The Distribution of Surface Fluxes and Boundary Layer Divergence in Midlatitude Ocean Storms

Abstract

Surface meteorological observations have been used to calculate the distributions of surface fluxes of momentum, sensible heat, and latent heat and the distributions of surface divergence and curl of surface stress which are characteristic of ocean storms in the Gulf of Alaska. Flux calculations were based on aerodynamic equations which include the effects of high wind speed and stratification of the surface layer. Distributions of divergence determined directly from surface winds were compared with those calculated using the curl of the surface stress. Results indicate that heat fluxes were weak or oven negative for the most intense storms in a band about 300 km wide immediately east of strong cold or occluded fronts. Maximum upward latent heat fluxes occurred to the west of the front, with secondary maxima along the eastern edge of the storm, beyond the 300 km band of weak flux. Surface convergence occurred to the east and divergence to the west of cold or occluded fronts. Vertical velocities calculated from the curl of the surface stress and including other important terms in the vorticity equation correspond in distribution and magnitude with measured divergences. Based on these independent calculations of vertical velocity and divergence, it can be inferred that the vertical gradient of stress was a maximum at the surface and decreased with height. The results provide a basis for assessing numerical models of ocean storms and for further developing and verifying parameterizations of surface fluxes.