On the seasonal variation of transport through the Tokara Strait

Abstract

Abstract:Results are described from a limited area barotropic model of the North Pacific with 1/3°xl/3 ° resolution and bounded by latitudes 10°N and 50°N and longitudes 120°E and 160°E. The model employs dynamics linearised about a state of rest and incorporates realistic bottom topography. It is driven by the seasonally varying part of the Hellerman and Rosenstein wind stress field and by inflow along the northern and eastern boundaries specified from a 1 ° x 1 ° version of the model applied to the whole North Pacific. The model-calculated transport variations through the Tokara Strait are similar to those of the observed seasonal sea level differences across the Strait, although the model appears to underestimate the amplitude of the signal by a factor of at least 2. The inclusion of realistic bottom topography is shown to be crucial in determining the model response.

Mechanism of the seasonal transport variation through the Tokara Strait

“…The similarity between both seasonal variations shown in Figs. 2 and 3(a) is surprisingly remarkable and is consistent with the results by Greatbatch and Goulding (1990). Next, Fig.…”

“…A seasonal transport variation at the Tokara Strait calculated in both models is similar to the variation of the sea level difference across the Tokara Strait, with a maximum in the summer and a minimum in the autumn. Capability of reproducing by the limited-area model means that the variation is not a large-scale phenomenon pointed out by Blaha and Reed (1982) but a local phenomenon pointed out by Greatbatch and Goulding (1990). This may be consistent with that Kuroshio velocity in the Tokara Strait does not correlate with the position of the Kuroshio axis over the Izu Ridge (Kawabe, 1988).…”

“…On the other hand, the amplitude of the seasonal variation in volume transport through the Tokara Strait cannot be well reproduced in the present study. Greatbatch and Goulding (1990) pointed out the possibility of increasing the amplitude of the seasonal signal if the density stratification and a representation of the mean flow of the Kuroshio. Considering that the seasonal variation of the sea level difference across the Tokara Strait can be reproduced by the simple barotropic model, it may be expected that energy transfer from a barotropic mode to a baroclinic mode locally occurs by the JEBER effect (Huthnance, 1984).…”

“…It should be noted that both terms are strongly associated with bottom topography. Greatbatch and Goulding (1990) demonstrated the important forcing terms for their model response at the Tokara Strait are those associated with the gradients of topography by comparing results between a model with and without bottom topography. The results shown in Fig.…”

“…On the other hand, Greatbatch and Goulding (1989) recently demonstrated that the seasonal transport variations predicted by a barotropic model are very similar to those of the observed annual cycle of sea level difference across the Tokara Strait. Furthermore, Greatbatch and Goulding (1990) examined in detail the seasonal variation of the transport through the Tokara Strait by using a limited-area barotropic model of the North Pacific with a fine-resolution, 1/3° × 1/3°. They demonstrated that the inclusion of realistic bottom topography is crucial in determining the model response and the important forcing terms for their model response at the Tokara Strait are those associated with the gradients of topography and not the curl of the surface wind stress.…”