Revisiting the Ocean's Nonisostatic Response to 5-Day Atmospheric Loading: New Results Based on Global Bottom Pressure Records and Numerical Modeling

We use bottom pressure records from 59 sites of the global tsunami warning system to examine the non-isostatic 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 degrees. 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.