The 15 January 2022 Eruption Of The Hunga Tonga Volcano: A Multi-Instrument Far-Field Ionospheric Disturbances Evaluation Over Europe.

On January 15, 2022 at 4:15 UT, the Hunga volcano in Tonga (20.54 S, 175.38 E) produced a powerful eruption. This eruption provides a unique opportunity to study ionospheric disturbances expected to be caused by such a strong natural phenomenon. Travelling ionospheric disturbances have been detected after large volcanic eruption already in the past. Because of the rarity of eruptions of this strength, this event is the first that can be studied with ionospheric data from modern instruments.

We focus on the detection of the far-field ionospheric effects of the eruption in Europe. Despite the large distance from the point of origin, atmospheric acoustic waves are detected travelling along great circles in both directions. These disturbances in the lower atmosphere in turn cause subsequent appearance of ionospheric signatures.

Dense observational networks providing both ionosonde observations and GNSS receivers are available in Europe. This allows us to track the passing disturbances with relatively high resolution in both time and space. We combine a variety of data, such as atmospheric pressure measurements, Doppler measurements, ionosonde soundings, GNSS derived TEC data, and in situ observations (from ESA Swarm mission) in order to study the disturbances across the region, including their vertical propagation.

The arrival times of the disturbances determined from vertical and oblique ionosonde soundings and from TEC and in situ measurements all agree with the predictions based on a single acoustic wave in the troposphere travelling around the globe. The velocities derived for the disturbances in the lower atmosphere from the pressure data in Dourbes and Ebre, between 300 m/s and 305 m/s, are also in good agreement with each other, as well as with values found in the literature. Although the period under consideration here was affected by some geomagnetic disturbances, we can therefore be reasonably sure that these medium scale disturbances were indeed the result of the eruption of the Hunga volcano.

This paper paves the way for a deeper understanding of TIDs and ionospheric disturbances caused by natural events inducing Litosphere-Atmosphere-Ionosphere coupling. This will be very useful for the GNSS community to mitigate the effects of such events on high-accuracy positioning and navigation.