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.