Studies of the E-Region Neutral Wind in the Auroral Ionosphere Using Two Long-Run Data

Abstract

EISCAT data obtained in the auroral ionosphere have been analyzed in terms of the E-region neutral wind behavior at three heights of 101, 109, and 119 km. We have analyzed two extended CP-1-H runs conducted over four consecutive days each for 21-25 September 1987 and 16-20 March 1988. Mean winds as well as tidal amplitudes and phases derived by both Fast Fourier Transform (FFT) and least square fit (LSF) methods are compared with those of corresponding seasonal winds from the quiet-time statistical study by Brekke et al. (1994). During 21-25 September 1987 the mean zonal wind derived by FFT with filling in zeroes in the data gaps blows eastward with a maximum of ∼20 m s-1 between 101 and 119 km and its direction is consistent with the average quiet-time fall wind. The directions of mean meridional and vertical winds, however, are opposite to those of the fall wind. The amplitudes and phases of the tidal winds are in reasonable agreement with those found. for fall quiet time. At 119 km the zonal wind shows a large enhancement during the very geomagnetically disturbed period between 16 UT on 22 September and 05 UT on 23 September and also for about 5 hours after the end of the disturbed period. During 16-20 March 1988 the amplitudes of the mean meridional and vertical winds are very small while the mean zonal wind blows eastward with a maximum of less than 18 m s-1 between 101 and 119 km, which is about half as large as that of the average quiet-time spring wind. Most diurnal meridional and semidiurnal horizontal wind amplitudes between 101 and 119 km are also about half of those found for spring quiet time. The height profiles of phases for most components are much the same as those of the spring wind. Comparisons are made with results obtained by the Sondre Stromfjord IS radar and model predictions, and geomagnetic disturbance effects on the wind are discussed.