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

• Main Authors: A. V. Mikhailov, M. Förster
• Format: Article
• Language: English
• Published: Copernicus Publications 1997-11-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/15/1429/1997/angeo-15-1429-1997.pdf

A self-consistent method for day-time F2-region modelling was applied to the analysis of Millstone Hill incoherent scatter observations during the storm period of March 16-22, 1990. The method allows us to calculate in a self-consistent way neutral composition, temperature and meridional wind as well as the ionized species height distribution. Theoretically calculated <i>N_e</i>(h) profiles fit the observed daytime ones with great accuracy in the whole range of heights above 150 km for both quiet and disturbed days. The overall increase in <i>T</i>_ex by 270 K from March 16 to March 22 reflects the increase of solar activity level during the period in question. A 30% decrease in [O] and a two-fold increase in [<i>N</i>₂] are calculated for the disturbed day of March 22 relative to quiet time prestorm conditions. Only a small reaction to the first geomagnetic disturbance on March 18 and the initial phase of the second storm on March 20 was found in [O] and [<i>N</i>₂] variations. The meridional neutral wind inferred from plasma vertical drift clearly demonstrates the dependence on the geomagnetic activity level being more equatorward on disturbed days. Small positive F2-layer storm effects on March 18 and 20 are totally attributed to the decrease in the northward neutral wind but not to changes in neutral composition. A moderate (by a factor of 1.5) O/<i>N</i>₂ ratio decrease relative to the MSIS-83 model prediction is required to describe the observed <i>N_mF</i>2 decrease on the most disturbed day of March 22, but virtually no change of this ratio is needed for March 21.