Large-scale transients in tropical convection with zonally symmetric SST distributions

The super-parameterized Community Atmosphere Model (SPCAM) is used to investigate the roles of various processes in producing large-scale transients of tropical convection on an aquaplanet with zonally symmetric sea surface temperature (SST) distributions. It is found that the red noise background in the spectra of tropical convection owes its existence to the relatively long (1-2 days) memory in column integrated moist static energy (MSE) anomalies and to the stirring by extratropical eddies and internal noise, in particular advection across meridional moisture gradient. When run in a setting similar to the simple linear model of Andersen and Kuang (2008), the tropical spectra from SPCAM are dominated by convectively coupled equatorial waves (CCEWs), in ways generally consistent with results from the simple model of Andersen and Kuang (2008), and there are no red noise background spectra. When a source of column-integrated MSE proportional to the local precipitation is added to the simple setting of Andersen and Kuang (2008), representing either reduced radiative cooling or enhanced surface latent/sensible heat fluxes, a planetary scale stationary mode emerges in both the simple model and in SPCAM. It is hoped that through these and additional idealized studies, the various mechanisms by which tropical modes can arise and the conditions in which the different mechanisms operate can be elucidated, providing a foundation for understanding tropical transients in the real atmosphere.