Relationships Between Radiation, Clouds, and Convection During DYNAMO

The relationships among radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the MJO (DYNAMO) field campaign. Specifically, column-net, as well as, vertical profiles of radiative fields computed over Gan Island (0.69°S, 73.2°E) in the central Indian Ocean (IO) are used along with a variational constraint analyses of large-scale fields centered on this location to examine three MJO events which occurred during the 3 month period (October to December 2011) over this region. Analyses of these data show that the intraseasonal variation of column-net radiative heating lags column-net convective heating on the order of a few days and enhances the convective signal by 15-20%. However ratios of anomalous to anomalous greater than 30% during the November suppressed period suggest that conditions for radiative-convective instability were present and may have contributed to the rapid development of the November MJO. Time-height plots of longwave (LW) and shortwave (SW) radiation exhibit tilted structures with height, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase the radiative profiles become increasing top-heavy with showing progressively less cooling. Temporal variations in the cloud radiative forcing (CRF) component of are dominated by LW effects with an intraseasonal amplitude 0.4 K/day. While CRF effects are quite sensitive to changes in high cloudiness, the tilted radiative structures appear more related to water vapor effects.