EPP

地球与行星物理

ISSN  2096-3955

CN  10-1502/P

2018 Vol.2(5)

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RESEARCH ARTICLE
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
Exohiss wave enhancement following substorm electron injection in the dayside magnetosphere
ZhongLei Gao, ZhenPeng Su, FuLiang Xiao, HuiNan Zheng, YuMing Wang, Shui Wang, H. E. Spence, G. D. Reeves, D. N. Baker, J. B. Blake, H. O. Funsten
2018, 2(5): 359-370. doi: 10.26464/epp2018033
Abstract:
Exohiss is a low-frequency structureless whistler-mode emission potentially contributing to the precipitation loss of radiation belt electrons outside the plasmasphere. Exohiss is usually considered the plasmaspheric hiss leaked out of the dayside plasmapause. However, the evolution of exohiss after the leakage has not been fully understood. Here we report the prompt enhancements of exohiss waves following substorm injections observed by Van Allen Probes. Within several minutes, the energetic electron fluxes around 100 keV were enhanced by up to 5 times, accompanied by an up to 10-time increase of the exohiss wave power. These substorm-injected electrons are shown to produce a new peak of linear growth rate in the exohiss band (< 0.1fce). The corresponding path-integrated growth rate of wave power within 10° latitude of the magnetic equatorial plane can reach 13.4, approximately explaining the observed enhancement of exohiss waves. These observations and simulations suggest that the substorm-injected energetic electrons could amplify the preexisting exohiss waves.
PLANETARY SCIENCE
Importance of electron distribution profiles to chorus wave driven evolution of Jovian radiation belt electrons
Jing Huang, XuDong Gu, BinBin Ni, Qiong Luo, Song Fu, Zheng Xiang, WenXun Zhang
2018, 2(5): 371-383. doi: 10.26464/epp2018035
Abstract:
Wave-particle interactions triggered by whistler-mode chorus waves are an important contributor to the Jovian radiation belt electron dynamics. While the sensitivity of chorus-driven electron scattering to the ambient magnetospheric and wave parameters has been investigated, there is rather limited understanding regarding the extent to which the dynamic evolution of Jovian radiation belt electrons, under the impact of chorus wave scattering, depends on the electron distribution profiles. We adopt a group of reasonable initial conditions based upon the available observations and models for quantitative analyses. We find that inclusion of pitch angle variation in initial conditions can result in increased electron losses at lower pitch angles and substantially modify the pitch angle evolution profiles of > ~500 keV electrons, while variations of electron energy spectrum tend to modify the evolution primarily of 1 MeV and 5 MeV electrons. Our results explicitly demonstrate the importance to the radiation belt electron dynamics in the Jovian magnetosphere of the initial shape of the electron phase space density, and indicate the extent to which variations in electron energy spectrum and pitch angle distribution can contribute to the evolution of Jovian radiation belt electrons caused by chorus wave scattering.
PLANETARY SCIENCE
Petrogenesis of basaltic shergottite NWA 8656
Ting Cao, Qi He, ZhuQing Xue
2018, 2(5): 384-397. doi: 10.26464/epp2018036
Abstract:
Most basaltic shergottites are too Mg-rich to represent parent melt compositions because they contain some cumulus pyroxenes. However, basaltic shergottite Northwest Africa (NWA) 8656 with subophitic texture can be used as the parent melt composition in petrogenetic studies because it contains no or rare cumulus pyroxenes. Its pyroxene cores (Mg# 66-68, the most magnesian) are in equilibrium with the bulk rock composition based on major (Fe-Mg) and trace elements (REE—rare earth elements). The patchy zoning of pyroxenes has been interpreted as reflecting a two-stage crystallization history: 1) crystallization of Mg-rich pyroxene cores at depth (50 km, the base of Martian crust), 2) crystallization of Fe-rich pyroxene rims at the shallow depth near the Martian surface with a fast cooling history. The crystallization of Fe-rich pyroxenes and the existence of different symplectites indicate that NWA 8656 underwent eruption. The oxygen fugacity of NWA 8656 (QFM –0.9±0.5) suggests an oxidized condition at the late-stage crystallization process, and the CI-normalized REE patterns of different minerals show enrichment in LREE, compared to that of depleted shergottites. Both of these observations suggest a relatively ITE (incompatible trace elements)-enriched signature of NWA 8656, similar to those of other enriched shergottites. The REE compositions of augite core and rim and plagioclase can be successfully reproduced by progressive crystallization without exogenous components, which indicates a closed magmatic system for NWA 8656. Consequently, we conclude that the ITE-enriched signature of NWA 8656 is inherited from an enriched mantle source rather than caused by crustal assimilation. Moreover, partial melting of depleted Martian mantle could not directly yield magmas that have geochemical characteristics similar to enriched shergottite parent magmas, so the enriched and depleted shergottites are derived from distinct mantle sources, and the mantle source of enriched shergottites would be expected to contain ilmenite.
PLANETARY SCIENCE
A new approach to study terrestrial yardang geomorphology based on high-resolution data acquired by unmanned aerial vehicles (UAVs): A showcase of whaleback yardangs in Qaidam Basin, NW China
Xiao Xiao, Jiang Wang, Jun Huang, Binlong Ye
2018, 2(5): 398-405. doi: 10.26464/epp2018037
Abstract:
Yardangs are wind-eroded ridges usually observed in arid regions on Earth and other planets. Previous geomorphology studies of terrestrial yardang fields depended on satellite data and limited fieldwork. The geometry measurements of those yardangs based on satellite data are limited to the length, the width, and the spacing between the yardangs; elevations could not be studied due to the relatively low resolution of the satellite acquired elevation data, e.g. digital elevation models (DEMs). However, the elevation information (e.g. heights of the yardang surfaces) and related information (e.g. slope) of the yardangs are critical to understanding the characteristics and evolution of these aeolian features. Here we report a novel approach, using unmanned aerial vehicles (UAVs) to generate centimeter-resolution orthomosaics and DEMs for the study of whaleback yardangs in Qaidam Basin, NW China. The ultra-high-resolution data provide new insights into the geomorphology characteristics and evolution of the whaleback yardangs in Qaidam Basin. These centimeter-resolution datasets also have important potential in: (1) high accuracy estimation of erosion volume; (2) modeling in very fine scale of wind dynamics related to yardang formation; (3) detailed comparative planetary geomorphology study for Mars, Venus, and Titan.
SOLID EARTH: SEISMOLOGY
Fine relocation, mechanism, and tectonic indications of middle-small earthquakes in the Central Tibetan Plateau
YuLan Li, BaoShan Wang, RiZheng He, HongWei Zheng, JiangYong Yan, Yao Li
2018, 2(5): 406-419. doi: 10.26464/epp2018038
Abstract:
The medium-small earthquakes that occurred in the middle part of Tibetan Plateau (32°N–36°N, 90°E–93°E) from August 2016 to June 2017 were relocated using the absolute earthquake location method Hypo2000. Compared to the reports of Chinese Seismological Networks, our relocation results are more clustered on the whole, the horizontal location differences exceed 10 km, and the focal depths are concentrated in 0–8 km, which indicates that the upper crust inside the Tibetan Plateau is tectonically active. In June 2017 altogether eight earthquakes above magnitude 3.0 took place; their relocated epicenters are concentrated around Gêladaindong. The relocation results of M<3.0 small earthquakes also showed obvious differences. Therefore, we used the CAP method to invert for the focal mechanisms of theM ≥3.0 earthquakes; results generally tally with the surface geological structures, indicating that the Tibetan Plateau is still under the strong compressional force from the India Plate. Among them the eight earthquakes that occurred near Gêladaindong in June 2017 are all of normal fault type or with some strike-slip at the same time; based on previous research results we conjecture that these events are intense shallow crust responses to deep crust-mantle activities.
SOLID EARTH: SEISMOLOGY
Seismic characteristics of the 15 February 2013 bolide explosion in Chelyabinsk, Russia
Zhi Wei, LianFeng Zhao, XiaoBi Xie, JinLai Hao, ZhenXing Yao
2018, 2(5): 420-429. doi: 10.26464/epp2018039
Abstract:
The seismological characteristics of the 15 February 2013 Chelyabinsk bolide explosion are investigated based on seismograms recorded at 50 stations with epicentral distances ranging from 229 to 4324 km. By using 8–25 s vertical-component Rayleigh waveforms, we obtain a surface-wave magnitude of 4.17±0.31 for this event. According to the relationship among the Rayleigh-wave magnitude, burst height and explosive yield, the explosion yield is estimated to be 686 kt. Using a single-force source to fit the observed Rayleigh waveforms, we obtain a single force of 1.03×1012 N, which is equivalent to the impact from the shock wave generated by the bolide explosion.
SOLID EARTH: EXPLORATION GEOPHYSICS
Two-dimensional regularized inversion of AMT data based on rotation invariant of Central impedance tensor
XiaoZhong Tong, JianXin Liu, AiYong Li
2018, 2(5): 430-437. doi: 10.26464/epp2018040
Abstract:
Considering the uncertainty of the electrical axis for two-dimensional audo-magnetotelluric (AMT) data processing, an AMT inversion method with the Central impedance tensor was presented. First, we present a calculation expression of the Central impedance tensor in AMT, which can be considered as the arithmetic mean of TE-polarization mode and TM-polarization mode in the two-dimensional geo-electrical model. Second, a least-squares iterative inversion algorithm is established, based on a smoothness-constrained model, and an improved L-curve method is adopted to determine the best regularization parameters. We then test the above inversion method with synthetic data and field data. The test results show that this two-dimensional AMT inversion scheme for the responses of Central impedance is effective and can reconstruct reasonable two-dimensional subsurface resistivity structures. We conclude that the Central impedance tensor is a useful tool for two-dimensional inversion of AMT data.