Towards Observing Tsunamis in the Ionosphere Using GPS TEC Measurements

Tsunamis have been a significant threat to humans living in coastal regions throughout recorded history. The recent tsunami of September 29, 2009 was a tragic reminder of this fact, as the waves caused over 180 deaths on the islands of Samoa, American Samoa, and Apia in the south Pacific. Recent modeling results and observations have demonstrated that the ionospheric signature of an ocean tsunami can potentially be detected as a traveling ionospheric disturbance (TID) produced by internal gravity waves propagating upward in the atmosphere [e. These tsunamigenic TIDs have been demonstrated to be present in ionospheric total electron content (TEC) measurements using ground-based GPS radio signals [e.g., Artru et al., (2005)] and satellite-based altimeter radar [Occhipinti et al., (2006)]. There are many remaining unanswered questions regarding the reliability of detecting tsunamigenic TIDs, including how to distinguish them from regular TIDs of non-tsunamigenic origin, as well as factors affecting the propagation of internal gravity waves into the ionosphere. Recent models show that the magnitude of variations in electron density in the ionosphere due to a tsunamigenic internal gravity wave can depend heavily on the local orientation of the magnetic field [e.g., Occhipinti et al., (2008)], as well as the direction of propagation of the tsunami itself, with meridianol (north-south) propagating waves producing much larger perturbations in TEC than waves propagating zonally (east-west) [Hickey et al., (2009)]. Such nuances may influence our ability to detect tsunamigenic TIDs, and should be thoroughly explored via data analysis of multiple events.