Thermospheric dynamics during the March 22, 1979, magnetic storm: 1. Model simulations

Abstract

The physical processes involved in the transfer of energy from the solar wind to the magnetosphere and its release associated with substorms on March 22, 1979, have been studied in detail by the Coordinated Data Analaysis Workshop 6 (CDAW 6). The information derived from the CDAW 6 study, as well as other information obtained from magnetospheric modeling, is used to prescribe the time‐dependent variations of the parameterizations for the auroral and magnetospheric convection models that are incorporated within the National Center for Atmospheric Research thermospheric general circulation model (TGCM). The period preceding the magnetic storm (March 21) was geomagnetically quiet, and the TGCM was run until a diurnally reproducible pattern was obtained. The time variations of auroral particle precipitation and enhanced magnetospheric convection on March 22 caused a considerable disturbance in the high‐latitude circulation, temperature, and composition during the storm period that began at about 1055 UT. Large‐ and medium‐scale disturbances were launched during the event that propagated to equatorial latitudes. The thermospheric response in the northern hemisphere was larger than that generated in the southern hemisphere, because the auroral oval and magnetospheric convection pattern in the northern hemisphere were in sunlight during the storm period whereas they were in darkness in the southern hemisphere. The storm response was also different in the upper and the lower thermosphere. In the upper thermosphere the winds generally followed the two‐cell pattern of magnetospheric convection with a lag of only ½ to 1 hour. In the lower thermosphere there was a pronounced asymmetry between the circulation cells on the dawnside and on the duskside of the polar cap. The circulation features in the lower thermosphere, once established, tended to persist several hours after the storm time forcings subsided. The TGCM‐calculated response to the storm is compared with predictions made by the mass spectrometer/incoherent scatter (MSIS‐83) empirical model. In a companion paper, TGCM predictions are compared with data obtained by a satellite electrostatic triaxial accelerometer system on board an orbiting satellite and with incoherent scatter radar data.