Ionospheric Response To Atmospheric Gravity Waves Induced By Tsunamis

Atmospheric gravity waves induced by tsunamis can propagate upwards into the ionosphere, and subsequently cause ionospheric disturbances. Using measurements from the GPS network, Scientists have reported observations of ionospheric disturbances fluctuated by atmospheric gravity waves following strong tsunamis. The thesis has chosen the 2004 Sumatra tsunami and the 2011 Tohoku tsunami as two representatives of the low-latitude and mid-latitude, respectively. Their ionospheric responses to the tsunami-driven gravity wave perturbations have been examined by using a neutral-ion coupling model.With observed wave parameters, we employ a liner, steady-state full-wave model to examine the detailed propagation properties of the gravity waves in a windy and non-isothermal atmosphere, which takes into account the dissipation due to eddy and molecular processes. Then we employ a neutral-ion coupling model to examine their ionospheric responses to the tsunami-driven gravity wave perturbations, which includes ion dynamics and chemistry. Finally, the simulation results are analyzed in comparison.Our analyses reveal that the F-region response has a significant latitudinal dependence, which is found due to the evident downward component of the geomagnetic field at midlatitudes, plus the contributions of the meridional and vertical are comparable. The effects of atmospheric gravity waves on the ionosphere driven by the 2004 Sumatra tsunami have shown a strong sensitivity to wave propagation direction at low latitudes. For the 2011 Tohoku tsunami, the fast acoustic-gravity wave propagating toward the southeast results in the largest total electron content(TEC) fluctuation. A combination of the geomagnetic inclination and averaged ocean depth mainly constrains an ionospheric response to a tsunami, which appears to be better discernible at midlatitudes. In this thesis, only tsunamis at low-latitude and mid-latitude in the Northern Hemisphere are taken into account, the results suggest a need for future assessments of their impacts accounting for ion-neutral interactions at much higher latitudes or midlatitudes in the Southern Hemisphere where the geomagnetic field is directed northward and upward.