Investigation of equatorial plasma bubble irregularities under quiet and disturbed geomagnetic conditions over the East African longitudinal sector in 2015

Abstract

In this paper, we investigated the behavior of equatorial plasma bubble irregularities under quiet and disturbed geomagnetic conditions in the year 2015. Total Electron Content (TEC) data was obtained from four Global Navigation Satellite System (GNSS) receivers situated at Addis Ababa (ADIS), Bahir Dar (BDMT), ASAB (ASAB), and Debark (DEBK). We used Rate of TEC change index (ROTI) to describe ionospheric irregularities associated with plasma bubbles. The monthly occurrence rates (MOR) is obtained to be higher in equinoctial and lower in solstitial months at all stations. Moreover, the seasonal occurrence rates of plasma bubbles (SOR) show equinoctial and solstitial asymmetries. The seasonal occurrence rate in March equinox is higher than that of the September equinox during both quiet and disturbed geomagnetic conditions. Similarly, higher occurrence rate is observed in June than December solstice in quiet geomagnetic conditions. We have also investigated that the occurrence rate of plasma bubble is higher in geomagnetic quiet conditions than disturbed conditions at all stations. Moreover, there is also excellent correlation with high degree of significance between the monthly occurrence rates of plasma bubbles and the monthly mean F10.7 index and sunspot number at all stations. The occurrence times of plasma bubbles are almost similar in the four stations and most of the irregularities (around 95 $\%$of the total irregularities) are observed in times between postsunset and midnight hours. The daily, monthly, and seasonal variations of ROTI also demonstrate similarity with the variation of the occurrence rates of plasma bubbles.