Observations on the variations of the field-aligned irregularities in the plasma bubbles at low-latitudes of China

The concurrent observation of the Hainan COherent Scatter Phased Array Radar (HCOPAR) and the 630 nm all-sky airglow imager was carried out on the night of 13 April 2015 in low-latitudes of China. The plasma bubble recorded by the airglow imager and the Field-Aligned Irregularities (FAIs) observed by the HCOPAR kept a good consistency. At the beginning, the FAIs were found to fill the entire plasma bubble, and they were drifting eastward together. During the dissipation process, the plasma bubble became wider and wider in zonal direction, while the airglow gray gradient on the eastern and western walls of the bubble had no much changes. Simultaneously, the echo Signal-to-Noise Ratio (SNR) of the irregularities in the bubble became lower and lower. The SNR at the depletion center decreased fastest, and the SNR of the FAIs on the western wall of the bubble fell more slowly than those in other parts. Polarization electric field in the bubble is suggested to have influence on the distribution of the FAIs. Gradient drift instability on the western wall supported the FAIs to live longer, and the FAIs on the eastern wall, namely on the front edge of the bubble, dissipated more rapidly.