Liqin Shi

Testing linear theory of EMIC waves in the inner magnetosphere: Cluster observations

In this paper, we test whether time periods with hot proton temperature anisotropy are associated with electromagnetic ion cyclotron (EMIC) waves and whether the plasma conditions during the observed waves satisfy the linear theory threshold condition. We identify 865 events observed by the Composition Distribution Function instrument onboard Cluster spacecraft 4 during 1 January 2001 to 1 January 2011 that exhibit a positive temperature anisotropy (A(hp)=T-h/T-vertical bar h-1) in the 10-40keV protons. The events occur over an L range from 4 to 10 in all magnetic local times and at magnetic latitudes (MLATs) within 50 degrees. Of these hot proton temperature anisotropy (HPTA) events, only 68 events have electromagnetic ion cyclotron (EMIC) waves. In these 68 HPTA events, for those at 3.8 1.0 nT(2)/Hz mainly appear in the region with f(EMIC)/f(H,eq) H bands satisfy A(hp)/(A(hp)+1)>f(EMIC)/f(H,lo), A(hp)/(A(hp)+1)>0.45xf(EMIC)/f(H,lo), and A(hp)/(A(hp)+1) 0.25. By testing a threshold equation for the EMIC instability based on linear theory, we find that for EMIC waves with |MLAT|10 degrees in the He, H, and>H bands, the percentages that satisfy the predicted conditions for wave growth by the threshold equation are 15.2%, 24.6%, and 25.6%. For the EMIC waves with |MLAT|>10 degrees the percentages that satisfy the wave growth predicted conditions are only 2.8%, 2.6%, and 0.0%. Finally, possible reasons for the low forecast accuracies of EMIC waves are suggested. Key Points We do the statistical analysis of EMIC waves from a 10year Cluster observation We test the A_hp versus EMIC wave frequency formula of Kennel and Petschek (1966) We test the linear theory derived by Blum et al. (2009)

A regional ionospheric TEC mapping technique over China and adjacent areas on the basis of data assimilation

In this paper, a regional total electron content (TEC) mapping technique over China and adjacent areas (70 degrees E-140 degrees E and 15 degrees N-55 degrees N) is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service. The regional TEC maps can be generated accordingly with the spatial and temporal resolution being 1 degrees x1 degrees and 5min, respectively. The accuracy and quality of the TEC mapping technique have been validated through the comparison with GNSS observations, the International Reference Ionosphere model values, the global ionosphere maps from Center for Orbit Determination of Europe, and the Massachusetts Institute of Technology Automated Processing of GPS TEC data from Madrigal database. The verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model, which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric TEC over China and adjacent areas.

A regional ionospheric TEC mapping technique over China and adjacent areas: GNSS data processing and DINEOF analysis

A technique is developed to derive two-dimensional maps of total electron content (TEC) over China and adjacent areas using Global Navigation Satellite System (GNSS) data from the Crustal Movement Observation Network of China (CMONOC) and the International Global Navigation Satellite System Service (IGS). A revised self-calibration of pseudo-range errors (SCORE) algorithm is used to derive the TEC and to determine the Differential Code Biases (DCBs) simultaneously. The accuracy and validity of this technique is verified in two ways. Firstly, the estimated TEC is compared with the results derived using DCBs from Center for Orbit Determination of Europe (CODE) under different solar activity conditions and seasons; secondly, sample TEC along the receiver-to-satellite ray paths are simulated by NeQuick model and are reprocessed by this TEC derivation technique to make the accuracy test. Two-dimensional maps of vertical TEC of ionospheric pierce points (IPPs) are obtained accordingly with a time resolution of 30 s. The data interpolating empirical orthogonal functions (DINEOF) technique is then used to make the extrapolation for the unknown or missing data points. The optimal EOF modes for data reconstruction are specified via cross-validation method. The regional TEC distribution over China and adjacent areas is scaled into grid size of 1° × 1° for each 5 min, which can well reflect the characteristic of large-scale regional variations and temporal evolution as well as the small-scale local features of ionosphere.创新点1. 利用中国及周边区域的地基GNSS观测数据进行TEC解算, 并采用伪距误差自校正技术来计算硬件偏差, 得到高精度TEC星下点数据。2. 采用经验正交函数法插值法构建覆盖中国及周边区域的高分辨率TEC地图

Midlatitude Plasma Bubbles Over China and Adjacent Areas During a Magnetic Storm on 8 September 2017

This paper presents observations of postsunset super plasma bubbles over China and adjacent areas during the second main phase of a storm on 8 September 2017. The signatures of the plasma bubbles can be seen or deduced from (1) deep field-aligned total electron content depletions embedded in regional ionospheric maps derived from dense Global Navigation Satellite System networks, (2) significant equatorial and midlatitudinal plasma bite-outs in electron density measurements on board Swarm satellites, and (3) enhancements of ionosonde virtual height and scintillation in local evening associated with strong southward interplanetary magnetic field. The bubbles/depletions covered a broad area mainly within 20∘–45∘N and 80∘–110∘E with bifurcated structures and persisted for nearly 5 hr (∼13–18 UT). One prominent feature is that the bubbles extended remarkably along the magnetic field lines in the form of depleted flux tubes, reaching up to midlatitude of around 50∘N (magnetic latitude: 45.5∘N) that maps to an altitude of 6,600 km over the magnetic equator. The maximum upward drift speed of the bubbles over the magnetic equator was about 700 m/s and gradually decreased with altitude and time. The possible triggering mechanism of the plasma bubbles was estimated to be storm time eastward prompt penetration electric field, while the traveling ionospheric disturbance could play a role in facilitating the latitudinal extension of the depletions.

Frequency sweep rates of rising tone electromagnetic ion cyclotron waves: Comparison between nonlinear theory and Cluster observation

Resonant pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves has been suggested to account for the rapid loss of ring current ions and radiation belt electrons. For the rising tone EMIC wave (classified as triggered EMIC emission), its frequency sweep rate strongly affects the efficiency of pitch-angle scattering. Based on the Cluster observations, we analyze three typical cases of rising tone EMIC waves. Two cases locate at the nightside (22.3 and 22.6 magnetic local time (MLT)) equatorial region and one case locates at the duskside (18MLT) higher magnetic latitude (λ = –9.3°) region. For the three cases, the time-dependent wave amplitude, cold electron density, and cold ion density ratio are derived from satellite data; while the ambient magnetic field, thermal proton perpendicular temperature, and the wave spectral can be directly provided by observation. These parameters are input into the nonlinear wave growth model to simulate the time-frequency evolutions of the rising tones. The simulated results show good agreements with the observations of the rising tones, providing further support for the previous finding that the rising tone EMIC wave is excited through the nonlinear wave growth process.

Spacecraft Surface-Charging Risk Index in Auroral Region

High-level spacecraft surface charging, which is frequently observed in the auroral region, may lead to electrostatic discharges and result in significant damage to the satellite. In this paper, we present preliminary results on the relationship between low earth orbit surface-charging events and the geomagnetic activity indices. The surface-charging events in the auroral regions are identified and listed based on precipitating ion/electron energy spectra measured by the Defense Meteorological Satellite Program spacecrafts in 2011–2014. Furthermore, the charging features (i.e., duration, charging level, and location) are investigated. The charging frequency distribution with respect to Kp, Ap, Dst, and AE are analyzed. It is shown that the charging frequency increases with increasing Kp index. The occurrence frequency of charging events with respect to Kp and magnetic local time is presented, which is useful in the real-time estimation of surface-charging occurrence possibility. The correlation coefficients (c.c.) for Kp and AE indices with the average charging level are compared. It is found that Kp serves as the best index owning to its largest c.c. and its simplicity. Since Kp can be forecasted through existing models, our results suggest that it can be used to predict the likelihood and level of spacecraft surface charging in the auroral region.