Abstract
We use bottom pressure records from 59 sites of the global tsunami warning system to examine the nonisostatic response of the World Ocean to surface air pressure forcing within the 4–6-day band. It is within this narrow “5-day” band that sea level fluctuations strongly depart from the isostatic inverted barometer response. Numerical simulations of the observed bottom pressures were conducted using a two-dimensional Princeton Ocean Model forced at the upper boundary by two versions of the air pressure loading: (i) an analytical version having the form of the westward propagating, 5-day Rossby–Haurwitz air pressure mode; and (ii) an observational version based on a 16-yr record of global-scale atmospheric reanalysis data with a spatial resolution of 2.5°. Simulations from the two models—consisting of barotropic standing waves of millibar amplitudes and near uniform phases in the Pacific, Atlantic, and Indian Oceans—are in close agreement and closely reproduce the observed bottom pressures. The marked similarity of the outputs from the two models and the ability of both models to accurately reproduce the seafloor pressure records indicate a pronounced dynamic response of the World Ocean to nonstationary air pressure fields resembling the theoretical Rossby–Haurwitz air pressure mode.
Significance Statement
Over the open ocean, a 1 mb fall (rise) in surface atmospheric pressure causes a 1 cm rise (fall) in sea level elevation. This well-documented “inverted barometer effect” is an isostatic process, accompanied by negligible horizontal movement of water. A dynamical exception occurs for time scales of around 5 days. This study couples a numerical ocean model to bottom pressure records from the worldwide tsunami warning system to show that the entire Pacific, Atlantic, and Indian Ocean basins slosh back and forth in a globally coherent manner in response to the Rossby–Haurwitz surface air pressure wave that travels westward around Earth every 5 days. The ocean currents generated by this process are presently under investigation.
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