気候モデルによるチベット山塊の役割の評価 Investigation of the Role of the Tibetan Plateau by Climate Model
Effects of mountains on climate are investigated by an atmospheric general circulation model coupled with a 50-m depth slab ocean model. A model simulation with the present-day orography reproduces most of the principal features of the observed climate. Another simulation without mountains (NM) is done and is compared with the one with mountains (M).<BR>Orography-originated stationary waves are separated from those induced by the existence of land-sea distribution. In northern winter, about two thirds of the stationary wave is explained by orography in this study. The wintertime subtropical jet in the upper troposphere in NM is more zonal and weaker than in M. The summertime subtropical jet in NM does not shift northward much and is located over China and Japan. The Asian summer monsoon in NM is substantially weaker than in M. Surface monsoon westerlies are weak, a rain belt stays south and the precipitation over India and China is less in the model without orography. On the other hand, the precipitation in the continental interior is large and the ground is wet in NM due to large moisture transport from the ocean.<BR>The global mean sea surface temperature in NM is warmer than in M. This occurs mainly from increased solar radiation into the ocean due to decreased lower tropospheric clouds over the subtropical eastern Pacific. Land surface temperature in NM is warmer than in M due to lapse-rate effect. However, the summertime surface temperature in Europe, Russia and Canada is cooler in NM than in M because ground surface in NM is wetter.