Some GCM Experiments of the Asian Summer Monsoon Related to Land Boundary Conditions.

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Abstract
The results of a 20-year simulation (control run) by the 5-layer MRI AGCM are analyzed for the Asian monsoon region for the summer season (June-September) and are compared with the observations. Overall large-scale features are simulated with considerable reality, though there are drawbacks such as a weak monsoon flow. Motivated by these drawbacks, some numerical experiments related to land-surface boundary conditions are performed. The cold bias in the low-level atmosphere over the Arabian peninsula found in the control run is alleviated by replacing swamp grid points of the Persian Gulf and the Red Sea with land points. The underestimated precipitation at the foothills of the Himalayas is alleviated to some extent by forcing ground to be wet over the Indian subcontinent. These experiments show the importance of land-surface processes for regional climate. However, the improvements in the above simulations are limited in regional scale and large-scale errors are not alleviated significantly. The simulation with worldwide elevated topography shows the significant weakening of the monsoon circulation, though regional-scale features show an improvement. This fact shows that the use of excessively high mountains deteriorates the simulation of the Asian summer monsoon circulation.

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