ИСТИНА

This study concerns with an unresolved problem of generation of long-lasting ionospheric electron content (EC) enhancements, so-called positive ionospheric storms at low-latitude, in response to the geomagnetic storms. A storm event on 14-15 December 2006 was analyzed by using data on vertical total electron content (VTEC) measured by a worldwide network of ground-based GPS receivers and data on 3D ionospheric EC tomography provided by COSMIC/GPS radio-occultation (RO) technique. It was shown that one of very important factors in the study of the ionospheric storms is consistent choice of the quiet time period. Previous studies of this event [Lei et al.,2008a,b; Pedatella et al.,2009] used moderately disturbed day on December 13 as a day of “quiet conditions”. In contrast, using a period on December 2-4, when the solar and geomagnetic activity was very quiet, allowed revealing prominent positive ionospheric storms on the initial, main and recovery phases of the geomagnetic storm. Analysis of the dynamics of the positive storm over the Pacific Ocean showed an increase of ionization at low latitudes and its uplifting up to heights of ~600 km during the storm main phase. Comparison of the VTEC dynamics with the electron fluxes demonstrate a good overlapping of the observed ionization enhancements with the low-energy particle precipitations at low latitudes above Pacific region. This fact indicates to importance of the magnetospheric mechanism in generation of the positive ionospheric storms.