Thermospheric dynamics during the March 22, 1979, magnetic storm: 2. Comparisons of model predictions with observations

Abstract

A comparison is made between simulations from the National Center for Atmospheric Research thermospheric general circulation model (TGCM), satellite electrostatic triaxial accelerometer measurements of neutral winds and total mass densities between 170 and 240 km, and mid‐latitude Thomson scatter measurements of neutral exospheric temperatures, for the isolated magnetic disturbance occurring on March 22, 1979, commonly referred to as the CDAW 6 interval. Points of consistency between theory and observation include (1) a localized region of daytime density enhancement (60% at 180 km) near the throat of the plasma convection pattern, (2) more structured density perturbations on the nightside propagating toward the equator, and (3) polar region winds of 250–600 m s−1 generally consistent with antisunward and return flows characteristic of a two‐cell pattern which persists for at least 6 hours after the magnetic disturbance has died away. The major points of discrepancy are (1) the excessive (factor of 2) TGCM estimates of the Millstone Hill exospheric temperature response, (2) relatedly, the comparatively pronounced equatorward penetration of the model's high‐latitute temperature and density enhancements in general, and (3) the measured reversals to eastward winds of 200 m s−1 near 50°–60° latitude, whereas the TGCM maintains a westward flow down to at least 40° latitude in the prenoon and premidnight sectors. We speculate that these differences may be caused by one or more of the following: (1) a more complex (structured) ion convection forcing than that parameterized within the TGCM model, (2) neglect of By‐induced variations in the ion convection pattern, (3) an incorrect positioning or orientation of the driving plasma convection pattern, or (4) inadequate modeling of high‐latitude ion densities in the TGCM, including the possible need for a coupled solution to the neutral wind and plasma distributions.