Northwest Pacific heat balance analysed using in-situ, model and satellite data

Heat balance within an ocean mixed layer is important since it describes whether ocean-atmosphere and ocean-climate interactions occur locally or remotely. In particular, a knowledge of heat balance will improve our understanding of the causes of variations in sea surface temperature and air-sea heat exchange. In this study, the heat balance mechanism is analysed on seasonal to interannual scales to resolve controversies between theory and observations. The study region is the Northwest Pacific where the role of the strong Kuroshio Extension geostrophic current on the heat balance has not been quantified previously. A combination of in-situ, model, and satellite data is used for the period October 1992 to September 1995. Components of the heat balance are determined as follows. The horizontal geostrophic heat advection is obtained using current velocities from satellite altimetry and a Gaussian jet model. Although its error reaches 150% of the signal, such evaluations of the signal and error level have not been achieved before. A validation of the velocity from the jet model is performed for the first time in the Northwest Pacific. The r.m.s. error is 17 cm S-1 or 46% of the signal. The vertical entrainment heat advection is estimated rigorously on a climatological monthly scale. This term is neglected in the heat budget since its maximum magnitude of 30 W m-2 is at least a factor of three smaller than those of the other balance terms. The heat storage rate is computed using mixed layer temperatures from satellite infrared imagery and mixed layer depths from subsurface temperature records. The horizontal Ekman heat advection is derived using model wind speeds. The seasonal and interannual heat advection by the Kuroshio Extension is insignificant in the basin-scale heat balance. It is less than 10% of the heat storage rate. The horizontal Ekman heat advection is also observed to be insignificant. It is concluded that the heat balance is achieved locally. The findings of the thesis provide several examples disapproving the influential theory on heat balance by Gill and Niiler. It is argued that their theory is incorrect because it neglects the effects of horizontal temperature gradient. Monthly net surface heat fluxes are derived from the sum of the heat balance terms. Errors in these fluxes are estimated thoroughly. The error in the three-year mean flux over the basin of 30 W m-2 is smaller in percentage terms than achieved by the best bulk-formulae method. However, this error level still exceeds that required by climate studies.