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.