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The meridional geostrophic transport (MGT) in the interior tropical North Pacific Ocean is estimated based on global ocean heat and salt content data. The decadal variations of the zonally and vertically integrated MGT in the tropical North Pacific Ocean are found to precede the Pacific decadal oscillation (PDO) by 1–3 years. The dynamics of the MGT are analyzed based on Sverdrup theory. It is found that the total meridional transport variability (MGT plus Ekman) is dominated by the MGT variability having positive correlations with the PDO index. The Sverdrup transports differ from the total meridional transport significantly and have insignificant correlations with PDO index, suggesting that the MGT variability is not controlled by the Sverdrup dynamics. In comparison, the simulated meridional transport variability in the models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) and the Ocean General Circulation Model for the Earth Simulator are dominated by the Sverdrup transports, having insignificant correlations with the simulated PDO indices. The comparison suggests that the non-Sverdrup component in the MGT is important for the predictability of PDO and that significant deficiencies exist in these models in simulating a realistic structure of the tropical ocean gyre variability and predicting the decadal climate variations associated with it. [ABSTRACT FROM AUTHOR]

Absolute geostrophic currents in the North Pacific Ocean are calculated from the newly gridded Argo profiling float data using the P-vector method for the period of 2004-11. The zonal geostrophic currents based on the Argo profile data are found to be stronger than those based on the traditional World Ocean Atlas 2009 ( WOA09) data. A westward mean geostrophic flow underneath the North Equatorial Countercurrent is identified using the Argo data, which is evidenced by sporadic direct current measurements and geostrophic calculations in history. This current originates east of the date line and transports more than 4 × 106 m3 s−1 of water westward in the subsurface northwestern tropical Pacific Ocean. The authors name this current the North Equatorial Subsurface Current. The transport in the geostrophic currents is compared with the Sverdrup theory and found to differ significantly in several locations. Analyses have shown that errors of wind stress estimation cannot account for all of the differences. The largest differences are found in the area immediately north and south of the bifurcation latitude of the North Equatorial Current west of the date line and in the recirculation area of the Kuroshio and its extension, where nonlinear activities are vigorous. It is, therefore, suggested that the linear dynamics of the Sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern Pacific Ocean. [ABSTRACT FROM AUTHOR]

The Argo array provides a unique dataset to explore variability of the subsurface ocean interior. This study considers the subtropical North Pacific Ocean during the period from 2004 to 2011, when Argo coverage has been relatively complete in time and space. Two distinct patterns of Argo dynamic height transport function () are observed: in 2004/05, the gyre is stronger, and in 2008/09 it is weaker. The orientation of the subtropical gyre also shifts over time: the predominantly zonal major axis shifts to a more northwest-southeast orientation in 2004/05 and to a more southwest-northeast orientation in 2008/09. The limited temporal range of the Argo observations does not allow analysis of the correlation of ocean transport and wind forcing in the basin for the multiyear time scale (6-8-yr period) typical of the dominant gyre patterns. The meridional geostrophic transport anomaly between 180° and 150°E is computed both from Argo data (0-2000 db) and from the Sverdrup relation (using reanalysis winds): similarities are observed in a latitude-time plane, consistent with local forcing playing an important role. A forcing contribution from the eastern subtropics will also reach the region of interest, but on a longer time scale, and it is not analyzed in this study. Compared with the 8-yr Argo record, the longer 19-yr time series of satellite altimetry shows a similar but somewhat modified pattern of variability. A longer Argo record will be needed to observe the decadal-scale fluctuations, to separate interannual and decadal signals, and to ensure statistical confidence in relating the wind forcing and the oceanic response. [ABSTRACT FROM AUTHOR]

High-resolution hydrographic observations were conducted in September 2002 to describe the detailed structure of frontal waves along the Kuroshio Extension. Frontal waves were observed both in the upper and intermediate layers, which corresponded to the depths of North Pacific Subtropical Mode Water and North Pacific Intermediate Water, respectively. The frontal wave in the upper layer preceded the intermediate-depth frontal wave by about 1/4 wavelength. The vertical phase lag created situations in which the low-salinity Oyashio water in the intermediate layer was superimposed below the upper-layer high-salinity Kuroshio water, thus forming a vertical salinity minimum. The frontal waves with a wavelength of about 200 km and a phase speed of 0.2–0.3 m s-1 propagating in the downstream direction were consistent with those from satellite images. Vertical velocity fields were estimated with the quasigeostrophic omega equation. Downwelling around the trough (from the crest to trough) of the intermediate-depth (upper layer) frontal wave and upwelling around the crest (from the trough to the crest) were similar to the features observed in the Gulf Stream meanders. The phase difference between the upper and intermediate layers suggested that the frontal waves were baroclinically unstable waves. [ABSTRACT FROM AUTHOR]