The Relationship between Oceanic Heat Transport and Surface Fluxes in the Western North Pacific: 1970–2000

Abstract

Part of the heat transported poleward from the Tropics by the ocean is stored near the energetic western boundary currents. These storage reservoirs provide a source of interannual to decadal climate fluctuations through their impact on the ocean–atmosphere heat fluxes. Changes in ocean heat storage result from the difference between surface fluxes and the convergence of oceanic heat transport. To estimate the heat budget for 26°–40°N, 140°E–180°, sea surface temperature and subsurface temperatures are assimilated into a one-dimensional model of the upper ocean that is forced by heat fluxes from the NCEP–NCAR reanalysis. Heat transport convergences are inferred as the residual of the heat budget for the period 1970–2000 using the “unknown control” from a Kalman filter/smoother technique. The estimates of heat transport convergence compare qualitatively with direct estimates from a three-dimensional model that uses geostrophic currents from the TOPEX/Poseidon radar altimeter for 1993–99; this period contains the largest lateral fluxes and the largest heat loss from the ocean in the 31-yr record. The analysis of the heat budget demonstrates that, on interannual to decadal time scales, the heat storage rate in the upper ocean is better correlated with lateral heat transport convergence than with surface fluxes. In addition, heat content and surface flux are negatively correlated, demonstrating the dominance of oceanic feedback over atmospheric forcing. The close relationship between heat content and surface fluxes suggests the possibility of predicting surface flux anomalies: there is a small but significant skill in predicting surface flux anomalies up to one year in advance using heat content. SST has no prediction skill.