Intraseasonal Convective Moistening in CMIP3 Models

A precise relationship between tropospheric moisture and convection is thought to be a key to the accurate simulation of tropical intraseasonal variability. An evaluation of the precipitation distribution and its fundamental physical relationship with relative humidity (RH) in the 14 climate models that participated in the Coupled Model Intercomparison Project phase 3 (CMIP3) is presented here. Most models tend to reside in a light rainfall regime that largely determines the models’ basic state, and the intraseasonal transition toward heavy precipitation is not as gradual as in the observations. Some of the precipitation biases are related to the deficiencies in the representation of the relationship between the precipitation and RH, and the moisture preconditioning ahead of intraseasonal convection. It is also shown that even for models with reasonable baroclinic temperature anomaly structures of the MJO, there are large biases in the intraseasonal specific humidity anomalies, some of which may b...