Estimation of low-frequency wind stress fluctuations over the open ocean.

Abstract

A simple, approximate formula for mean wind stress is given in terms of the mean and variance of the wind fluctuations over the averaging period. The formula is nonlinear with respect to the mean wind speed. The formula is tested using 3 h wind observations from eight North Atlantic Ocean Weather Ships. Mean wind stress is calculated (1) by vector averaging the 3 h wind stresses, and (2) by applying the approximate formula. For an averaging period of 4 months the two methods agree to within + OR - 0.025 Pa, 95% of the time. A straightforward method is described and validated for the estimation of vector mean wind and variance fields, and thus mean stress fields, over the open ocean. The zonally integrated Sverdrup transport across 45 DEGREE N is also calculated and shown to exhibit significant interannual fluctuations. (from authors' abstract)