Comparisons of theoretical models and observations of the thermosphere and ionosphere during extremely disturbed geomagnetic conditions during the last solar cycle

Abstract

During the last solar cycle, a series of major geomagnetic disturbances, at times of moderate to high solar activity, were well observed by a combination of ground-based and space-borne instruments capable of observing both thermospheric and ionospheric structure, dynamics and their responses to geomagnetic inputs. A wide range of information is now available describing the major geomagnetic driving processes, and their magnitudes and large-scale variations during major disturbances, as a result of concerted experimental programmes of the past 6 to 8 years. Using these data, some of the largest geomagnetic disturbances recorded during the past 30 years have been simulated. Observations from Dynamics Explorer and ESRO IV, in addition to those from ground-based Fabry-Perot interferometers, provide detailed thermospheric data against which these simulated disturbances can be compared. These are presented as several case studies. The simulations provide a considerable insight into the behaviour of the thermosphere during extreme events, in addition to a valuable body of data for examination of extreme conditions of the thermospheric and ionospheric environment for spacecraft operations.