Role of the Tibetan plateau glaciers in the Asian summer monsoon

Abstract

The Tibetan plateau (TP) plays an important role in the Asian summer monsoon (ASM) dynamics as a heat source during the pre-monsoon and monsoon seasons. A significant contribution to the pre-monsoon TP heating comes from the sensible heat flux (SHF), which depend on the surface properties. A glaciated surface would have a different SHF compared to a non-glaciated surface. Therefore, the TP glaciers potentially can also impact the hydrological cycle in the Asian continent by impacting the ASM rainfall via its contribution to the total plateau heating. However, there is no assessment of this putative link available. Here, we attempt to qualitatively study the role of TP glaciers on ASM by analyzing the sensitivity of an atmospheric model to the absence of TP glaciers. We find that the absence of the glaciers is most felt in climatologically less snowy regions (which are mostly located at the south-central boundary of the TP during the pre-monsoon season), which leads to positive SHF anomalies. The resulting positive diabatic heating leads to rising air in the eastern TP and sinking air in the western TP. This altered circulation in turn leads to a positive SHF memory in the western TP, which persists until the end of the monsoon season. The impact of SHF anomalies on diabatic heating results in a large-scale subsidence over the ASM domain. The net result is a reduced seasonal ASM rainfall. Given the relentless warming and the vulnerability of glaciers to warming, this is another flag in the ASM variability and change that needs further attention.