[A-CG30] 熱帯におけるマルチスケール大気海洋相互作用

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

*宮本 歩¹、中村 尚¹、宮坂 貴文²、小坂 優¹、謝 尚平³ (1.東京大学先端科学技術研究センター、2.気象業務支援センター、3.カリフォルニア大学サンディエゴ校スクリプス海洋研究所)

キーワード：下層雲、北太平洋

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.