Comparative study of the high‐latitude E region ion and neutral temperatures in the polar cap and the auroral region derived from the EISCAT radar observations

Abstract

The ion and neutral temperatures in the auroral region have been compared with those in the polar cap based upon simultaneous measurements with the EISCAT‐UHF radar at Tromsø and the EISCAT Svalbard radar (ESR) at Longyearbyen from March 8 to 12 in 1999. The E region ion temperature at Tromsø does not show any characteristic difference between dayside and nightside except for a tendency to increase slightly during the nights. At Longyearbyen, however, the E region ion temperature shows the opposite sense of the day‐night asymmetry, i.e., being higher in the dayside than in the nightside. The day‐night asymmetry of the neutral temperature estimated from the measured ion temperature has the same feature as the day‐night asymmetry of the ion temperature. The dayside E region neutral temperature at Longyearbyen is higher than that at Tromsø, particularly at and above 110 km. The difference between them increases with increasing altitude. The E region neutral temperatures derived from the two EISCAT radars have been compared with the temperature predicted by the mass spectrometer/incoherent scatter (MSISE‐90) model. The dayside neutral temperature at Tromsø is consistent to the MSIS temperature. In contrast, the dayside E region neutral temperature at Longyearbyen is significantly higher than the MSISE‐90 model temperature. Energetics which account for the distributions of the ion and neutral temperatures are also discussed.