Can an impulsive variation of the solar wind plasma pressure trigger a plasma bubble? A case study based on CSES,Swarm and THEMIS data

During the August 25, 2018 geomagnetic storm, the new borne CSES-01 satellite and the Swarm A satellite detected a really large equatorial plasma bubble (EPB) in the post-midnight sector over western Africa. We investigated the features of this deep ionospheric plasma depletion using data from the Langmuir probes on-board CSES-01 and Swarm A satellites, and data from the high-precision magnetometer and the electric field detector instruments on-board CSES-01. Using also plasma and magnetic field data from THEMIS-E satellite we found that, during the passage of the magnetic cloud that drove the geomagnetic storm, an impulsive variation lasting about ten minutes characterized the solar wind (SW) pressure. The analysis of the delay time, between the occurrence of such impulsive variation and the detection of the plasma bubble, suggests a possible link between the SW pressure impulsive variation as identified by THEMIS-E and the generation of the EPB as detected by CSES-01 and Swarm A. We put forward the hypothesis that the SW pressure impulsive variation might have triggered an eastward prompt penetrating electric field that propagated from high to equatorial latitudes, overlapping in the nightside region to the zonal westward electric field, causing either a reduction or an inversion, at the base of the EPB triggering.     

A study of the plasmasphere density distribution using computed tomography methods from the EUV radiation data

In this paper, we introduce a new topic for imaging plasmasphere density with CT techniques. Both parallel-beam and fan-beam reconstruction formulas are derived with a special weighting function. Different from the traditional X-ray CT, the extreme ultraviolet (EUV) radiation may be totally absorbed by the Earth. Only the portion between the Earth and the detector enters the EUV sensor and be measured. The key step in our derivation is to remove the complete absorption effect with a specific weighting function. Computer-simulation studies are present to verify our formulas for the plasmasphere density.     

Structure and properties of the Earth's plasmasphere

The widely used concept of the plasmapause as the last closed electric field equipotential in the equatorial plane of the magnetosphere is oversimplified. The field aligned plasma motions are of substantial importance in the plasmapause formation and should be taken into account. Distributions of the main plasma parameters measured from the Prognoz-5 satellite are presented. The diurnal variations of the plasmapause height and the plasmasphere thermal properties are discussed.     

Thermospheric neutral density response to solar forcing

Recent measurements by the Solar EUV (Extreme Ultra Violet) Experiment (SEE) aboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics satellite (TIMED) provide solar EUV spectral irradiance with adequate spectral and temporal resolution, and thus the opportunity to use solar measurements directly in upper atmospheric general circulation models. Thermospheric neutral density is simulated with the NCAR Thermosphere–Ionosphere–Electrodynamic General Circulation Model (TIEGCM) using TIMED/SEE measurements and using the EUVAC solar proxy model. Neutral density is also calculated using the NRLMSISE-00 empirical model. These modeled densities are then compared to density measurements derived from satellite drag data. It is found that using measured solar irradiance in the general circulation model can improve density calculations compared to using the solar proxy model. It is also found that the general circulation model can improve upon the empirical model in simulating geomagnetic storm effects and the solar cycle variation of neutral density.     

磁尾中性片与磁尾正交曲线坐标系

根据磁尾中性计随地磁倾角变化的特点用光滑函数拟合中性片曲面模式,并用ISEE卫星的磁场资料来确定曲面参数。本中性片模式既保持了中性片的基本变化特征,又可以在近地处光滑过渡到赤道面。在此基础上,建立了一个以中性片曲面为坐标面的磁尾正交曲线坐标系。这个坐标系随地磁倾角的变化而变化,用这个坐标系可将不同的地磁倾角的磁场位形变换成地磁倾角为零时的标准形式,从而便于分析卫星的观测数据。      

Do ring current ions set the outer plasmasphere in motion?

GEOS-2 experiments have observed on a regular basis the transition from teh plasmasphere to the trough revealing a more tenuous and energetic population. This transition occured typically between 18 and 21 h local time under quiet geomagnetic conditions. On the plasmasphere side of the transition, large electric fields of several mV/m, mainly in the duskward direction, were observed. The present statistical results, over one year of data, assess clearly the mean magnitude and direction of these electric fields in relation to the boundary between these two plasma regimes under quiet geomagnetic conditions. The possibility of ring current energetic ions loosing part of their energy to the plasmasphere and accelerating this plasma sunward will be discussed.     

Characteristics of field line resonance type geomagnetic pulsations and variations of plasmaspheric plasma density distribution

The period of field line resonance (FLR) type geomagnetic pulsations depends on the length of the field line and on the plasma density in the inner magnetosphere (plasmasphere), where field lines are closed. Here as FLR period, the period belonging to the maximum occurrence frequency of the occurrence frequency spectrum (equivalent resonance curve) of pulsations has been considered. The resonance system may be replaced by an equivalent resonant circuit. The plasma density would correspond to the ohmic load. The plasma in the plasmasphere originates from the ionosphere, thus FLR period, occurrence frequency are also affected by the maximum electron density in the ionosphere. The FLR period has shown an enhancement with increasing F region electron density, while the occurrence frequency indicated diminishing trend (possible damping effect). Thus, the increased plasma density may be the cause of the decreased occurrence of FLR type pulsations in the winter months of solar activity maximum years (winter anomaly).     

连续磁活动对等离子体层演化的影响

利用嫦娥三号极紫外相机观测的2014年2月21日等离子体层极紫外对数图像，分析了一系列磁活动状态下等离子体层晨侧视角的演化.由等离子体层质子的相空间分布，模拟了2014年2月18—22日发生一系列磁暴事件时等离子体层在磁赤道面的演化.通过观测与模拟发现，等离子体层实际的填充速度大于模拟时等离子体层的填充速度.推测昏侧与日侧之间的羽结构对侧面视角下向阳侧等离子体层顶的位置会造成影响.模拟中等离子体层整体对磁暴的响应在3h内，大磁暴对等离子体层的影响时间较长，可以达到1～2天.连续的磁暴事件对等离子体层的影响有叠加的效果.等离子体层的回填比侵蚀需要更长的时间.      

Quasi-biennial oscillation in GPS VTEC measurements

The quasi-biennial oscillation, QBO, a well known periodicity in the equatorial stratospheric zonal winds, is also found in ionospheric parameters and in solar and geomagnetic activity indices. Many authors speculated about the link between the QBO in solar and geomagnetic activity and the QBO in atmospheric parameters. In this work we analyze the presence of the QBO in the ionosphere using the Vertical Total Electron Content (VTEC) values obtained from Global Navigation Satellite System (GNSS) measurements during the period 1999–2012. In particular, we used IONEX files, i.e. the International GNSS Service (IGS) ionospheric products. IONEX provide VTEC values around the world at 2-h intervals. From these data we compute global and zonal averages of VTEC at different local times at mid and equatorial geomagnetic latitudes. VTEC and Extreme Ultra Violet (EUV) solar flux time series are analyzed using a wavelet multi resolution analysis. In all cases the QBO is detected among other expected periodicities.     

Theoretical simulation of electron density and temperature distribution at Indian equatorial and low latitude ionosphere

The electron density and temperature distribution of the equatorial and low latitude ionosphere in the Indian sector has been investigated by simultaneously solving the continuity, momentum and energy balance equations of ion and electron flux along geomagnetic field lines from the Northern to the Southern hemisphere. Model algorithm is presented and results are compared with the electron density and electron temperature measured in situ by Indian SROSS C2 satellite at an altitude of ∼500 km within 31°S–34°N and 75 ± 10°E that covers the Indian sector during a period of low solar activity. Equatorial Ionization Anomaly (EIA) observed in electron density, morning and afternoon enhancements, equatorial trough in electron temperature have been simulated by the model within reasonable limits of accuracy besides reproducing other normal diurnal features of density and temperature.     

DEMETER and DMSP satellite observations of the disturbed H/O ratio caused by Earth’s seismic activity in the Sumatra area during December 2004

In the present paper, plasma probe data taken from DEMETER and DMSP-F15 satellites were used to study the ion density and temperature disturbances in the morning topside ionosphere, caused by seismic activity at low latitudes. French DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) micro-satellite mission had been especially designed to provide global scale observations in the topside ionosphere over seismically active regions. Onboard the DEMETER satellite, the thermal plasma instrument called “Instrument Analyser de Plasma” (IAP) provides ion mass and densities, ion temperature, three component ion drift and ion density irregularities measurements. As a part of “Defense Meteorological Satellite Program”, DMSP-F15 satellite is on orbit operation since 1999. It provides ionospheric plasma diagnostics by means of the “Special Sensor-Ion, Electron and Scintillations” (SSIES-2) instrument. We examined few examples of possible seismic effects in the equatorial ionosphere, probably associated with seismic activity during December month in the area of Sumatra Island, including main shock of giant Sumatra event. It is found that the localized topside ionospheric disturbances appear close to the epicenters of certain earthquakes in the Sumatra region. In two cases, ion H⁺/O⁺ ratio rises more than one hour before the main shock, due to the O⁺ density decrease at the winter side of the geomagnetic equator, with longitudinally closest location to the epicenter of the earthquakes. These anomalous depletions in O⁺ density do exist in all cases of SSIES-2 data. Particularly for Sumatra main event, more than one hour after the main shock, we observe large-scale depletion in O⁺ density northward of the geomagnetic equator at winter side hemisphere. Associated with O⁺ depletion, ion temperature latitudinal profile around the geomagnetic equator shows enhanced asymmetry with minimum at the summer side and maximum in positive Ti deviation from mean value at the winter side. This disturbance lasted for more than three hours, later in time observed at the same place by IAP/DEMETER.     

Analysis of the ionosphere/plasmasphere electron content variability during strong geomagnetic storm

The ionosphere/plasmasphere electron content (PEC) variations during strong geomagnetic storms in November 2004 were estimated by combining of mid-latitude Kharkov incoherent scatter radar observations and GPS TEC data derived from global TEC maps. The comparison between two independent measurements was performed by analysis of the height-temporal distribution for specific location corresponding to the mid-latitudes of Europe. The percentage contribution of PEC to GPS TEC indicated the clear dependence from the time with maximal values (more than 70%) during night-time. During day-time the lesser values (30–45%) were observed for quiet geomagnetic conditions and rather high values of the PEC contribution to GPS TEC (up to 90%) were observed during strong negative storm. These changes can be explained by the competing effects of electric fields and winds, which tend to raise the layer to the region with lower loss rate and movement of the ionospheric plasma to the plasmasphere.     

Alfven波在微电离大气中的衰减特性研究

利用简单的偶极子地磁场模型以及大气电子密度和电导率模式, 分析地面产生的磁扰动以Alfven波的模式传播到近地空间区域. 这种地面的磁扰动可能干扰近地空间卫星对空间磁扰动的观测. 通过对地面磁扰动Alfven波模式1000 km高度内的衰减情况进行模拟, 认为在近地空间采用地磁偶极子模型是合理的. 由于衰减随扰动频率的增大而急剧增强, 分析还得到了近地卫星能够探测到地面磁扰动的最大频率. 计算结果表明, Alfven波的衰减主要集中在高度50 km以下, 这个区域内的大气电导率极其微弱, 使Alfven波的传播受到极大衰减. 0.4 Hz以下的Alfven波沿磁力线传播到1000 km高度后衰减结为原来扰动幅度的千分之一, 因此频率在0.4 Hz以下的Alfven波可能会干扰低轨卫星探测磁场脉动.      

一种NRLMSISE-00模型太阳辐射校正方法

根据空间天气的状态,调整大气模型的相关输入参数能够减小模型的计算误差.通过对比CHAMP卫星在轨大气密度探测数据与NRLMSISE-00模式的计算结果发现,通过调整F_10.7的输入,使轨道大气密度积分的模式计算结果与探测结果之间的误差达到最小,此时的F_10.7被称为理想F_10.7输入（F*）.进一步的分析发现,F*与太阳紫外辐射MgII指数存在很好的相关性,因此可以选择其他的太阳紫外辐射代理参数取代F_10.7,从而减小模型计算误差.本文采用神经网络技术,建立新的太阳紫外辐射代理参量F_euv与MgII,F_10.7等的对应模型,能够根据当日参数值计算F_euv.研究结果表明,新的代理参数能够有效减小NRLMSISE-00的计算误差.      

Variations in the thermosphere and ionosphere response to the 17–20 April 2002 geomagnetic storms

The responses of the thermospheric density and ionospheric foF2 to the intense magnetic storms event on 17–20 April were analyzed by using data from CHAMP/STAR and ionosonde stations respectively, and NRLMSISE-00 and IRI-2007 models were used to simulate. The models can capture the tendency of changes, especially under quiet or moderate geomagnetic conditions, but are less accurate under geomagnetic storms. The thermospheric density is sensitive to the EUV emission and geomagnetic activity, and double-peak structure appeared in the dayside. On 19 April dayside, TADs traveled toward the equator with phase speeds of the order of 300–750 m/s, interfered near the equator to produce a total density perturbation of 25%, and then passed through each other and into the opposite hemisphere. For ionospheric foF2, there are non-symmetric hemispheres’ features during the intense geomagnetic activities. In details, middle latitudes in the north and high latitudes in both hemispheres are negative ionospheric storms, and the maximum amplitudes of δfoF2$\delta \mathit{foF}2$ is about 60%, but the amplitudes decrease from the higher to lower latitudes in the Southern Hemisphere. Meanwhile, the equatorial station shows positive phase, and the maximum value is about 100%. Finally, the mechanisms for these features will be discussed in this study.     

Modeling of ionospheric parameter variations in East Asia during the moderate geomagnetic disturbances

The results of modeling of ionospheric disturbances observed in the East Asian region during moderate storms are presented. The numerical model for ionosphere–plasmasphere coupling developed at the ISTP SB RAS is used to interpret the data of observations at ionospheric stations located in the longitudinal sector of 90–130°E at latitudes from auroral zone to equator. There is obtained a reasonable agreement between measurements and modeling results for winter and equinox. In the summer ionosphere, at the background of high ionization by the solar EUV radiation in the quiet geomagnetic period the meridional thermospheric wind strongly impacts the electron concentration in the middle and auroral ionosphere. The consistent calculations of the thermospheric wind permit to obtain the model results which are closer to summer observations. The actual information about the space-time variations of thermosphere and magnetosphere parameters should be taken into account during storms.     

Polar ionosphere and geomagnetic response for the flux transfer events: A case study

On April 15th 2003, Cluster crossed the dayside magnetopause boundary and observed a series flux transfer events (FTEs) during the interval from 0630 to 0730 UT. During this period, the interplanetary magnetic field (IMF) showed a negative z component and a positive y component. Simultaneous corresponding transient plasma flows were identified in the near-conjugate polar ionosphere by the CUTLASS Finland HF radar, and the geomagnetic field disturbances were observed by the IMAGE ground-based magnetometers. By combing these data and applying the Cooling model, we show that the transient plasma flows and the geomagnetic field disturbances are closely related to the dayside FTEs.     

冷而密的等离子体片及其对磁尾等离子体片分布特性的影响

地球磁尾等离子体片在太阳风-磁层耦合过程中起着重要的作用，其中冷而密的等离子体片是地磁活动平静期太阳风等离子体进入磁层的重要区域.以往的研究通常没有利用局地探测数据针对冷而密的等离子体片发生率在地心太阳磁层坐标系（GSM）中xy平面分布的统计分析.本文利用GEOTAIL卫星1996-2016年的局地测量数据，给出了等离子体片密度、温度及冷而密的等离子体片发生率的二维分布.与温度具有晨昏对称分布不同，等离子体片数密度呈现明显的晨昏不对称性，并且冷而密的等离子体片发生率在晨侧较高.