The Use of Mean Atmospheric Forcing in an Ocean Mixed-Layer Model

Abstract

Simulations of the oceanic mixed layer at Ocean Weather Ship Papa are used to study the sensitivity of the 30-day predictions of mixed-layer depth and temperature to the time resolution and averaging of the atmospheric forcing during spring, summer and autumn. The model simulations are sensitive to the length of the averaging window applied to the atmospheric forcing. Both the detail and trends in the mixed-layer depth and temperature deviate more from the control run when the length of the averaging window is increased. The effect of averaging the meteorological observations prior to calculating the surface fluxes is examined separately from the case in which the fluxes are calculated prior to the averaging. The cases which use forcing calculated from averages of the actual observations better simulate the detail and trend in mixed-layer depth of 30-day windows in the spring, summer and autumn than cases which use forcing based on the average of the calculated fluxes. By contrast, forcing based on an average of the calculated fluxes leads to better predictions of the detail and tend in the sea-surface temperature than the cases which use average observations to compute an average forcing.