[A-CG30] Multi-scale ocean-atmosphere interaction in the tropics

[ACG30-02] Radiative impacts of low clouds on the subtropical North Pacific climate

*Ayumu Miyamoto¹, Hisashi Nakamura¹, Takafumi Miyasaka², Yu Kosaka¹, Shang-Ping Xie³ (1.Research Center for Advanced Science and Technology,The University of Tokyo, 2.Japan Meteorological Business Support Center, 3.Scripps Institution of Oceanography, University of California San Diego)

Keywords:Low clouds, North Pacific

Low clouds that cool the Earth radiatively are extensive off California over the North Pacific. The present study assesses their radiative impacts on the subtropical North Pacific climate with coupled general circulation model experiments. Comparison of a freely coupled control experiment with a sensitivity experiment where low-cloud radiative effect off California is artificially switched off demonstrates that low clouds lower sea surface temperature (SST) and reinforce the subtropical anticyclone locally. These responses extend southwestward from off California, suggestive of wind-evaporation-SST feedback. Following enhanced albedo effect of low clouds in spring and summer, the responses become strongest in summer and autumn in association with suppressed deep convective precipitation. In these seasons, low clouds strengthen surface trade winds and upper-tropospheric subtropical westerly jet, explaining 25% of climatological vertical wind shear around Hawaii. Low clouds thus act to protect Hawaii from hurricanes by lowering SST and increasing vertical wind shear.