Temporal and spatial components in the storm‐time ionospheric disturbances

摘要

The variations of ionospheric and thermospheric disturbances in satellite data during geomagnetic storms are often understood as storm‐phase‐dependent temporal variations. However, the nonuniform spatial distribution of disturbances and their corotation also produce an apparent temporal variation. In this case study of the ionospheric disturbances during the 20 November 2003 storm, we examine the contribution of the spatial component to the storm‐time behavior of ionospheric disturbances. The equatorward boundary of the negative ionospheric storm observed at noon by the Challenging Minisatellite Payload (CHAMP) shows apparent equatorward and poleward movements as the storm progresses. The global total electron content (TEC) maps show that the apparent behavior of the negative ionospheric storm is related to the corotation of the spatially nonuniform ionospheric disturbances. The behavior of the negative ionospheric storm is closely associated with the evolution of the thermospheric neutral composition disturbance. The middle‐latitude steep plasma density gradient appears in the dusk and premidnight sectors during the storm period. The temporal evolution of the global TEC maps shows that the steep density gradient is not created by an instantaneous response of the ionosphere to the storm. A severe positive ionospheric storm is created in the dayside during the main phase of the storm, and the corotation of the daytime positive ionospheric storm is primarily responsible for the steep density gradients in the dusk and premidnight sectors.