Study of anomalous electron temperature variations in the topside ionosphere using HINOTORI satellite data

摘要

Electron temperature (T_e) and electron density (N_e) measurements from the Japanese Astronomy Satellite HINOTORI for the high-solar activity period (February-November, 1981) are examined exclusively to study anomalous electron temperature enhancements observed in the topside ionosphere around 600 km in altitude. Basically, T_e enhancements are categorised into two types. The first type is where anomalous T_e enhancements are found to be as high as 3000 K above the average level over the South American Magnetic Field Anomaly zone (SAMA) on several occasions; however, less marked enhancements were observed over other longitudes in both the hemispheres with a strong bias in 20 to 30°geomagnetic latitude belt. T_e enhancements, especially of larger magnitudes, are mainly observed during May-July months (southern winter) in SAMA during evening hours. Generally, N_e shows a decreasing trend during the periods of T_e enhancement but it is noted that the magnitude of T_e enhancement in such cases is not proportional to the corresponding decreases in N_e. The second type of T_e enhancements are observed, mostly during evening hours of equinoctial months, on both sides of the equator collocated with the crests of the well-known equatorial ionization anomaly (EIA). The magnitude of temperature enhancements of second type is found to be proportional to the corresponding electron density enhancements. The results are presented and discussed in terms of zonal winds, winter anomaly in electron density and electrodynamical drift.