Structure of the Mixed Layer and Estimates of Sea Surface Fluxes during TOGA-COARE IOP

Abstract

The present paper is the second part of our study on features of the boundary layer during TOGA-COARE TOP. Utilizing the observational dataset obtained by the Japanese R/V Hakuho-maru for 11-27 November, 1992 during TOGA-COARE TOP at 0, 156E, the ocean surface fluxes were estimated by three different bulk schemes. Firstly, a near-linear relation between the neutral drag coefficient and wind speed was used. Then, the stability-dependent drag and heat transfer coefficients were iteratively solved. Based on the thus-derived transfer coefficients the momentum, sensible, and latent heat fluxes were estimated, which amount to 0.0316N/m2, 10.2W/m2 and 190.3W/m2, respectively. The regional wind field strongly modulated the magnitude of surface fluxes, with four westerly wind episodes corresponding to much greater fluxes than those for the east trade wind. The magnitude of surface fluxes is also dependent upon the atmospheric stability, in particular for a weak wind condition. The net surface heat flux was estimated, indicating that a considerable amount of heat was transported from the underlying ocean into the atmosphere. Finally, an accuracy analysis was made through a comparison with direct measurements by the eddy-correlation method and other bulk method estimates, showing that the bulk-derived fluxes are acceptable with high confidence.Through this study, it has been realized that the full range of wind structures and conditions, from the ambient trade-wind regime through the episodic westerly wind regime, may exert a significant impact on the structures of mixed layers and the ocean-atmosphere fluxes of heat, moisture and momentum.