To Abstract List
The SST and upper-ocean heat content of the North Pacific (including the tropical Pacific) have been studied using an upper-ocean GCM coupled to an advective atmospheric mixed layer model. A hybrid vertical mixing scheme is used for the ocean mixed layer and interior mixing. The model grid is stretched such that the resolutions are about 1/4° - 1/3° in the equatorial region, 1/3° - 1/2° in the Kuroshio and its extension regions, and 1/2° to 3° in the rest of the basin. The large-scale dynamics, such as the equatorial currents, low-latitude western boundary currents, and the Kuroshio and its extension, have been reproduced. In particular, the model Kuroshio separates from the boundary between 35°N and 37°N, a latitude range comparable to that of the observed Kuroshio separation. The simulated annual mean climatology of SST is less than 2°C apart from the observed annual mean climatology over most of the model domain. The largest discrepancies occur in the south equatorial region and the subpolar gyre and along the California and Peru coasts. Sensitivities of the SST simulation to different wind stress products, including COADS, Hellerman and ECMWF, have been tested. The result shows that the simulated annual mean SST climatology does not change much over most of the model domain. However, a large warming occurs in the Kuroshio separation area when the Hellerman wind is used. This is because in this case the Oyashio is weaker and the Kuroshio water thus penetrates further to the north.
A hindcasting run for the period of 1969-1989 have reproduced the major El Niño events in the tropical Pacific and the trans-Pacific propagations of the warming anomalies associated with these events in the eastern Pacific. The run has also shown the gyre-scale advection of warming/cooling anomalies generated in the Kuroshio Extension and North Pacific Current regions around both the subtropical and subpolar gyres.
The interaction between the tropical Pacific and extratropical North Pacific Oceans at interannual and decadal scales has also been investigated through two additional runs, in which either the tropical ocean or the extratropical ocean are excluded from the model domain. By excluding the tropical ocean, the trans-Pacific propagating warming anomalies from the El Niño events are no longer observed in the extratropical ocean, and the interannual and decadal variabilities of the extratropical SST and upper-ocean heat content are generally smaller. These changes indicate the importance of the tropical ocean to the extratropical variability. By excluding the extratropical ocean, however, the tropical El Niño events are affected at minor levels, which indicates the local oceanic nature of these tropical interannual variations.
To Pacific Workshop
To WOCE Home Page