A Numerical Study on Impacts of Greenhouse Gases on Asian Summer Monsoon

Abstract

The concentration of greenhouse gases in the atmosphere has increased continuously since industrial revolution and significantly impacted the global climate, of which global warming is the most direct and prominent manifestation. The Community Atmosphere Model V5.1 (CAM5.1) is examined and used to simulate multiple meteorological elements of Asian summer monsoon using the reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research), and the results show that it could reproduce the main features of Asian summer monsoon well. Sensitivity experiments are then carried out to study the response mechanism of Asian summer monsoon to greenhouse gas increase in terms of energy transformation, which adopt greenhouse gases emission scenarios of 2000 and 1850 respectively. The models are run for 20 years from 1991 to 2010, and the results of the latter 10 years in summer (June to August) are analyzed.With increasing greenhouse gases concentration, the surface air temperature in the Asian continent is mostly increasing, except for the Arabian Peninsula and northwestern Indian Peninsula. The monsoon is strengthened in central Indian Peninsula, Indo-China Peninsula and eastern China. In addition, monsoon precipitation increases in the central and northern Indian Peninsula, northern and central Indo-China Peninsula, and eastern China, while decreases in southern Indian Peninsula, southern Tibetan plateau, central and western China, the Philippines and Japan. Correlation analysis of atmospheric energy budget and conversion shows that increased greenhouse gases concentration enhances the atmospheric heat sources by means of increasing the convective condensational latent heat. The increase in atmospheric heat sources results in an increase of full potential energy. Thus, there are positive transformations of full potential energy to kinetic energy of divergent wind, and the transformation of kinetic energy from divergent wind to non-divergent wind also increases, which ultimately enhances the summer monsoon over central Indian Peninsula, Indo-China Peninsula and eastern China. Further analysis shows that the increase of convective condensational latent heat is the result of the decrease of atmospheric stability, the enhancement of convective activity, the increase of cloud thickness and the increase of convective precipitation caused by the increase of greenhouse gases concentration. Meanwhile, the increase of convective precipitation is the main cause for the increase of total precipitation.

Keywords

• greenhouse gases
• inhomogeneous heating
• total potential energy