Monitoring and Modelling of ionospheric disturbances by means of GRACE, GOCE and Swarm in-situ observations

The main objective of the ESA-funded project COSTO (Contribution of Swarm data to the prompt detection of Tsunamis and other natural hazards) is to better characterize, understand and discover coupling processes and interactions between the ionosphere, the lower atmosphere and the Earth’s surface as well as sea level vertical displacements. Together with our project partners from the University of Warmia and Mazury (UWM), the National Observatory of Athens (NOA) and the Universitat Politecnica de Catalunya (UPC) we focus in COSTO to tsunamis that are the result of earthquakes (EQ), volcano eruptions or landslides.

In the scope of COSTO a roadmap was developed to detect the vertical and horizontal propagation of Travelling Ionospheric Disturbances (TID) in the observations of Low Earth Orbiting (LEO) satellites. Under the assumption that the TIDs triggered by tsunamis behave in approximately the same way for different EQ / tsunami events, this roadmap can be applied also to other events. In this regard, the Tohoku-Oki EQ in 2011 and the Chile EQ in 2015 were studied in detail. The aim of investigating these events is to detect the TIDs in the near vicinity of the propagating tsunami. Thereby, given tsunami propagation models serve as a rough orientation to determine the moments in time and positions for which there is co-location with selected LEO satellites/missions, namely GRACE, GOCE and Swarm. GOCE with an altitude of around 280km and the GRACE satellites with an altitude of around 450km flew over the region where the Tohoku-Oki tsunami was located, about 2.5 hours after the EQ. Using wavelet transform, similar signatures with periods of 10-30 seconds could be detected in the top-side STEC observations of GOCE as well as in the Ka-band observations of GRACE at the time of the overflight. These signatures can be related to the gravity wave originating from the tsunami. Similar signatures were detected in the signals from the GRACE Ka-band observations and in the Swarm Langmuir Probe measurements at an altitude of 450 km for the 2015 Chile tsunami. These roadmap studies provided the first opportunity to observe the vertical and horizontal tsunami induced gravity waves in the ionosphere.