Effects of large-scale mountains on surface climate - A coupled ocean-atmosphere general circulation model study

Effect of mountain uplift on climate is investigated by a global coupled ocean-atmosphere general circulation model with an emphasis on surface temperature changes. Results of the no-mountain run (NM) are compared with those of the control run with the present-day orography (M). When the lapserate effect is eliminated, continent interior becomes warmer with mountain uplift because clouds become fewer and the surface drier due to decreased moisture transport. On the other hand, South Asia and East Asia become cooler because summer monsoon precipitation is stronger, which makes the land surface wetter and increases clouds. Over the ocean, the existence of orography has a role to reduce sea surface temperatures (SST), particularly over the subtropical eastern oceans. This occurs because evaporation is larger due to stronger trade winds and also less solar radiation reaches the surface due to more low-level clouds, both associated with stronger subtropical anticyclones in M. The subtropical gyre is stronger in M than in NM and therefore, the Kuroshio Current is stronger in M. When the effect of the ocean general circulation is not included, the SST over the western north Pacific becomes much lower in M than in NM because of stronger cold air outbreak from Siberia in winter in M. Thus, the ocean circulation changes act to reduce the SST changes by heat transport.