Abstract

An improved estimate of the Kuroshio transport and its seasonal variation derived from the WOCE PCM-1 moored current meter array east of Taiwan is combined with various wind products and available hydrographic data in the ocean interior to determine the meridional heat transport at 24°N in the North Pacific. The resulting seasonal cycle of meridional heat transport has a minimum (southward) heat flux, -0.07 PW, in January and February, and a broad maximum in the second half of the year with a peak of 1.01 PW in July and a secondary maximum of 0.9 PW in November. The annual mean heat transport is 0.55 PW, with an uncertainty of 0.2 PW. This estimate is in good agreement with Macdonald and Wunsch's (1996) estimate of 0.5±0.3 PW, but lower than Bryden et al.'s (1991) estimate of 0.76±0.3 PW, both of which were mainly based on the one-time trans-Pacific hydrographic section (P03) along 24°N.

The Parallel Ocean Program (POP) model simulation of the meridional heat flux at 24°N compares favorably with the observations with regard to both the seasonal variation and the annual mean value. The model fields are used to investigate the heat flux mechanism across 24°N and its partitioning into vertical and horizontal cells. Consistent with Bryden et al. (1991), the vertical and horizontal cells are found to contribute about equally to the heat flux and they are confined in the upper ocean on the annual mean and longer time scales. However, for the seasonal variation, the vertical cell dominates the variation and involves circulation changes through the entire water column, while the horizontal cell heat flux remains nearly constant year-round.

The new estimate of meridional ocean heat flux across 24°N in the Pacific obtained from this study is combined with an updated estimate in the Atlantic at this latitude by Fillenbaum et al.(1997) to yield the total oceanic heat flux across the latitude circle of 24°N. The combined annual mean is 2.0±0.4 PW. The annual range is 1.7 PW, with maximum in August (2.7 PW) and minimum in February (1.0 PW). This is the first such estimate of the seasonal cycle of the world ocean heat flux across 24°N from direct oceanographic observations.