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地球与行星物理

ISSN  2096-3955

CN  10-1502/P

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SOLID EARTH: SEISMOLOGY
Depth variation of the Conrad discontinuity in the Qaidam Basin, northwestern China, and its crustal dynamic implications
Biao Yang, YanBin Wang, Li Zhao, LiMing Yang, ChengNing Sha
Recently Published , doi: 10.26464/epp2021030
[Abstract](12) [FullText HTML](6) [PDF 1344KB](0)
Abstract:
We use broadband records from a dense seismic network deployed in and around the Qaidam Basin in northwestern China to analyze the crustal phases and investigate the depth of the Conrad and Moho discontinuities as well as the P-wave velocity. Waveform cross-correlation is used to assist in the identification of the crustal phases and in determining their arrival times. Depth of the Conrad discontinuity is determined by fitting the travel times of Conrad-diffracted P-waves using a two-layer model. The depth of the Conrad discontinuity under the eastern part of the basin is shallower than the western part, which can be attributed to different crustal shortening mechanisms. The upper crust shortening in the western part of the basin leads to thickening of the upper crust, while multiple thrust faults result in the rise of the Conrad discontinuity in the east. These two different mechanisms determine the depth change of the Conrad discontinuity in the basin from the west to the east, which is supported by the results in this study.
SPACE PHYSICS
Analysis of the correlation between horizontal wind and 11-year solar activity over Langfang, China
Bing Cai, QingChen Xu, Xiong Hu, Xuan Cheng, JunFeng Yang, Wen Li
Recently Published , doi: 10.26464/epp2021029
[Abstract](84) [FullText HTML](3) [PDF 512KB](2)
Abstract:
In this study, long term observations of medium frequency (MF) radar at Langfang site (39.4°N, 116.7°E) from 2009 to 2020 have been used to analyze the dependence of the 11-year solar cycle on horizontal winds in the local mesosphere and lower thermosphere (MLT). The results show that the zonal wind is positively correlated with solar activity during spring at 80–84 km, and during summer at 80–82 km; the meridional wind is positively correlated with solar activity during spring at 84–88 km and during summer at 84–90 km. In contrast, the results show no correlation between the horizontal wind and solar activity in autumn and winter. We attempt to explain the correlations in terms of the changes in stratospheric temperature and the net flux of gravity waves during solar activities. In addition, annual and semiannual oscillations of the zonal/meridional wind were found by using the least squares fitting method on daily horizontal winds, which show negative correlations with solar activity at heights of 80–90 km.
SOLID EARTH: GEODYNAMICS
Thermal structure of continental subduction zone: high temperature caused by the removal of the preceding oceanic slab
Ting Luo, Wei Leng
Recently Published , doi: 10.26464/epp2021027
[Abstract](136) [FullText HTML](20) [PDF 323KB](12)
Abstract:
The thermal structure of the continental subduction zone can be deduced from high-pressure and ultra-high-pressure rock samples or numerical simulation. However, petrological data indicate that the temperature of subducted continental plates is generally higher than that derived from numerical simulation. In this paper, a two-dimensional kinematic model is used to study the thermal structure of continental subduction zones, with or without a preceding oceanic slab. The results show that the removal of the preceding oceanic slab can effectively increase the slab surface temperature of the continental subduction zone in the early stage of subduction. This can sufficiently explain the difference between the cold thermal structure obtained from previous modeling results and the hot thermal structure obtained from rock sample data.
SPACE PHYSICS: INTERPLANETARY PHYSICS
Propagation of large-scale solar wind events in the outer heliosphere from a numerical MHD simulation
XiaoCheng Guo, YuCheng Zhou, Chi Wang, Ying D. Liu
Recently Published , doi: 10.26464/epp2021024
[Abstract](226) [FullText HTML](29) [PDF 1526KB](4)
Abstract:
Voyager 1 occasionally detected sudden jumps of the local interstellar magnetic field strength since its heliopause crossing in August 2012. These events were believed to be associated with outward propagating solar wind shocks originating in the inner heliosphere. Here we investigate the correlation between interstellar shocks and large-scale solar wind events by means of numerical MHD simulation. The solar wind is simplified as a symmetric flow near the equatorial plane, and the interstellar neutrals are treated as a constant flow with a fixed density distribution along the upwind direction of the local interstellar medium. The charge exchanges between the solar wind plasma and the interstellar neutrals are taken into account. At a heliocentric distance of 1 AU, the solar wind data from OMNI, STEREO A and B during the period between 2010 and 2017 are used as the inner boundary conditions to drive the simulation. The simulation results showed that the solar wind gradually merges into large-scale structures as the radial distance increases, consistent with observations by New Horizons. After propagating into the inner heliosheath, the shocks are fully developed and the corresponding pressure pulses roughly agree with the observations by Voyager 2 in the inner heliosheath. The arrival of the shocks beyond the heliopause is estimated and found to be consistent with the observed signatures of interstellar shocks by Voyager 1. The possible origins of interstellar shocks in the inner heliosheath are discussed based on the simulation.
SPACE PHYSICS: INTERPLANETARY PHYSICS
Dynamics of the charged particles released from a Sun-grazing comet in the solar corona
ChuanPeng Hou, JianSen He, Lei Zhang, Ying Wang, Die Duan
Recently Published , doi: 10.26464/epp2021023
[Abstract](189) [FullText HTML](60) [PDF 2121KB](1)
Abstract:
The sun-grazing comet C/2011 W3 (Lovejoy) showed a distorted, unconventional tail morphology near its perihelion (1.2Rs). Based on the “Solar Corona and Inner Heliosphere” modeling result of the magnetic field and plasma dynamics in the solar corona, we use the Runge-Kutta method to simulate the moving trajectory of charged dust and ion particles released at different positions from the C/2011 W3 orbit. We find that the dust particles near the sun, which are subject to a strong magnetic Lorentz force, travel differently from their counterparts distant from the sun, where the latter are mainly affected by the solar gravitational force and radiation pressure. According to the simulation results, we propose that the magnetic mirror effect can rebound the charged dust particles back away from the sun and be regarded as one crucial cause of the dust-free zone formation. We find that ions mainly move along magnetic field lines at an acute angle to the comet's direction of motion. The cometary ions' movement direction was determined by the comet's velocity and the coronal magnetic field, which are responsible for the C/2011 W3’s unique comet tail shape near perihelion. Additionally, the ion particles also experience perpendicular drift motion, mainly dominated by the electric field drift, which is similar to and can be used to approximate the solar wind's transverse velocity at its source region.

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Anomalous changes of temperature and ozone QBOs in 2015-2017 from radiosonde observation and MERRA-2 reanalysis
XiaoYan Bai, KaiMing Huang, ShaoDong Zhang, ChunMing Huang, and Yun Gong
Accepted Articles , doi: 10.26464/epp2021028
[Abstract](142) [PDF](7)
Abstract:
Anomalous change of zonal wind quasi-biennial oscillation (QBO) in winter 2015-2016 has received close attention. Combining radiosonde and satellite observations and reanalysis data, we investigate anomalous changes in temperature and ozone QBOs from the lower to middle stratosphere. As wind shear direction is reversed due to unexpected changes of zonal wind QBO at about 24-30 km, the shortest cold phase at 21-27 km appears in temperature QBO, which is different from completely interrupted westward phase in zonal wind QBO, while the longest cold phase above almost 27 km lasts for 2-3 years from 2015 to 2017 owing to the absence of corresponding warm phase. Meridional scale reduction of temperature QBO causes a small temperature anomaly, thus thermal wind relationship looks seemingly different from that in the other regular QBO cycles. QBO in ozone mixing ratio anomaly shows a double-peak with inverse phase, and its phase below (above) 30 km is in agreement with (opposite to) the phase of temperature QBO because of different control mechanisms of ozone. Following temperature QBO variation, QBO in ozone mixing ratio anomaly exhibits a less positive phase at 20-30 km in 2016-2017, and a very long positive phase above 30 km from 2015 to 2017. QBO in total column ozone shows a small peak in winter 2016-2017 since ozone is mainly concentrated at 20 to 30 km. Anomalous changes of temperature and ozone QBOs due to unexcepted QBO zonal wind variation can be well explained according to thermal wind balance and thermodynamic balance.
Determination of the local magnitudes of small earthquakes using dense seismic array in the Changning-Zhaotong shale gas field, Southern Sichuan Basin
Wen Yang, GuoYi Chen, LingYuan Meng, Yang Zang, HaiJiang Zhang, JunLun Li
Accepted Articles , doi: 10.26464/epp2021026
[Abstract](134) [PDF](12)
Abstract:
With the development of unconventional shale gas in the southern Sichuan Basin seismicity has increased significantly in the region in recent years. Though the existing regional sparse seismic stations can capture most earthquakes with M_L≥2.5, a great number of smaller earthquakes are often omitted due to the limited detection capacity. With the advent of portable seismic nodes, many dense arrays for monitoring seismicity in the unconventional oil and gas fields have been deployed, and the magnitudes of those earthquakes are key for understanding the local fault reactivation and seismic potentials. However, the current national standard for determining the local magnitudes was not specifically designed for monitoring stations in close proximity, and it uses a calibration function with a minimal step of 5 km in the epicentral distance. That is, the current national standard tends to overestimate the local magnitudes for stations in short epicentral distances, and can result in discrepancy in magnitude measurement for dense arrays. In this study, we propose a new local magnitude formula which corrects the overestimated magnitudes in shorter distances, and yields accurate event magnitudes for small earthquakes in the Changning-Zhaotong shale gas field in the southern Sichuan Basin monitored by dense seismic arrays in close proximity. The formula is used to determine the local magnitudes of 7,500 events monitored by a two-phased dense array with several hundred 5 Hz 3C nodes deployed from the end of February 2019 to early May 2019 in the Changning-Zhaotong shale gas field. The magnitude of completeness (M_C) using the dense array is -0.1, compared to M_C 1.1 by the sparser Chinese Seismic Network (CSN). In addition, using a machine learning detection and picking procedure, we successfully identify and process some 14,000 earthquakes from the continuous waveforms, a ten-fold increase over the catalog recorded by CSN for the same period, and the M_C is further reduced to -0.3 from -0.1 compared to the catalog obtained via manual processing using the same dense array. The proposed local magnitude formula can be adopted for calculating accurate local magnitudes of earthquakes monitored by dense arrays in the shale gas fields in the southern Sichuan Basin in the future, and help to better characterize the local seismic risks and potentials.

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REVIEW
SOLID EARTH: GEODYNAMICS
Reviewing subduction initiation and the origin of plate tectonics: What do we learn from present-day Earth?
Gang Lu, Liang Zhao, Ling Chen, Bo Wan, FuYuan Wu
2021, 5(2): 123 -140   doi: 10.26464/epp2021014
Abstract:
The theory of plate tectonics came together in the 1960s, achieving wide acceptance after 1968. Since then it has been the most successful framework for investigations of Earth’s evolution. Subduction of the oceanic lithosphere, as the engine that drives plate tectonics, has played a key role in the theory. However, one of the biggest unanswered questions in Earth science is how the first subduction was initiated, and hence how plate tectonics began. The main challenge is how the strong lithosphere could break and bend if plate tectonics-related weakness and slab-pull force were both absent. In this work we review state-of-the-art subduction initiation (SI) models with a focus on their prerequisites and related driving mechanisms. We note that the plume-lithosphere-interaction and mantle-convection models do not rely on the operation of existing plate tectonics and thus may be capable of explaining the first SI. Re-investigation of plate-driving mechanisms reveals that mantle drag may be the missing driving force for surface plates, capable of triggering initiation of the first subduction. We propose a composite driving mechanism, suggesting that plate tectonics may be driven by both subducting slabs and convection currents in the mantle. We also discuss and try to answer the following question: Why has plate tectonics been observed only on Earth?
RESEARCH ARTICLE
GEODESY AND GRAVITY
Far-field coseismic gravity changes related to the 2015 MW7.8 Nepal (Gorkha) earthquake observed by superconducting gravimeters in Chinese mainland
LeLin Xing, ZiWei Liu, JianGang Jia, ShuQing Wu, ZhengSong Chen, XiaoWei Niu
2021, 5(2): 141 -148   doi: 10.26464/epp2021018
Abstract:
Using data from five SGs at four stations in Chinese mainland, obvious permanent gravity changes caused by the 2015 MW7.8 Nepal (Gorkha) earthquake were detected. We analyzed the gravity effects from ground vertical deformation (VD) using co-site continuous GPS (cGPS) data collocated at the Lijiang and the Wuhan station, and hydrological effects using GLDAS models and groundwater level records. After removing these effects, SG observations before and after the earthquake revealed obvious permanent gravity changes: −3.0 μGal, 7.3 μGal and 8.0 μGal at Lhasa, Lijiang and Wuhan station, respectively. We found that the gravity changes cannot be explained by the results of dislocation theory.
SOLID EARTH: COMPUTATIONAL GEOPHYSICS
Three-dimensional frequency-domain full waveform inversion based on the nearly-analytic discrete method
DeYao Zhang, WenYong Pan, DingHui Yang, LingYun Qiu, XingPeng Dong, WeiJuan Meng
2021, 5(2): 149 -157   doi: 10.26464/epp2021022
Abstract:
The nearly analytic discrete (NAD) method is a kind of finite difference method with advantages of high accuracy and stability. Previous studies have investigated the NAD method for simulating wave propagation in the time-domain. This study applies the NAD method to solving three-dimensional (3D) acoustic wave equations in the frequency-domain. This forward modeling approach is then used as the “engine” for implementing 3D frequency-domain full waveform inversion (FWI). In the numerical modeling experiments, synthetic examples are first given to show the superiority of the NAD method in forward modeling compared with traditional finite difference methods. Synthetic 3D frequency-domain FWI experiments are then carried out to examine the effectiveness of the proposed methods. The inversion results show that the NAD method is more suitable than traditional methods, in terms of computational cost and stability, for 3D frequency-domain FWI, and represents an effective approach for inversion of subsurface model structures.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
Energetic electron detection packages on board Chinese navigation satellites in MEO
YuGuang Ye, Hong Zou, Qiu-Gang Zong, HongFei Chen, JiQing Zou, WeiHong Shi, XiangQian Yu, WeiYing Zhong, YongFu Wang, YiXin Hao, ZhiYang Liu, XiangHong Jia, Bo Wang, XiaoPing Yang, XiaoYun Hao
2021, 5(2): 158 -179   doi: 10.26464/epp2021021
Abstract:
Energetic electron measurements and spacecraft charging are of great significance for theoretical research in space physics and space weather applications. In this paper, the energetic electron detection package (EEDP) deployed on three Chinese navigation satellites in medium Earth orbit (MEO) is reviewed. The instrument was developed by the space science payload team led by Peking University. The EEDP includes a pinhole medium-energy electron spectrometer (MES), a high-energy electron detector (HED) based on ΔE-E telescope technology, and a deep dielectric charging monitor (DDCM). The MES measures the energy spectra of 50−600 keV electrons from nine directions with a 180°×30° field of view (FOV). The HED measures the energy spectrum of 0.5−3.0 MeV electrons from one direction with a 30° cone-angle FOV. The ground test and calibration results indicate that these three sensors exhibit excellent performance. Preliminary observations show that the electron spectra measured by the MES and HED are in good agreement with the results from the magnetic electron-ion spectrometer (MagEIS) of the Van Allen Probes spacecraft, with an average relative deviation of 27.3% for the energy spectra. The charging currents and voltages measured by the DDCM during storms are consistent with the high-energy electron observations of the HED, demonstrating the effectiveness of the DDCM. The observations of the EEDP on board the three MEO satellites can provide important support for theoretical research on the radiation belts and the applications related to space weather.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
Correlating the interplanetary factors to distinguish extreme and major geomagnetic storms
Ragini Balachandran, Li-Jen Chen, Shan Wang, Mei-Ching Fok
2021, 5(2): 180 -186   doi: 10.26464/epp2021015
Abstract:
We investigate the correlation between Disturbance Storm Time (Dst) characteristics and solar wind conditions for the main phase of geomagnetic storms, seeking possible factors that distinguish extreme storms (minimum Dst <−250 nT) and major storms (minimum Dst <−100 nT). In our analysis of 170 storms, there is a marked correlation between the average rate of change of Dst during a storm’s main phase (ΔDstt) and the storm’s minimum Dst, indicating a faster ΔDstt as storm intensity increases. Extreme events add a new regime to ΔDstt, the hourly time derivative of Dst (dDst/dt), and sustained periods of large amplitudes for southward interplanetary magnetic field Bz and solar wind convection electric field Ey. We find that Ey is a less efficient driver of dDst/dt for extreme storms compared to major storms, even after incorporating the effects of solar wind pressure and ring current decay. When minimum Dst is correlated with minimum Bz, we observe a similar divergence, with extreme storms tending to have more negative Dst than the trend predicted on the basis of major storms. Our results enable further improvements in existing models for storm predictions, including extreme events, based on interplanetary measurements.
SPACE PHYSICS
Exploring the occurrence rate of PMSE-Es by Digisonde at Tromsø
HaiLong Li, ShuCan Ge, Lin Meng, MaoYan Wang, Abdur Rauf, Safi Ullah
2021, 5(2): 187 -195   doi: 10.26464/epp2021017
Abstract:
Polar mesosphere summer echoes (PMSE) are observed simultaneously with Digisonde and EISCAT VHF radar. The phenomenon of irregular Es layers is called PMSE-like or PMSE-Es (Polar Mesosphere Summer Echoes-Es) and has some relationship with real PMSE. In this paper, the characteristics of irregular Es layers at 80–100 km were observed by Digisonde at Tromsø during 2003–2014 are statistically analyzed with ionograms. The diurnal, day-to-day and year-to-year variations and discrepancies of occurrence rate between PMSE and PMSE-Es are compared with the statistical results observed by Esrange MST radar (ESRAD), and the reasons are discussed. The results show that the trends in the occurrence rate of PMSE-Es are similar to the trends in the occurrence rate of PMSE, but there are some notable differences. The occurrence rate of PMSE-Es is much lower than the occurrence rate of PMSE. The minimum value of PMSE-Es appears 1–2 hours earlier than the minimum value of the PMSE occurrence rate, while PMSE-Es appear earlier than PMSE in the year. In addition, there is a significant positive correlation between the annual average occurrence rates of PMSE and PMSE-Es. PMSE-Es is a relatively important occurrence in the polar mesopause. Analysis of its characteristics can provide new ideas and methods for studying the formation mechanism of PMSE.
SPACE PHYSICS
Effect of ions on conductivity and permittivity in the Polar Mesosphere Summer Echoes region
Safi Ullah, HaiLong Li, Abdur Rauf, Lin Meng, Bin Wang, ShuCan Ge, MaoYan Wang
2021, 5(2): 196 -204   doi: 10.26464/epp2021016
Abstract:
For the first time, the effect of ions on complex conductivity and permittivity of dusty plasma at Polar Mesosphere Summer Echoes (PMSE) altitude is analyzed. Because of ions higher mass and smaller thermal velocity, generally, their effects are not considered in the study of electromagnetic properties of dusty plasmas. In this study, we modified the equations of conductivity and permittivity by adding the effect of ions. In the PMSE altitude region between 80 and 90 km, a local reduction in electron density (i.e., an electron bite-out), is produced by electron absorption onto dust particles. The bite-out condition contains high dust density and smaller electron density. From simulation results in comparatively strong bite-out conditions, we found that the ion effects on conductivity become significant with smaller dust size, lower electron temperature, and lower neutral density. For comparatively weak bite-out conditions, the ion effects on conductivity become significant with larger dust size, higher electron temperature, and higher neutral density. On the other hand, for different dust sizes, electron temperatures and neutral density, the ion effects on complex permittivity become significant only in very strong bite-out conditions. Based on these simulation results, we conclude that, in the absence of electron bite-out conditions, the effect of ions on complex conductivity and permittivity is not significant and can be ignored. However, during bite-out conditions, the effect of ions becomes significant and cannot be ignored because it significantly changes the conductivity and permittivity of dusty plasmas.
SPACE PHYSICS
On the ion distributions at the separatrices during symmetric magnetic reconnection
HongTao Huang, YiQun Yu, JinBin Cao, Lei Dai, RongSheng Wang
2021, 5(2): 205 -217   doi: 10.26464/epp2021019
Abstract:
A particle-in-cell simulation of symmetric reconnection with zero guide field is carried out to understand the dynamics of ions along the separatrices. Through the investigation of ion velocity distributions at different moments and locations along the separatrices, a typical distribution is found: two counter-streaming populations in the perpendicular direction, with another two populations accelerated into distinct energy levels in the parallel direction. Backward tracing of ions reveals that the counter-streaming cores are mostly composed of ions initially located at the same side of the separatrix, while the other two accelerated populations in the parallel direction are composed of ions crossing through the neutral sheet. Through analysis of energy conversion of these populations, it is found that the ion energization along the separatrix is attributable primarily to the Hall electric field, while that in the region between the two separatrices is caused primarily by the induced reconnection electric field. For the counter-streaming population, the low-energy ions that cross the separatrix twice are affected by both Hall and reconnection electric fields, while the high-energy ions that directly enter the separatrix from the unperturbed plasma are energized mainly by the Hall electric field. For the two energized populations in the parallel direction, the ions with lower-energy are accelerated mainly by the in-plane electric field and the Hall electric field on the opposite side of the separatrix, whereas the ions with higher-energy not only experience the same energization process but also are constantly accelerated by the reconnection electric field.
LETTER
A new inversion method for reconstruction of plasmaspheric He+ density from EUV images
Ya Huang, Lei Dai, Chi Wang, RongLan Xu, Liang Li
2021, 5(2): 218 -222   doi: 10.26464/epp2021020
Abstract:
The Computer Tomography (CT) method is used for remote sensing the Earth’s plasmasphere. One challenge for image reconstruction is insufficient projection data, mainly caused by limited projection angles. In this study, we apply the Algebraic Reconstruction Technique (ART) and the minimization of the image Total Variation (TV) method, with a combination of priori knowledge of north–south symmetry, to reconstruct plasmaspheric He+ density from simulated EUV images. The results demonstrate that incorporating priori assumption can be particularly useful when the projection data is insufficient. This method has good performance even with a projection angle of less than 150 degrees. The method of our study is expected to have applications in the Soft X-ray Imager (SXI) reconstruction for the Solar wind–Magnetosphere–Ionosphere Link Explorer (SMILE) mission.
show more results
Corotating drift-bounce resonance of plasmaspheric electron with poloidal ULF waves
Qiu-Gang Zong, YongFu Wang, Jie Ren, XuZhi Zhou, SuiYan Fu, Robert Rankin, Hui Zhang
2017, 1(1): 2-12   doi: 10.26464/epp2017002
Ambient noise surface wave tomography of marginal seas in east Asia
Qing Wang, XiaoDong Song, JianYe Ren
2017, 1(1): 13-25   doi: 10.26464/epp2017003
A seismic model for crustal structure in North China Craton
TianYu Zheng, YongHong Duan, WeiWei Xu, YinShuang Ai
2017, 1(1): 26-34   doi: 10.26464/epp2017004
A brief review of equatorial ionization anomaly and ionospheric irregularities
Nanan Balan, LiBo Liu, HuiJun Le
2018, 2(4): 257-275   doi: 10.26464/epp2018025
Thermal structures of the Pacific lithosphere from magnetic anomaly inversion
Chun-Feng Li, Jian Wang
2018, 2(1): 52-66   doi: 10.26464/epp2018005
The first joint experimental results between SURA and CSES
XueMin Zhang, Vladimir Frolov, ShuFan Zhao, Chen Zhou, YaLu Wang, Alexander Ryabov, DuLin Zhai
2018, 2(6): 527-537   doi: 10.26464/epp2018051
Different earthquake patterns for two neighboring fault segments within the Haiyuan Fault zone
ZhiKun Ren, ZhuQi Zhang, PeiZhen Zhang
2018, 2(1): 67-73   doi: 10.26464/epp2018006
Radiation belt electron scattering by whistler-mode chorus in the Jovian magnetosphere: Importance of ambient and wave parameters
BinBin Ni, Jing Huang, YaSong Ge, Jun Cui, Yong Wei, XuDong Gu, Song Fu, Zheng Xiang, ZhengYu Zhao
2018, 2(1): 1-14   doi: 10.26464/epp2018001
Exact local refinement using Fourier interpolation for nonuniform-grid modeling
JinHai Zhang, ZhenXing Yao
2017, 1(1): 58-62   doi: 10.26464/epp2017008
A simulation study of 630 nm and 557.7 nm airglow variations due to dissociative recombination and thermal electrons by high-power HF heating
Tong Dang, JiuHou Lei, XianKang Dou, WeiXing Wan
2017, 1(1): 44-52   doi: 10.26464/epp2017006

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