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

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 data, but a global characterization of such response, including details at mid and high latitudes, has been lacking. Here, we explore two products based on inversions of daily Gravity Recovery and Climate Experiment (GRACE) observations to obtain a first quasi-global look at the associated ocean bottom pressure (p(b)) 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-based p(b) fields. Correlation analysis points to the Rossby-Haurwitz surface pressure wave as the main forcing for the observed large-scale p(b) anomalies. 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, and Patagonian shelf), with model experiments indicating they are mainly forced by winds. Inferences on energetics based on GRACE solutions 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. Comparisons with in situ p(b) and Earth rotation data suggest that the satellite-based p(b) estimates at 5-day period are somewhat more realistic than those of the GRACE de-aliasing products and comparable to another independent ocean model. Results illustrate the potential of space gravity measurements for examining large-scale oceanic variability at subweekly periods.