CAM Heating Experiments and the Role of the Background Atmosphere in MJO Propagation

The Community Atmospheric Model 4.0 (CAM4) is used to study the propagation properties of the MJO. CAM4 is modified to accept additional heating that is allowed to interact with the model physics, thus simulating the two-way interaction between convection and the large-scale environment. When a spherical blob of bottom-heavy heating representing large-scale convection is inserted into the tropical Indian Ocean, it appears to excite several modes of synoptic variability. These modes manifest themselves most clearly in the moist static energy (MSE) anomalies. The same heating applied to a variety of background atmospheres can excite different responses: eastward propagation at MJO speeds, eastward propagation at Kelvin wave speeds, westward propagation, and, in some cases, no propagation. Investigation into the background atmospheres reveals a dry mid-troposphere that can realistically support MJO-like propagation. In this study, we further attempt to quantify the variables in an atmosphere that can allow convection to propagate eastward at MJO speeds. We also attempt to investigate what variables (moisture, temperature, winds, etc.) critically determine the difference between MJO and non-MJO convective evolution.