Investigation of the latitudinal occurrence rate of ionospheric plasma bubble in case of strong and weak pre–reversal enhancement in Southeast Asia

Abstract

We used ionosonde and GPS receivers during March–April in 2004–2005 and 2011–2015 to investigate the latitudinal variation of equatorial plasma bubble (EPB) occurrence rate in cases of strong and weak pre-reversal enhancement (PRE). The ionosonde at Chumphon in Thailand was used to estimate the PRE strength. Ten GPS receivers in Southeast Asia, ranging from magnetic latitude (ML) of 4.4°S to 21.6°S, were used to investigate the latitudinal variation of EPB occurrence rate. In the case of strong PRE, the EPB occurrence rates decrease from 38.9% to 34.9% at ML of 4.4°S–7.2°S. Continuously, the occurrence rate increases and reaches the peak (44%) at ML of 9.3°S; afterward, the occurrence rate rapidly decreases and reaches below 5% at ML of 21.6°S. In the case of weak PRE, the occurrence rate decreases from 21.8% at ML of 4.4°S, seems constant (15.3%–16%) at ML of 8.2°S–12.1°S, and reaches less than 5% at ML of 16.1°S. Generally, the EPB occurrence rate and its latitudinal extension in case of strong PRE are higher than that in case of weak PRE. Interestingly, we found that the latitudinal occurrence rate peak of the EPB in case of strong is farther than that in case of weak PRE.