Tuesday, 11 January 2005
Analysis of wind stress algorithms and computation of the the wind stress curl in Bodega Bay, California
The inhomogeneity of the wind stress and the wind stress curl in coastal regions significantly affects oceanic currents and upwelling/downwelling processes. Three wind stress schemes of various complexities have been chosen to evaluate the extent to which the selection of a method will alter the wind stress and the wind stress curl. The simplest scheme was the bulk formula assuming neutral conditions and directly relating the wind stress to the wind speed. A more advanced scheme is based on simple treatment of atmospheric stability through the sea-air temperature difference in addition to the wind dependence. The most advanced algorithm included full treatment of atmospheric dynamics and thermodynamics processes at the sea-air interface using the surface similarity theory. In order to evaluate the importance of atmospheric stability, humidity, and temperature correction, sensitivity tests were performed for various wind speeds. A diamond-shape setup of Bodega Bay buoys during the field program was used for the comparison of the wind stress curl based on input from different wind stress schemes. Computed results show that significant discrepancies exist in the computed wind stress among the schemes (especially for low-wind conditions) and the differences among computed curl appear to be not directly related to the values of the wind stress. During the analyzed period in summer 2001, positive, upwelling-favorable wind stress curl episodes corresponded to minima in the sea-surface temperature, while relaxation periods with low wind stress corresponded to the increase in the sea-surface temperature.