The sensitivity of intraseasonal variability in the NCAR CCM3 to changes in convective parameterization

Removing these effects greatly reduces intraseasonal variability in the model. Convective evaporation processes in McRAS affect intraseasonal variability mainly through their time-mean effects and not through their variations. Convective rain evaporation and unsaturated downdrafts improve the modeled specific humidity and temperature climates of the Tropics and increase convection on the equator.

Intraseasonal variability in CCM3 with McRAS is not improved by increasing the boundary layer relative humidity threshold for initiation of convection, contrary to the results of Wang and Schlesinger. In fact, intraseasonal variability is reduced for higher thresholds. The largest intraseasonal moisture variations during a model Madden-Julian oscillation life cycle occur above the boundary layer, and humidity variations within the boundary layer are small.