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 ob-servations showed that the wave frequency was higher inside the plasmasphere than outside. The mechanism generating these ULF waves and possible diagnos-ing of the "classical plasmapause" location with the ULF wave were discussed.

Calculation of the extreme ultraviolet radiation of the earth's plasmasphere

The dynamic global core plasma model(DGCPM) is used in this paper to calculate the He+ density distribution of the Earth's plasmasphere and to investigate the configurations and 30.4 nm radiation properties of the plasmasphere.Validation comparisons between the simulation results and IMAGE mission observations show:That the equatorial structure of the plasmapause is mainly located near 5.5 RE and the typical scale of plasmasphere shrinking or expansion within 10 min is approximately 0.1 RE;that the plasmaspheric shoulders are formed and rotate noon-ward from the dawn sector under the conditions of strong southward turning of the interplanetary magnetic field(IMF);that the plasmaspheric plumes will rotate dawn-ward from the night sector and become narrow for the southward turning of the IMF.The simulated images from the lunar orbit show that the plasmasphere locating within the geocentric distance of 5.5 RE corresponds to field of view(FOV) of 10.7°×10.7° for the moon-based EUV imager,and that the 30.4 nm radiation intensity of the plasmasphere is 0.1-11.4 R.The plasmaspheric shoulders and plumes locating toward the moon-side are for the first time simulated with typical scale level of 0.1 RE from the side view of the moon.These simulated results provide an important theoretical basis for the lunar-based EUV camera design.

Simulation of EUV Imaging and 3-D Cone-Beam CT Reconstruction on the Plasmasphere

A three-dimensional （3-D） phantom for the density distribution of the plasmasphere is established. The imaging processes of the extreme ultraviolet （EUV） Imager are computer-simulated, in which the Earth shelter is treated as a main problem. A modified ART method is devised to resolve the incomplete data reconstruction problem to validate and evaluate the proposed methods. The cone-beam EUV data are simu- lated based on the 3-D phantom from both a circular and semi-circular trajectories. Quantitative reconstruc- tion results demonstrate the correctness of the proposed modified ART algorithm. The CT technique can be used to calculate the global density of the plasmasphere from the EUV data.

A new inversion method for reconstruction of plasmaspheric He^(+)density from EUV images

The Computer Tomography(CT)method is used for remote sensing the Earth’s plasmasphere.One challenge for image reconstruction is insufficient projection data,mainly caused by limited projection angles.In this study,we apply the Algebraic Reconstruction Technique(ART)and the minimization of the image Total Variation(TV)method,with a combination of priori knowledge of north–south symmetry,to reconstruct plasmaspheric He+density from simulated EUV images.The results demonstrate that incorporating priori assumption can be particularly useful when the projection data is insufficient.This method has good performance even with a projection angle of less than 150 degrees.The method of our study is expected to have applications in the Soft X-ray Imager(SXI)reconstruction for the Solar wind–Magnetosphere–Ionosphere Link Explorer(SMILE)mission.

Correlations between plasmapause evolutions and auroral signatures during substorms observed by Chang'e-3 EUV Camera

The plasmapause locations determined from the Chang'e-3(CE-3) Extreme Ultraviolet Camera(EUVC) images and the auroral boundaries determined from the Defense Meteorological Satellite Program(DMSP) Special Sensor Ultraviolet Spectrographic Imager(SSUSI) images are used to investigate the plasmaspheric evolutions during substorms. The most important finding is a nightside pointing plasmaspheric plume observed at 23:05 UT on 21 April 2014 under quiet solar wind and geomagnetic conditions, which drifted from the dusk sector. High correlations between the plasmapause evolutions and the auroral signatures exist during substorms. After substorm onset, the plasmapause erosion and the equatorward expansion of the auroral oval occur almost simultaneously in both MLT and UT, and then both the erosion and the expansion propagate westward and eastward. It is suggested that the plasmaspheric erosion and its MLT propagations are induced by the enhanced earthward plasma convection during substorm period, and the substorm dipolarization causes pitch-angle scattering of plasma sheet electrons and the resulting precipitation excites aurora emissions at the same time.

Second-Order Resonant Interaction of Ring Current Protons with Whistler-Mode Waves

We present a study on the second-order resonant interaction between the ring current protons with Whistler-mode waves propagating near the quasi electrostatic limit following the previous second-order resonant theory. The diffusion coefficients are proportional to the electric field amplitude E, much greater than those for the regular first-order resonance, which are proportional to the electric field amplitudes square E^2. Numerical calculations for the pitch angle scattering are performed for typical energies of protons Ek = 50 keV and 100 keV at locations L = 2 and L = 3.5. The timescale for the loss process of protons by the Whistler waves is found to approach one hour, comparable to that by the EMIC waves, suggesting that Whistler waves may also contribute significantly to the ring current decay under appropriate conditions.

Corotating drift-bounce resonance of plasmaspheric electron with poloidal ULF waves

The purpose of this paper is to understand how low energy plasmaspheric electrons respond to ULF waves excited by interplanetary shocks impinging on magnetosphere. It is found that both energy and pitch angle dispersed plasmaspheric electrons with energy of a few eV to tens of eV can be generated simultaneously by the interplanetary shock. The subsequent period of successive dispersion signatures is around 40 s and is consistent with the ULF wave period(third harmonic). By tracing back the energy and pitch angle dispersion signatures, the position of the electron injection region is found to be off-equator at around -32° in the southern hemisphere. This can be explained as the result of injected electrons being accelerated by higher harmonic ULF waves(e.g. third harmonic) which carry a larger amplitude electric field off-equator. The dispersion signatures are due to the flux modulations(or accelerations) of " local" plasmaspheric electrons rather than electrons from the ionosphere. With the observed wave-borne large electric field excited by the interplanetary shock impact, the kinetic energy can increase to a maximum of 23 percent in one bouncing cycle for plasmaspheric electrons satisfying the drift-bounce resonance condition by taking account of both the corotating drift and bounce motion of the local plasmaspheric electron.

Cold plasma redistribution throughout geospace

The redistribution of the electrically charged cold plasma of ionospheric origin involves the equatorial,low,mid,auroral,and polar-latitude regions in a multi-step,system-wide process linking the regions of geospace.Observations with ground and space-based instruments characterize the geospace plume-regularly occurring channels of enhanced plasma density flowing at both ionospheric and magnetospheric altitudes.Convection in the SAPS channel transports the eroded material to the noontime cusp in the ionosphere and to the dayside magnetopause at high altitudes.As the fluxes of cold plume plasma traverse the cusp and enter the polar cap,they form the polar tongue of ionization.At the cusp the plume plasma provides a rich source of heavy ions for the magnetospheric injection and acceleration via the mechanisms operative on those field lines.

Ultra low frequency waves impact on radiation belt energetic particles

One of the most fundamental important issues in the space physics is to understand how solar wind energy transports into the inner magnetosphere.Ultra low frequency(ULF)wave in the magnetosphere and its impact on energetic particles,such as the wave-particle resonance,modulation,and particle acceleration,are extremely important topics in the Earth’s radiation belt dynamics and solar wind― magnetospheric coupling.In this review,we briefly introduce the recent advances on ULF waves study. Further,we will explore the density structures and ion compositions around the plasmaspheric boundary layer(PBL)and discuss its possible relation to the ULF waves.

Plasmaspheric trough evolution under different conditions of subauroral ion drift

The statistical characteristics of the subauroral ion drift (SAID) in the ionosphere and the plasmaspheric trough evolution under different conditions of SAID were investigated in this paper, based on 566 SAID events observed by Akebono, Astrid-2, DE-2, and Freja satellites. The relationships between the latitudinal location of SAID and the Kp, AL, and Dst indices for these events were also discussed. It was found that the SAID events happened mainly at invariant latitude (ILAT) of 60.4° and magnetic local time (MLT) of 21.6 MLT and that 92.4% of the events happened when the Kp index was below 5.0, indicating a medium geomagnetic activity. The latitudinal half-width of SAID varied from 0.5° to 3.0° with a typical half-width of 1.0°. The SAID would happen at low latitudes if the geomagnetic activity was high. The effects of SAID on equatorial outer plas- masphere trough evolutions were studied with the dynamic global core plasma model (DGCPM) driven by the statistical results of SAID signatures. It was noted that locations, shapes and density of troughs vary with ILAT, MLT, latitudinal width, cross polar cap potential and lifetime of SAID events. The evolution of a trough is determined by the extent of SAID electric field penetrating into plasmasphere and not all SAID events can result in trough formations.