Effects of mountain uplift on global monsoon precipitation

This study explores the role of the global mountain uplift (MU), which occurred during the middle and late Cenozoic, in modulating global monsoon precipitation using the Meteorological Research Institute atmosphere-ocean coupled model experiments. First, the MU causes changes in the annual mean of major monsoon precipitation. Although the annual mean precipitation over the entire globe remains about the same from the no-mountain experiment (MU0) to the realistic MU (MU1), that over the Asian-Australian monsoon region and Americas increases by about 16% and 9%, respectively. Second, the MU plays an essential role in advancing seasonal march, and summer-monsoon onset, especially in the Northern Hemisphere, by shaping pre-monsoon circulation. The rainy seasons are lengthened as a result of the earlier onset of the summer monsoon since the monsoon retreat is not sensitive to the MU. The East Asian monsoon is a unique consequence of the MU, while other monsoons are attributed primarily to land-sea distribution. Third, the strength of the global monsoon is shown to be substantially affected by the MU. In particular, the second annual cycle (AC) mode of global precipitation (the spring-autumn asymmetry mode) is more sensitive to the progressive MU than the first mode of the AC (the solstice mode), suggesting that the MU may have a greater impact during transition seasons than solstice seasons. Finally, the MU strongly modulates interannual variation in global monsoon precipitation in relation to El Niño and Southern Oscillation (ENSO). The Progressive MU changes not only the spatial distribution but also the periodicity of the first and second AC mode of global precipitation on interannual timescale.