Response of Monsoonal Precipitation to Greenhouse Warming in a Model Hierarchy

Abstract:

We have previously shown how, while land-sea contrast is not necessary to generate a monsoon (e.g., Bordoni and Schneider 2008), continental geometry still affects the monsoon timing, strength, and poleward extent (Hui and Bordoni, 2020). GCMs in the CMIP5 robustly project a delay in the timing of monsoon onset, but the extent to which this response is influenced by continental geometry has not been explored. In this work, we aim to study the response of monsoonal precipitation, in its intensity, spatial pattern, and onset timing, to climate change using a model hierarchy First, we explore the response of aquaplanet monsoons under a wide range of climates generated by rescaling the prescribed longwave optical depth in an idealized GCM. Within these simulations, we observe a delay in monsoon onset with warming that is observed well using both the angular momentum budget and energetic frameworks. Next, over the same range of climates we will run simulations with different zonally symmetric configurations of Northern Hemisphere land, to combine both the effects of the presence of land and a warming climate and inform us on how continental geometry may affect how the monsoon responds to different climates. Our analysis focuses on investigating changes in the monsoon using both the angular momentum budget and energetic frameworks to connect the changes in the temporal progression and spatial extent of the monsoonal precipitation to changes in the large-scale tropical circulation and net energy input into the atmospheric column. We plan to also explore whether these two frameworks can be reconciled and whether the relative influence of the constraints each framework provides evolves under different climates.