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WITHDRAWN Theoretical Investigations of Earth- and Sea-Earth Coupled Very-Long Period Atmospheric Waves

Description: 

WITHDRAWN In the wake of the 2022 Tonga atmospheric explosion, we study a number of theoretical aspects of the structure of the very long period atmospheric gravity waves it generated, especially when coupled with an oceanic column. We base our investigations on two methodologies: Harkrider's [1964] algorithm, which extends to an atmospheric column the concept of a Haskell propagator for a flat-layered model; and Kanamori's code [pers. comm., 1977] for the computation of the Earth's spheroidal modes, adapted to an Earth structure featuring an atmosphere and possibly an oceanic column. Our principal results indicate that the eigenfunction of the gravity wave in the atmosphere is essentially independent of the presence of an oceanic layer and of its thickness. However the response of the water surface to the overpressure carried by the wave decreasses sharply with water depth, which is the opposite of the behavior of a classical tsunami obeying Green's Law, as confirmed by observations in the Bering Sea. We also show that the ratio between such sea surface amplitude and ocean-bottom overpressure is strongly dependent on the depth of the water column, thus rendering improper for the direct interpretation of ocean-coupled air waves the constant ratio of 1 cm/mbar, used in the routine reporting of DART data and valid only for tsunami waves under the shallow-water approximation. Finally, we investigate in detail the coupling of the atmosphere and the solid Earth in the absence of horizontal propagation, and show that the system resonates (as expected on physical grounds) at the Brunt-Väisälä frequency, rather than at the acoustic cutoff one, the latter suggested by Kanamori, Mori and Harkrider [1994].

Session: Exploiting Explosion Sources: Advancements in Seismic Source Physics

Type: Oral

Date: 4/19/2023

Presentation Time: 05:15 PM (local time)

Presenting Author: Emile A. Okal

Student Presenter: No

Invited Presentation: 

Authors