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
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
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.
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.
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.
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
Bibcode: 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 Fe) and helium abundance (A He)
for T3 ICMEs are less than 12% and 7%, respectively. The Q Fe
and A He 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 Fe) inside
ICMEs is associated with higher A He. The Q Fe
and A He are both positively correlated with the flare
intensities. The A He 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
Bibcode: 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.
Aims: We investigate the relationship between chromospheric jets
and coronal activities, such as coronal plumes and jets.
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.
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−1, 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−1. 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−1, suggesting that both cool and hot
jets can be coupled.
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.
Movies associated to Figs. 1, 5, and 7 are available at https://www.aanda.org
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
Bibcode: 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
Bibcode: 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 Mm2. 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
Mm2 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-1 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
Bibcode: 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
Bibcode: 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-1 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-1. The temperature, emission measure, and density of
these blobs are about 3 MK, 2.0 × 1028 cm-5, and
1.2 × 1010 cm-3, 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-1 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
Bibcode: 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
Bibcode: 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 ×104arcsec2 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.
Bibcode: 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 (AHe), 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 AHe 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
Bibcode: 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
Bibcode: 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-1. 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-2 with an error of ∼1.0 km s-2
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-1.
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
Bibcode: 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-1) 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-1. 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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/vA
(where vA is the local Alfven speed) for the solar wind as
a whole. The CH windmeasurements are concentrated at higher A_He and
v_αp/vA 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
Bibcode: 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
Bibcode: 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-1 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
Bibcode: 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
Bibcode: 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
Bibcode: 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-1
in the transition region that is consistent with a flux-emerging
picture, while a redshift of about 10 km s-1 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 × 109
cm-3 to 4 × 109 cm-3. The electron
density of a transition-region loop is also measured and found to be
about 5 × 1010 cm-3, 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
Bibcode: 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
(AHe) and the speed difference between helium ions and
protons (vαp) for coronal holes (CHs), active regions (ARs),
and the quiet Sun (QS). We find bimodal distributions in the space of
AHe and vαp/vA (where vA
is the local Alfvén speed) for the solar wind as a whole. The CH
wind measurements are concentrated at higher AHe and
vαp/vA values with a smaller AHe
distribution range, while the AR and QS wind is associated with
lower AHe and vαp/vA, and a
larger AHe distribution range. The magnetic diversity
of the source regions and the physical processes related to it are
possibly responsible for the different properties of AHe
and vαp/vA. 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
Bibcode: 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
Bibcode: 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-1. 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
Bibcode: 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-1
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
Bibcode: 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 ×
1012 cm-3, 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
Bibcode: 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 (<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
Bibcode: 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-1 and the fast at
∼600 km s-1. An anti-correlation between the solar wind
speeds and the O7+/O6+ 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}{Fe}/{N}{{O}} range and its average values
all decrease with the increasing solar wind speed in different types of
solar wind. The {N}{Fe}/{N}{{O}} 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}{Fe}/{N}{{O}}
(∼ 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
O7+/O6+ 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}{Fe}/{N}{{O}} 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
Bibcode: 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
Bibcode: 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-1, while the NUB found in sit-and-stare data possesses
an additional component at ∼50 km s-1 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
Bibcode: 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 arcsec2 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-1. 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-1 with an average of
24 km s-1. 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
Bibcode: 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.
Bibcode: 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-1 at one end to 20
km s-1 at the other end of the loops. Nonthermal velocities
of 15 ∼ 25 km s-1 were determined. Magnetic cancellation
with a rate of 1015 Mx s-1 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 1015 Mx
s-1 and explosive-event line profiles with enhanced wings
of up to 200 km s-1 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}15 Mx s-1 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
Bibcode: 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
Bibcode: 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 O7+/O6+ 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
O7+/O6+ ratios. On the other hand, during each
activity phase, the AR winds tend to be the slowest and are associated
with the highest O7+/O6+ 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−1, 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
Bibcode: 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-1 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 ×
1014 Mx s-1 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
Bibcode: 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-1 at 1.02
R ⊙, 15 km s-1 at 1.03 R ⊙, and
25 km s-1 at 1.05 R ⊙. 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 ⊙, EIS also deduced a
density of 1.3 × 108 cm-3, resulting in a proton
flux of about 4.2 × 109 cm-2 s-1
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
Bibcode: 2014ApJ...792...41Y
Altcode: 2014arXiv1407.1544Y
The Solar Optical Telescope on board Hinode observed a sunspot (AR
11836) with two light bridges (LBs) on 2013 August 31. We analyzed
a two-hour Ca II H emission intensity data set and detected strong
five-minute oscillation power on both LBs and in the inner penumbra. The
time-distance plot reveals that the five-minute oscillation phase
does not vary significantly along the thin bridge, indicating that
the oscillations are likely to originate from underneath it. The slit
taken along the central axis of the wide LB exhibits a standing wave
feature. However, at the center of the wide bridge, the five-minute
oscillation power is found to be stronger than at its sides. Moreover,
the time-distance plot across the wide bridge exhibits a herringbone
pattern that indicates a counter-stream of two running waves, which
originated at the bridge's sides. Thus, the five-minute oscillations
on the wide bridge also resemble the properties of running penumbral
waves. The five-minute oscillations are suppressed in the umbra, while
the three-minute oscillations occupy all three cores of the sunspot's
umbra, separated by the LBs. The three-minute oscillations were found
to be in phase at both sides of the LBs. This may indicate that either
LBs do not affect umbral oscillations, or that umbral oscillations
at different umbral cores share the same source. It also indicates
that LBs are rather shallow objects situated in the upper part of the
umbra. We found that umbral flashes (UFs) follow the life cycles of
umbral oscillations with much larger amplitudes. They cannot propagate
across LBs. UFs dominate the three-minute oscillation power within
each core; however, they do not disrupt the phase of umbral oscillation.
Title: 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
Bibcode: 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
Bibcode: 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.