Climate Processes in CMIP5: Process-oriented diagnostics of tropical intraseasonal variability

Complementary efforts are underway by the NOAA MAPP CMIP5 Task Force and the WGNE MJO Task Force to develop process-oriented model diagnostics to explain why some climate models produce better simulations of tropical intraseasonal variability. We will present examples of diagnostics based on tropospheric moisture and the vertically-integrated moist static energy (MSE) budgets that show particular promise in distinguishing intraseasonal variability simulation capabilities. The Madden-Julian oscillation and Intra-Americas Sea boreal summer intraseasonal variability are the target phenomena. The diagnostic analysis not only focuses on long climate simulations, but is also applied to model hindcasts for the DYNAMO field phase of Fall 2011.

Models with superior simulations of variability tend to be associated with lower gross moist stability (GMS), which is a diagnostic derived from the vertically-integrated MSE budget that characterizes how efficiently convection and associated divergent circulations discharge moisture from the column. Both the vertical profiles of diabatic heating and MSE influence the ability to destabilize intraseasonal modes of variability, reflected in lower GMS. In some cases, the diagnostic analysis indicates that models may be producing realistic intraseasonal variability for the wrong reasons, with common mean state precipitation biases being produced for models with strong intraseasonal variability. In addition to MSE budget diagnostics, we will also provide examples of process-oriented diagnostics based on tropospheric relative humidity, with particular application to intraseasonal variability in the Intra-Americas Sea.