Detection of Extensive Equatorial Plasma Depletions After the 2022 Tongan Volcanic Eruption From Multiple Geodetic Satellite Ranging Systems.

We present a number of unique observations of ionospheric anomalies following the Hunga‐Tonga Hunga‐Ha'apai (HTHH) volcanic eruption on 15 January 2022. All are based on non‐dedicated geodetic satellite systems: Global Positioning System tracking of Low Earth Orbit (LEO) CubeSats, intersatellite tracking between two GRACE Follow‐On satellites, satellite radar altimeters to the ocean surface, and Doppler radio beacons from ground stations to LEO geodetic satellites. Their observations revealed the development of anomalously large trough‐like plasma depletions, along with plasma bubbles, in the equatorial regions of the Pacific and East Asian sectors. Trough‐like plasma depletions appeared to be confined within approximately ±20° magnetic latitude, accompanied by density enhancements just outside this latitude range. These plasma depletions and enhancements were aligned with the magnetic equator and occurred across broad longitudes. They were detected in regions where atmospheric waves from the HTHH eruption passed through around the time of the sunset terminator. We interpret these phenomena in terms of the E dynamo electric fields driven by atmospheric waves from the eruption. The uplift of the ionosphere beyond satellite altitudes, followed by subsequent plasma diffusion to higher latitudes along magnetic field lines, results in the formation of trough‐like plasma depletions around the magnetic equator and density enhancement at higher latitudes. The detection of plasma bubbles in the Asian sector during the non‐bubble season (January) is likely associated with the uplift of the ionosphere at the sunset terminator. Plain Language Summary: Satellite‐based ranging measurements use radio signals, which are impacted by electrons in the Earth's atmosphere. A correction for electron density must be applied to the ranging measurement prior to its scientific use. We have found that, after the Tonga volcanic eruption on 15 January 2022, the necessary corrections in the equatorial region were much smaller than usual for four geodetic satellites systems including GPS, GRACE Follow‐On, satellite altimeters, and DORIS radio beacons. This implies a reduction in electron content in the Earth's ionosphere in the equatorial region. Our observations demonstrate that the spatial and temporal patterns of the reduction are associated with the atmospheric pressure waves generated by the eruption. We suggest electric fields driven by atmospheric waves from the eruption as the source of equatorial electron density depletions. Key Points: Geodetic satellites detected plasma depletions and enhancements at low latitudes after the Tongan volcanic eruption on 15 January 2022These phenomena were observed within the region affected by the atmospheric waves propagated from the eruptionWe suggest that E‐region dynamo electric fields are a plausible source of the plasma density modulation at low latitudes [ABSTRACT FROM AUTHOR]