DYNAMO MJO Events Simulated by a Coupled Atmosphere-Ocean-Wave Model: Sensitivity on Surface Fluxes

The Coupled Ocean-Atmosphere-Wave –Sediment Transport (COAWST) model is a fully coupled modeling system with the Weather Research and Forecasting (WRF) model as its atmosphere component, the Regional Ocean Modeling System (ROMS) as its ocean component, and the Simulating Wave Nearshore (SWAN) as its wave component. Both the October and November MJO event during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign are studied using the COAWST model. Results show that small variations in the sea surface skin temperatures, on the order of ~ 0.3 K, have a large impact on precipitation intensity in simulated MJO events. In this study, we focus on the sensible and latent heat fluxes at the ocean surface and their roles in simulated MJO precipitation features and their propagations across the Indian Ocean. Both model sensitivity tests and surface observations are used to understand feedbacks between convection and surface fluxes. Diurnal cycle of the SST and surface fluxes are also studied using both the COAWST model and the WRF model with imposed, idealized SST variations. The results show that the WRF model has much larger sensitivity to the absolute value of the sea surface skin temperature than to its diurnal variations in both the October and November MJO events. However, there are many differences in the way the simulated precipitation responds to changes of SST and to the imposed SST diurnal cycles. For example, the simulated eastward propagating wave signals are much weaker in the November case than in the October case, although the observations show similar strengths for both eastward and westward propagation signals embedded in the MJO precipitation envelop. Lastly, we will show how interactive wave simulations affect the simulated surface fluxes and the MJO precipitation structures.