Equinoctial asymmetry of ionospheric vertical plasma drifts and its effect onF-region plasma density

Abstract

[1] The equinoctial asymmetry of the ionospheric vertical E × B plasma drift velocity (V⊥) in the equatorial F region is investigated based on observations from ROCSAT-1 during 1999 to 2004. It is found that the observed asymmetry exhibits obvious local time dependence with three noticeable features. First, in the Eastern Hemisphere during the interval between 0900 and 1300 LT, V⊥ is obviously higher at the northern spring equinox (March–April) than at the autumn equinox (September–October). Second, there is a pronounced asymmetry for wave number 4 longitudinal structures of V⊥, which exist almost throughout the daytime and even extend into the evening sector at autumn equinox, while they appear mainly at noon and prenoon at spring equinox. Third, around sunset we find an obvious asymmetry of the prereversal enhancement (PRE); the maximum PRE velocity is higher at autumn than at spring equinox in the longitude range from 320° to 150°, and the opposite situation occurs at other longitudes. On the basis of the drift observation mentioned, we also simulate the effect of the V⊥ asymmetry on the ionospheric plasma density by running the Theoretical Ionospheric Model of the Earth, Institute of Geology and Geophysics, Chinese Academy of Sciences (TIME-IGGCAS). It is found that the daytime V⊥ asymmetry can partly explain the equinoctial asymmetry in daytime low-latitude ionospheric plasma density observed by L. Liu et al. (J. Geophys. Res., 115, A09307).