Impact of the ocean diurnal cycle on the North Atlantic mean sea surface temperatures in a regionally coupled model

This study investigates the mechanisms by which the ocean diurnal cycle can affect the ocean mean state in the North Atlantic region. We perform two ocean-atmosphere regionally coupled simulations (20 degrees N-80 degrees N, 80 degrees W-40 degrees E) using the CNRMOM1D ocean model coupled to the ARPEGE4 atmospheric model: one with a 1 h coupling frequency (C1h) and another with a 24 h coupling frequency (C24h). The comparison between both experiments shows that accounting for the ocean diurnal cycle tends to warm up the surface ocean at high latitudes and cool it down in the subtropics during the boreal summer season (June-August). In the subtropics, the leading cause for the formation of the negative surface temperature anomalies is the fact that the nocturnal entrainment heat flux overcompensates the diurnal absorption of solar heat flux. Both in the subtropics and in the high latitudes, the surface temperature anomalies are involved in a positive feedback loop: the cold (warm) surface anomalies favour a decrease (increase) in evaporation, a decrease (increase) in tropospheric humidity, a decrease (increase) in down-welling longwave radiative flux which in turn favours the surface cooling (warming). Furthermore, the decrease in meridional sea surface temperature gradient affects the large-scale atmospheric circulation by a decrease in the zonal mean flow. (C) 2013 Elsevier B.V. All rights reserved.