资源环境科技发展态势分析平台

We show that 21st century increase in radiative forcing does not significantly impact the frequency of South Asian summer monsoon depressions (MDs) or their trajectories in the Coupled Model Intercomparison Project Phase 5 general circulation models (GCMs). A significant relationship exists between the climatological occurrences of MDs and the strength of the background upper (lower) tropospheric meridional (zonal) winds and tropospheric moisture in the core genesis region of MDs. Likewise, there is a strong relationship between the strength of the meridional tropospheric temperature gradient in the GCMs and the trajectories of MDs over land. While monsoon dynamics progressively weakens in the future, atmospheric moisture exhibits a strong increase, limiting the impact of changes in dynamics on the frequency of MDs. Moreover, the weakening of meridional tropospheric temperature gradient in the future is substantially weaker than its inherent underestimation in the GCMs. Our results also indicate that future increases in the extreme wet events are dominated by nondepression day occurrences, which may render the monsoon extremes less predictable in the future.

Plain Language Summary Monsoon depressions (MDs) are one of the most important synoptic scale transient weather systems that transport large amount of moisture over the South Asian landmass and contribute significantly to the total precipitation. In this study, we investigate representation of MDs in the Coupled Model Intercomparison Project Phase 5 general circulation models, their simulated responses to increase in radiative forcing during the 21st century under Representative Concentration Pathway 8.5, and the resulting changes in precipitation characteristics at intraseasonal time scales. We show that 21st century increase in radiative forcing does not significantly impact the frequency of South Asian summer monsoon depressions or their trajectories in the general circulation models. Our results indicate a significant relationship between the climatological occurrences of MDs and the background upper (lower) tropospheric meridional (zonal) winds and tropospheric moisture in the core genesis region of MDs. While monsoon dynamics progressively weakens in the future, atmospheric moisture exhibits a strong increase, limiting the impact of changes in dynamics on the frequency of MDs. Our results also indicate that future increase in the extreme wet events is dominated by nondepression day extremes, which may render the monsoon extremes less predictable in the future.