Concurrent Observations of Plasma Bubbles and Field-Aligned Irregularities in Low-Latitudes of China

The Hainan COherent scatter Phased Array Radar (HCOPAR) and the 630 nm All-Sky Airglow Imager conducted simultaneous observations of the bottom-side Field-Aligned Irregularities (FAIs) and the dissipative equatorial plasma bubbles (EPBs) at low latitudes of China on 23 September 2014 and 13 April 2015, respectively. The 3m-scale irregularities inside the EPBs in the different dissipation phases are compared. In the early phase of equatorial plasma bubble dissipation, the echo occurrence rate and intensity on the western wall of EPBs were much higher than those in other parts, which is attributed to the gradient drift instability on the western wall. It is also found that there is a kind of secondary instability making contributions to the generation of meter-scale irregularities in different parts of bubbles. In the later phase of dissipation, the FAIs echo occurrence rate and intensity in all parts of bubbles decreased greatly, especially the difference between those on the eastern and western walls became very small, and the echoes in the depletion center almost disappeared. It is suggested that due to the decrease in the density gradient in the bubbles and the slowdown of eastward drift of bubbles, the influence of gradient drift instability on the western wall weakened significantly. Besides, the low-frequency drift instability and the subsequent secondary instability were suppressed. This study has revealed more details about the roles of plasma instabilities in the different dissipation phases and shed light on the driving mechanisms of meter-scale irregularities inside the large-scale bubbles.