Electron Density Reduction Caused by the Tonga Volcano Eruption on January 15, 2022

The explosive Tonga volcano is among the unique ones. Its order of magnitude is the same as Krakatoa (1883), St. Helens (1980), El Chichón (1982), and Pinatubo (1991) volcanoes. The uniqueness of the Tonga volcano lies in the fact that the products of eruption of the Tonga volcano rose to a record height of 50–58 km, whereas the height of eruption of the most powerful Krakatoa volcano reached only 40–55 km. The Tonga volcano has estimates of 3.9 × 10¹⁸ J for thermal energy, approximately 5.8 for volcanic explosive index VEI, approximately 5.5 for volcano magnitude M, and approximately 10.8 for eruption intensity I. We have estimated the explosion energy to be 16–18 Mt TNT. The problems of proving that a decrease in the total electron content (TEC), which was observed on January 15, 2022, in the ionosphere, was caused by the Tonga volcano explosion, and determining the principal parameters of the ionospheric hole are very urgent problems. This study is aimed at analyzing the parameters of the ionospheric hole created by the Tonga volcano explosion on January 15, 2022. Well-known GPS technologies are used to obtain data on time variations of the ionospheric TEC in the vertical column by measuring the pseudo-range and the integrated phase data at two frequencies along the path to each GPS satellite. The space weather conditions were favorable for observing the ionospheric effects caused by the explosion of the Tonga volcano. The calendar dates of January 13 and 17, which are used as reference days, were the least disturbed ones. The main results are as follows. It was found that the TEC on the reference days varied almost monotonically. Aperiodic and quasi-periodic variations of TEC were observed on the day of volcano eruption. Aperiodic variations are associated with a decrease in the TEC. This effect is called the ionospheric hole. It has been proven that the ionospheric hole is caused by a volcanic explosion. The delay time of the hole increases with an increase in the distance between the volcano and the observation site, while both the absolute value of the TEC and the relative value of its decrease are reduced. According to estimates, the horizontal size of the ionospheric hole did not exceed 10 Mm, and the time delay of its appearance did not exceed 122 min. The vertical speed of disturbance propagation was 36–72 m/s, and the horizontal speed was 2.2 km/s. The lifetime of the ionospheric hole was 120–200 min. The TEC in the ionospheric hole was reduced by approximately 2.5–10 TECU, which is a function of the distance from the volcano to the observation site, and the relative decrease ranged from –17 to –34%.