Intense Equatorial Electrojet and Counter Electrojet Caused by the 15 January 2022 Tonga Volcanic Eruption: Space‐ and Ground‐Based Observations

We present space‐ and ground‐based multi‐instrument observations demonstrating the impact of the 2022 Tonga volcanic eruption on dayside equatorial electrodynamics. A strong counter electrojet (CEJ) was observed by Swarm and ground‐based magnetometers on 15 January after the Tonga eruption and during the recovery phase of a moderate geomagnetic storm. Swarm also observed an enhanced equatorial electrojet (EEJ) preceding the CEJ in the previous orbit. The observed EEJ and CEJ exhibited complex spatiotemporal variations. We combine them with the Ionospheric Connection Explorer neutral wind measurements to disentangle the potential mechanisms. Our analysis indicates that the geomagnetic storm had minimal impact; instead, a large‐scale atmospheric disturbance propagating eastward from the Tonga eruption site was the most likely driver for the observed intensification and directional reversal of the equatorial electrojet. The CEJ was associated with strong eastward zonal winds in the E‐region ionosphere, as a direct response to the lower atmosphere forcing. Plain Language Summary The Earth's E‐region ionosphere (∼100–150 km altitude) consists of both ionized and neutral gasses, and the two components are coupled through ion‐neutral collisions. The state of this region is closely influenced by neutral atmospheric activities from the lower atmosphere and the variability of the solar drivers. On 15 January 2022, the Tonga volcano had a massive eruption and injected an enormous amount of mass and energy into the atmosphere causing disturbances in the E‐region ionosphere or even higher. There was also a moderate geomagnetic storm that started 1 day before the eruption and ended days after. These conditions offer a unique opportunity to understand the different roles they play in controlling the ionosphere. Coordinated observations, including the atmosphere, ionosphere, and magnetosphere, were made from both space and on the ground during this event. We analyzed the magnetic field and neutral wind data and found that a large‐scale atmospheric disturbance generated by the volcano eruption was responsible for the observed directional reversal of the dayside equatorial electric field and electric current. Key Points Space‐ and ground‐based observations reveal dramatic equatorial electrojet variations caused by the Tonga volcanic eruption Strong eastward turning of atmospheric zonal winds in the E‐region is responsible for the directional reversal of the equatorial elect