DETERMINING TORQUES OVER THE OCEAN AND THEIR ROLE IN THE PLANETARY MOMENTUM BUDGET

Knowledge of wind torques at the atmosphere-ocean interface is importa nt in understanding the global angular momentum balance. A surface win d data set that combines special sensor microwave/imager (SSM/I) and E uropean Centre for Medium Range Weather Forecasts (ECMWF) wind product s and covers the period July 1987 to June 1989 is used to estimate zon al torques over the global ocean. Comparison of these fields and field s computed from ECMWF wind analyses alone shows substantial difference s in the statistics of both locally and globally integrated torques; t he impact of SSM/I data on the torque analysis is largest over the Ind ian Ocean and eastern Pacific regions. The characteristics of the torq ues from the combined SSM/I-ECMWF data set are evaluated. In general, local torques show the largest means and variances over mid-latitudes (especially in the southern ocean), with fluctuations at periods short er than 1 month dominating the records. In contrast, variability in th e globally integrated ocean torque is largest at seasonal time scales (3 months to 1 year); midsouthern and tropical northern latitudes cont ribute substantially to this variability. Comparison between the globa l ocean torque and atmospheric angular momentum M indicates that indir ect exchanges of momentum between the atmosphere and solid Earth via o ceanic stresses cannot be neglected at seasonal time scales. Intraseas onal fluctuations (1-3 months) in both tropical and global ocean torqu es are coherent with M but too weak to account alone for the variabili ty in M. At submonthly periods the ocean torque is apparently not impo rtant in the atmospheric momentum balance.