On the occurrence of equatorial F-region irregularities during solar minimum using radio occultation measurements (original) (raw)
Previous ground observations have revealed a correlation that exists between equatorial plasma bubbles, evening equatorial ionization anomaly (EIA), and prereversal E B drift velocity using latitudinal arrays of ionospheric sounders, such as in the Indian and American regions. Besides the ground measurements, the space-based observations also provide a convenient way to study the global-scale variations. On the basis of in situ data collected from DMSP, ROCSAT-1, and CHAMP satellites, we investigated the correlation of seasonal/longitudinal variations of plasma bubble (PB) occurrence, evening EIA, and prereversal E B drifts on magnetically quiet days during the solar maximum years (2000–2002). In general, the observational results provide consistent evidences that the large-scale variations in seasonal/longitudinal distribution of evening EIA and PB occurrence rates are well-correlated with the observed evening prereversal E B drifts and that some of the small-scale longitudinal variations (such as wave number-4 structure during equinox) of evening EIA exist before the occurrence of the prereversal enhancement and coincide with the daytime equatorial electrojet. In such cases, the small-scale longitudinal variation of PB occurrence rates may result from the evening EIA small-scale longitudinal structures. The evening prereversal E B drifts, together with the longitudinal variations of evening EIA, are assumed to play a role in determining the longitudinal variations of equatorial and low-latitude PB occurrence rates.