Time dependent thermospheric neutral response to the 2-11 November 1993 storm period

Many satellite and ground-based observations from 2-11 November 1993 were c ombined in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) p rocedure to derive realistic time dependent global distributions of the aur oral precipitation and ionospheric convection. These were then used as inpu ts to the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) to simulate the thermospheric and ionospheric response during the storm period. The November 1993 storm was an unusually strong storm associa ted with a recurring high speed stream of solar plasma velocity in the decl ining phase of the solar cycle. Significant gravity waves with phase speeds of about 700 m/s caused by Joule heating were present in the upper thermos phere as perturbations to the neutral temperature and wind fields, especial ly on 4 November. The observed gravity waves in the meridional wind and in the height of the electron density peak at several southern hemisphere stat ions were generally reproduced by the model using the AMIE high latitude in puts. Both model and observed equatorward winds were enhanced during the pe ak of the storm at Millstone Hill and at Australian ionosonde stations. The observed neutral temperature at Millstone Hill increased about 400 K durin g the night on 4 November, returning to normal on 9 November, while the mod el increased 300 K the first night at that location but was still elevated on 11 November. Enhanced westward winds during the storm were evident in th e UARS WIND Imaging Interferometer (WINDII) data. The enhanced westward win ds in the model were largest around 40-45 degrees magnetic latitude at nigh t, and also tended to be largest in the longitudes containing the magnetic poles. The peak westward wind enhancements at 0 LT reached about 250 mi's a t 300 km, and about 100 m/s at 125 km the first day of the storm at 40 degr ees magnetic latitude. At 20 degrees magnetic latitude, the maximum westwar d wind enhancements at 125 km at 0 LT appeared 2-4 days after the major par t of the storm, indicating very long time constants in the lower thermosphe re. The model showed global average neutral temperature enhancements of 188 K after the peak of the storm that decayed with time, and which correlated with variations 8 h earlier in the Dst index and in the electric potential drop input from AMIE. The global average temperature enhancement of 188 K corresponded to a potential drop increase of only about 105 kV. The results showed that the TIEGCM using realistic AMIE auroral forcings were able to reproduce many of the observed time dependent features of this long-lived g eomagnetic storm. The overall global average exospheric temperature variati on correlated well with the time variation of the cross-tail potential drop and the Dst index during the storm period. However, the enhanced westward winds at mid-latitudes were strongly related to the corrected Joule heating defined by the time dependent AMIE inputs. (C) 1999 Elsevier Science Ltd. All rights reserved.