Statistical backgrounds of topside-ionospheric electron density and temperature and their variations during geomagnetic activity

Abstract

Electron density and temperature measured by DEMETER satellite at 710 km altitude from 17 November 2004 to 30 November 2005 are collected, and their statistical averages are calculated in each geographic cells of 2 degrees (lat) X 4 degrees (Ion) under different geomagnetic conditions. The statistical results indicate that whenever the geomagnetically quiet or active times the electron density distribution has a large Wedell Sea Anomaly (WSA) region (30 degrees W similar to 180 degrees W and 30 S 75 S, where the nighttime density of plasma is larger than the daytime) and the low-density nighttime midlatitude trough (MIT) regions (35 degrees N similar to 60 degrees N and 35 degrees S similar to 60 degrees S) in the topside ionosphere, and the electron density is maximum near the magnetic dip equator (+/- 20 degrees), indicating that Equatorial Ionization Anomaly (EIA) does not exist in the topside ionosphere of 710 km altitude. Though the geomagnetic activity causes the global increase of electron density and the latitude expanding of equatorial density peak, it does not obviously change the spatial ranges of the WSA and MIT regions. In contrast to the electron density distribution, the electron temperature is the minimum near the magnetic dip equator, whereas it is the maximum near the plasmapause, and the geomagnetic activity merely leads to the increase of electron temperature near the plasmapause.