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ISSN  2096-3955

CN  10-1502/P

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On the solar activity dependence of midnight equatorial plasma bubbles during June solstice periods
K. K. Ajith, S. Tulasi Ram, GuoZhu Li, M. Yamamoto, K. Hozumi, C. Y. Yatini, P. Supnithi
Recently Published , doi: 10.26464/epp2021039
[Abstract](68) [FullText HTML](14) [PDF 8629KB](5)
The occurrence of midnight Equatorial Plasma Bubbles (EPBs) during the June solstice period of the ascending phase of solar cycle 24, from 2010 to 2014, was studied using data from the 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia. The analysis shows that the occurrence of midnight hour EPBs was at its maximum during the low solar activity year 2010 and monotonically decreased thereafter with increasing solar activity. Details of the dependence of midnight hour EPB occurrence on solar activity were investigated using SAMI2 model simulation with a realistic input of E × B drift velocity data obtained from the CINDI-IVM onboard the C/NOFS satellite. Results obtained from term-by-term analysis of the flux tube integrated linear growth rate of RT instability indicate that the formation of a high flux tube electron content height gradient (steep vertical gradient) region at higher altitudes, due to the elevated F layer, is the key factor enhancing the growth rate of RT instability during low solar activity June solstices. Other factors are discussed in light of the relatively weak westward zonal electric field in the presence of the equatorward neutral wind and north-to-south transequatorial wind around the midnight hours of low solar activity June solstices. Also discussed are the initial seeding of RT instability by MSTIDs and how the threshold height required for EPB development varies with solar activity.
Review of ionospheric irregularities and ionospheric electrodynamic coupling in the middle latitude region
Yi Liu, Chen Zhou, Tong Xu, Qiong Tang, ZhongXin Deng, GuanYi Chen, ZhuangKai Wang
Recently Published , doi: 10.26464/epp2021025
[Abstract](362) [FullText HTML](50) [PDF 14023KB](14)
This paper briefly reviews ionospheric irregularities that occur in the E and F regions at mid-latitudes. Sporadic E (ES) is a common ionospheric irregularity phenomenon that is first noticed in the E layer. ES mainly appears during daytime in summer hemispheres, and is formed primarily from neutral wind shear in the mesosphere and lower thermosphere (MLT) region. Field-aligned irregularity (FAI) in the E region is also observed by Very High Frequency (VHF) radar in mid-latitude regions. FAI frequently occurs after sunset in summer hemispheres, and spectrum features of E region FAI echoes suggest that type-2 irregularity is dominant in the nighttime ionosphere. A close relationship between ES and E region FAI implies that ES may be a possible source of E region FAI in the nighttime ionosphere. Strong neutral wind shear, steep ES plasma density gradient, and a polarized electric field are the significant factors affecting the formation of E region FAI. At mid-latitudes, joint observational experiments including ionosonde, VHF radar, Global Positioning System (GPS) stations, and all-sky optical images have revealed strong connections across different scales of ionospheric irregularities in the nighttime F region, such as spread F (SF), medium-scale traveling ionospheric disturbances (MSTID), and F region FAI. Observations suggest that different scales of ionospheric irregularities are generally attributed to the Perkins instability and subsequently excited gradient drift instability. Nighttime MSTID can further evolve into small-scale structures through a nonlinear cascade process when a steep plasma density gradient exists at the bottom of the F region. In addition, the effect of ionospheric electrodynamic coupling processes, including ionospheric E-F coupling and inter-hemispheric coupling on the generation of ionospheric irregularities, becomes more prominent due to the significant dip angle and equipotentiality of magnetic field lines in the mid-latitude ionosphere. Polarized electric fields can map to different ionospheric regions and excite plasma instabilities which form ionospheric irregularities. Nevertheless, the mapping efficiency of a polarized electric field depends on the ionospheric background and spatial scale of the field.
Teleseismic waves reveal anisotropic poroelastic response of wastewater disposal reservoir
Andrew J Barbour, Nicholas M Beeler
Recently Published , doi: 10.26464/epp2021034
[Abstract](353) [FullText HTML](101) [PDF 1789KB](28)
Connecting earthquake nucleation in basement rock to fluid injection in basal, sedimentary reservoirs, depends heavily on choices related to the poroelastic properties of the fluid-rock system, thermo-chemical effects notwithstanding. Direct constraints on these parameters outside of laboratory settings are rare, and it is commonly assumed that the rock layers are isotropic. With the Arbuckle wastewater disposal reservoir in Osage County, Oklahoma, high-frequency formation pressure changes and collocated broadband ground velocities measured during the passing of large teleseismic waves show a poroelastic response of the reservoir that is both azimuthally variable and anisotropic; this includes evidence of static shifts in pressure that presumably relate to changes in local permeability. The azimuthal dependence in both the static response and shear coupling appears related to tectonic stress and strain indicators such as the orientations of the maximum horizontal stress and faults and fractures. Using dynamic strains from a nearby borehole strainmeter, we show that the ratio of shear to volumetric strain coupling is \begin{document}$ \sim 0.41 $\end{document} which implies a mean Skempton's coefficient of \begin{document}$ A = 0.24 $\end{document} over the plausible range of the undrained Poisson's ratio. Since these observations are made at relatively low confining pressure and differential stress, we suggest that the hydraulically conductive fracture network is a primary control on the coupling between pore pressure diffusion and elastic stresses in response to natural or anthropogenic sources.
Determination of the local magnitudes of small earthquakes using a dense seismic array in the Changning−Zhaotong Shale Gas Field, Southern Sichuan Basin
Wen Yang, GuoYi Chen, LingYuan Meng, Yang Zang, HaiJiang Zhang, JunLun Li
Recently Published , doi: 10.26464/epp2021026
[Abstract](660) [FullText HTML](158) [PDF 4574KB](23)
With the development of unconventional shale gas in the southern Sichuan Basin, seismicity in the region has increased significantly in recent years. Though the existing sparse regional seismic stations can capture most earthquakes with \begin{document}$ {M}_{\mathrm{L}}\ge 2.5 $\end{document}, a great number of smaller earthquakes are often omitted due to limited detection capacity. With the advent of portable seismic nodes, many dense arrays for monitoring seismicity in the unconventional oil and gas fields have been deployed, and the magnitudes of those earthquakes are key to understand the local fault reactivation and seismic potentials. However, the current national standard for determining the local magnitudes was not specifically designed for monitoring stations in close proximity, utilizing a calibration function with a minimal resolution of 5 km in the epicentral distance. That is, the current national standard tends to overestimate the local magnitudes for stations within short epicentral distances, and can result in discrepancies for dense arrays. In this study, we propose a new local magnitude formula which corrects the overestimated magnitudes for shorter distances, yielding accurate event magnitudes for small earthquakes in the Changning−Zhaotong shale gas field in the southern Sichuan Basin, monitored by dense seismic arrays in close proximity. The formula is used to determine the local magnitudes of 7,500 events monitored by a two-phased dense array with several hundred 5 Hz 3C nodes deployed from the end of February 2019 to early May 2019 in the Changning−Zhaotong shale gas field. The magnitude of completeness (\begin{document}$ {M}_{\mathrm{C}} $\end{document}) using the dense array is −0.1, compared to \begin{document}$ {M}_{\mathrm{C}} $\end{document} 1.1 by the sparser Chinese Seismic Network (CSN). In addition, using a machine learning detection and picking procedure, we successfully identify and process some 14,000 earthquakes from the continuous waveforms, a ten-fold increase over the catalog recorded by CSN for the same period, and the \begin{document}$ {M}_{\mathrm{C}} $\end{document} 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 future earthquakes using dense arrays in the shale gas fields of the Sichuan Basin. This will help to better characterize the local seismic risks and potentials.


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Influence of reference states on Jupiter’s dynamo simulations
LongHui Yuan, YuFeng Lin, Chris A. Jones
2021, 5(4): 305 -313   doi: 10.26464/epp2021041
Jupiter’s magnetic field is thought to be generated in its deep metallic hydrogen region through dynamo action, yet the detailed dynamic process remains poorly understood. Numerical simulations have produced Jupiter-like magnetic fields, albeit using different control parameters and reference state models. In this study, we investigate the influence of different reference state models, based on ab initio calculations and based on the polytropic equation of state. In doing so, we perform five anelastic convection dynamo simulations that can be divided into two groups. In each group, different reference states are used while other control parameters and conditions are set to be identical. We find the reference state model can be very influential for the simulations in which buoyancy force is dominant over the Lorentz force. In this regime, different dynamical outcomes can be attributed to the effective buoyancy force resulting from different reference states. For simulations in which the Lorentz force is dominant over the buoyancy force, however, dynamo actions tend to be insensitive to different reference state models. If Jupiter’s dynamo is in a strong field regime, i.e., the Lorentz force plays a dominant role, our numerical results suggest that Jupiter’s internal reference state, which remains poorly constrained, may play a minor role in the dynamo process of the planet.
Large-scale episodic enhancements of relativistic electron intensities in Jupiter's radiation belt
ChongJing Yuan, YiQiao Zuo, Elias Roussos, Yong Wei, YiXin Hao, YiXin Sun, Norbert Krupp
2021, 5(4): 314 -326   doi: 10.26464/epp2021037
Previous studies indicate that, in the Jovian magnetosphere, the long-term trend of the radial profile of relativistic electron intensities is primarily shaped by slow radial diffusion. However, measurements by the Galileo spacecraft reveal the existence of transient increases in MeV electron intensities well above the ambient distribution. It is unclear how common such transient enhancements are, and to which dynamic processes in Jupiter's magnetosphere their occurrence is linked. We investigate the radial distributions of \begin{document}$>$\end{document}11 MeV and \begin{document}$>$\end{document}1 MeV electron intensities from \begin{document}$9R_{J}$\end{document} to \begin{document}$40R_{J}$\end{document} (\begin{document}$R_{J}=71492\;{\rm{km}}$\end{document} denotes the Jovian radius), measured by the Galileo spacecraft from 1996 to 2002. We find transient enhancements of MeV electrons during seven Galileo crossings, mostly occurring around ~20RJ. An apparent dawn-dusk asymmetry of their occurrence is resolved, with a majority of events discovered at dawn. This dawn-dusk asymmetry, as well as the average recurrence time scale of a few days, implies a potential relationship between the MeV electron transients and the storm-like dynamics in the middle and outer magnetosphere detected using a variety of Galileo, Juno and remote sensing aurora observations. We suggest that the observations of some of these transients in the inner magnetosphere may result from a synergy between the convective transport by a large-scale dawn-dusk electric field and the sources provided by injections in the middle magnetosphere.
Response of atmospheric carbon dioxide to the secular variation of weakening geomagnetic field in whole atmosphere simulations
Xu Zhou, XinAn Yue, Han-Li Liu, Yong Wei, YongXin Pan
2021, 5(4): 327 -336   doi: 10.26464/epp2021040
Responses of atmospheric carbon dioxide (CO2) density to geomagnetic secular variation are investigated using the Whole Atmosphere Community Climate Model-eXtended (WACCM-X). Our ensemble simulations show that CO2 volume mixing ratios (VMRs) increase at high latitudes and decrease at mid and low latitudes by several ppmv in response to a 50% weakening of the geomagnetic field. Statistically significant changes in CO2 are mainly found above ~90 km altitude and primarily redetermine the energy budget at ~100–110 km. Our analysis of transformed Eulerian mean (TEM) circulation found that CO2 change is caused by enhanced upwelling at high latitudes and downwelling at mid and low latitudes as a result of increased Joule heating. We further analyzed the atmospheric CO2 response to realistic geomagnetic weakening between 1978 and 2013, and found increasing (decreasing) CO2 VMRs at high latitudes (mid and low latitudes) accordingly. For the first time, our simulation results demonstrate that the impact of geomagnetic variation on atmospheric CO2 distribution is noticeable on a time scale of decades.
Preservation and variation of ion-to-electron temperature ratio in the plasma sheet in geo-magnetotail
ChuXin Chen
2021, 5(4): 337 -347   doi: 10.26464/epp2021035
The ion-to-electron temperature ratio is a good indicator of the processes involved in solar wind plasma entering and being transported inside Earth’s plasma sheet. In this study, we have demonstrated that patchy magnetic reconnection has the potential to preserve the ion-to-electron temperature ratio under certain conditions. If the charged particles are non-adiabatically accelerated no more than once in a single reconnection, the temperature ratio would be preserved; on the other hand, this ratio would not be preserved if they are accelerated multiple times. Consequently, under a northward interplanetary magnetic field (IMF) condition, the reconnection in the nonlinear phase of the Kelvin–Helmholtz instability is the dominant process for solar-originated plasma entering the Earth’s magnetosphere, and the ion-to-electron temperature ratio is preserved inside the plasma sheet. When the direction of the IMF is southward, the reflection of electrons from the magnetic mirror point, and subsequent multiple non-adiabatic accelerations at the reconnection site, are the primary reasons for the observed low ion-to-electron temperature ratio close to the Earth at midnight. While reconnections that occur in the night-side far tail might preserve the ratio, turbulence on the boundaries of the bursty bulk flows (BBFs) could change the ratio in the far tail through the violation of the frozen-in condition of the ions. The plateau in the contour of the calculated ion-to-electron temperature ratio in the down tail distance between 40 and 60 Earth radii may explain the strong correlation between the ion and electron temperatures in the outer central plasma sheet, which has not been clearly understood till date.
Upper crustal velocity and seismogenic environment of the M7.0 Jiuzhaigou earthquake region in Sichuan, China
DaHu Li, ZhiFeng Ding, Yan Zhan, PingPing Wu, LiJun Chang, XiangYu Sun
2021, 5(4): 348 -361   doi: 10.26464/epp2021038
On August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China. The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad. The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area; the complex tectonic background and the reason(s) for the frequent seismicity in the Jiuzhaigou earthquake region are unclear. In order to reveal the characteristics of the deep medium and the seismogenic environment of the M7.0 Jiuzhaigou earthquake region, and to interpret the tectonic background and genesis of the seismicity comprehensively, in this paper, we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale, dense mobile seismic array (China Array) for the northern section of the North–South Seismic Belt around Jiuzhaigou earthquake region. Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region, we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region, its deep tectonic environment, and the ongoing seismic risk in this region. We report that: the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity; the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology; the M7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust; the mainshock of the M7.0 earthquake occurred in the upper crust; the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence. The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB (Songpan–Garzê Block) stretches into MSM (Minshan Mountain), and migrates to the northeast, but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block. Our results reveal an uneven distribution of high- and low-velocity structures around the Tazang segment of the East Kunlun fault zone. Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault, it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu–Maqên segment of the East Kunlun fault zone.
A preliminary report of the Yangbi, Yunnan, MS6.4 earthquake of May 21, 2021
ZhiGao Yang, Jie Liu, Xue-Mei Zhang, WenZe Deng, GuangBao Du, XiYan Wu
2021, 5(4): 362 -364   doi: 10.26464/epp2021036
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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 brief review of equatorial ionization anomaly and ionospheric irregularities
Nanan Balan, LiBo Liu, HuiJun Le
2018, 2(4): 257-275   doi: 10.26464/epp2018025
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
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
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
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
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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