Sensitivity of the tropical Pacific Ocean simulation to the temporal and spatial resolution of wind forcing

The effects of temporal and spatial smoothing of wind forcing were evaluate d in a model simulation of the tropical Pacific Ocean variability during th e onset phase of the 1997/1998 El Nino. A total of 16 experiments were perf ormed using the NASA scatterometer wind data smoothed at time intervals fro m 1 to 30 days and on spatial scales from 1 degrees to 10 degrees. A major effect of the temporal smoothing of winds is to warm sea surface temperatur e (SST) by reducing the energy input for vertical turbulent mixing. When th e daily wind forcing was replaced by the monthly average, the mean SST incr eased by 0.5 degrees to 1 degrees over most of the tropical Pacific. The sp atial smoothing of winds is not as effective as the temporal smoothing in c ausing SST warming, but it has a more severe influence on dynamical ocean r esponse for smoothing scales above 5 degrees. The onset of the 1997/1998 Fl Nino can be successfully simulated using the wind forcing averaged to mont hly intervals and 2 degrees squares. For climate models the spatial smoothi ng of wind forcing on scales larger than the width of the equatorial wavegu ide is a more serious limitation than the temporal smoothing on scales up t o 1 month.