A statistical study of the magnetic signatures of the unique Tonga volcanic explosion of 15 January 2022

Abstract. For the first time, a statistical study has been conducted of the geomagnetic bay and quasi-periodic disturbances based on the datasets collected at 19 recording stations participating in INTERMAGNET Magnetic Observatories. In order to identify the disturbances from the volcanic explosion, a preliminary analysis has been used of the state of space weather during the catastrophic Tonga volcanic explosion of 15 January 2022. We summarize the main results as follows: The non-monotony of the variations in the strength of all geomagnetic field components increased appreciably on the day of the explosion as compared to the variations observed during the days used as a quiet time reference, while the eastward component of the geomagnetic field exhibited an up to 60-nT increase in variability. The duration and time delay of the bay disturbances increased with distance from the volcano, while their amplitude decreased. The propagation speeds of the bay disturbances at various observatories were determined to be in the 700–1,000 m/s range. Six groups of time delays of quasi-sinusoidal disturbances have been identified in a simultaneous analysis for the first time; they correspond to the apparent speeds of 4 km/s, 1.5 km/s, 1 km/s, as well as 500 m/s, 313 m/s, and 200 m/s. The time delay in each group increased with distance away from the volcano. The agreement between theoretical estimates and the observational data testify to the adequacy of the mechanism adopted for the generation of the disturbances.