Nonlinear effects of variable winds on ocean stress climatologies

Author: R.D. Rosen and Rui M. Ponte
October 6, 2003
Journal Article
Journal of Climate

Ponte, R.M., and R.D. Rosen, 2004. Nonlinear effects of variable winds on ocean stress climatologies, Journal of Climate, 17, 1283-1293.

Variability in surface winds at subseasonal time scales can affect the estimates of the mean and seasonal stress over the ocean, owing to the nonlinear dependence of stress on wind speed. A global ocean wind product that merges the European Centre for Medium-Range Weather Forecasts (ECMWF) fields with satellite and in situ data is used to assess the nonlinear effects of wind variability, in particular synoptic signals (taken here to include all periods of <6 days), on estimates of the mean and the seasonal cycle in zonal and meridional stress. Climatologies based on the period March 1988–February 1999 are considered. Synoptic effects are most pronounced at mid- and high latitudes, where they can amount up to 20% of the mean or seasonal stress. Uncertainties in stress values associated with synoptic wind errors are assessed by comparing estimates from merged-data winds to those from original ECMWF winds. Differences in synoptic winds contribute noticeably to the stress differences. Outside the Tropics, uncertainties related to synoptic wind terms can have amplitudes of more than 20% of the total estimated uncertainty for mean and seasonal zonal stress, with much higher values for the meridional stress. Implications of these findings for studies of the atmospheric and oceanic circulations are discussed. Results point to the importance of accurately determining wind variability at subweekly periods, thereby placing constraints on sampling strategies for observing winds over the ocean.