Diagnosing MJO and convection behaviour in SP-CAM and CAM simulation

A comparison of MJO and convection behaviour between standard-CAM and SP-CAM model simulation is carried out in this paper. In SP-CAM, a cloud system resolved model is used to replace the convective parameterization scheme in standard-CAM. A preliminary results with SP-CAM is that the poorly simulated MJO in CAM has been dramatically improved in SP-CAM.

The different behaviour of local convection and MJO related convection between two model simulations reveals that the following aspects of convection characteristics might contribute to the improvement of MJO simulation in SP-CAM over CAM: a steeply increasing function of precipitation relative to saturation fraction; the precipitation is solely related with an upper-troposphere moisture anomaly; stratiform heat profile associated with deep convection; positive co-relationship between precipitation and surface latent heat flux; associated with deep convection, a moisture re-charge and discharge, and also zonal wind transition.

Even though SP-CAM captures MJO frequency and wave number well, comparing to the observed MJO events there are still some physics are missing, such as destabilization by shallow cumulii, immediately dying effect of westly wind burst after the precipitation maximum and the asymmetry in terms of time for the charge and re-charge of instability.