T. V. Kozelova

Local gradient of energetic ion flux during dipolarization on 6–7RE

Abstract Injections of energetic particles and dipolarization of magnetic field are well-known signatures of magnetospheric substorm in the near-earth region of plasma sheet. However, the physical processes associated with these phenomena are not fully understood. The pressure gradient and anisotropy are significant parameters for understanding of physics of the substorm development. Kozelova et al. [Geomagn. Aeronomy 26, 621, 1986] found in study of GEOS 2 data that the anticorrelation between the proton and electron fluxes is connected with the western edge of the expansive auroral bulge (with the spatial extent >100 km and with duration near 10 min). Inside the active region, where the dipolarization is observed, the proton fluxes are reduced and the electric field is directed westward. The increase (or decrease) of proton flux may be interpreted as satellite entry into the region of enhanced (or decreased) plasma pressure since energetic protons give the main contribution to the pressure. Here we examined the CRRES data from several detectors which measured the particles in a different directions. We found the similar variations of the energetic particle fluxes (protons >37 keV and electrons >21.5 keV) associated with the local dipolarization, however these variations were observed during the shorter interval of 30–40 s [Kozelova et al., Geomagn. Aeronomy 43, 513, 2003]. Sometimes the azimuthal anisotropy of proton fluxes of different energy may be different and the flux variations are noncoherent within a small spatial region comparable to the proton gyroradius (here from 350 to 1400 km). Dispersionless energetic electron injection coincides with the dipolarization and with the drop of the 37–54 keV proton flux. This proton drop begins eastward of the CRRES and then expand westward with the velocity of 130–350 km/s.

Total ion pressure changes with L shell in the nightside inner magnetosphere

[1]xa0The total ion plasma pressure has been estimated in the equatorial plane of the magnetosphere from the CRRES measurements when the satellite crossed the magnetic shells from L ∼ 2.3 to L ∼ 6.6 in the night sector of ∼20–24 MLT. The data of the LEPA and the EPAS particle detectors as well as the magnetic field data on the CRRES satellite have been used for two events with the AE < 300 nT before the substorm onset. It is found that the gross radial structure of the plasma pressure constructed along the CRRES orbit exhibits a maximum at L ∼ 3 and then a gradual decrease with distance from the Earth. Along with these usual features of the plasma pressure profile, we revealed an additional maximum of the total ion pressure, which appears at L ∼ 4.6–4.9. It is located earthward of the Alfven boundaries of low-energy electrons. From the analysis of the energy composition of plasma pressure we conclude that this additional maximum is a result of enhancement of the pressure of ions with energies <30 keV which was observed ∼20 min after a small enhancement of magnetic activity. We suppose that dynamical changes in the electric field and particle density in the plasma sheet are the dominant processes that form the observed peculiarity in the radial profile of the total ion pressure. These dynamical changes lead to a shift of convection boundaries and to acceleration of ion flux which was formed by preexisting quasi-steady convection.

Energetic particle bursts before the main substorm injection

Abstract We examine the relationship between the energetic electron bursts (15 – 30 s) observed before the main injection and the changes in the magnetic field during substorms on the CRRES. Pitch angle distrubution (PAD) of electron flux during these bursts and injections depends on the spacecraft position relative to the cross-tail current sheet and boundaries of energetic particle trapped region. Near the inner edge of plasma sheet (PS) the pancake PAD was observed. Inside the PS and near the outer energetic particle trapped boundary the cigar and isotropic PADs were observed. The lack of dispersion in some observed injection events are evidence of local acceleration. The burst onsets correlate with the magnetic bursts of ∂Bz/∂t with the time duration ∼ 2–4 s. It is likely that particles are accelerated by induced E field arising from these observed magnetic bursts.