Intense Equatorial Electrojet and Counter Electrojet caused by the 15
January 2022 Tonga Volcanic Eruption: Space and Ground-based
Observations
Abstract
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 (ICON) 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.