Evolution of plasmaspheric structures in geostationary orbit according to the LANL MPA 1994_084 data of 16-24 february 2001

The plasmaspheric structures with high concentration N i of cold ions of energies from 1 to 130 eV in geostationary orbit have been determined from the LANL 1994_084 data of 16-24 February 2001. Among six plasmaspheric structures determined, five were observed in the afternoon/dusk sector (one structure per day on 19-23 February) and one in the midnight sector (20 February). All plasmaspheric structures were recorded in the regions with low (as compared with hot ions, 0.13-45 keV/e) electron concentration, 0.03-45 keV/q. According to the published data, the afternoon plasmaspheric structure of 23 February was a plasmaspheric plume clearly seen on the images taken by the IMAGE EUV instrument. Ions in the afternoon/dusk structures were shown to move from the Earth and westward at average velocities of 6-7 and 10-16 km/s, respectively. Convection electric field strength E cd was determined from ion velocities for each structure and its surrounding area. Average Е сd values in the afternoon/dusk structures were 1.21-1.83 mV/m, which were 5-10 times more than estimates of the convection field strength E c corresponding to these values in time and calculated from the solar wind velocity and from IMF В у, B z components. The findings demonstrate local amplification of the magnetospheric convection electric field in the plasmaspheric structures crossing the geostationary orbit.