56 Toward the Use of Convective Quasi-Equilibrium as a Predictor for Changes in the Seasonal Cycle of Tropical Precipitation in Aquaplanet Simulations

Monday, 26 June 2017
Salon A-E (Marriott Portland Downtown Waterfront)
Bryce E. Harrop, PNNL, Richland, WA; and J. Lu and L. R. Leung

Handout (5.6 MB)

Convective Quasi-Equilibrium (CQE) is shown to be a skillful predictor of precipitation change owing to CO2-induced warming across a suite of aquaplanet simulations. Simulations from the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP) verify a linear relationship between precipitation rate and the curvature in the sub-cloud moist entropy field (a marker for when the environment is favorable for a direct overturning circulation to develop). The seasonal cycle of zonal mean precipitation is well correlated in space-time with this curvature term. The linear relationship between these two metrics can be derived from control experiments and used to predict changes in the seasonal cycle of zonal mean precipitation in 4xCO2 experiments with slab ocean boundary conditions. These predicted precipitation changes show skill compared to a null hypothesis of a simple “wet-get-wetter” framework where precipitation increases by a fixed percentage equal to the annual tropical mean increase. The curvature metric also shows improvement in predicting precipitation changes compared to the simpler method of relating precipitation directly to the sub-cloud moist entropy field.
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