EPP

地球与行星物理

ISSN  2096-3955

CN  10-1502/P

2022 Vol.6(4)

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RESEARCH ARTICLE
SPACE PHYSICS:IONOSPHERIC PHYSICS
Incoherent scatter radar (ISR) observations of high-frequency enhanced ion and plasma lines induced by X/O mode pumping around the critical altitude
Jun Wu, Jian Wu, I. Haggstrom, Tong Xu, ZhengWen Xu, YanLi Hu
2022, 6(4): 305-312. doi: 10.26464/epp2022038
Abstract:
Analysis of Incoherent Scatter Radar (ISR) data collected during an experiment involving alternating O/X mode pumping reveals that the high-frequency enhanced ion line (HFIL) and plasma line (HFPL) did not appear immediately after the onset of pumping, but were delayed by a few seconds. By examining the initial behaviors of the ion line, plasma line, and electron temperature, as well as ionosphere conditions, we find that (1) the HFIL and HFPL were delayed not only in the X mode pumping but also in the O mode pumping and (2) the HFIL was not observed prior to enhancement of the electron temperature. Our analysis suggests that (1) leakage of the X mode to the O mode pumping may not be ignored and (2) spatiotemporal uncertainties and spatiotemporal variations in the profiles of ion mass and electron density may have played important roles in the apparent failure of the Bragg condition to apply; (3) nevertheless, the absence of parametric decay instability (PDI) cannot be ruled out, due to our inability to match conditions caused by the spatiotemporal uncertainties.
SPACE PHYSICS: IONOSPHERIC PHYSICS
Ionospheric TEC and plasma anomalies possibly associated with the 14 July 2019 Mw7.2 Indonesia Laiwui earthquake, from analysis of GPS and CSES data
YuanZheng Wen, Dan Tao, GuangXue Wang, JiaYi Zong, JinBin Cao, Roberto Battiston, ZhiMa ZeRen, XuHui Shen
2022, 6(4): 313-328. doi: 10.26464/epp2022028
Abstract:
This study presents signatures of seismo-ionospheric perturbations possibly related to the 14 July 2019 \begin{document}$ {M}_{w} $\end{document}7.2 Laiwui earthquake, detected by a cross-validation analysis of total electron content (TEC) data of the global ionospheric map (GIM) from GPS and plasma parameter data recorded by the China Seismo-Electromagnetic Satellite (CSES). After separating pre-seismic ionospheric phenomena from the ionospheric disturbances due to the magnetospheric and solar activities, we have identified three positive temporal anomalies, around the epicenter, at 1 day, 3 days and 8 days before the earthquake (14 July 2019), along with a negative anomaly 6 days after the earthquake. These results agree well with the TEC spatial variations in latitude–longitude–time (LLT) maps. To confirm these anomalies further, we employed the moving mean method (MMM) to analyze ionospheric plasma parameters (electron, \begin{document}$ {\mathrm{O}}^{+} $\end{document}and \begin{document}$ {\mathrm{H}\mathrm{e}}^{+} $\end{document}densities) recorded by the Langmuir probe (LAP) and Plasma Analyzer Package (PAP) onboard the CSES. The analysis detected on, on Day Two, Day Four, and Day Seven before the earthquake, remarkable enhancements along the orbits around when in proximity to the epicenter. To make the investigations still more convincing, we compared the orbits on which anomalous readings were recorded to their corresponding four nearest revisiting orbits; the comparison did indeed indicate the existence of plasma parameter anomalies that appear to be associated with the Laiwui earthquake. All these results illustrate that the unusual ionospheric perturbations detected through GPS and CSES data are possibly associated with the \begin{document}$ {M}_{w}7.2 $\end{document} Laiwui earthquake, which suggests that at least some earthquakes may be predicted by alertness to pre-seismic ionospheric anomalies over regions known to be at seismic risk. This case study also contributes additional information of value to our understanding of lithosphere–atmosphere–ionosphere coupling.
Effects of polarization-reverse
Effects of polarization-reversed electromagnetic ion cyclotron waves on the ring current dynamics
MingHui Zhu, YiQun Yu, Xing Cao, BinBin Ni, XingBin Tian, JinBin Cao, Vania K. Jordanova
2022, 6(4): 329-338. doi: 10.26464/epp2022037
Abstract:
Electromagnetic ion cyclotron (EMIC) waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics. Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization. However, recent studies have found that the reversal of polarization, which occurs at higher latitudes along the wave propagation path, can change the wave-induced pitch angle diffusion coefficients. Whether such a polarization reversal can influence the global ring current dynamics remains unknown. In this study, we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current–atmosphere interactions model (RAM). The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or >100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized. Additionally, the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal, especially during prestorm time and the recovery phase, but the effects are not large during the main phase. This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E < 10 keV, an energy range that is not strongly affected by the polarization reversal.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
Statistical study of “trunk-like” heavy ion structures in the inner magnetosphere
Hao Zhang, YaBing Wang, JianYong Lu
2022, 6(4): 339-349. doi: 10.26464/epp2022032
Abstract:
We present a statistical study of “trunk-like” structures observed in He+ and O+ in the inner magnetosphere. The main characteristic of these structures is that the energy of the peak flux decreases earthward. Using observations from the Helium Oxygen Proton Electron (HOPE) instrument onboard Van Allen Probe A, we identify the trunks observed from November 2012 to June 2019 and obtain the universal time, L shell, magnetic local time (MLT), and energy information of each trunk’s root and tip. We then investigate the behavior of trunks in terms of their frequency of occurrence, temporal evolution, spatial and energy distribution, and trunk dependence on different geomagnetic indices. We find that (1) the trunks are always located at L = 1.5−4.0 and have a preferential location mainly concentrated at MLT = 18−24, (2) the sector within MLT = 14−16 is a forbidden zone without trunk roots, and (3) the energy of He+ trunks is the largest near dusk and gradually decreases in the counterclockwise direction, whereas the energy of O+ trunks is relatively evenly distributed with MLT and L. The differences between He+ and O+ trunks are probably due to the different charge exchange and Coulomb collision lifetime. The dependence on different geomagnetic indices indicates that the trunk structures occur more frequently during relatively quiet periods.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
A machine-learning-based electron density (MLED) model in the inner magnetosphere
QingHua Zhou, YunXiang Chen, FuLiang Xiao, Sai Zhang, Si Liu, Chang Yang, YiHua He, ZhongLei Gao
2022, 6(4): 350-358. doi: 10.26464/epp2022036
Abstract:
Plasma density is an important factor in determining wave-particle interactions in the magnetosphere. We develop a machine-learning-based electron density (MLED) model in the inner magnetosphere using electron density data from Van Allen Probes between September 25, 2012 and August 30, 2019. This MLED model is a physics-based nonlinear network that employs fundamental physical principles to describe variations of electron density. It predicts the plasmapause location under different geomagnetic conditions, and models separately the electron densities of the plasmasphere and of the trough. We train the model using gradient descent and backpropagation algorithms, which are widely used to deal effectively with nonlinear relationships among physical quantities in space plasma environments. The model gives explicit expressions with few parameters and describes the associations of electron density with geomagnetic activity, solar cycle, and seasonal effects. Under various geomagnetic conditions, the electron densities calculated by this model agree well with empirical observations and provide a good description of plasmapause movement. This MLED model, which can be easily incorporated into previously developed radiation belt models, promises to be very helpful in modeling and improving forecasting of radiation belt electron dynamics.
A new inclination-based method to evaluate the global geomagnetic configuration and axial dipole moment
KaiHua Xu, Fei He, Yong Wei, Ross N. Mitchell, Si Chen, YuQi Wang, ZhaoJin Rong
2022, 6(4): 359-365. doi: 10.26464/epp2022030
Abstract:
The strength and configuration of the geomagnetic field control the average shape of the magnetosphere. The pure dipole assumption and the virtual dipole moment (VDM), determined by individual records, have been widely adopted to evaluate the strength of the geomagnetic field in geological time. However, such an assumption might not be valid during geomagnetic transitions, such as reversals and excursions. The traditional spherical harmonic modeling of the geomagnetic field could be difficult to implement because accurate global records are lacking. Here, we report that an empirical relationship exists between the ratio of the VDM to the true axial dipole moment (VDM/ADM) and the ratio of the power of the axial dipole to that of the non-axial dipole (AD/NAD) based on a new method utilizing globally distributed inclination records. The root mean square global deviation of inclination (RMSΔI) to the standard inclination distribution of the AD was fitted to the AD/NAD with a cubic polynomial by utilizing a large number of geodynamo simulations. Tests with geomagnetic field models showed that the AD/NAD derived from the RMSΔI agreed well with that calculated by using the Gauss coefficients, and the estimated ADM was consistent with the true value. Finally, the application of volcanic records during the Laschamp excursion showed the VDM might overestimate the ADM by a factor of 3. Our new method will be useful in future studies that characterize the configuration of the geomagnetic field and the strength of the axial dipole.
Vertical crustal deformation velocity and its influencing factors over the Qinghai–Tibet Plateau based on satellite gravity data
HuRong Duan, JunGang Guo, LingKang Chen, JiaShuang Jiao, HeTing Jian
2022, 6(4): 366-377. doi: 10.26464/epp2022034
Abstract:
The uplift of the Qinghai–Tibet Plateau (TP) strongly influences climate change, both regionally and globally. Surface observation data from this region have limited coverage and are difficult to obtain. Consequently, the vertical crustal deformation velocity (VCDV) distribution of the TP is poorly constrained. In this study, the VCDV from the TP was inverted by using data from the gravity recovery and climate experiment (GRACE). We were able to obtain the vertical crustal movement by deducting the hydrological factors, based on the assumption that the gravity signal detected by GRACE is mainly composed of hydrological factors and vertical crustal movement. From the vertical crustal movement, we inverted the distribution of the VCDV across the TP. The results showed that the VCDV of the southern, eastern, and northern TP is ~1.1 mm/a, ~0.5 mm/a, and −0.1 mm/a, respectively, whereas that of the region between the Qilian Haiyuan Fault and the Kunlun Fault is ~0.0 mm/a. These results are consistent with the distribution of crustal deformation, thrust earthquakes and faults, and regional lithospheric activity. The hydrology, crustal thickness, and topographic factors did not change the overall distribution of the VCDV across the TP. The influence of hydrological factors is marked, with the maximum differences being approximately −0.4 mm/a in the northwest and 1.0 mm/a in the central area. The results of this study are significant for understanding the kinematics of the TP.
SOLID EARTH: GEODESY AND GRAVITY
Interpretation of locally high gravity anomalies using terrestrial gravity data in Bagodo, North Cameroon
Apollinaire Bouba, Kasi Njeudjang, Loudi Yap, Bouba Saidou, Joseph Kamguia, Tabod Charles Tabod
2022, 6(4): 378-384. doi: 10.26464/epp2022033
Abstract:
In this work, we interpreted gravity data to determine the structural characteristics responsible for high-gravity anomalies in Bagodo, North Cameroon. These anomalies had not previously been characterized through a local study. Thus, we undertook a regional–residual separation of the gravity anomalies by using the polynomial method. Geophysical signatures of near-surface small-extent geological structures were revealed. To conduct a quantitative interpretation of the gravity anomalies, one profile was drawn on a residual Bouguer anomaly map and then interpreted by spectral analysis, the ideal body solution, and 2.5-dimensional modeling. Our results showed that the intrusive body in the Bagodo area consists of two trapezoidal blocks. The first and second blocks have roofs approximately 7.5 and 14 km deep, respectively, whereas their bases are approximately 17 km deep. These values are in agreement with those obtained by the ideal body solution, which showed two cells with a density contrast of 0.3 g·cm−3 in comparison with the surrounding rocks. The density of this body was estimated to be approximately 3 g·cm−3. The topography of these rocks showed that they are basaltic rocks that would have cooled in fracture zones as an intrusion.
Application of active-source surface waves in urban underground space detection: A case study of Rongcheng County, Hebei, China
GuangWen Wang, HaiYan Wang, HongQiang Li, ZhanWu Lu, WenHui Li, TaiRan Xu
2022, 6(4): 385-398. doi: 10.26464/epp2022039
Abstract:
Active-source surface wave exploration is advantageous because it has high imaging accuracy, is not affected by high-speed layers, and has a low cost; thus, it has unique advantages for investigating shallow surface structures. For the development and utilization of urban underground space, two parameters in the shallow surface are important, namely, the shear wave velocity (VS) and the predominant period of the site, which determine the elevation and aseismic grade of the building design. The traditional method is mainly to obtain the two above-mentioned parameters through testing and measuring drilling samples. However, this method is extremely expensive and time consuming. Therefore, in this research, we used the multichannel surface wave acquisition method to extract the fundamental dispersion curve of single-shot data by using the phase shift method and obtain the VS characteristics in the uppermost 40 m by inversion. We arrived at the following two conclusions based on the VS profile. First, the study area can be roughly divided into five layers, among which the layers 0−8 m, 14−20 m, and 20−30 m are low-velocity layers, corresponding to miscellaneous fill, a water-bearing sand layer, and a sand layer; therefore, the VS is relatively low. In contrast, the layers at 8−14 m and 30−40 m are high-velocity layers that are mainly composed of clay, with a relatively better compactness and relatively high VS values. In addition, a low-speed anomaly appears abruptly in the high-speed area at 20−40 m. This anomaly, when combined with geological data, suggests that it is an ancient river channel. Second, from the VS value, the \begin{document}$ {V}_{Se} $\end{document} (equivalent shear wave velocity) was calculated. The construction site soil was categorized as class III, with good conditions for engineering geology. In addition, we calculated the predominant period of the site to be 0.56–0.77 s based on the VS. Therefore, in the overall structural design of the foundation engineering, the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.
SOLID EARTH: COMPUTATIONAL GEOPHYSICS
The anisotropy of hexagonal close-packed iron under inner core conditions: the effect of light elements
Wei Zhang, Mei Tang, ZhenWei Niu
2022, 6(4): 399-423. doi: 10.26464/epp2022035
Abstract:
In recent decades, global seismic observations have identified increasingly complex anisotropy of the Earth’s inner core. Numerous seismic studies have confirmed hemispherical variations in the inner core’s anisotropy. Here, based on ab initio molecular dynamics calculations, we report how the anisotropy of hexagonal close-packed (hcp)-iron, under inner core conditions, could be altered when alloyed with light elements. We find that light elements in binary allows with iron — hcp-Fe-X (X = C, O, Si, and S) — could have significant effects on density, sound velocities, and anisotropy, compared with the behavior of pure hcp-iron; the anisotropy of these binary alloys depends on combined effects of temperature and the particular alloying light element. Furthermore, the change in anisotropy strength with increasing temperature can be charted for each alloy. Alloying pure iron with some light elements such as C or O actually does not increase but decreases core anisotropy at high temperatures. But the light element S can significantly enhance the elastic anisotropy strength of hcp-Fe.
PERSPECTIVE
SOLID EARTH: TECTONOPHYSICS
No seamount subduction, no magmatic arc?
XiaoBo He, JunTao Tao, Yi Cao, FaBin Pan, EnYuan He, LingMin Cao, YiXian Zheng
2022, 6(4): 424-429. doi: 10.26464/epp2022031
Abstract:
Water is essential for the formation of a magmatic arc by lowering the melting temperature of materials in the mantle wedge. As such, it is logical to attribute the absence of a magmatic arc to insufficient water released from the subducting plate, although a number of other factors may cause volcanic arc quiescence as well, such as a slab window or flat slab subduction. In this contribution, we present a possible but testable correlation between the occurrence of a magmatic arc and seamount subduction in light of bathymetric data obtained near trenches. This correlation, if it holds true, in turn means that a magmatic arc is unlikely to occur when the subducting slabs have not been severely fractured and that one of the main reasons for excluding effects such as the slab window or flat slab subduction may be that the plate is not accompanied by seamounts. Therefore, the role that seamount subduction plays in recycling water back into the mantle deserves more attention from the earth sciences community.