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In the Sumatra earthquake that occurred on December 26, 2004, significant ionospheric variations were detected immediately after the earthquake in both the TEC (total electron content) data of GPS (Global Positioning System) and the ionosonde data. A magnetic pulsation with a period of about 4 min was also observed in Phimai, Thailand. Recent studies have suggested that these events are associated with acoustic waves excited by a sudden large-scale displacement of the sea surface around the epicenter. In order to study these phenomena quantitatively, a time-dependent two-dimensional nonhydrostatic compressible atmosphere-ionosphere model has been used and compared with relevant data. By modeling in sea surface perturbation, we were able to reproduce an atmospheric oscillation with a period of about 4 min in the upper atmosphere above the epicenter. The electron density variations observed by GPS/TEC and by ionosondes were also reproduced fairly well. We found that the observed TIDs (traveling ionospheric disturbances) with long periods are caused by the ducted thermospheric gravity waves produced in the thermosphere through acoustic pulse from the epicenter. The good overall agreement between the simulation results and observations indicates that numerical simulation with the nonhydrostatic compressible atmosphere-ionosphere model could be a useful tool to investigate the relationship between variations in the upper atmosphere and various sources of disturbances in the lower atmosphere.

A numerical simulation of ionospheric and atmospheric variations associated with the Sumatra earthquake on December 26, 2004