is 180° when EI is assumed, it is ∼90°
  when NEI is incorporated for the parameters we choose. We conclude
  that in addition to viewing angles and instrumental resolutions, NEI
  further complicates the detection of FSMs in spectroscopic measurements
  of coronal loops in the EUV passband.

---------------------------------------------------------
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: Magnetic Loops above a Small Flux-emerging Region Observed
    by IRIS, Hinode, and SDO
Authors: Huang, Zhenghua
2018ApJ...869..175H    Altcode: 2018arXiv181103219H
  I report on observations of a set of magnetic loops above a region
  with late-phase flux emergence taken by IRIS, Hinode, and SDO. The
  loop system consists of many transition-region loop threads that are
  5″-12″ in length and ∼0.″5 in width and coronal loops with
  similar length and ∼2″ width. Although the loop system consists
  of threads with different temperatures, most individual loop threads
  have temperatures in a narrow range. In the middle of the loop system,
  there is a clear systematic blueshift of about 10 km s<SUP>-1</SUP>
  in the transition region that is consistent with a flux-emerging
  picture, while a redshift of about 10 km s<SUP>-1</SUP> in the
  corona is observed. The nonthermal velocity of the loop system is
  smaller than that of the surrounding region in the transition region
  but is comparable that in the corona. The electron densities of the
  coronal counterpart of the loop system range from 1 × 10<SUP>9</SUP>
  cm<SUP>-3</SUP> to 4 × 10<SUP>9</SUP> cm<SUP>-3</SUP>. The electron
  density of a transition-region loop is also measured and found to be
  about 5 × 10<SUP>10</SUP> cm<SUP>-3</SUP>, a magnitude larger than that
  in the coronal loops. In agreement with imaging data, the temperature
  profiles derived from the differential emission measurement technique
  confirm that some of the loops have been heated to corona level. Our
  observations indicate that the flux emergence in its late phase is much
  different from that at the early stage. While the observed transition
  region is dominated by emerging flux, these emerging loops could be
  heated to corona level, and the heating (if via nonthermal processes)
  most likely takes place only after they reach the transition region
  or lower corona.

---------------------------------------------------------
Title: Helium abundance and speed difference between helium ions
    and protons in the solar wind from coronal holes, active regions,
    and quiet Sun
Authors: Fu, Hui; Madjarska, Maria S.; Li, Bo; Xia, Lidong; Huang,
   Zhenghua
2018MNRAS.478.1884F    Altcode: 2018arXiv180502880F; 2018MNRAS.tmp.1157F
  Two main models have been developed to explain the mechanisms of
  release, heating, and acceleration of the nascent solar wind, the
  wave-turbulence-driven (WTD) models and reconnection-loop-opening
  (RLO) models, in which the plasma release processes are fundamentally
  different. Given that the statistical observational properties
  of helium ions produced in magnetically diverse solar regions
  could provide valuable information for the solar wind modelling,
  we examine the statistical properties of the helium abundance
  (A<SUB>He</SUB>) and the speed difference between helium ions and
  protons (v<SUB>αp</SUB>) for coronal holes (CHs), active regions (ARs),
  and the quiet Sun (QS). We find bimodal distributions in the space of
  A<SUB>He</SUB> and v<SUB>αp</SUB>/v<SUB>A</SUB> (where v<SUB>A</SUB>
  is the local Alfvén speed) for the solar wind as a whole. The CH
  wind measurements are concentrated at higher A<SUB>He</SUB> and
  v<SUB>αp</SUB>/v<SUB>A</SUB> values with a smaller A<SUB>He</SUB>
  distribution range, while the AR and QS wind is associated with
  lower A<SUB>He</SUB> and v<SUB>αp</SUB>/v<SUB>A</SUB>, and a
  larger A<SUB>He</SUB> distribution range. The magnetic diversity
  of the source regions and the physical processes related to it are
  possibly responsible for the different properties of A<SUB>He</SUB>
  and v<SUB>αp</SUB>/v<SUB>A</SUB>. The statistical results suggest
  that the two solar wind generation mechanisms, WTD and RLO, work in
  parallel in all solar wind source regions. In CH regions WTD plays a
  major role, whereas the RLO mechanism is more important in AR and QS.

---------------------------------------------------------
Title: Two-sided-loop Jets Associated with Magnetic Reconnection
    between Emerging Loops and Twisted Filament Threads
Authors: Zheng, Ruisheng; Chen, Yao; Huang, Zhenghua; Wang, Bing;
   Song, Hongqiang; Ning, Hao
2018ApJ...861..108Z    Altcode: 2018arXiv180600957Z
  Coronal jets are always produced by magnetic reconnection between
  emerging flux and pre-existing overlying magnetic fields. When the
  overlying field is vertical/oblique or horizontal, the coronal jet will
  appear as anemone type or two-sided-loop type. Most observational jets
  are of the anemone type, and only a few two-sided-loop jets have been
  reported. Using the high-quality data from New Vacuum Solar Telescope,
  Interface Region Imaging Spectrograph, and Solar Dynamics Observatory,
  we present an example of two-sided-loop jets simultaneously observed
  in the chromosphere, transition region, and corona. The continuous
  emergence of magnetic flux brought in successively, the emergence
  of coronal loops and the slow rise of overlying horizontal filament
  threads. The following occurred sequentially: the deformation of
  the loops, the plasmoid ejection from the loop top, and pairs of loop
  brightenings and jets moving along the untwisting filament threads. All
  of the observational results indicate that magnetic reconnection
  exists between the emerging loops and the overlying horizontal filament
  threads, and it is the first example of two-sided-loop jets associated
  with ejected plasmoids and twisted overlying fields.

---------------------------------------------------------
Title: Observations of Upward Propagating Waves in the Transition
    Region and Corona above Sunspots
Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo; Fu, Hui
2018ApJ...855...65H    Altcode: 2018arXiv180107515H
  We present observations of persistent oscillations of some bright
  features in the upper-chromosphere/transition region above sunspots
  taken by IRIS SJ 1400 Å and upward propagating quasi-periodic
  disturbances along coronal loops rooted in the same region taken by
  the AIA 171 Å passband. The oscillations of the features are cyclic
  oscillatory motions without any obvious damping. The amplitudes of
  the spatial displacements of the oscillations are about 1″. The
  apparent velocities of the oscillations are comparable to the sound
  speed in the chromosphere, but the upward motions are slightly larger
  than that of the downward. The intensity variations can take 24%-53%
  of the background, suggesting nonlinearity of the oscillations. The
  FFT power spectra of the oscillations show a dominant peak at a
  period of about 3 minutes, which is consistent with the omnipresent
  3 minute oscillations in sunspots. The amplitudes of the intensity
  variations of the upward propagating coronal disturbances are 10%-15%
  of the background. The coronal disturbances have a period of about 3
  minutes, and propagate upward along the coronal loops with apparent
  velocities in a range of 30 ∼ 80 km s<SUP>-1</SUP>. We propose a
  scenario in which the observed transition region oscillations are
  powered continuously by upward propagating shocks, and the upward
  propagating coronal disturbances can be the recurrent plasma flows
  driven by shocks or responses of degenerated shocks that become slow
  magnetic-acoustic waves after heating the plasma in the coronal loops
  at their transition-region bases.

---------------------------------------------------------
Title: A Magnetic Reconnection Event in the Solar Atmosphere Driven
    by Relaxation of a Twisted Arch Filament System
Authors: Huang, Zhenghua; Mou, Chaozhou; Fu, Hui; Deng, Linhua; Li,
   Bo; Xia, Lidong
2018ApJ...853L..26H    Altcode: 2018arXiv180105983H
  We present high-resolution observations of a magnetic reconnection
  event in the solar atmosphere taken with the New Vacuum Solar Telescope,
  Atmospheric Imaging Assembly (AIA), and Helioseismic and Magnetic Imager
  (HMI). The reconnection event occurred between the threads of a twisted
  arch filament system (AFS) and coronal loops. Our observations reveal
  that the relaxation of the twisted AFS drives some of its threads to
  encounter the coronal loops, providing inflows of the reconnection. The
  reconnection is evidenced by flared X-shape features in the AIA images,
  a current-sheet-like feature apparently connecting post-reconnection
  loops in the Hα + 1 Å images, small-scale magnetic cancelation in
  the HMI magnetograms and flows with speeds of 40-80 km s<SUP>-1</SUP>
  along the coronal loops. The post-reconnection coronal loops seen in the
  AIA 94 Å passband appear to remain bright for a relatively long time,
  suggesting that they have been heated and/or filled up by dense plasmas
  previously stored in the AFS threads. Our observations suggest that the
  twisted magnetic system could release its free magnetic energy into the
  upper solar atmosphere through reconnection processes. While the plasma
  pressure in the reconnecting flux tubes are significantly different,
  the reconfiguration of field lines could result in transferring of
  mass among them and induce heating therein.

---------------------------------------------------------
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: The Plasma Parameters and Geometry of Cool and Warm Active
    Region Loops
Authors: Xie, Haixia; Madjarska, Maria S.; Li, Bo; Huang, Zhenghua;
   Xia, Lidong; Wiegelmann, Thomas; Fu, Hui; Mou, Chaozhou
2017ApJ...842...38X    Altcode: 2017arXiv170502564X
  How the solar corona is heated to high temperatures remains an unsolved
  mystery in solar physics. In the present study we analyze observations
  of 50 whole active region loops taken with the Extreme-ultraviolet
  Imaging Spectrometer on board the Hinode satellite. Eleven loops were
  classified as cool loops (&lt;1 MK) and 39 as warm loops (1-2 MK). We
  study their plasma parameters, such as densities, temperatures,
  filling factors, nonthermal velocities, and Doppler velocities. We
  combine spectroscopic analysis with linear force-free magnetic field
  extrapolation to derive the 3D structure and positioning of the loops,
  their lengths and heights, and the magnetic field strength along
  the loops. We use density-sensitive line pairs from Fe xii, Fe xiii,
  Si x, and Mg vii ions to obtain electron densities by taking special
  care of intensity background subtraction. The emission measure loci
  method is used to obtain the loop temperatures. We find that the loops
  are nearly isothermal along the line of sight. Their filling factors
  are between 8% and 89%. We also compare the observed parameters with
  the theoretical Rosner-Tucker-Vaiana (RTV) scaling law. We find that
  most of the loops are in an overpressure state relative to the RTV
  predictions. In a follow-up study, we will report a heating model of a
  parallel-cascade-based mechanism and will compare the model parameters
  with the loop plasma and structural parameters derived here.

---------------------------------------------------------
Title: Charge States and FIP Bias of the Solar Wind from Coronal
    Holes, Active Regions, and Quiet Sun
Authors: Fu, Hui; Madjarska, Maria S.; Xia, LiDong; Li, Bo; Huang,
   ZhengHua; Wangguan, Zhipeng
2017ApJ...836..169F    Altcode: 2017arXiv170107610F
  Connecting in situ measured solar-wind plasma properties with typical
  regions on the Sun can provide an effective constraint and test to
  various solar wind models. We examine the statistical characteristics of
  the solar wind with an origin in different types of source regions. We
  find that the speed distribution of coronal-hole (CH) wind is bimodal
  with the slow wind peaking at ∼400 km s<SUP>-1</SUP> and the fast at
  ∼600 km s<SUP>-1</SUP>. An anti-correlation between the solar wind
  speeds and the O<SUP>7+</SUP>/O<SUP>6+</SUP> ion ratio remains valid in
  all three types of solar wind as well during the three studied solar
  cycle activity phases, I.e., solar maximum, decline, and minimum. The
  {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}} range and its average values
  all decrease with the increasing solar wind speed in different types of
  solar wind. The {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}} range (0.06-0.40,
  first ionization potential (FIP) bias range 1-7) for active region
  wind is wider than for CH wind (0.06-0.20, FIP bias range 1-3),
  while the minimum value of {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}}
  (∼ 0.06) does not change with the variation of speed, and it
  is similar for all source regions. The two-peak distribution
  of CH wind and the anti-correlation between the speed and
  O<SUP>7+</SUP>/O<SUP>6+</SUP> in all three types of solar wind can
  be explained qualitatively by both the wave-turbulence-driven and
  reconnection-loop-opening (RLO) models, whereas the distribution
  features of {N}<SUB>{Fe</SUB>}/{N}<SUB>{{O</SUB>}} in different
  source regions of solar wind can be explained more reasonably by the
  RLO models.

---------------------------------------------------------
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: Narrow-line-width UV Bursts in the Transition Region above
    Sunspots Observed by IRIS
Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo;
   Madjarska, Maria S.; Fu, Hui; Mou, Chaozhou; Xie, Haixia
2016ApJ...829L..30H    Altcode: 2016arXiv160804892H
  Various small-scale structures abound in the solar atmosphere above
  active regions, playing an important role in the dynamics and evolution
  therein. We report on a new class of small-scale transition region
  structures in active regions, characterized by strong emissions but
  extremely narrow Si IV line profiles as found in observations taken
  with the Interface Region Imaging Spectrograph (IRIS). Tentatively
  named as narrow-line-width UV bursts (NUBs), these structures are
  located above sunspots and comprise one or multiple compact bright
  cores at sub-arcsecond scales. We found six NUBs in two data sets
  (a raster and a sit-and-stare data set). Among these, four events
  are short-lived with a duration of ∼10 minutes, while two last
  for more than 36 minutes. All NUBs have Doppler shifts of 15-18 km
  s<SUP>-1</SUP>, while the NUB found in sit-and-stare data possesses
  an additional component at ∼50 km s<SUP>-1</SUP> found only in the
  C II and Mg II lines. Given that these events are found to play a
  role in the local dynamics, it is important to further investigate
  the physical mechanisms that generate these phenomena and their role
  in the mass transport in sunspots.

---------------------------------------------------------
Title: Transition region bright dots in active regions observed by
    the interface region imaging spectrograph
Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo;
   Madjarska, Maria S.; Fu, Hui
2016AIPC.1720b0001H    Altcode: 2018arXiv180308294H
  The Interface Region Imaging Spectrograph (IRIS) reveals numerous
  small-scale (sub-arcsecond) brightenings that appear as bright dots
  sparkling the solar transition region in active regions. Here,
  we report a statistical study on these transition-region bright
  dots. We use an automatic approach to identify 2742 dots in a Si IV
  raster image. We find that the average spatial size of the dots is
  0.8 arcsec<SUP>2</SUP> and most of them are located in the faculae
  area. Their Doppler velocities obtained from the Si IV 1394 Å line
  range from -20 to 20 km s<SUP>-1</SUP>. Among these 2742 dots, 1224 are
  predominantly blue-shifted and 1518 are red-shifted. Their non-thermal
  velocities range from 4 to 50 km s<SUP>-1</SUP> with an average of
  24 km s<SUP>-1</SUP>. We speculate that the bright dots studied here
  are small-scale impulsive energetic events that can heat the active
  region corona.

---------------------------------------------------------
Title: Magnetic Flux Supplement to Coronal Bright Points
Authors: Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong; Madjarska,
   Maria S.; Li, Bo; Fu, Hui; Jiao, Fangran; Hou, Zhenyong
2016ApJ...818....9M    Altcode: 2015arXiv151109215M
  Coronal bright points (BPs) are associated with magnetic bipolar
  features (MBFs) and magnetic cancellation. Here we investigate how
  BP-associated MBFs form and how the consequent magnetic cancellation
  occurs. We analyze longitudinal magnetograms from the Helioseismic and
  Magnetic Imager to investigate the photospheric magnetic flux evolution
  of 70 BPs. From images taken in the 193 Å passband of the Atmospheric
  Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from
  2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three
  processes, namely, emergence, convergence, and local coalescence of
  the magnetic fluxes. The formation of an MBF can involve more than one
  of these processes. Out of the 70 cases, flux emergence is the main
  process of an MBF buildup of 52 BPs, mainly convergence is seen in 28,
  and 14 cases are associated with local coalescence. For MBFs formed by
  bipolar emergence, the time difference between the flux emergence and
  the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr
  with an average of 1.3 hr. While magnetic cancellation is found in all
  70 BPs, it can occur in three different ways: (I) between an MBF and
  small weak magnetic features (in 33 BPs); (II) within an MBF with the
  two polarities moving toward each other from a large distance (34 BPs);
  (III) within an MBF whose two main polarities emerge in the same place
  simultaneously (3 BPs). While an MBF builds up the skeleton of a BP,
  we find that the magnetic activities responsible for the BP heating
  may involve small weak fields.

---------------------------------------------------------
Title: Cool Transition Region Loops Observed by the Interface Region
    Imaging Spectrograph
Authors: Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S.
2015ApJ...810...46H    Altcode: 2015arXiv150707594H
  We report on the first Interface Region Imaging Spectrograph (IRIS)
  study of cool transition region loops, a class of loops that has
  received little attention in the literature. A cluster of such loops
  was observed on the solar disk in active region NOAA11934, in the
  Si iv 1402.8 Å spectral raster and 1400 Å slit-jaw images. We
  divide the loops into three groups and study their dynamics. The
  first group comprises relatively stable loops, with 382-626 km
  cross-sections. Observed Doppler velocities are suggestive of siphon
  flows, gradually changing from -10 km s<SUP>-1</SUP> at one end to 20
  km s<SUP>-1</SUP> at the other end of the loops. Nonthermal velocities
  of 15 ∼ 25 km s<SUP>-1</SUP> were determined. Magnetic cancellation
  with a rate of 10<SUP>15</SUP> Mx s<SUP>-1</SUP> is found at the
  blueshifted footpoints. These physical properties suggest that these
  loops are impulsively heated by magnetic reconnection, and the siphon
  flows play an important role in the energy redistribution. The second
  group corresponds to two footpoints rooted in mixed-magnetic-polarity
  regions, where magnetic cancellation with a rate of 10<SUP>15</SUP> Mx
  s<SUP>-1</SUP> and explosive-event line profiles with enhanced wings
  of up to 200 km s<SUP>-1</SUP> were observed. In the third group,
  interaction between two cool loop systems is observed. Evidence for
  magnetic reconnection between the two loop systems is reflected in the
  explosive-event line profiles and magnetic cancellation with a rate of
  3× {10}<SUP>15</SUP> Mx s<SUP>-1</SUP> observed in the corresponding
  area. The IRIS has provided opportunity for in-depth investigations
  of cool transition region loops. Further numerical experiments are
  crucial for understanding their physics and their roles in the coronal
  heating processes.

---------------------------------------------------------
Title: Sources of Quasi-periodic Propagating Disturbances above a
    Solar Polar Coronal Hole
Authors: Jiao, Fangran; Xia, Lidong; Li, Bo; Huang, Zhenghua; Li,
   Xing; Chandrashekhar, Kalugodu; Mou, Chaozhou; Fu, Hui
2015ApJ...809L..17J    Altcode: 2015arXiv150708440J
  Quasi-periodic propagating disturbances (PDs) are ubiquitous in polar
  coronal holes on the Sun. It remains unclear as to what generates
  PDs. In this work, we investigate how the PDs are generated in the solar
  atmosphere by analyzing a four-hour data set taken by the Atmospheric
  Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We find
  convincing evidence that spicular activities in the solar transition
  region, as seen in the AIA 304 Å passband, are responsible for PDs
  in the corona as revealed in the AIA 171 Å images. We conclude that
  spicules are an important source that triggers coronal PDs.

---------------------------------------------------------
Title: Coronal Sources and In Situ Properties of the Solar Winds
    Sampled by ACE During 1999 - 2008
Authors: Fu, Hui; Li, Bo; Li, Xing; Huang, Zhenghua; Mou, Chaozhou;
   Jiao, Fangran; Xia, Lidong
2015SoPh..290.1399F    Altcode: 2015arXiv150500407F; 2015SoPh..tmp...50F
  We identify the coronal sources of the solar winds sampled by the
  ACE spacecraft during 1999 - 2008 and examine the in situ solar wind
  properties as a function of wind sources. The standard two-step mapping
  technique is adopted to establish the photospheric footpoints of the
  magnetic flux tubes along which the ACE winds flow. The footpoints
  are then placed in the context of EIT 284 Å images and photospheric
  magnetograms, allowing us to categorize the sources into four groups:
  coronal holes (CHs), active regions (ARs), the quiet Sun (QS), and
  "undefined". This practice also enables us to establish the response to
  solar activity of the fractions occupied by each type of solar wind,
  and of their speeds and O<SUP>7+</SUP>/O<SUP>6+</SUP> ratios measured
  in situ. We find that during the maximum phase, the majority of ACE
  winds originate from ARs. During the declining phase, CHs and ARs
  are equally important contributors to the ACE solar winds. The QS
  contribution increases with decreasing solar activity and maximizes
  in the minimum phase when the QS appears to be the primary supplier
  of the ACE winds. With decreasing activity, the winds from all
  sources tend to become cooler, as represented by the increasingly low
  O<SUP>7+</SUP>/O<SUP>6+</SUP> ratios. On the other hand, during each
  activity phase, the AR winds tend to be the slowest and are associated
  with the highest O<SUP>7+</SUP>/O<SUP>6+</SUP> ratios, while the
  CH winds correspond to the other extreme, with the QS winds lying in
  between. Applying the same analysis method to the slow winds alone, here
  defined as the winds with speeds lower than 500 km s<SUP>−1</SUP>, we
  find basically the same overall behavior, as far as the contributions
  of individual groups of sources are concerned. This statistical study
  indicates that QS regions are an important source of the solar wind
  during the minimum phase.

---------------------------------------------------------
Title: Explosive Events on a Subarcsecond Scale in IRIS Observations:
    A Case Study
Authors: Huang, Zhenghua; Madjarska, Maria S.; Xia, Lidong; Doyle,
   J. G.; Galsgaard, Klaus; Fu, Hui
2014ApJ...797...88H    Altcode: 2014arXiv1409.6425H
  We present a study of a typical explosive event (EE) at subarcsecond
  scale witnessed by strong non-Gaussian profiles with blue- and
  redshifted emission of up to 150 km s<SUP>-1</SUP> seen in the
  transition region Si IV 1402.8 Å, and the chromospheric Mg II
  k 2796.4 Å and C II 1334.5 Å observed by the Interface Region
  Imaging Spectrograph (IRIS) at unprecedented spatial and spectral
  resolution. For the first time an EE is found to be associated with
  very small-scale (~120 km wide) plasma ejection followed by retraction
  in the chromosphere. These small-scale jets originate from a compact
  bright-point-like structure of ~1.”5 size as seen in the IRIS 1330
  Å images. SDO/AIA and SDO/HMI co-observations show that the EE lies
  in the footpoint of a complex loop-like brightening system. The EE is
  detected in the higher temperature channels of AIA 171 Å, 193 Å,
  and 131 Å, suggesting that it reaches a higher temperature of log
  T = 5.36 ± 0.06 (K). Brightenings observed in the AIA channels with
  durations 90-120 s are probably caused by the plasma ejections seen
  in the chromosphere. The wings of the C II line behave in a similar
  manner to the Si IV'S, indicating close formation temperatures, while
  the Mg II k wings show additional Doppler-shifted emission. Magnetic
  convergence or emergence followed by cancellation at a rate of 5 ×
  10<SUP>14</SUP> Mx s<SUP>-1</SUP> is associated with the EE region. The
  combined changes of the locations and the flux of different magnetic
  patches suggest that magnetic reconnection must have taken place. Our
  results challenge several theories put forward in the past to explain
  non-Gaussian line profiles, i.e., EEs. Our case study on its own,
  however, cannot reject these theories; thus, further in-depth studies
  on the phenomena producing EEs are required.

---------------------------------------------------------
Title: Measurements of Outflow Velocities in on-disk Plumes from
    EIS/Hinode Observations
Authors: Fu, Hui; Xia, Lidong; Li, Bo; Huang, Zhenghua; Jiao, Fangran;
   Mou, Chaozhou
2014ApJ...794..109F    Altcode: 2014arXiv1408.5473F
  The contribution of plumes to the solar wind has been subject to
  hot debate in the past decades. The EUV Imaging Spectrometer (EIS)
  on board Hinode provides a unique means to deduce outflow velocities
  at coronal heights via direct Doppler shift measurements of coronal
  emission lines. Such direct Doppler shift measurements were not possible
  with previous spectrometers. We measure the outflow velocity at coronal
  heights in several on-disk long-duration plumes, which are located in
  coronal holes (CHs) and show significant blueshifts throughout the
  entire observational period. In one case, a plume is measured four
  hours apart. The deduced outflow velocities are consistent, suggesting
  that the flows are quasi-steady. Furthermore, we provide an outflow
  velocity profile along the plumes, finding that the velocity corrected
  for the line-of-sight effect can reach 10 km s<SUP>-1</SUP> at 1.02
  R <SUB>⊙</SUB>, 15 km s<SUP>-1</SUP> at 1.03 R <SUB>⊙</SUB>, and
  25 km s<SUP>-1</SUP> at 1.05 R <SUB>⊙</SUB>. This clear signature of
  steady acceleration, combined with the fact that there is no significant
  blueshift at the base of plumes, provides an important constraint on
  plume models. At the height of 1.03 R <SUB>⊙</SUB>, EIS also deduced a
  density of 1.3 × 10<SUP>8</SUP> cm<SUP>-3</SUP>, resulting in a proton
  flux of about 4.2 × 10<SUP>9</SUP> cm<SUP>-2</SUP> s<SUP>-1</SUP>
  scaled to 1 AU, which is an order of magnitude higher than the proton
  input to a typical solar wind if a radial expansion is assumed. This
  suggests that CH plumes may be an important source of the solar wind.

---------------------------------------------------------
Title: Oscillations in a Sunspot with Light Bridges
Authors: Yuan, Ding; Nakariakov, Valery M.; Huang, Zhenghua; Li, Bo;
   Su, Jiangtao; Yan, Yihua; Tan, Baolin
2014ApJ...792...41Y    Altcode: 2014arXiv1407.1544Y
  The Solar Optical Telescope on board Hinode observed a sunspot (AR
  11836) with two light bridges (LBs) on 2013 August 31. We analyzed
  a two-hour Ca II H emission intensity data set and detected strong
  five-minute oscillation power on both LBs and in the inner penumbra. The
  time-distance plot reveals that the five-minute oscillation phase
  does not vary significantly along the thin bridge, indicating that
  the oscillations are likely to originate from underneath it. The slit
  taken along the central axis of the wide LB exhibits a standing wave
  feature. However, at the center of the wide bridge, the five-minute
  oscillation power is found to be stronger than at its sides. Moreover,
  the time-distance plot across the wide bridge exhibits a herringbone
  pattern that indicates a counter-stream of two running waves, which
  originated at the bridge's sides. Thus, the five-minute oscillations
  on the wide bridge also resemble the properties of running penumbral
  waves. The five-minute oscillations are suppressed in the umbra, while
  the three-minute oscillations occupy all three cores of the sunspot's
  umbra, separated by the LBs. The three-minute oscillations were found
  to be in phase at both sides of the LBs. This may indicate that either
  LBs do not affect umbral oscillations, or that umbral oscillations
  at different umbral cores share the same source. It also indicates
  that LBs are rather shallow objects situated in the upper part of the
  umbra. We found that umbral flashes (UFs) follow the life cycles of
  umbral oscillations with much larger amplitudes. They cannot propagate
  across LBs. UFs dominate the three-minute oscillation power within
  each core; however, they do not disrupt the phase of umbral oscillation.

---------------------------------------------------------
Title: Evolution of magnetic field corresponding to X-ray brightening
    events in coronal holes and quiet Sun
Authors: Huang, Zhenghua; Madjarska, Maria; Doyle, Gerry; Lamb, Derek
2013IAUS..294..155H    Altcode:
  We study the magnetic field structure and evolution for 26 X-ray
  brightening events in coronal holes and quiet Sun regions, including
  bright points and jets. We found that all brightening events are
  associated with bipolar regions and caused by magnetic flux emergence
  followed by cancellation. The emission fluctuations seen in the X-ray
  bright points are associated with reoccurring magnetic cancellation
  in the footpoints. An X-ray jet presents similar magnetic behaviour in
  the footpoints but its magnetic flux cancellation rate is much higher
  than in the bright point. Comparing coronal holes and the quiet Sun, we
  do not find differences in their corresponding magnetic field behavior.

---------------------------------------------------------
Title: Jets from coronal holes - possible source of the slow
    solar wind
Authors: Madjarska, Maria; Huang, Zhenghua; Subramanian, Srividya;
   Doyle, Gerry
2013EGUGA..15.2455M    Altcode:
  We will report on statistical studies on the occurrence rate, plasma
  properties, dynamics and structural evolution, including the magnetic
  field evolution, of small-scale transients in and along the boundaries
  of equatorial coronal holes. A comparison is made with quiet-Sun
  transients. We use multi-instrument observations from the photosphere
  to the corona comprising imaging, magnetogram and imaging spectroscopy
  data from EIS, XRT and SOT on board Hinode and SUMER onboard SoHO. The
  visual analysis of these transients reveals that around 70% of them
  in equatorial, polar and transient coronal holes and their boundaries
  show expanding loop structures and/or collimated outflows, i.e. jets. In
  the quiet Sun only 30% of the brightenings show flows with most of them
  appearing to be contained in the solar corona by closed magnetic field
  lines. This strongly suggests that magnetic reconnection of co-spatial
  open and closed magnetic field lines creates the necessary conditions
  for plasma outflows to large distances. The ejected plasma always
  originates from preexisting or newly emerging (at X-ray temperatures)
  bright points. We will discuss in detail the evolution of individual
  jets and the possibility whether these phenomena could be one of the
  sources of the slow solar wind.