A study on wind-driven circulation in the subarctic North Pacific using TOPEX/POSEIDON altimeter data

Time-dependent wind-driven circulation in the subarctic region in the North Pacific is investigated by using TOPEX/POSEIDON (T/P) altimeter data and European Centre for Medium-Range Weather Forecasts (ECMWF) wind data for about 2 years. The first empirical orthogonal function (EOF) of the sea level anomaly (SLA) without the variation related to the steric height change (SLA∗) represents a basin-sized oscillation, which is associated with the spin-up and spin-down of the subarctic gyre. Moreover, the time series of the first EOF corresponds to the Oyashio current variation measured by the moored current meter at about 1250-m depth. The first and third EOFs of the wind stress curl fields represent basin-sized south-north oscillations being associated with changes in intensity and the latitudinal position of the Aleutian low. Time series of both the dominant EOFs of the SLA∗ and the wind stress curl anomaly are correlated well, which suggests that dominant variation of the SLA∗ is mainly controlled by the wind stress curl fields represented by the first and third EOFs. The time series of the first EOF of the SLA∗ is in agreement with that of Sverdrup transport estimated by the wind stress curl near 40°N with a correlation of 0.70. Both standard deviations of the T/P SLA-derived transports in the interior and the western boundary regions are consistent with that of the Sverdrup transport in the same order of magnitude. These results suggest that sea surface height variation in the subarctic North Pacific is approximately explained by the time-dependent wind-driven circulation.