Since tens of years perturbations have been observed in the ionosphere prior to earthquakes (between a few hours and a few days before). But the mechanism to understand how the earthquake preparation in a seismic area can induce a change in the ionosphere is the subject of intense debate. In this paper we present various atmospheric and ionospheric perturbations observed prior to large earthquakes in order to support a model of coupling between the lithosphere, the atmosphere, and the ionosphere.

This study presents a new approach to assimilate FORMOSAT-3/COSMIC radio occultation (RO) slant total electron content (TEC) data as well as ground-based GPS slant TEC data into the International Reference Ionosphere to reconstruct 3-D ionospheric election density structure. Our new ionospheric data assimilation model that employs the location-dependent background model error covariance outperforms the earlier assimilation model with the location-independent background model error covariance.