COMPARISON OF SATELLITE ELECTRON-DENSITY AND TEMPERATURE-MEASUREMENTS AT LOW LATITUDES WITH A PLASMASPHERE-IONOSPHERE MODEL

Observations made by the Hinotori satellite of the latitude and diurnal variations of electron density and temperature near 600 km altitude in the low-latitude region are studied by comparison with values from the Sheffield University plasmasphere-ionosphere model (SUPIM). The model results show that the observed features of higher electron density in the summer hemisphere and higher electron temperature in the winter hemisphere are caused principally by the difference in the summer and winter hemisphere values of the meridional neutral wind. Closer agreement between the modeled and observed values is obtained when the interhemisphere difference in the meridional wind, as given by the horizontal wind model (HWM) 90, is reduced and when the peak value of the daytime poleward wind is moved to the afternoon sector in the winter hemisphere and to the morning sector in the summer hemisphere. The model results also show that the altitude variation of the vertical ExB drift velocity plays an important role in the development of the ionospheric equatorial anomaly. The latitude and diurnal variations of the modeled electron density and temperature are in good agreement with the observations when the ExB drift velocity used by the model is in accord with the observations made by the AE-E satellite for magnetic field lines with apex altitude less than 400 km and at Arecibo for magnetic field lines with apex altitude greater than 2000 km; linear interpolation of the observed values is used for the intermediate magnetic field lines.