Observation and Analysis of Plasma Bubbles in Hainan during the Magnetic Storm in March 2015

This study utilizes the optical observation data from the 630 nm all-sky airglow imager, the data from the ionospheric digital ionosonde, and the data of the echo intensity of the Very High Frequency (VHF) coherent scatter radar at the Fuke Station in Hainan of the Meridian Project (19.5°N, 109.1°E). In combination with the geomagnetic horizontal component data from the Dalat Geomagnetic Station (11.9°N, 108.5°E; GL:2.5°) and the PHU Thuy Geomagnetic Station (21.0°N, 105.9°E; GL:11.5°), as well as the observations of the interplanetary magnetic field and solar wind speed from the ACE satellite, the study is carried out on the variations of the ionospheric plasma bubbles/irregularity structures over Hainan during the super geomagnetic storm in March 2015. The results show that the appearance of pre-midnight plasma bubbles and the uplift of the virtual height at the bottom of the ionosphere after sunset were observed both before and after the geomagnetic storm. However, the plasma bubbles observed after the end of the geomagnetic storm were of a fossil structure, which may be due to the fact that the ionospheric electric field during the occurrence period of the plasma bubbles on that day showed a westward polarity, which was not conducive to the development of the plasma bubbles. The uplift of the virtual height at the bottom of the ionosphere during the geomagnetic storm was significantly suppressed, and no plasma bubbles were observed at the Fuke station. The analysis of the variations of the interplanetary electric/magnetic field and the geomagnetic horizontal component shows that the Pre-Reversal Enhancement (PRE) electric field before the ionospheric reversal during the geomagnetic storm may have been successively suppressed by the over-shielding penetrating electric field with a westward polarity and the Disturbance Dynamo Electric Field (DDEF), resulting in a decrease in the Rayleigh-Taylor instability, which is not conducive to the development of the plasma bubble/ionospheric irregularity structures.