A sea in the sky? Evidence of meteotsunami signatures in the ionosphere

Meteotsunamis, as the name suggests, are atmospherically generated tsunamis, most often formed during fast passage of a mesoscale atmospheric disturbance, such as convective storm capable of ducting gravity waves and rapidly changing surface air pressure. Energy from the atmosphere is transferred to the water body and the resulting high-frequency (T < 2h) sea level disturbances can exceed one meter if amplified by Proudman or Greenspan resonance. These extreme events can cause a substantial damage to coastal communities and may even lead to human causalities, which have been reported around the world. Thus, it is vitally important to be able to forecast such events in a timely manner. However, such meteotsunami events are hard to predict due to limited spatial coverage of tide gauges as well as due to convective storms, i.e., their shape, speed, propagation direction and intensity changing in time, to which—on top of coastal ocean bathymetry modulations—intensity of meteotsunamis is dependent. Previous studies have shown that various hazardous natural phenomena—such as earthquakes, volcano eruptions, strong convective storms and tsunamis—can produce detectable ionospheric disturbances measurable by perturbations of the ionospheric total electron content (TEC) opening a possibility for earlier warning. To date, only one study has investigated ionospheric TEC perturbation associated with meteotsunamis, focusing on an event along the eastern coast of the United States, with encouraging result. To check whether similar approach could be applied for other parts of the globe, this study investigates a meteotsunami observed at Australian south-east coast which formed on 30 April 2020. Conditions for the upward propagation of meteotsunami-generated atmospheric gravity waves (AGWs) into the ionosphere are checked by using linear gravity wave theory. Observational evidence is assessed by utilizing space-based radio occultation (RO) measurements from Global Navigational Satellite System (GNSS), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperatures and ground-based GNSS TEC observations. Our result reveals evidence of free propagation of meteotsunami-generated AGWs into the upper atmosphere along with associated variability in ionospheric TEC of approximately 1 TECU. These findings support the potential of ionospheric observations as a complementary tool for meteotsunami signal detection and possibly early warning.