ISSN  2096-3955

CN  10-1502/P

2018 Vol.2(4)

Display Mode:          |     

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
Following a brief history and progress of ionospheric research, this paper presents a brief review of the recent developments in the understanding of two major phenomena in low and mid latitude ionosphere—the equatorial ionization anomaly (EIA) and involved equatorial plasma fountain (EPF) and ionospheric irregularities. Unlike the easy-to-understand misinterpretations, the EPF involves field perpendicularE×B plasma drift and field-aligned plasma diffusion acting together and plasma flowing in the direction of the resultant at all points along the field lines at all altitudes. The EIA is formed mainly from the removal of plasma from around the equator by the upward E×B drift creating the trough and consequently the crests with small accumulation of plasma at the crests when the crests are within ~±20° magnetic latitudes and no accumulation when they are beyond ~±25° magnetic latitudes. The strong EIA under magnetically active conditions arises from the simultaneous impulsive action of eastward prompt penetration electric field and equatorward neutral wind. Intense ionospheric irregularities develop in the post-sunset bottom-side equatorial ionosphere when it rises to high altitudes, and evolve nonlinearly into the topside. Pre-reversal enhancement (PRE) of the vertical upward E×B drift and its fluctuations amplified during PRE provide the driving force and seed, with neutral wind and gravity waves being the primary sources. At low solar activity especially in summer when fast varying PRE is absent, the slow varying gravity waves including large scale waves (LSW) seem to act as both driver and seed for weak irregularities. At mid latitudes, the irregularities are weak and associated with medium scale traveling ionospheric disturbances (MSTIDs). A low latitude minimum in the occurrence of the irregularities at March equinox predicted by theoretical models is identified. The minimum occurs on the poleward side of the EIA crest and shifts equatorward from ~25° magnetic latitudes at high solar activity to below 17° at low solar activity.
The FGOALS climate system model as a modeling tool for supporting climate sciences: An overview
TianJun Zhou, Bin Wang, YongQiang Yu, YiMin Liu, WeiPeng Zheng, LiJuan Li, Bo Wu, PengFei Lin, Zhun Guo, WenMin Man, Qing Bao, AnMin Duan, HaiLong Liu, XiaoLong Chen, Bian He, JianDong Li, LiWei Zou, XiaoCong Wang, LiXia Zhang, Yong Sun, WenXia Zhang
2018, 2(4): 276-291. doi: 10.26464/epp2018026
Climate system models are useful tools for understanding the interactions among the components of the climate system and predicting/projecting future climate change. The development of climate models has been a central focus of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP) since the establishment of the laboratory in 1985. In China, many pioneering component models and fully coupled models of the climate system have been developed by LASG/IAP. The fully coupled climate system developed in the recent decade is named FGOALS (Flexible Global Ocean-Atmosphere-Land System Model). In this paper, an application-oriented review of the LASG/IAP FGOALS model is presented. The improved model performances are demonstrated in the context of cloud-radiation processes, Asian monsoon, ENSO phenomena, Atlantic Meridional Overturning Circulation (AMOC) and sea ice. The FGOALS model has contributed to both CMIP5 (Coupled Model Intercomparison Project-phase 5) and IPCC (Intergovernmental Panel on Climate Change) AR5 (the Fifth Assessment Report). The release of FGOALS data has supported the publication of nearly 500 papers around the world. The results of FGOALS are cited ~106 times in the IPCC WG1 (Working Group 1) AR5. In addition to the traditional long-term simulations and projections, near-term decadal climate prediction is a new set of CMIP experiment, progress of LAGS/IAP in the development of near-term decadal prediction system is reviewed. The FGOALS model has supported many Chinese national-level research projects and contributed to the national climate change assessment report. The crucial role of FGOALS as a modeling tool for supporting climate sciences is highlighted by demonstrating the model’s performances in the simulation of the evolution of Earth’s climate from the past to the future.
Optimization of the Mars ionospheric radio occultation retrieval
JunYi Wang, XinAn Yue, Yong Wei, WeiXing Wan
2018, 2(4): 292-302. doi: 10.26464/epp2018027
Electron density is a key parameter to characterize Martian ionospheric structure and dynamics. Based on the ephemeris and auxiliary information derived from the Spacecraft, Planet, Instruments, C-matrix, and Events (SPICE) toolkit, we calculated the bending angle of signal path from the frequency residuals measured by the Mars Express Radio Science Experiment (MaRS) of the Mars Express (MEX) mission under the assumption of a spherically symmetric ionosphere. We stratified the ionosphere into layers and assumed a linear change of bending angle between layers, to derive profiles in radial distance of refractivity with the optimized parameters of upper integral limit of 4890 km and baseline correction boundary of 3690 km. Meanwhile, we also compared the retrieved electron density profiles between the frequency residuals of the single-frequency and differential Doppler of the dual-frequency. In total, ~640 electron density profiles of Martian ionosphere between April 2004 and April 2015 were retrieved successfully. There are 24 profiles identified manually that exhibit an additional sporadic layer occurrence below the normal two-layers. We also found that the peak altitude of this layer increases with the main peak altitude.
Modeling the Jovian magnetosphere under an antiparallel interplanetary magnetic field from a global MHD simulation
YuXian Wang, XiaoCheng Guo, BinBin Tang, WenYa Li, Chi Wang
2018, 2(4): 303-309. doi: 10.26464/epp2018028
We present preliminary results of a new global Magnetohydrodynamics (MHD) simulation model of the Jovian magnetosphere. The model incorporates mass loading from Jupiter's satellite Io, the planet's fast corotation, and electrostatic coupling between its magnetosphere and ionosphere (M-I coupling). The basic configuration of the Jovian magnetosphere including the equatorial plasma flow pattern, the corotation enforcement current system, and the field aligned currents (FACs) in the ionosphere are presented under an antiparallel interplanetary magnetic field (IMF) condition. The simulation model results for equatorial density and pressure profiles are consistent with results from data-based empirical models. It is also found that there are similarities between the FACs distribution in the ionosphere and the observed aurora features, showing the potential application of the simple ionospheric model to the complicated M-I coupling. This model will help deepen our understanding of the global dynamics of the Jovian magnetosphere.
Source complexity of the 2016 MW7.8 Kaikoura (New Zealand) earthquake revealed from teleseismic and InSAR data
HaiLin Du, Xu Zhang, LiSheng Xu, WanPeng Feng, Lei Yi, Peng Li
2018, 2(4): 310-326. doi: 10.26464/epp2018029
On November 13, 2016, an MW7.8 earthquake struck Kaikoura in South Island of New Zealand. By means of back-projection of array recordings, ASTFs-analysis of global seismic recordings, and joint inversion of global seismic data and co-seismic InSAR data, we investigated complexity of the earthquake source. The result shows that the 2016 MW7.8 Kaikoura earthquake ruptured about 100 s unilaterally from south to northeast (~N28°–33°E), producing a rupture area about 160 km long and about 50 km wide and releasing scalar moment 1.01×1021 Nm. In particular, the rupture area consisted of two slip asperities, with one close to the initial rupture point having a maximal slip value ~6.9 m while the other far away in the northeast having a maximal slip value ~9.3 m. The first asperity slipped for about 65 s and the second one started 40 s after the first one had initiated. The two slipped simultaneously for about 25 s. Furthermore, the first had a nearly thrust slip while the second had both thrust and strike slip. It is interesting that the rupture velocity was not constant, and the whole process may be divided into 5 stages in which the velocities were estimated to be 1.4 km/s, 0 km/s, 2.1 km/s, 0 km/s and 1.1 km/s, respectively. The high-frequency sources distributed nearly along the lower edge of the rupture area, the high-frequency radiating mainly occurred at launching of the asperities, and it seemed that no high-frequency energy was radiated when the rupturing was going to stop.
Probabilistic seismic hazard assessment of Nepal using multiple seismic source models
Md Moklesur Rahman, Ling Bai
2018, 2(4): 327-341. doi: 10.26464/epp2018030
The potential for devastating earthquakes in the Himalayan orogeny has long been recognized. The 2015 MW7.8 Gorkha, Nepal earthquake has heightened the likelihood that major earthquakes will occur along this orogenic belt in the future. Reliable seismic hazard assessment is a critical element in development of policy for seismic hazard mitigation and risk reduction. In this study, we conduct probabilistic seismic hazard assessment using three different seismogenic source models (smoothed gridded, linear, and areal sources) based on the complicated tectonics of the study area. Two sets of ground motion prediction equations are combined in a standard logic tree by taking into account the epistemic uncertainties in hazard estimation. Long-term slip rates and paleoseismic records are also incorporated in the linear source model. Peak ground acceleration and spectral acceleration at 0.2 s and 1.0 s for 2% and 10% probabilities of exceedance in 50 years are estimated. The resulting maps show significant spatial variation in seismic hazard levels. The region of the Lesser Himalaya is found to have high seismic hazard potential. Along the Main Himalayan Thrust from east to west beneath the Main Central Thrust, large earthquakes have occurred regularly in history; hazard values in this region are found to be higher than those shown on existing hazard maps. In essence, the combination of long span earthquake catalogs and multiple seismogenic source models gives improved seismic hazard constraints in Nepal.
Changes in diffuse reflectance spectroscopy properties of hematite in sediments from the North Pacific Ocean and implications for eolian dust evolution history
Qiang Zhang, QingSong Liu
2018, 2(4): 342-350. doi: 10.26464/epp2018031
Eolian dust preserved in deep-sea sediments of the North Pacific Ocean (NPO) is an important recorder of paleoclimatic and paleoenvironmental changes in the Asian inland. To better understand changes in the dust provenances, in this study diffuse reflectance spectroscopy (DRS) was used to extract the eolian signal recorded in sediments of ODP Hole 885A recovered from the NPO. First, we systematically investigated sieving effects on the DRS data; then band positions of hematite (obtained from the second order derivative curves of the K-M remission function spectrum derived from the DRS) were used to distinguish different provenances of the eolian dust preserved in the pelagic sediments of this hole. Our results show that the sieving (38 μm) process can suppress effectively the experimental errors. Eolian signatures from Chinese Loess Plateau (CLP) sources and non-CLP-sources have been identified in the pelagic sediments of ODP Hole 885A from the late Pliocene to the early Pleistocene. The provenance differences account for the discrepancies in the eolian records recovered from the pelagic sediments in the NPO and profiles in the CLP. Temporal changes in dust provenances are caused by the latitudinal movement of the westerly jet mainstream. The hematite DRS band position is a useful tool to distinguish the provenance of eolian components preserved in pelagic sediments.
Deployment of a short-term geophysical field survey to monitor acoustic signals associated with the Windsor Hum
Elizabeth A. Silber
2018, 2(4): 351-358. doi: 10.26464/epp2018032
The Hum is a widespread phenomenon, reported in many parts of the world. It manifests itself in the form of a hum, rumble and pulsing, often felt as a sensation more than an audible sound. Starting in 2011, residents of Windsor, Ontario, Canada started reporting intermittent low frequency sound, widely referred to as the Hum (and dubbed the Windsor Hum). This report outlines the deployment of a short term geophysical field survey, performed during 2013 in Windsor, Ontario, Canada, aimed at monitoring the airwave signals associated with the Windsor Hum. The summary of the low frequency sound array deployment is presented and discussed.