Neogene mountain uplift and the asynchronous evolution of the summer monsoons in Asia based on regional climate modeling experiments

The Cenozoic global cooling was accompanied by hydrological changes which exhibited great regionality. In Asia, such changes were characterized by the inception and intensification of the Asian summer monsoon primarily caused by regional tectonic changes, such as the uplift of the Tibetan Plateau and the retreat of the Paratethys Sea. However, the more detailed spatiotemporal evolution of the Asian summer monsoon remains controversial owing to the uncertainty of our knowledge in the effect of the Asian orogeny on the summer monsoon climate and its interaction with global cooling. In this study, the regional climate model CCLM3.2 with a high spatial resolution is employed to investigate the climatic impact of individual parts of the Tibetan Plateau and the surrounding mountains. Sensitivity experiments consider the successive growth of different parts of the Asian orography in the Neogene to analyse their effects on the Asian summer monsoon. Our results reveal that, different from the bulk mountain uplift (i.e. the uplift of the whole Tibetan Plateau or the whole Asian orography) which induces a synchronous strengthening of both the Indian and East Asian summer monsoon, the regional mountain uplift can lead to an out-of-phase summer monsoon changes in India and East Asia. This provides new insights to the evolution of the Asian summer monsoon and its relation to the tectonic changes and the global cooling in the Neogene.