Is the Influence of Stability on the Sea Surface Heat Flux Important?

Abstract

AbstractObservations of the heat flux over the open sea and in the coastal zone are analyzed to reexamine the relation of the heat flux to the air–sea temperature difference and wind speed. The study begins by examining problems with different methods for estimating the air–sea temperature difference. The difference between the air and within-water temperature is found to be most suitable for one dataset, while the difference between the air and the radiometrically measured sea surface temperature must be used for the second dataset. On average, the heat flux is linearly proportional to the product of the air–sea temperature difference and wind speed corresponding to approximately constant transfer coefficient for heat CH. Deviations of the heat flux from this simple relationship were generally weakly related or unrelated to the surface bulk Richardson number Rb, even for the coastal zone site. Similar results are also found for the moisture flux. In contrast to the general success of constant transfer coefficient for heat, CH plotted directly as a function of Rb is systematically related to the square root of Rb. The role of the wind speed as a shared variable between CH and Rb also predicts such a square root dependence, suggesting that the relationship could be largely due to self-correlation, which is also supported by a nominal study of self-correlation. However, confident isolation of the influences of stability, self-correlation, uncertainties in the air–sea temperature difference, and other physics requires more extensive data.