Latitude and solar-cycle patterns in the response of the ionosphere F2-layer to geomagnetic activity

The F2-layer response to geomagnetic activity is studied using the daily mean and local-time variations of the (disturbed/quiet) ratio of the peak electron density NmF2. Data for 53 stations are binned by local time, season, and geomagnetic activity. The mean level has a well-defined variation with latitude, attributed to neutral composition changes caused by a global-scale storm circulation. There are systematic differences in the local-time average of the (disturbed/quiet) ratio of NmF2 between three solar cycles, which may indicate long-term changes in thermospheric composition that possibly arise from different levels of solar activity in the three cycles. Comparison with storm simulations using a coupled thermosphere-ionosphere-plasmasphere model reinforce the conclusion that the principal F2-layer storm effects are due to composition changes. (C) 1997 COSPAR. Published by Elsevier Science Ltd.