Abstract:
Using the 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia, the nocturnal
evolution of equatorial plasma bubbles (EPBs) was examined during the moderate solar activity years
2011–2012. While the evolution of EPBs was mostly (86%) confined to post sunset hours (1900–2100 LT)
during equinoxes, in contrast, the majority of EPBs (~71%) in June solstice found evolve around the midnight
hours (2200–0300 LT). The mechanisms behind the fresh evolution of summer time midnight EPBs were
investigated, for the first time, through SAMI2 model simulations with a realistic input of background ExB drift
variation derived from CINDI IVM on board C/NOFS satellite. The term-by-term analysis of linear growth rate
of RT instability indicates that the formation of high flux tube electron content height gradient (KF) (steep
vertical gradient) region at higher altitudes is the key factor for the enhanced growth rate of RT instability. The
responsible factors are discussed in light of relatively weak westward zonal electric field in the presence of
equatorward neutral wind and bottomside recombination around the midnight hours of June solstice. The
effects of neutral winds and weak westward electric fields on the uplift of equatorial F layer were examined
separately using controlled SAMI2 simulations. The results indicate that relatively larger linear growth rate is
more likely to occur around midnight during June solstice because of relatively weak westward electric field
than other local times in the presence of equatorward meridional wind.
