It is assumed that the principal means for conveying wind stress to the ocean's uppermost layer is in an Ekman layer of ten's to a hundred meters thickness in which the stress is balanced by the Coriolis force. The result is net mass transport to the right (left) of the wind in the northern (southern) hemisphere. The velocity vectors form a spiral to the right (left) which decays exponentially with depth if the eddy viscosity is uniform. The principal justification for the theory has been that the ocean's general circulation beneath the Ekman layer is in the proper sense as to be driven by convergent or divergent Ekman transports. Direct and repeated confirmation of Ekman layers in the open ocean has only occurred relatively recently. Davis et al. [1981] showed a mixed layer response to the winds in the northeastern Pacific which was clearly Ekman-like. Price et al. [1987] demonstrated the spiral Ekman layer structure in the subtropical North Atlantic; verification required adjusting the averaging directions daily to follow the wind. Rudnick and Weller [1993] showed that the time dependent response to the changing wind direction in the same subtropical North Atlantic region was accounted for in theory of time-dependent Ekman layers. In the California Current region, Chereskin [personal communication] has observed, using a moored acoustic Doppler current profiler (ADCP), an Ekman-type response to winds which were nearly steady over several months; a fit of the observed spiral to the classical Ekman model suggests that the eddy viscosity is not uniform. Niiler [1994], using the large cumulative surface drifter data set for the Pacific, has demonstrated that the 15 meter mean ageostrophic velocity is clearly to the right of the wind in the northern hemisphere and to the left in the southern hemisphere, consistent with the general sense of Ekman theory.
Hellerman and Rosenstein's [1983] discussion of the climatological wind stress, curl and Sverdrup transport remains the most complete description of the winds in the refereed literature. Wind products which are available at this time are based on ship measurements [ e.g., Adamec et al., 1993], or on analyzed products from the European Centre for Medium Range Forecasting and from the National Meteorological Center. Various combinations of the different wind products are being used by numerical modelers to drive general circulation models, and in observational studies of the wind driven circulation.