Long-term impacts of ocean wave-dependent roughness on global climate systems

Abstract

Ocean surface waves can play an active role in climate systems, but they are often ignored in Global Climate Models (GCMs). Wave-dependent surface roughness was implemented within the Atmospheric GCM (MRI-AGCM) using the spectral wave model WAVEWATCH III. Two types of wave-dependent roughness, due to wave steepness and to wave age, were considered. Climate simulations with wave-dependent roughness were compared to simulations with just wind speed-dependent roughness. In climate simulation with wave steepness-dependent roughness, the spatial distribution of roughness is correlated to that of swell dominance. In simulation with wave age-dependent roughness, the spatial distribution of roughness is correlated to that of wind direction stationarity. Both simulations show reduced roughness in the tropics, which leads to an enhancement of surface wind speeds by up to 15%; these enhanced wind speeds are closer to observations compared with the baseline simulation with just wind speed-dependent roughness. We find that the reduced roughness and the enhanced wind speeds in the tropics lead to significant changes in atmospheric circulation, as in Hadley circulation and precipitation. The characteristic responses of the Hadley circulation and precipitation to changing sea surface roughness are presented.