Numerical experiments for global barotropic ocean variability induced by surface disturbances

Sachiko Yoshida

This study examines high-frequency sea level variabilities induced by surface air pressure loading in comparison those induced by surface wind stress and tidal forcings. The numerical poles of a barotropic ocean model are shifted to the land to cover the whole global ocean. The presence of the Arctic Ocean in the model affects the northwestern Atlantic Ocean through propagation of Kelvin waves. The air pressure induces sea surface variability stronger than that forced by surface wind for the most of the global ocean except for the Southern Ocean. We estimate the westward propagating atmospheric S2 tide by harmonic analysis to avoid the aliasing effect from 6-hourly atmospheric data. The amplitude of ocean response to the atmospheric S2 reaches 20% of that generated by the tidal potential. The sea level variability ratio of non-IB to IB responses clarifies that the non-IB compo
nent becomes important for periods shorter than 2 to 5 days at mid-latitudes, but the dividing periods become longer than 10days in the tropics. Especially in the low-latitude Atlantic Ocean, the non-IB component dominates the variability for longer periods compared with the other tropical regions. Results of CEOF analysis suggest that the energy propagation from the Arctic Ocean to the tropical Atlantic is one of the major causes that intensify the non-IB signals in the Atlantic. In the Arctic Ocean, the water mass oscillates through the strait between the Arctic and the North Atlantic at the period of 10 days with the amplitude of about 1 to 2 Sv. The dominant frequency of the oscillation corresponds to the average surface pressure variability over the Arctic Ocean.