The Characteristics and Possible Mechanisms of the Strongest Ionospheric Irregularities in March 2024

A geomagnetic storm occurred on 3 March 2024, with the minimum SYM-H reaching −127 nT. Although this geomagnetic storm was not very strong, the ionospheric irregularities on this day resulted in a strong ionospheric scintillation. The amplitude scintillation index was larger than 1.0. Global Navigation Satellite System (GNSS) receivers experienced numerous cycle slips and loss of lock of carrier phase over a large longitudinal range of ~30 degrees within ~5 h in the south of China. The occurrence of cycle slips over such a long duration and extensive longitudinal range is rarely reported. Ground-based GNSS receivers, ionosondes and in situ satellite measurements were utilized to analyze the characteristics of the equatorial plasma bubbles (EPBs) during this event. The EPBs began before the main phase of the geomagnetic storm and extended to 30°N in latitude. Possible physical mechanisms for the initial generation and the development of the EPBs are discussed. It is believed that different mechanisms played vital roles in the initial generation and development of the EPBs before and after the onset of the main phase of the geomagnetic storm. Moreover, a large-scale wave structure (LSWS) could potentially serve as the seeding source of the EPBs.