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

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.