Perturbed-parameter hindcasts of the MJO with CAM5

Description

The Madden-Julian Oscillation (MJO) is a dominant source of intraseasonal variability precipitation and is a subject of strong interest to ARM and ASR. In an attempt to understand and improve the typically poor simulations of MJO by climate models, we have performed perturbed-parameter hindcasts with the fifth version of the Community Atmosphere Model. Our hindcasts are initialized with analysis data for a 2009-2010 strong MJO event that is a focus of the Years Of Tropical Convection project, and they were performed as part of Cloud-Associated Parameterization Testbed. With Latin Hypercube sampling of 16 parameters contained in the parameterizations of shallow convection, deep convection and large-scale clouds from a predetermined range of their acceptable values, we have performed 500 hindcasts of 20-day length. The initial analysis suggests that the MJO could be improved through greater evaporation of deep convective precipitation and less efficient autoconversion of deep convective condensate to precipitation. The initial analyses also suggest that making deep convective plumes less dilute by lowering the lateral entrainment rate would degrade the MJO hindcasts from the default version of CAM5, which already performs respectably in hindcasts of MJO forecast indices, if not precipitation.