The role of tilted heating in the evolution of the MJO

There has been much discussion about the role of tilted heating in the evolution of the MJO. It is believed that the inability of many general circulation models to produce a robust MJO is directly related to deficiencies in the model-produced tropical heating distributions. Given the MJO’s importance in tropical climate, we need to better understand what heating distributions are required in climate models to produce strong MJOs. This study addresses the role of tilted heating in the Community Atmospheric Model version 4 (CAM4). Idealized and observed heating distributions are added to the tropical atmosphere in CAM4. These include heating that tilts westward with height in the lower and upper atmosphere, as well as various tilted and untilted heating in the form of either idealized blobs or observations derived from the Tropical Rainfall Measuring Mission Precipitation Radar and the International Satellite Cloud Climatology Project. We find that low-level heating ahead of the MJO convective center is critical for the initial strengthening and later maintenance of the MJO. However, tilted heating is not necessary to simulate a realistic MJO. In addition, excess upper level heating, whether tilted or not, appears to degrade the MJO signal, although Rossby wave modes are evident only in runs with additional upper level heating. Kelvin waves are evident during strong MJOs for all simulations but are only visible over the central Pacific. Results suggest that accurate shallow convective parameterizations may be more important than deep convective ones in the evolution of the MJO.