Heating in the tropical atmosphere: what level of detail is critical for accurate MJO simulations in GCMs?

Abstract

Dozens of studies have been done in recent years documenting factors in large-scale models that affect the simulation of the Madden–Julian oscillation (MJO). All of these studies discuss processes that affect heating in some facet. In this study, we examine various heating adjustments in Community Atmospheric Model version 4 (CAM4) to determine what the vertical and horizontal heating distributions need to look like in order to simulate a realistic MJO. Heating is added to CAM4 using two different methods. In the first method, we add top-, bottom-, or middle-heavy heating blobs at various locations for each phase of the MJO. We describe a new technique for adding these heating perturbations in CAM4. In the second method, we add observed latent heating profiles from the tropical rainfall measuring mission Precipitation Radar to CAM4 in order to more accurately depict both the horizontal and vertical distribution of heating throughout the Tropics. We find that a realistic vertical and horizontal distribution of heating is critical for accurate representation of the MJO in CAM4. Observed heating distributions are top-heavy, but merely putting idealized top-heavy heating blobs into CAM4 does not produce an MJO as realistic as inputting the observed spatial distributions. Improvements in the simulation of the MJO are also seen with an interactive ocean, but the improvements are not as large as those seen using realistic heating distributions and prescribed SSTs.