Progress in developing a storm-time ionospheric correction model

One important ionospheric tool currently missing is a successful storm-time prediction model. The most obvious, long-lived, coherent features of the ionospheric response to a geomagnetic storm are the deep ion depletions ("negative phase"), that typically develop in the summer hemisphere during the driven phase of a storm, and persist well into the recovery. An empirical model is presented that is designed to capture the long-lived ion depletions in the midlatitude summer hemisphere. The algorithm is based on a new index: the integral of the hemispheric auroral power as specified by the TIROS/NOAA measurements of precipitating particles. The integral sums the auroral power over the previous 30 hours with a weighting function. The index is designed to be a measure of the change in neutral composition induced by the magnetospheric sources. Recent advances in physically-based modeling of the upper atmosphere have improved understanding of the processes controlling the ionospheric response to geomagnetic storms, and confirm the theory that the "negative phase" is mainly caused by changes in neutral composition. This understanding from physically-based modeling has guided us in the choice of a relatively simple empirical expression to capture the ionospheric response to storms. The algorithm assumes a non-linear relationship between the F-region ionospheric response and the index. The algorithm improves on climatological predictions by reducing storm-time ionospheric variance to values close to pre-storm levels, (C) 1998 COSPAR. Published by Elsevier Science Ltd.