19 results on '"Limei Yan"'
Search Results
2. Ancient Auroral Records Compiled From Korean Historical Books
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Kaihua Xu, Limei Yan, Xinan Yue, Yong Wei, Yuqi Wang, Si Chen, and Fei He
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Geophysics ,Geography ,Space and Planetary Science ,Climatology ,Airglow ,Space weather - Published
- 2021
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3. Evolution of the X-ray Profile of the Crab Pulsar
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Jian-Ping Yuan, Ming-Yu Ge, Hao Tong, Yu Lu, ShiJie Zheng, Fangjun Lu, Shuang-Nan Zhang, and Limei Yan
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Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Crab Pulsar ,Astrophysics::High Energy Astrophysical Phenomena ,X-ray ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Span (engineering) ,01 natural sciences ,Flux ratio ,010305 fluids & plasmas ,Pulse (physics) ,Pulsar ,Space and Planetary Science ,0103 physical sciences ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics - Abstract
Using the archive data from the Rossi X-ray Timing Explorer ({\sl RXTE}), we have studied the evolution of the X-ray profile of the Crab pulsar in a time span of 11 years. The X-ray profiles, as characterized by a few parameters, changed slightly but significantly in these years: the separation of the two peaks increased with a rate $0.88\pm0.20\,\textordmasculine$\,per century, the flux ratio of the second pulse to the first pulse decreased with $(3.64\pm0.86)\times10^{-2}$\,per century, and the pulse widths of the two pulses descended with $1.44\pm0.15\,\textordmasculine$\, and $1.09\pm0.73\,\textordmasculine$\,per century, respectively. The evolutionary trends of the above parameters are similar to the radio results, but the values are different. We briefly discussed the constraints of these X-ray properties on the geometry of the emission region of this pulsar. more...
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- 2019
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4. Statistical Properties of Solar Wind Upstream of Mars: MAVEN Observations
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Jiansen He, Di Liu, Malcolm Dunlop, Zhaojin Rong, Yong Wei, Jiawei Gao, Kai Fan, Lucy Klinger, and Limei Yan
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Physics ,Solar wind ,Planetary science ,Space and Planetary Science ,Astronomy and Astrophysics ,Upstream (networking) ,Mars Exploration Program ,Astrobiology - Abstract
Using the data sets of Mars Atmosphere and Volatile EvolutioN and OMNI for the period 2014 October 10–2020 February 14 and the heliocentric distance of 1–1.66 au, we investigate the statistical properties of solar wind upstream of Mars for the first time. The key parameters, including interplanetary magnetic field (IMF), proton density (N), bulk velocity (∣ V ∣), and dynamic pressure (P dyn), are surveyed with regard to variations of solar activity level and heliocentric distance. We find that the parameters ∣IMF∣, N, and P dyn monotonously decrease with heliocentric distance. Both ∣IMF∣ and P dyn are generally stronger at a higher solar activity level (F 10.7 ≥ 70 sfu), while such activity has little relevance to N. In contrast, ∣ V ∣ basically keeps a median of about 370 km s−1 and is insensitive to the solar activity level and heliocentric distance. We also find that the IMF upstream of Mars at the higher solar activity level has a much smaller spiral angle in the inward sector; thus, IMF seems “straighter” than that in the outward sector, although that is not so for the inward sector of the upstream of Earth. Our statistical survey can be used as a reference for upstream solar wind of Mars at 1.4 ∼ 1.7 au, and could benefit the studies on solar wind as well as the Martian space environment. more...
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- 2021
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5. Influence of intermittency on the anisotropy of magnetic structure functions of solar wind turbulence
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Jiansen He, Limei Yan, Chuanyi Tu, Eckart Marsch, Zhongtian Pei, Xin Wang, and Linghua Wang
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Physics ,Spectral index ,Turbulence ,01 natural sciences ,Spectral line ,law.invention ,Magnetic field ,Computational physics ,Solar wind ,Geophysics ,Classical mechanics ,Space and Planetary Science ,law ,Intermittency ,0103 physical sciences ,010306 general physics ,Anisotropy ,010303 astronomy & astrophysics ,Scaling - Abstract
Intermittency appears to be connected with the spectral anisotropy of solar wind turbulence. We use the Local Intermittency Measure to identify and remove intermittency from the magnetic field data measured by the Ulysses spacecraft in fast solar wind. Structure functions are calculated based on the time sequences as obtained before and after removing intermittency and arranged by time scale (τ) and ΘRB (the angle between local mean magnetic field B0 and radial direction R). Thus, the scaling exponent (ξ(p, ΘRB)) of every structure function of order (p) is obtained for different angles. Before removing intermittency, ξ(p, ΘRB) shows a distinctive dependence on ΘRB: from monofractal scaling law at ΘRB ~0° to multifractal scaling law at ΘRB ~90°. In contrast after eliminating the intermittency, ξ(p, ΘRB) is found to be more monofractal for all ΘRB. The extended structure-function model is applied to ξ(p, ΘRB), revealing differences of its fitting parameters α (a proxy of the power spectral index) and P1 (fragmentation fraction) for the cases with and without intermittency. Parameter α shows an evident angular trend falling from 1.9 to 1.6 for the case with intermittency but has a relatively flat profile around 1.8 for the case without intermittency. Parameter P1 rises from around 0.5 to above 0.8 with increasing ΘRB for the intermittency case and is located between 0.5 and 0.8 for the case lacking intermittency. Therefore, we may infer that it is the anisotropy of intermittency that causes the scaling anisotropy of energy spectra and the unequal fragmentation of energy cascading. more...
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- 2016
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6. Time evolution of the X-ray and gamma-ray fluxes of the Crab pulsar
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Youli Tuo, Fangjun Lu, Ming-Yu Ge, Limei Yan, ShiJie Zheng, Zhuo Li, L. M. Song, and J. L. Qu
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Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,010308 nuclear & particles physics ,Crab Pulsar ,Astrophysics::High Energy Astrophysical Phenomena ,Proportional counter ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Spectral line ,law.invention ,Luminosity ,Telescope ,High Energy Physics - Phenomenology ,High Energy Physics - Phenomenology (hep-ph) ,Pulsar ,Spitzer Space Telescope ,Space and Planetary Science ,law ,0103 physical sciences ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,Fermi Gamma-ray Space Telescope - Abstract
We studied the evolution of the X-ray and gamma-ray spectra of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer (RXTE) and 9-year observations from the Fermi Gamma-ray Space Telescope (FGST). By fitting the spectrum of each observation, we obtained the corresponding flux, and then analysed the long term evolution of the X-ray (or gamma-ray) luminosities as well as their correlations with the spin down power of the pulsar. The X-ray flux in 5-60 keV obtained by the Proportional Counter Array (PCA) of RXTE decreases with a rate of (-2.4+/-0.4)*10^(-14) erg cm^(-2) s^(-1) per day. The X-ray flux in 15-250 keV obtained by the High Energy X-ray Timing Experiment (HEXTE) of RXTE and the gamma-ray flux in 0.1-300 GeV by the Large Area Telescope (LAT) onboard FGST show similar decreasing trend, but are unsignificant statistically. The 5--60 keV X-ray luminosity L_(X) is correlated with the spin down power L_(sd) by L_(X) propto L_(sd)^(1.6+/-0.3), which is similar to the statistical results for young pulsars., 21 pages, 4 figures, 2 tables,accepted for publication in ApJ more...
- Published
- 2018
7. Turbulence and Heating in the Flank and Wake Regions of a Coronal Mass Ejection
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Jiansen He, Linghua Wang, Limei Yan, Lei Zhang, Steven Tomczyk, H. Q. Song, Hui Tian, and Siteng Fan
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Physics ,010504 meteorology & atmospheric sciences ,Turbulence ,Oscillation ,Astronomy and Astrophysics ,Magnetic reconnection ,Astrophysics ,01 natural sciences ,Vortex ,Solar wind ,Flow velocity ,Space and Planetary Science ,0103 physical sciences ,Coronal mass ejection ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Line (formation) - Abstract
As a coronal mass ejection (CME) passes, the flank and wake regions are typically strongly disturbed. Various instruments, including the Large Angle and Spectroscopic Coronagraph (LASCO), the Atmospheric Imaging Assembly (AIA), and the Coronal Multi-channel Polarimeter (CoMP), observed a CME close to the east limb on 26 October 2013. A hot ( ${\approx}\,10~\mbox{MK}$ ) rising blob was detected on the east limb, with an initial ejection flow speed of ${\approx}\, 330~\mbox{km}\,\mbox{s}^{-1}$ . The magnetic structures on both sides and in the wake of the CME were strongly distorted, showing initiation of turbulent motions with Doppler-shift oscillations enhanced from ${\approx}\, \pm 3~\mbox{km}\,\mbox{s}^{-1}$ to ${\approx}\, \pm 15~\mbox{km}\,\mbox{s}^{-1}$ and effective thermal velocities from ${\approx}\,30~\mbox{km}\,\mbox{s}^{-1}$ to ${\approx}\,60~\mbox{km}\,\mbox{s}^{-1}$ , according to the CoMP observations at the Fe xiii line. The CoMP Doppler-shift maps suggest that the turbulence behaved differently at various heights; it showed clear wave-like torsional oscillations at lower altitudes, which are interpreted as the antiphase oscillation of an alternating red/blue Doppler shift across the strands at the flank. The turbulence seems to appear differently in the channels of different temperatures. Its turnover time was ${\approx}\,1000$ seconds for the Fe 171 A channel, while it was ${\approx}\,500$ seconds for the Fe 193 A channel. Mainly horizontal swaying rotations were observed in the Fe 171 A channel, while more vertical vortices were seen in the Fe 193 A channel. The differential-emission-measure profiles in the flank and wake regions have two components that evolve differently: the cool component decreased over time, evidently indicating a drop-out of cool materials due to ejection, while the hot component increased dramatically, probably because of the heating process, which is suspected to be a result of magnetic reconnection and turbulence dissipation. These results suggest a new turbulence-heating scenario of the solar corona and solar wind. more...
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- 2018
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8. Insight-HXMT observations of the New Black Hole Candidate MAXI J1535-571: timing analysis
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Wei Zhang, Yi-Qiao Dong, Cheng-Cheng Guo, X. L. Cao, Fu-Guo Xie, Xian Hou, Yupeng Xu, Jiancheng Wang, Xian Li, Jundan Nie, Y. G. Li, Yunchao Liu, Z. Chang, Yujuan Liu, C. L. Zou, Luhua Jiang, Y. J. Yang, W. C. Jiang, C. Z. Liu, Wei Cui, Mao-Shun Li, J. K. Deng, J. F. Zhou, Tianmeng Zhang, B. B. Wu, Jia Huo, X. H. Ma, Ju Guan, J. F. Ji, Xiaobo Li, ShaoZhen Liu, Tianran Chen, Shan-Shan Weng, Gang Chen, Yu-Dong Gu, Lian Tao, Y. X. Zhu, Li-Ming Song, Ming-Yu Ge, Xiao-Jing Liu, Bing Li, Guobao Zhang, Xue-Feng Lu, H. W. Liu, Shuinai Zhang, W. Z. Zhang, Yuan-Yuan Du, Z. L. Zhang, Y. S. Wang, Wenxiong Li, GuoQing Liu, Y. H. Tan, L. Chen, Wenfei Yu, Hsiang-Kuang Chang, S. N. Zhang, Chuan-Peng Zhang, Ya Fang Huang, Y. Nang, C. L. Zhang, Limei Yan, S. Yang, G. H. Gao, Wan-Chang Zhang, Y. P. Chen, Can Güngör, Y. B. Chen, Ti-Pei Li, M. Wu, Y. Zhang, G. F. Wang, Y. L. Tuo, J. Y. Liao, H. M. Zhang, J. W. Yang, Y. F. Zhang, Bo Lu, Xuchao Zhao, M. X. Fu, Jia Zhang, C. K. Li, H. Wang, Wei Hu, Z. Zhang, X. X. Li, Weiguang Cui, Qing-He Zhang, Zhuo Li, Qingcui Bu, Shu-Mei Jia, W. S. Wang, Shaolin Xiong, HongSheng Zhao, H. Xu, Ge Ou, Y. J. Zhang, Z. W. Li, Da-Wei Han, H. Gao, S. J. Zheng, Tao Luo, X. H. Liang, Min Gao, J. Zhao, J. L. Qu, Liang Sun, Albert K. H. Kong, Aimei Zhang, Gang Li, N. Sai, Yu-Xuan Zhu, Bin Meng, Fangjun Lu, Y. J. Jin, J. Jin, R. C. Shang, WenHui Tao, G. C. Xiao, F. Zhang, and XiangYang Wen more...
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Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Static timing analysis ,Centroid ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Phase lag ,law.invention ,Black hole ,Telescope ,Amplitude ,Space and Planetary Science ,law ,0103 physical sciences ,Modulation (music) ,Intermediate state ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics - Abstract
We present the X-ray timing results of the new black hole candidate (BHC) MAXI J1535-571 during its 2017 outburst from Hard X-ray Modulation Telescope (\emph{Insight}-HXMT) observations taken from 2017 September 6 to 23. Following the definitions given by \citet{Belloni2010}, we find that the source exhibits state transitions from Low/Hard state (LHS) to Hard Intermediate state (HIMS) and eventually to Soft Intermediate state (SIMS). Quasi-periodic oscillations (QPOs) are found in the intermediate states, which suggest different types of QPOs. With the large effective area of \emph{Insight}-HXMT at high energies, we are able to present the energy dependence of the QPO amplitude and centroid frequency up to 100 keV which is rarely explored by previous satellites. We also find that the phase lag at the type-C QPOs centroid frequency is negative (soft lags) and strongly correlated with the centroid frequency. By assuming a geometrical origin of type-C QPOs, the source is consistent with being a high inclination system., Comment: 12 pages, 11 figures, Sumbitted to ApJ more...
- Published
- 2018
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9. Sunspot Light Walls Suppressed by Nearby Brightenings
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Jun Zhang, Robertus Erdélyi, Yijun Hou, Xiaohong Li, Shuhong Yang, and Limei Yan
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Physics ,Photosphere ,Sunspot ,010504 meteorology & atmospheric sciences ,Oscillation ,Flux ,FOS: Physical sciences ,Astronomy and Astrophysics ,Magnetic reconnection ,First light ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Amplitude ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Magnetic pressure ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,0105 earth and related environmental sciences - Abstract
Light walls, as ensembles of oscillating bright structures rooted in sunspot light bridges, have not been well studied, although they are important for understanding sunspot properties. Using the Interface Region Imaging Spectrograph and Solar Dynamics Observatory observations, here we study the evolution of two oscillating light walls each within its own active region (AR). The emission of each light wall decays greatly after the appearance of adjacent brightenings. For the first light wall, rooted within AR 12565, the average height, amplitude, and oscillation period significantly decrease from 3.5 Mm, 1.7 Mm, and 8.5 min to 1.6 Mm, 0.4 Mm, and 3.0 min, respectively. For the second light wall, rooted within AR 12597, the mean height, amplitude, and oscillation period of the light wall decrease from 2.1 Mm, 0.5 Mm, and 3.0 min to 1.5 Mm, 0.2 Mm, and 2.1 min, respectively. Particularly, a part of the second light wall becomes even invisible after the influence of nearby brightening. These results reveal that the light walls are suppressed by nearby brightenings. Considering the complex magnetic topology in light bridges, we conjecture that the fading of light walls may be caused by a drop in the magnetic pressure, where flux is cancelled by magnetic reconnection at the site of the nearby brightening. Another hypothesis is that the wall fading is due to the suppression of driver source (p-mode oscillation), resulting from the nearby avalanche of downward particles along reconnected brightening loops., 6 pages, 5 figures, accepted for publication in ApJL more...
- Published
- 2017
10. Phase Evolution of the Crab Pulsar between Radio and X-ray
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Lu Yuzhang, Youli Tuo, Ming-Yu Ge, Jin-Lin Han, Limei Yan, Fangjun Lu, Shuang-Nan Zhang, S. J. Zheng, Y. J. Du, Hao Tong, and J. P. Yuan
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Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Crab Pulsar ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Jodrell Bank Observatory ,Astrophysics ,Ephemeris ,01 natural sciences ,law.invention ,Telescope ,Interstellar medium ,010104 statistics & probability ,Amplitude ,Pulsar ,Space and Planetary Science ,law ,0103 physical sciences ,0101 mathematics ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,Noise (radio) - Abstract
We study the X-ray phases of the Crab pulsar utilizing the 11-year observations from the Rossi X-ray Timing Explorer, 6-year radio observations from the Nanshan Telescope, and the ephemeris from Jodrell Bank Observatory. It is found that the X-ray phases in different energy bands and the radio phases from Nanshan Telescope show similar behaviors, including long-time evolution and short-time variations. Such strong correlations between the X-ray and radio phases imply that the radio and X-ray timing noises are both generated from the pulsar spin that cannot be well described by the the monthly ephemeris from the Jodrell Bank observatory. When using the Nanshan phases as references to study the X-ray timing noise, it has a significantly smaller variation amplitude and shows no long-time evolution, with a change rate of $(-1.1\pm1.1)\times10^{-7}$ periods per day. These results show that the distance of the X-ray and radio emission regions on the Crab pulsar has no detectable secular change, and it is unlikely that timing-noises resulted from any unique physical processes in the radio or X-ray emitting regions. The similar behaviors of the X-ray and radio timing noises also imply that the variation of the interstellar medium is not the origin of the Crab pulsar's timing noises, which is consistent with the results obtained from the multi-frequency radio observations of PSR B1540-06., Comment: 26 pages, 5 figures. Accepted for publication in ApJ more...
- Published
- 2017
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11. Observations of counter-propagating Alfvénic and compressive fluctuations in the chromosphere
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Jiansen He, Zi-Xu Liu, and Limei Yan
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Physics ,education.field_of_study ,Wave propagation ,Turbulence ,Oscillation ,Population ,Astronomy and Astrophysics ,Astrophysics ,Solar prominence ,Amplitude ,Space and Planetary Science ,Physics::Space Physics ,Astrophysics::Solar and Stellar Astrophysics ,Phase velocity ,education ,Chromosphere - Abstract
Recent observations have found that chromospheric spicules behave like Alfvfluctuations. Low-frequency Alfvwaves are predicted to partially reflect in the transition region that has a gradient in the Alfv´ en speed, thereby producing inward Alfv´ en waves, which may interact nonlinearly with outward Alfvwaves to generate Alfv´ enic turbulence. However, the signature of Alfvturbulence in the chromosphere has not yet been quantitatively analyzed with observations. Here we an- alyze some characteristics related to Alfvturbulence with the observations from Hinode/SOT. We decompose the height-time diagram of the transverse oscillations to separate the outward and inward propagating Alfvsignals. The counter- propagating waves are found to have similar amplitude, period and phase speed, sug- gesting a state having an approximate balance in bi-directional energy fluxes. Counter- propagation of intensity oscillation with lower propagation speed is also presented, probably indicating the presence of slow mode waves. Moreover, we attempt to esti- mate the Elsspectra of the chromospheric turbulence for the first time. The rela- tive fluctuations in the magnetic field may be measured as the local slope of wave-like shapes in spicules. The resulting low-frequency Els¨ asser power spectra look similar to each other without showing a dominant population, which confirms these counter- propagating low-frequency Alfvwaves are in a state of balanced flux. These obser- vational results are believed to help us better understand the nature of chromospheric turbulence as well as chromospheric heating. more...
- Published
- 2014
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12. Revisiting the Strongest Martian X-Ray Halo Observed by XMM-Newton on 2003 November 19–21
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Lihui Chai, Zhaojin Rong, Yong Wei, Jiawei Gao, Limei Yan, and Lingling Zhao
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Martian ,Physics ,X-ray astronomy ,Space and Planetary Science ,X-ray ,Astronomy and Astrophysics ,Mars Exploration Program ,Halo ,Astrophysics ,Exosphere - Published
- 2019
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13. A New Method to Comprehensively Diagnose Shock Waves in the Solar Atmosphere Based on Simultaneous Spectroscopic and Imaging Observations
- Author
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Limei Yan, Lei Zhang, Jiansen He, Linghua Wang, Yong Wei, and Wenzhi Ruan
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Shock wave ,Physics ,010504 meteorology & atmospheric sciences ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy and Astrophysics ,Plasma ,Solar atmosphere ,01 natural sciences ,Shock (mechanics) ,Computational physics ,symbols.namesake ,Space and Planetary Science ,0103 physical sciences ,symbols ,Dissipative system ,Astrophysics::Solar and Stellar Astrophysics ,010303 astronomy & astrophysics ,Spectrograph ,Doppler effect ,Radiant intensity ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences - Abstract
Shock waves are believed to play an important role in plasma heating. The shock-like temporal jumps in radiation intensity and Doppler shift have been identified in the solar atmosphere. However, a quantitative diagnosis of the shocks in the solar atmosphere is still lacking, seriously hindering the understanding of shock dissipative heating of the solar atmosphere. Here, we propose a new method to realize the goal of the shock quantitative diagnosis, based on Rankine–Hugoniot equations and taking the advantages of simultaneous imaging and spectroscopic observations from, e.g., IRIS (Interface Region Imaging Spectrograph). Because of this method, the key parameters of shock candidates can be derived, such as the bulk velocity and temperature of the plasma in the upstream and downstream, the propagation speed and direction. The method is applied to the shock candidates observed by IRIS, and the overall characteristics of the shocks are revealed quantitatively for the first time. This method is also tested with the help of forward modeling, i.e., virtual observations of simulated shocks. The parameters obtained from the method are consistent with the parameters of the shock formed in the model and are independent of the viewing direction. Therefore, the method we proposed here is applicable to the quantitative and comprehensive diagnosis of the observed shocks in the solar atmosphere. more...
- Published
- 2018
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14. Mass and energy supply of a cool coronal loop near its apex
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Limei Yan, Hardi Peter, Lidong Xia, Linghua Wang, and Jiansen He
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Physics ,010504 meteorology & atmospheric sciences ,Astronomy and Astrophysics ,Context (language use) ,Magnetic reconnection ,Plasma ,Coronal loop ,Astrophysics ,01 natural sciences ,Magnetic flux ,Magnetic field ,Loop (topology) ,Magnetogram ,Space and Planetary Science ,0103 physical sciences ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
Context. Different models for the heating of solar corona assume or predict different locations of the energy input: concentrated at the footpoints, at the apex, or uniformly distributed. The brightening of a loop could be due to the increase in electron density ne, the temperature T, or a mixture of both.Aim. We investigate possible reasons for the brightening of a cool loop at transition region temperatures through imaging and spectral observation.Methods. We observed a loop with the Interface Region Imaging Spectrograph (IRIS) and used the slit-jaw images together with spectra taken at a fixed slit position to study the evolution of plasma properties in and below the loop. We used spectra of Si iv, which forms at around 80 000 K in equilibrium, to identify plasma motions and derive electron densities from the ratio of inter-combination lines of O IV. Additional observations from the Solar Dynamics Observatory (SDO) were employed to study the response at coronal temperatures (Atmospheric Imaging Assembly, AIA) and to investigate the surface magnetic field below the loop (Helioseismic and Magnetic Imager, HMI).Results. The loop first appears at transition region temperatures and later also at coronal temperatures, indicating a heating of the plasma in the loop. The appearance of hot plasma in the loop coincides with a possible accelerating upflow seen in Si IV, with the Doppler velocity shifting continuously from ~−70 km s−1 to ~−265 km s−1. The 3D magnetic field lines extrapolated from the HMI magnetogram indicate possible magnetic reconnection between small-scale magnetic flux tubes below or near the loop apex. At the same time, an additional intensity enhancement near the loop apex is visible in the IRIS slit-jaw images at 1400 Å. These observations suggest that the loop is probably heated by the interaction between the loop and the upflows, which are accelerated by the magnetic reconnection between small-scale magnetic flux tubes at lower altitudes. Before and after the possible heating phase, the intensity changes in the optically thin (Si IV) and optical thick line (C II) are mainly contributed by the density variation without significant heating.Conclusions. We therefore provide evidence for the heating of an envelope loop that is affected by accelerating upflows, which are probably launched by magnetic reconnection between small-scale magnetic flux tubes underneath the envelope loop. This study emphasizes that in the complex upper atmosphere of the Sun, the dynamics of the 3D coupled magnetic field and flow field plays a key role in thermalizing 1D structures such as coronal loops. more...
- Published
- 2018
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15. Self-absorption in the solar transition region
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Hui Tian, Feng Chen, Lei Zhang, Linghua Wang, Hardi Peter, Limei Yan, Krzysztof Barczynski, Chuanyi Tu, Jiansen He, and Lidong Xia
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Physics ,Opacity ,Absorption spectroscopy ,Solar transition region ,Stratification (water) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Magnetic reconnection ,Astrophysics ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Astrophysics::Solar and Stellar Astrophysics ,Emission spectrum ,Self-absorption ,Chromosphere ,Solar and Stellar Astrophysics (astro-ph.SR) - Abstract
Transient brightenings in the transition region of the Sun have been studied for decades and are usually related to magnetic reconnection. Recently, absorption features due to chromospheric lines have been identified in transition region emission lines raising the question of the thermal stratification during such reconnection events. We analyse data from the Interface Region Imaging Spectrograph (IRIS) in an emerging active region. Here the spectral profiles show clear self-absorption features in the transition region lines of Si\,{\sc{iv}}. While some indications existed that opacity effects might play some role in strong transition region lines, self-absorption has not been observed before. We show why previous instruments could not observe such self-absorption features, and discuss some implications of this observation for the corresponding structure of reconnection events in the atmosphere. Based on this we speculate that a range of phenomena, such as explosive events, blinkers or Ellerman bombs, are just different aspects of the same reconnection event occurring at different heights in the atmosphere., Comment: Accepted for publication in ApJ more...
- Published
- 2015
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16. Formation of Cool and Warm Jets by Magnetic Flux Emerging from the Solar Chromosphere to Transition Region
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Lei Zhang, Hardi Peter, Jiansen He, Limei Yan, Linghua Wang, Liping Yang, and Chuanyi Tu
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Physics ,010504 meteorology & atmospheric sciences ,Space and Planetary Science ,0103 physical sciences ,Astronomy and Astrophysics ,Astrophysics ,010303 astronomy & astrophysics ,01 natural sciences ,Chromosphere ,Magnetic flux ,0105 earth and related environmental sciences - Published
- 2017
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17. SPECTRAL ANISOTROPY OF ELSÄSSER VARIABLES IN TWO-DIMENSIONAL WAVE-VECTOR SPACE AS OBSERVED IN THE FAST SOLAR WIND TURBULENCE
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Xin Wang, Robert T. Wicks, E. Marsch, Jiansen He, Lei Zhang, Limei Yan, Christopher H. K. Chen, Linghua Wang, and Chuanyi Tu
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MHD TURBULENCE ,HELICITY ,FOS: Physical sciences ,Astronomy & Astrophysics ,Kinetic energy ,Magnetohydrodynamic turbulence ,01 natural sciences ,Alfvén wave ,Physics - Space Physics ,DEPENDENCE ,0103 physical sciences ,waves ,Wave vector ,010306 general physics ,Anisotropy ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Physics ,Science & Technology ,Magnetic energy ,turbulence ,Astronomy and Astrophysics ,FLUCTUATIONS ,SIMULATIONS ,EVOLUTION ,Space Physics (physics.space-ph) ,Magnetic field ,Computational physics ,0201 Astronomical And Space Sciences ,Solar wind ,solar wind ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,RESIDUAL ENERGY ,Physical Sciences ,MAGNETOHYDRODYNAMIC TURBULENCE ,MEAN MAGNETIC-FIELD - Abstract
Intensive studies have been conducted to understand the anisotropy of solar wind turbulence. However, the anisotropy of Elsässer variables (${{\boldsymbol{Z}}}^{\pm }$) in 2D wave-vector space has yet to be investigated. Here we first verify the transformation based on the projection-slice theorem between the power spectral density ${\mathrm{PSD}}_{2{\rm{D}}}({k}_{\parallel },{k}_{\perp })$ and the spatial correlation function ${\mathrm{CF}}_{2{\rm{D}}}({r}_{\parallel },{r}_{\perp }).$ Based on the application of the transformation to the magnetic field and the particle measurements from the WIND spacecraft, we investigate the spectral anisotropy of Elsässer variables (${{\boldsymbol{Z}}}^{\pm }$), and the distribution of residual energy ${E}_{{\rm{R}}},$ Alfvén ratio ${R}_{{\rm{A}}}$, and Elsässer ratio ${R}_{{\rm{E}}}$ in the $({k}_{\parallel },{k}_{\perp })$ space. The spectra ${\mathrm{PSD}}_{2{\rm{D}}}({k}_{\parallel },{k}_{\perp })$ of ${\boldsymbol{B}}$, ${\boldsymbol{V}}$, and ${{\boldsymbol{Z}}}_{\mathrm{major}}$ (the larger of ${{\boldsymbol{Z}}}^{\pm }$) show a similar pattern that ${\mathrm{PSD}}_{2{\rm{D}}}({k}_{\parallel },{k}_{\perp })$ is mainly distributed along a ridge inclined toward the k⊥ axis. This is probably the signature of the oblique Alfvénic fluctuations propagating outwardly. Unlike those of ${\boldsymbol{B}}$, ${\boldsymbol{V}}$, and ${{\boldsymbol{Z}}}_{\mathrm{major}},$ the spectrum ${\mathrm{PSD}}_{2{\rm{D}}}({k}_{\parallel },{k}_{\perp })$ of ${{\boldsymbol{Z}}}_{\mathrm{minor}}$ is distributed mainly along the k⊥ axis. Close to the k⊥ axis, $| {E}_{{\rm{R}}}| $ becomes larger while ${R}_{{\rm{A}}}$ becomes smaller, suggesting that the dominance of magnetic energy over kinetic energy becomes more significant at small k∥. ${R}_{{\rm{E}}}$ is larger at small k∥, implying that ${\mathrm{PSD}}_{2{\rm{D}}}({k}_{\parallel },{k}_{\perp })$ of ${{\boldsymbol{Z}}}_{\mathrm{minor}}$ is more concentrated along the k⊥ direction as compared to that of ${{\boldsymbol{Z}}}_{\mathrm{major}}.$ The residual energy condensate at small k∥ is consistent with simulation results in which ${E}_{{\rm{R}}}$ is spontaneously generated by Alfvén wave interaction. more...
- Published
- 2016
- Full Text
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18. OBSERVATIONAL EVIDENCE FOR THE CAUSES AND CONSEQUENCES OF CHROMOSPHERIC RECONNECTION
- Author
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Jiansen He, Fangran Jiao, Limei Yan, and Lidong Xia
- Subjects
Physics ,Jet (fluid) ,Advection ,Astrophysics::High Energy Astrophysical Phenomena ,Astronomy ,Astronomy and Astrophysics ,Magnetic reconnection ,Plasmoid ,Astrophysics ,Observational evidence ,Space and Planetary Science ,Ambient field ,Physics::Space Physics ,Astrophysics::Solar and Stellar Astrophysics ,Chromosphere - Abstract
The chromospheric anemone jets with an inverse “Y” shape are ubiquitous, as revealed by the Solar Optical Telescope observations. These jets are considered to be consequences of chromospheric magnetic reconnections. Although these jets have been studied intensively, the dynamics and their driving causes remain unclear observationally. In this work, we report a case of a chromospheric jet showing complete observational evidence for the cause and consequence of chromospheric intermittent reconnection. The intermittent eruption of this jet shows two distinct quasi-periods, 50–60 s and 600–700 s. The short-period eruptions may be related to the plasmoid-induced reconnection, and the long-period ones may be interpreted as sequences of cycles of energy storage and release during magnetic reconnections. The observations also reveal Alfvenic waves with a mean period around 88 s and a maximum transverse displacement around 0.″26. The jet is hosted by a loop moving smoothly with a horizontal speed of ∼0.4 km s−1. Our results provide observational evidence supporting the magnetic reconnection model of the formation of the chromospheric jets with related products, in which the loop advection drives intermittent magnetic reconnections, and the reconnection outflows carrying plasmoids collide further with the ambient field lines and finally excite waves and jets. more...
- Published
- 2015
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19. INJECTION OF PLASMA INTO THE NASCENT SOLAR WIND VIA RECONNECTION DRIVEN BY SUPERGRANULAR ADVECTION
- Author
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Jiansen He, Limei Yan, Liping Yang, Chuanyi Tu, Lei Zhang, Wenlei Chen, Hardi Peter, Eckart Marsch, Xueshang Feng, and Linghua Wang
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Mass flux ,Physics ,business.product_category ,Astronomy and Astrophysics ,Magnetic reconnection ,Coronal loop ,Mechanics ,Astrophysics ,Nanoflares ,Solar wind ,Space and Planetary Science ,Physics::Space Physics ,Astrophysics::Solar and Stellar Astrophysics ,Funnel ,Magnetohydrodynamics ,business ,Chromosphere - Abstract
To understand the origin of the solar wind is one of the key research topics in modern solar and heliospheric physics. Previous solar wind models assumed that plasma flows outward along a steady magnetic flux tube that reaches continuously from the photosphere through the chromosphere into the corona. Inspired by more recent comprehensive observations, Tu et al. suggested a new scenario for the origin of the solar wind, in which it flows out in a magnetically open coronal funnel and mass is provided to the funnel by small-scale side loops. Thus mass is supplied by means of magnetic reconnection that is driven by supergranular convection. To validate this scenario and simulate the processes involved, a 2.5 dimensional (2.5D) numerical MHD model is established in the present paper. In our simulation a closed loop moves toward an open funnel, which has opposite polarity and is located at the edge of a supergranulation cell, and magnetic reconnection is triggered and continues while gradually opening up one half of the closed loop. Its other half connects with the root of the open funnel and forms a new closed loop which is submerged by a reconnection plasma stream flowing downward. Thus we find that the outflowing plasma in the newly reconnected funnel originates not only from the upward reconnection flow but also from the high-pressure leg of the originally closed loop. This implies an efficient supply of mass from the dense loop to the dilute funnel. The mass flux of the outflow released from the funnel considered in our study is calculated to be appropriate for providing the mass flux at the coronal base of the solar wind, though additional heating and acceleration mechanisms are necessary to keep the velocity at the higher location. Our numerical model demonstrates that in the funnel the mass for the solar wind may be supplied from adjacent closed loops via magnetic reconnection as well as directly from the footpoints of open funnels. more...
- Published
- 2013
- Full Text
- View/download PDF
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