Ionospheric effects at low latitudes during the March 22, 1979, geomagnetic storm

Abstract

This paper investigates the response of the equatorial ionosphere to the neutral atmosphere perturbations produced by the magnetic storm of March 22, 1979. A numerical model of the equatorial ionosphere is used to calculate the maximum electron densities and F layer heights associated with a storm‐perturbed neutral atmosphere and circulation model. The neutral atmosphere model is not influenced by the ionosphere model, but it utilizes an empirical ionospheric model to parameterize ion drag effects. Possible electric field perturbations due to the storm are ignored. The neutral atmosphere and dynamics are simulated by the National Center for Atmospheric Research thermospheric general circulation model (TGCM) for the storm day of March 22, 1979, and the preceding quiet day. The most striking feature of the TGCM storm day simulations is the presence of waves in the neutral composition, wind, and temperature fields which propagate from high latitudes to the equator. The TGCM‐calculated fields for the two days are input into a low‐latitude ionosphere model which calculates nmax and hmax between ±20° dip latitude. Wavelike oscillations are evident in the resulting predictions of nmax and hmax. The calculated nighttime 6300‐Å airglow emission and the altitude profiles of electron concentration are also highly perturbed by the storm. Examination of ionosonde data for March 22, 1979, shows remarkable agreement between the measured and predicted changes in f0F2 and hmax near 140°W. Poorer agreement near 70°W may be due to the neglect of electric field perturbations and the approximations inherent in the modeling. The results of these simulations indicate that the major factor influencing the storm time ionospheric behavior in this case is the neutral wind.