The idealized simulations of the CFMIP and CMIP5 ensembles have been instrumental in fostering progress in our understanding of tropical precipitation biases and sensitivity to forcings. We suggest to expand on those efforts and we propose that a set of idealized simulations, designed after the CFMIP ones, be performed by as many modeling group as possible.

The aim of these simulations will be to explore the dynamics of the annual cycle of tropical rainfall in different climate states: present day, mid-holocene, and under global warming. Specifically, we aim to explore the relative roles of changes in radiative input and lower boundary conditions in inducing changes in the annual cycle of tropical land and ocean precipitation  and to explore the extent and importance of the interaction between marine and continental environments.

Our initial suggestion, to be refined in consultation with interested modeling groups:

Ideally, we suggest running simulations with a slab ocean model of fixed depth (30m), with seasonally and diurnally varying insolation (corresponding to modern day parameters in the control runs, exept for eccentricity, which is set to 0), and a prescribed inter-hemispheric oceanic Q-flux. The control configuration will be an aquaplanet. In another configuration, the slab ocean equations are modified to mimic an idealized equatorial continent with uniform vegetation and soil moisture and extending in latitude to 30N-30S and in longitude from 0 to 45E is added.  

Thus the simulations to be performed would be: 

1. Aqua Slab Control

2. Continent Slab Control

3. (1.) + abrupt increase to 4xCO2

4. (2.) + abrupt increase to 4xCO2

5. (2.), but with eccentricity

Download our working draft of the protocol for the proposed slab simulations here.

For comments, questions, or suggestions, please contact us.