Day-to-day thermosphere parameter variation as deduced from Millstone Hill incoherent scatter radar observations during March 16-22, 1990 magnetic storm period

摘要

A self-consistent method for day-timeF2-region modelling was applied to the analysis of Millstone Hill incoherentscatter observations during the storm period of March 16-22, 1990. The methodallows us to calculate in a self-consistent way neutral composition, temperatureand meridional wind as well as the ionized species height distribution.Theoretically calculated N_e(h) profiles fit the observeddaytime ones with great accuracy in the whole range of heights above 150 km forboth quiet and disturbed days. The overall increase in T_ex by270 K from March 16 to March 22 reflects the increase of solar activity levelduring the period in question. A 30% decrease in [O] and a two-fold increase in[N₂] are calculated for the disturbed day of March 22 relativeto quiet time prestorm conditions. Only a small reaction to the firstgeomagnetic disturbance on March 18 and the initial phase of the second storm onMarch 20 was found in [O] and [N₂] variations. The meridionalneutral wind inferred from plasma vertical drift clearly demonstrates thedependence on the geomagnetic activity level being more equatorward on disturbeddays. Small positive F2-layer storm effects on March 18 and 20 are totallyattributed to the decrease in the northward neutral wind but not to changes inneutral composition. A moderate (by a factor of 1.5) O/N₂ratio decrease relative to the MSIS-83 model prediction is required to describethe observed N_mF2 decrease on the most disturbed day of March22, but virtually no change of this ratio is needed for March 21.