ИСТИНА

Recurrent magnetic storms are accompanied by various ionospheric disturbances of different temporal and spatial scales. The scales are related to the origin of disturbances. We analyzed low-latitude ionospheric storms with 2-hour resolution by using global ionospheric maps of vertical total electron content derived from the ground based GPS network in time period from 2004 to 2009. It was found that positive ionospheric storms have largest temporal and spatial scales: the duration can exceed ten hours, latitudinal and longitudinal extensions can reach up to 40 and 120 degrees, respectively. In contrast, negative ionospheric storms have ~2 time smaller scales: duration of several hours, latitudinal and latitudinal extents of ~20 and 60 degrees, respectively. The different scales indicate to different origin of positive and negative ionospheric storms. The large-scale positive storms result from global impact of electrodynamical and magnetospheric mechanisms. The middle-scale negative storms can be related to changes of chemical composition produced by enhanced thermospheric circulation.