Monsoons and their Response to Climate Change in Idealized GCM Experiments

Monsoons are prominent features of the tropical and subtropical atmospheric circulation, affecting 60% of the world's population (Wang 2006) and sustaining rapidly growing economies. Understanding how monsoons will change with changing climate is of pressing societal importance, and yet remains a challenge: Many studies have explored the impact of global warming on monsoons, but many questions remain unanswered. In this study, we perform experiments with an idealized General Circulation Model (GCM) to investigate the response to climate change of an idealized monsoon on a single pole-to-pole rectangular continent of fixed longitudinal width. The climate is varied by perturbing the atmospheric longwave absorber, in analogy to changes in greenhouse gas concentrations. We use the moist static energy, moisture and zonal momentum budgets (e.g., Chou et al. 2001, Bordoni and Schneider 2008) to interpret the simulated changes in monsoon onset, circulation strength and precipitation. Each budget is decomposed into mean, stationary and transient eddy fluxes, to explore the relative role of these circulations in the maintenance of the monsoonal precipitation. We specifically focus on how mechanisms deemed important in present-day monsoonal convergence regions, such as soil moisture availability, horizontal ventilation of moist static energy, Rossby wave dynamics, and divergence of ocean heat transport, change as the climate is varied, thereby affecting the monsoon.