Understanding the Neutral Atmospheric and Ionospheric Disturbances in Response to Hunga Tonga Volcanic Eruption (2022)

The Hunga Tonga-Hunga Ha'apai volcanic eruption (hereafter Tonga eruption) occurred on January 15, 2022, was the largest eruption since 1991, also the largest underwater explosion ever recorded. The intensity of Tonga eruption as well as its unique feature of massive water vapor emission makes it a rare and representative case to study the coupling of the whole atmosphere within a short period of time, due to its intense and fast-propagating forcing that is easily recognized when compared to other extreme phenomena. Previous studies have examined the impacts of Tonga eruption on the energy deposition in the neutral atmosphere and the associated wave signatures observed in the ionosphere, among others. This study aims to combine the disturbances observed in different altitude regions of the whole atmosphere in reponse to the Tonga eruption, in order to investigate the vertical coupling between the neutral atmosphere and the ionosphere and understand the underlined physics of ion-neutral interactions.

We approach this goal by utilizing the state-of-the-art whole atmosphere model WACCM-X. Our work includes two runs with solar quiet condition: (1) a free-run WACCM-X simulation with an initial pressure perturbation to simulate the Tonga eruption following Liu et al (2023) to be used as our reference, and (2) a specified dynamics regime configured, namely the SD-WACCM-X simulation with its lower atmosphere nudged with the reanalysis data as a more realistic representation. Our results show Lamb wave features consistent with Liu et al. (2023), and gravity wave signatures due to the strong overshoot of water vapor. Gravity wave momentum flux is calculated to show the vertical energy variation, which is then correlated to the intensity of the observed travelling ionospheric disturbances as a preliminary demonstration of the ion-neutral couplings. Among the neutral atmospheric drivers, we focus on the contribution of neutral winds in the ionosphere by studying its impacts on the ion-neutral collisions and the ion drift velocities. Modeled simulations are also compared with ERA5 thermal variables in the neutral atmosphere, and Madrigal GNSS TEC measurements in the ionosphere, where differences due to data resolution, measuring technique and the lower atmospheric constraints are noticed.