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ISSN  2096-3955

CN  10-1502/P

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Xiaocheng Guo, Yucheng Zhou, Chi Wang, and Ying D. Liu
Accepted Articles , doi: 10.26464/epp2021024
[Abstract](81) [PDF](0)
Voyager 1 occasionally detected the sudden jumps of the local interstellar magnetic field strength since its heliopause crossing in August 2012. These events were believed to be associated with the outward propagating shocks that had the solar wind origin in the inner heliosphere. Here we investigate the correlation between the interstellar shocks and the large-scale solar wind events by means of the 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-exchange 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 the year 2010 and 2017, are used as the inner boundary conditions to drive the simulation. The simulation results showed that the solar wind gradually merge into large-scale structures as the radial distance increases, being consistent with the observations by New Horizons. After propagating into the inner heliosheath, the shocks are fully developed and the corresponding pressure pulses roughly agree with the observation by Voyager 2 in the inner heliosheath. The arrival of the shocks beyond heliopause are estimated and found to be consistent with the observed signatures of interstellar shocks by Voyager 1. The possible origins of the interstellar shocks in the inner heliosheath are discussed based on the simulation.
Influence of lunar eclipse of 15 April 2014 on the intrinsic background current noises in fission chamber
Anatolii D. Skorbun , Gennadii I. Odinokin, Oleksandr A. Kuchmagra
Accepted Articles , doi: 10.26464/epp2021023
[Abstract](57) [PDF](0)
An intrinsic noise of such a device as ionisation fission chamber for neutron detection has been measured during the lunar eclipse of 15 April 2014. The causes for the noise, in the absence of a particular source of neutrons, are electronics noises, alpha-decay of radioactive material inside the chamber and registration of these alpha particles by the registered system, and occasional background neutrons. The values of time intervals between moments of pulses registration were the subject of analysing. It revealed that in the moments when the Moon crossed an edge of an umbra or penumbra, the sets of the shortest intervals (increased numbers of pulses) are observed. The duration of these sets are about tens microseconds, and they clearly exceed the noise level. The possible causes for such effect are discussed: influence of some emission from Sun, gravitation field changing, changing of an interplanetary magnetic field, bursts of neutrons during Sun-Earth-Moon interaction, unknown “cosmophysical factors”.

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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
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?
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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
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.
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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
Thermal structures of the Pacific lithosphere from magnetic anomaly inversion
Chun-Feng Li, Jian Wang
2018, 2(1): 52-66   doi: 10.26464/epp2018005
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
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
Monitoring the geospace response to the Great American Solar Eclipse on 21 August 2017
Shun-Rong Zhang, Philip J. Erickson, Larisa P. Goncharenko, Anthea J. Coster, Nathaniel A. Frissell
2017, 1(1): 72-76   doi: 10.26464/epp2017011

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