Study on the plasma irregularities of the low-latitude ionospheric region using satellite observations

Abstract

This work describes the global distribution and the characteristic features of equatorial plasma irregularities: equatorial plasma bubble (EPB) and low-latitude plasma blob. Primary data set was in-situ measurements of Korea Multi-Purpose Satellite-1 (KOMPSAT-1) at an altitude of 680 km at 2230 LT during the solar maximum period from June 2000 to August 2001. As supplementary data, ionospheric observation of DMSP F13 and F15 was used. EPBs can be observed at all longitudes around the magnetic dip equator in the equinoctial seasons with the peak occurrence in the American-Atlantic-African regions. During the northern summer EPBs occur predominantly in the magnetic north in the Indian and west Pacific regions, but are totally suppressed in the American-Atlantic sectors. During the northern winter EPBs are highly promoted in the America-Atlantic sectors but are suppressed in other longitude sectors, especially, in the Pacific sector. To explain the global EPB distributions, we investigate the growth conditions of Rayleigh-Taylor instability in several longitude sectors using the Mass Spectrometer Incoherent Scatter (MSIS) and International Reference Ionosphere (IRI) models. The simulation results indicate that the global EPB distribution can be understood better by considering the upward plasma drift velocity at post-sunset time weighted by the flux-tube integrated electron content in the lower F region. Meantime, the EPB occurrence is nearly anti-correlated with the degree of asymmetry in latitudinal plasma distribution at 1800 LT, 2130 LT, and 2250. So the asymmetry also can be used as a rough index for EPB forecast. The seasonal-longitudinal change of the asymmetry is in conflict with the current simple theories of inter-hemispheric plasma transport. Some other elements such as the thermospheric parameters should be considered. The relationship between $K_p$ index and EPB occurrence is consistent with existing reports. The effect of 27-day solar cycle is not cl...