Global Monsoon Variability in the CESM1-CAM5 Last Millennium Ensemble

Abstract:

The characteristics and causes of decadal to multi-centennial variability in the global monsoon are explored using the multi-member ensemble of simulations from the CESM1-CAM5 Last Millennium Ensemble Project (CESM-LM). The ensemble consists of multiple (>2) members in which the variability of individual forcings (solar, orbital, volcanic, land use / land cover, and greenhouse gas) is specified. In a larger number of members (>6), all forcings are specified and these, along with an extended control integration, are used to to estimate internal variability and distinguish it from forced changes in the global monsoon system.

This analysis examines the relevance of the global monsoon concept, which suggests coherent variability across the monsoon systems, to simulated variability since 850. The analysis also examines the ability of the CESM-LM model configuration to reproduce key features of the global monsoon in the present day while distinguishing between regional monsoon systems, and land-ocean and inter-hemispheric contrasts across timescales. Implications for interpreting the 20th Century record and future monsoon projections are explored.