Sources of Inter-Model Scatter in TRACMIP, the Tropical Rain Belts with an Annual Cycle and Continent—Model Intercomparison Project

We introduce a new idealized multi-AGCM experiment, TRACMIP (Tropical Rain belts with an Annual cycle and Continent - Model Intercomparison Project), which examines how land-ocean zonal and seasonal asymmetries determine the responses of tropical circulation to warming and precession. The dataset is free to the community and includes output from 14 different slab-ocean aquaplanet AGCMs at two levels of CO2 (preindustrial and 4x), two geographies (with and without an idealized flat "continent" in 30N-30S, 0-45E) and two orbits (circular and eccentric.)

The spatial patterns of tropical precipitation in the control aquaplanet simulations, its modification by the introduction of land, and its response to climate change vary dramatically between the models, even in this simple setup. We will use recent ideas on the local moist energy balance of the tropical atmosphere to diagnose some of the causes of this diversity. Our goal is to trace intermodel differences in circulation and precipitation to differences in the cloud and clear-sky radiative effects and the gross moist stability, and ultimately to the cloud and convective parameterizations themselves. This will give insight into what determines the monsoons, Walker cells and other zonal-seasonal asymmetries in the tropical atmosphere.