资源环境科技发展态势分析平台

In this study, the weakening of the orographic rainfall for the period 2000-2011 during the Indian summer monsoon (JJA) is investigated using the regional climate model RegCM 4.5. Analysis reveals that when sulfate aerosol feedback is included in the model run, the simulated temperature shows a cooling of the continental upper troposphere by 0.3 degrees C. At the same time, the sulfate aerosol loading in the atmosphere had induced cooling of 0.2 degrees C of the lower troposphere over the Indian region. Consequently, the simulated zonal wind fields show a weakening at the upper and lower tropospheric levels, particularly where the semi-permanent systems that drive the monsoon circulations are located. It is suggested that the weakening of zonal winds has caused a suppression of the orographic rainfall along the west coast of India (Western Ghats), as evident from the observations. Concurrently, the simulations indicate a sulfate aerosol induced reduction in orographic monsoon rainfall over the southern Western Ghats, whereas their effect is insignificant in controlling the orographic rainfall in the northern Western Ghats. Moreover, our analysis indicates a decline in rainfall over the Himalayan foothills when the sulfate aerosol feedbacks are included, which corroborates well with the observations.