Ionospheric Disturbances after the 2022 Hunga Tonga-Hunga Ha'apai Eruption above Indonesia from GNSS-TEC Observations

On 15 January 2022, a VEI 5 eruption occurred at the submarine Hunga Tonga-Hunga Ha'apai (HTHH) Volcano in the Southwest Pacific, causing an ash plume reaching a height of 50-55 km. The eruption generated strong acoustic-gravity waves in the near-field and stations all over the world recorded Lamb waves (LW) that travelled around the earth multiple times at a speed of similar to 0.3 km/s. Here we report ionospheric anomalies due to the LW over Indonesian islands, 5000-10,000 km away from the volcano, in terms of changes in total electron contents (TEC) using the nationwide network of GNSS stations. We detected ionospheric anomalies travelling above Indonesia several times both westward and eastward. The first passage of LW over Java caused strong TEC increases of >12 TECU. The wave circled the earth and returned to Java on subsequent days. The second passage was recorded early 1/17, the anomaly decayed to 6 TECU. We also detected the passage of long-path waves propagating from west to east. In addition to such anomalies, we examined the existence of ionospheric disturbances apparently propagating from the geomagnetic conjugate point of the volcano that could possibly emerge in Indonesia. However, their signatures in Indonesia were not clear.