Global Ocean Response to the 5-Day Rossby-Haurwitz Atmospheric Mode Seen by GRACE

Abstract

A dynamic response of the ocean to surface pressure loading by the well-known 5-day Rossby-Haurwitz mode in the atmosphere has been inferred from limited in situ tide gauge and bottom pressure data, but a global characterization of such response, including details at mid and high latitudes, has been lacking. Here we explore two daily data products from the Gravity Recovery and Climate Experiment (GRACE) mission to obtain a first quasi-global look at the associated ocean bottom pressure (OBP) signals at 5-day period. The previously reported in-phase behavior over the Atlantic basin, seesaw between the Atlantic and Pacific, and westward propagation in the Pacific are all seen in the GRACE solutions. Other previously unknown features include relatively strong responses in the Southern Ocean and also some shallow coastal regions (e.g., North Sea, East Siberian shelf, Patagonian shelf). Correlation analysis points to the Rossby-Haurwitz surface pressure wave as the main forcing for the observed large-scale OBP anomalies, while wind-driven signals are more spatially confined. The GRACE observations are found to be consistent with in situ OBP data and also with model simulations of the 5-day ocean variability where no in situ data is available. Inferences on energetics based on data and model results point to decay time scales shorter than the oscillation period, with substantial kinetic energy and dissipation located over a few topographic features in the Southern Ocean. Results illustrate the potential of space gravity measurements for examining large-scale oceanic variability at sub-weekly periods.