An 11–level numerical model of the atmospheric circulation which has a prescribed seasonal variation of insulation and sea surface temperatures is integrated with respect to time for approximately three model years. The model is global in domain and incorporates a smoothed mountain topography. In order to investigate the role that mountains play in the south Asian monsoon circulation, a second numerical experiment, exactly the same as the first except that all mountains are removed, is integrated with respect to time from 25 March through July. Analysis of the model with mountains reveals that the large–scale circulation associated with the south Asian monsoon is well simulated. However, the onset of the monsoon is approximately 10–15 days later than normal, and the atmosphere over the western Pacific seems to he dynamically too active, while the atmosphere over the northern reaches of the Bay of Bengal and northern India is relatively inactive. Comparison of the simulation with mountains with th... Abstract An 11–level numerical model of the atmospheric circulation which has a prescribed seasonal variation of insulation and sea surface temperatures is integrated with respect to time for approximately three model years. The model is global in domain and incorporates a smoothed mountain topography. In order to investigate the role that mountains play in the south Asian monsoon circulation, a second numerical experiment, exactly the same as the first except that all mountains are removed, is integrated with respect to time from 25 March through July. Analysis of the model with mountains reveals that the large–scale circulation associated with the south Asian monsoon is well simulated. However, the onset of the monsoon is approximately 10–15 days later than normal, and the atmosphere over the western Pacific seems to he dynamically too active, while the atmosphere over the northern reaches of the Bay of Bengal and northern India is relatively inactive. Comparison of the simulation with mountains with th...