Global ionospheric TEC response to a strong magnetic storm

The global characteristics of the ionospheric storm and irregularities as well as propagation of TEC (total electron content) disturbances during the strong magnetic storm occurring in November 2004 were investigated by using the data of the IGS network. For the response of the global ionospheric TEC to this strong magnetic storm, the following features are noticeable: 1) the maximum of the ionospheric storm phase occurred around the main phase maximum of the magnetic storm; 2) the TEC response in equatorial and low latitudes was more remarkable than that in mid-high latitudes; 3) as a whole, the storm phase in the northern hemisphere was mainly positive, and it was negative in the southern hemisphere; 4) during the whole magnetic storm from November 7 to 11, the locations where the maxima of the positive and negative ionospheric storm phases occurred were nearly invariant to the Sun at low and equatorial latitudes, i.e. the 24-h recurrence. Analyzing results of TEC rate and its standard deviation showed that the ionospheric irregularities and disturbances in the global mainly occurred around the main phase maximum of the storm, and they distributed in a large longitudinal region for both day and night in mid-high latitudes and they generated and developed only after the sunset, and lasted out to the midnight in equatorial and low latitudes. The disturbance propagation parameters were also estimated by using the wavelet reconstruction and cross-correlation technologies for a set of spaced stations in the Northern America. Supported by the National Natural Science Foundation of China (Grant Nos. 40474055, 40504019)     

Near-Earth bursty bulk flows and AE index

With the 4-s resolution data of the magnetometer and the ion plasma analyzer on TC-1 from June to November of each year during the period of 2004-2006, we statistically analyzed the occurrence rate of both convective and field-aligned bursty flows (FABFs). A near-Earth bursty bulk flow (NEBBF) occurred during both the quiet time and substorm process. In general, the magnetic field and the plasma density began oscillating with the appearance of the NEBBF associated with a distinct increase of the AE index. The increase of AE index during the NEBBF was more than 100 nT in both quiet time and substorm process. The statistical analysis indicated that the occurrence rates of the FABFs were nearly the same in the different stages of the AE index, but the occurrence rate of the NEBBFs was much higher in the growth stage of the AE index, indicating that the NEBBFs were directly related to the growth and expansion phases of the substorm. The observations suggested that the quite large number of BBFs from the mid magnetotail could enter into the near-Earth tail and play important role in triggering the substorm onset. Supported by the National Natural Science Foundation of China (Grant Nos. 40704031, 40674091 and 40536030)     

Tomographic imagine of ionospheric structures and disturbances in the region of East-Asian equatorial anomaly

Experiments of ionospheric tomography at low latitudes along 120°E meridian and some findings from analyses of such experimental data are presented. An improved reconstruction algorithm of computerized ionospheric tomography is proposed. In this algorithm, both differential Doppler phase and differential Doppler frequency data are jointly used and the integral phase constants are determined in the reconstruction process. Our findings indicate that the reconstructed ionospheric equatorial anomaly crests usually show a tilt in rough alignment with the local geomagnetic field, coinciding with the feature predicted by the fountain mechanism. The crest locations are found to move daily in response to changes in equatorial electrodynamics. When the crest moves from one day to the next day, the tilting angle changes so as to be still aligned with the local magnetic field. It is statistically found that an equator-ward motion of the crests is accompanied with a latitudinal broadening of the crest region. The r     

In-flight observations of electromagnetic interferences emitted by satellite

Using the data from STAFF/TC-1, this paper for the first time analyzes the electromagnetic interferences of Chinese scientific satellite. The electromagnetic interference of satellite exists mainly below 30 Hz, but can extend to 190 Hz with an obviously decreasing power spectral density. The electromagnetic interferences at frequencies below 190 Hz have good correlation with the solar aspect angle. The electromagnetic interferences at frequencies between 190 and 830 Hz have also correlation with solar aspect angle. However, the electromagnetic interferences at frequencies above 830 Hz have no correlation with the solar aspect angle. The correlation coefficient between solar aspect angel and electromagnetic interferences is around 0.90. The larger the solar aspect angle, the stronger the satellite electromagnetic interference. When the solar aspect angle increases from 90.6° to 93.6°, the electromagnetic interferences at frequencies <10 Hz increase by 8 times and those at frequencies 190–830 Hz increase by 60%. This close association of electromagnetic interferences with the solar aspect angle indicates that the solar aspect angle is the main factor to determine the electromagnetic interferences. The electromagnetic interferences of satellite in sunlight are larger than those in eclipse. The electromagnetic interference produced by solar panel occupies about 87% in the low frequency band (<100 Hz) and 94% in the high frequency band (>100 Hz) of the total electromagnetic interference produced by satellite. These in flight observations of electromagnetic radiation of satellites will be very helpful to the designs of future satellites of space sciences or earthquake sciences. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2008AA12A216), the National Science & Technology Supporting Program during the Eleventh Five-Year Plan, the National Natural Science Foundation of China (Grant No. 40523006), the National Basic Research Program of China (“973” Project) (Grant No. 2006CB806305), and the Specialized Research Fund for State Key Laboratories     

TC-1 observation of ion high-speed flow reversal in the near-Earth plasma sheet during substorm

Based on measurements of FGM and HIA on board TC-1 at its apogee on September 14, 2004, we analyzed the ion high-speed flows in the near-Earth plasma sheet observed during the substorm expansion phase. Strong tailward high-speed flows (Vx ∼ −350 km/s) were first seen at about X ∼ −13.2 R_E in near-Earth magnetotail, one minute later the flows reversed from tailward to earthward. The reversal process occurred quickly after the substorm expansion onset. The near-Earth magnetotail plasma sheet was one of key regions for substorm onset. Our analysis showed that the ion flow reversal from tailward to earthward was likely to be in close relation with the substorm expansion initiation and might play an important role in triggering the substorm expansion onset. Supported by the National Natural Science Foundation of China (Grant Nos. 40620130094, 40731054, 40704027, 40390150)     

Variations of the relativistic electron flux after a magnetospheric compression event

On January 21, 2015, a sharp increase of the solar wind dynamic pressure impacted the magnetosphere. The magnetopause moved inward to the region L 8 without causing a geomagnetic storm. The flux of the relativistic electrons in the outer radiation belt decreased by half during this event based on the observations of the particle radiation monitor(PRM) of the fourth of the China-Brazil Earth Resource Satellites(CBERS-4). The flux remained low for approximately 11 d; it did not recover after a small magnetic storm on January 26 but after a small magnetic storm on February 2. The loss and recovery of the relativistic electrons during this event are investigated using the PRM data, medium-and high-energy electron observations of NOAA-15 and the Van Allen Probes, medium-energy electron observations of GOES-13, and wave observations of the Van Allen Probes. This study shows that the loss of energetic electrons in this event is related to magnetospheric compression. The chorus waves accelerate the medium-energy electrons, which causes the recovery of relativistic electrons. The Van Allen Probes detected strong chorus waves in the region L =3–6 from January 21 to February 2. However, the flux of medium-energy electrons was low in the region. This implies that the long-lasting lack of recovery of the relativistic electrons after this event is due to the lack of the medium-energy"seed" electrons. The medium-energy electrons in the outer radiation belt may be a clue to predict the recovery of relativistic electrons.     

Butterfly distribution of Earth’s radiation belt relativistic electrons induced by dayside chorus

Previous theoretical studies have shown that dayside chorus can produce butterfly distribution of energetic electrons in the Earth’s radiation belts by preferentially accelerating medium pitch angle electrons, but this requires the further confirmation from high-resolution satellite observation. Here, we report correlated Van Allen Probes data on wave and particle during the 11–13 April, 2014 geomagnetic storm. We find that a butterfly pitch angle distribution of relativistic electrons is formed around the location L = 4.52, corresponding to the presence of enhanced dayside chorus. Using a Gaussian distribution fit to the observed chorus spectra, we calculate the bounce-averaged diffusion rates and solve two-dimensional Fokker-Planck equation. Numerical results demonstrate that acceleration by dayside chorus can yield the electron flux evolution both in the energy and butterfly pitch angle distribution comparable to the observation, providing a further evidence for the formation of butterfly distribution of relativistic electrons driven by very low frequency (VLF) plasma waves.     

Electron dynamics and wave activities associated with mirror mode structures in the near-Earth magnetotail

We report the observation of mirror mode structures by Cluster spacecraft at around X~-16 RE in the Earth’s magnetotail.The wavelength of the mirror structure is larger than 7000 km,corresponding to tens of ion gyroradii.Features of the mirror structures are similar to those detected in the magnetosheath:the anti-correlation between the magnetic field strength and plasma density,zero phase velocity in the plasma rest frame and linear polarization.The structures were observed in a region bounded by two dipolarizations during a substorm intensification.Thus,the dipolarization process may provide a plasma condition facilitating the growth of the mirror mode structures.Another interesting feature is the electron dynamics within the mirror structures.Thermal electron energy flux has an enhancement at 0°and 180°pitch angles inside the magnetic dips of the first three mirror structures and an enhancement at 90°pitch angle inside the magnetic dip of the last structure.The different electron distribution inside the mirror structures might be a result of different evolution stages of the mirror wave.The last structure may be in the nonlinear stage of the mirror instability,whereas the three others with quasi-sinusoidal waveforms may be in the linear stage.In addition,we found that intense whistler waves were confined within the magnetic dips.We conjecture that whistler waves observed in the first three dips were generated in a remote region,then they were trapped in the mirror mode troughs and transported toward the spacecraft;while the whistler wave detected in the last dip was excited locally by the electron anisotropy instability.     

Coordinated Cluster/Double Star observations of dayside flux transfer events on 6 April 2004

With the Double Star Program TC1 in the equatorial orbit and Cluster tetrahedron in the high latitude polar orbit, a conjunct observation of FTEs on the dayside magnetopause (MP) on April 6, 2004 is presented in this study. The FTEs observed by TC1 at low latitudes are characterized to be generated in the subsolar region and the obtained flux tube axes orientate along the predicted low latitude component magnetic reconnection X-line, indicating that these FTEs were more likely to be generated through multiple X-line reconnection or single X-line bursty reconnection. During the same period, Cluster also encountered a series of magnetosheath FTEs with their axes pointing roughly along the interplanetary magnetic field. At last, the global FTE configuration is obtained from observations in different locations, which is in good agreement with the “elbow shape” model. Supported by the NSFC (Grant No. 40731056) and the Chinese Key Research Project (Grant No. 2006CB806300)     

Ultra low frequency waves observed by Double Star TC-1 in the plasmasphere boundary layer

The characteristic and properties of ULF waves in the plasmasphere boundary layer during two very quiet periods are present. The ULF waves were detected by Double Star TC-1 when the spacecraft passed through the plasmasphere in an outbound and inbound trajectories, respectively. A clear association between the ULF waves and periodic variations of energetic ions fluxes was observed. The observations showed that the wave frequency was higher inside the plasmasphere than outside. The mechanism generating these ULF waves and possible diagnosing of the “classical plasmapause” location with the ULF wave were discussed. Supported by the National Natural Science Foundation of China (Grant Nos. 40504017, 40636031)     

New progress of Double Star-Cluster joint exploration and study

The magnetic reconnection of magnetosphere and the magnetospheric space storms (including magnetospheric substorm, magnetic storm, magnetospheric particle storm) has long been one of the most challenging subjects in the solar-terrestrial physics. The reconnection mechanism and global triggering process of the magnetospheric space storms are still unclear up to now. Based on the Double Star Program (DSP) and Cluster joint measurements, we have observed the solar wind density hole, the component magnetic field reconnection in the magnetopause, the structures of magnetic storm ring current, global and multi-scale driven and triggering processes of magnetospheric substorm. In this paper we will briefly introduce these results.     

TIME-IGGCAS model validation: Comparisons with empirical models and observations

The TIME-IGGCAS (Theoretical Ionospheric Model of the Earth in Institute of Geology and Geophysics, Chinese Academy of Sciences) has been developed recently on the basis of previous works. To test its validity, we have made comparisons of model results with other typical empirical ionospheric models (IRI, NeQuick-ITUR, and TItheridge temperature models) and multi-observations (GPS, Ionosondes, Topex, DMSP, FORMOSAT, and CHAMP) in this paper. Several conclusions are obtained from our comparisons. The modeled electron density and electron and ion temperatures are quantitatively in good agreement with those of empirical models and observations. TIME-IGGCAS can model the electron density variations versus several factors such as local time, latitude, and season very well and can reproduce most anomalistic features of ionosphere including equatorial anomaly, winter anomaly, and semiannual anomaly. These results imply a good base for the development of ionospheric data assimilation model in the future. TIME-IGGCAS underestimates electron temperature and overestimates ion temperature in comparison with either empirical models or observations. The model results have relatively large deviations near sunrise time and sunset time and at the low altitudes. These results give us a reference to improve the model and enhance its performance in the future. Supported by the KIP Pilot Project of CAS (Grant No. kzcx2-yw-123), National Natural Science Foundation of China (Grant Nos. 40636032 and 40725014), and National Key Basic Research Project of China (Grant No. 2006CB806306)     

Shrinkage of magnetosphere observed by TC-1 satellite during the high-speed solar wind stream

During the interval 06:14–07:30 UT on August 24, 2005, since the Earth’s magnetopause was suddenly compressed by the persistent high-speed solar wind stream with the southward component of the interplanetary magnetic field (IMF), the magnetopause moved inward for about 3.1 R_E. Meanwhile, TC-1 satellite shifted from northern plasma sheet to the northern lobe/mantle region, although it kept inward flying during the interval 06:00–07:30UT. The shift of TC-1 from the plasma sheet to the lobe/mantle is caused by the simultaneous inward displacements of the plasma sheet and near-Earth lobe/mantle region, and their inward movement velocity is larger than the inward motion velocity of TC-1. The joint inward displacements of the magnetopause, the lobe/mantle region and the plasma sheet indicate that the whole magnetosphere shrinks inward due to the magnetospheric compression by the high-speed solar wind stream, and the magnetospheric ions are attached to the magnetic field lines (i.e. ‘frozen’ in magnetic field) and move inward in the shrinking process of magnetosphere. The large shrinkage of magnetosphere indicates that the near-Earth magnetotail compression caused by the strong solar wind dynamic pressure is much larger than its thickening caused by the southward component of the IMF, and the locations of magnetospheric regions with different plasmas vary remarkably with the variation of the solar wind dynamic pressure. Supported by the National Natural Science Foundation of China (Grant Nos. 40604018, 40523006), CSSAR (Grant No. O72114AA4S), Scientific Research Start-up Foundation for President Prize of CAS, 973 Program of China (Grant No. 2006CB806305) and the Specialized Research Fund for State Key Laboratories     

Thermospheric circulation model in meridian plane (I)——Storm time variations in thermal status and circulation

A thermospheric circulation model in meridian plane (TCMMP) is introduced and a case study on the variations in night side thermosphere caused by energy deposition in auroral oval during a single magnetic substorm is expounded. Calculations show that TCMMP can correctly reflect the thermospheric thermal status and circulation patterns during storm time and the results are in agreement with previous theoretical and observational ones. This paper and other works also show the validity of TCMMP in researches on medium and large scale changes in mid- and low latitude thermosphere. Results also support strongly some related theory about the cause of ionospheric storms, expecially the negative phase storms.     

Multi-spacecraft observations of ULF waves during the recovery phase of magnetic storm on October 30, 2003

Based on observations obtained by Cluster C1, GOES 10, 12, and Polar, the global ULF wave properties are studied during the recovery phase of a very intense magnetic storm-Halloween storm (October 31, 2003, 21:00–23:00 UT). The results indicate that the ULF waves’ properties observed by different satellites, such as amplitude, period, etc. show large variations. This can be interpreted as that Field Line Resonance (FLR) might take place in the region where Cluster C1 passed. The compressional wave of the cavity mode coupled with FLR’s shear Alfven wave and fed energy to the latter, forming a large-amplitude toroidal mode. From the point of period, Cluster C1 observed the shortest period, GOES 10, 12 observed the middle, while Polar observed the longest. The wave period of toroidal mode observed by Cluster C1 kept almost unchanging when Cluster C1 passed L range from 11.7 to 5.3. Using the Squared Wavelet Coherence analysis method, we estimated that the FLR region in the dayside magnetosphere could expand to at least 4 local time widths. The toroidal mode observed by Polar was a standing wave, while the poloidal mode was a propagating wave, the observation results could be well explained by the waveguide mode theory. Since the solarwind speed V _x was −800 km/s and the dynamic pressure varied little, we speculated that the source of the ULF wave was the Kelvin-Helmholtz instability at the magnetopause triggered by high speed solarwind. Supported by the National Natural Science Foundation of China(Grant Nos. 40425004, 40528005, 40390152) and the National Basic Research Program of China (Grant No. 2006CB806305)     

Surveys on magnetospheric plasmas based on the Double Star Project (DSP) exploration

The equatorial and polar satellites of the Double Star Project (DSP) were launched successfully on December 29, 2003 and July 25, 2004, respectively, and both of them are operating smoothly. The DSP provides a good opportunity for investigating the structure of the magnetosphere. Based on the DSP data collected during 2004, we have surveyed the distribution of the magnetic fields and plasmas in the magnetosphere. It is found that: (1) Near the Earth’s equatorial plane within geocentric distances of less than 7 R_E, the Earth’s magnetic field is dipolar. In the vicinity of the magnetopause, the magnetic field is enhanced by a factor of about 1.5, and on the nightside, the magnetic field can vary significantly from the Earth’s dipole field, likely caused by the presence of the near-Earth tail current sheet. (2) In the day-side magnetosheath, the electron and ion densities are usually both in the range of 10–30 cm⁻³; the ion and electron temperatures are usually about 200 and 50 eV, respectively. The flow pattern is usually smooth, with a low velocity in the subsolar region and with significantly higher velocities in the dawn and dusk flanks. (3) In the region between the magnetopause and plasmasphere the density is low, approximately 0.5–5 cm⁻³, and the temperature is high, about 1–10 keV for ions and 0.1–5 keV for electrons. The ion temperature has an apparent anisotropy, with the ratio of the perpendicular and parallel temperatures being about 1.0–1.3 for the night-and dusk-side magnetosphere and about 1.3–2.0 for the day-and dawn-side magnetosphere. There is an evident sunward convection of about 50 km/s in the magnetosphere. On the dawn side, the flow becomes somewhat turbulent, and in the vicinity of the night-noon meridian plane, the convection is rather slow. (4) The high-energy electrons with energies higher than 2 MeV are mainly located in the regions with 3 < L < 4.5; the size of the high-energy electrons area varies with time, it may expand and shrink occasionally according to different solar wind conditions and magnetic activities. Supported by the National Natural Science Foundation of China (Grant Nos. 40621003, 40728005, 40674094, and 40390150), Ministry of Science and Technology of China (Grant No. 2006CB806305), and Hundred Talents Program of the CAS     

Climatology of global gravity wave activity and dissipation revealed by SABER/TIMED temperature observations

Gravity wave activity and dissipation in the height range from the low stratosphere to the low thermosphere(25–115 km)covering latitudes between 50°S and 50°N are statistically studied by using 9-year(January 22,2002–December 31,2010)SABER/TIMED temperature data.We propose a method to extract realistic gravity wave fluctuations from the temperature profiles and treat square temperature fluctuations as GW activity.Overall,the gravity wave activity generally increases with height.Near the equator(0°–10°),the gravity wave activity shows a quasi-biennial variation in the stratosphere(below 40 km)while from 20°to 30°,it exhibits an annual variation below 40 km;in low latitudes(0°–30°)between the upper stratosphere and the low thermosphere(40–115 km),the gravity wave activity shows a semi-annual variation.In middle latitudes(40°–50°),the gravity wave activity has a clear annual variation below 85 km.In addition,we observe a four-monthly variation with peaks occurring usually in April,August,December in the northern hemisphere and in February,June,October in the southern hemisphere,respectively,above 85 km in middle latitudes,which has been seldom reported in gravity wave activity.In order to study the dissipation of gravity wave propagation,we calculate the gravity wave dissipation ratio,which is defined as the ratio of the gravity wave growth scale height to the atmosphere density scale height.The height variation of the dissipation ratio indicates that strong gravity wave dissipation mainly concentrates in the three height regions:the stratosphere(30–60 km),the mesopause(around 85 km)and the low thermosphere(above 100 km).Besides,gravity wave energy enhancement can be also observed in the background atmosphere.     

Iterative inversion of global magnetospheric information from energy neutral atom (ENA) images recorded by the TC-2/NUADU instrument

A method is presented for retrieving the magnetospheric ion distribution from Energetic Neutral Atom (ENA) measurements made by the NUADU instrument on the TC-2 spacecraft. Based on the already well-established method of constrained linear inversion, an iterance technique suitable for the low count ENA measurements has been developed which is tolerant of the noise background. By the iterance technique, it is possible for the first time to simultaneously retrieve the magnetospheric ion distribution and the exospheric neutral density, and further to recover global ENA emissions in three dimensions. The technique is applied to a representative ENA image recorded in energy channel 2 (protons: 50–81 keV) of the NUADU instrument during a major geomagnetic storm and it is, thereby, shown that the retrieval method developed provides a useful tool for extracting ion distribution information from ENA data. Supported by the National Natural Science Foundation of China (Grant No. 40674083) and Chinese National Key Laboratory research outlay (Grant No. 40523006). SMcKL acknowledges with appreciation the support of Enterprise Ireland     

Solar wind transport into magnetosphere caused by magnetic reconnection at high latitude magnetopause during northward IMF: Cluster-DSP conjunction observations

An event of Cluster-Double Star conjunction observations of magnetic reconnection at high latitude magnetopause nightside of both cusps and solar wind transport into magnetosphere caused by such reconnection process has been investigated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) the direction of the accelerated flows, with its sunward component V _x , dawnward component V _y , northward component V _z , is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component B _y ; (3) reconnection can heat plasma more in parallel direction than in perpendicular direction, to a level of about 4 keV; (4) with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magnetosphere. This event presents further observational evidence for magnetic reconnection at high latitude magnetopause nightside of both cusps as an important mechanism of solar wind transport into magnetosphere. Supported by the Ministry of Science and Technology of China (Grant No. 2006CB806305), the National Natural Science Foundation of China (Grant Nos. 40621003, 40674094), and the Hundred Talents Program of the CAS