Air-Sea Interaction and Moist Static Energy Budget in COAMPS Extended-Range Simulations during DYNAMO

COAMPS®1 extended-range simulations are performed for the two-month period of the Dynamics of the Madden Julian Oscillation (DYNAMO) field campaign to investigate the impact of air-sea interaction and energy transfer processes on initiation and propagation of MJO. Numerical experiments include: i) uncoupled runs with fixed SST, ii) SST that is updated daily with analyses, and iii) fully interactive two-way coupled simulations. Experiments are performed at 45-km and 27-km horizontal resolution. Results indicate that the 27-km coupled simulation provides the best representation of convectively-coupled Kelvin waves and the propagation of the MJO over the Maritime continent and into the western Pacific by comparing to all the other runs. They also show that the bias becomes relatively smaller than the biases from the other runs with increased lead time.

The 27-km coupled simulation has the strongest coherence between the column-integrated moist static energy (MSE), latent heat release and the initiation and propagation of MJO. The time tendency of MSE increases to a maximum before the active phase of the MJO and subsequently decreases during and after the MJO. Diagnostics show horizontal advection of MSE anomalies enhances the moistening processes prior to the peak in MJO actively, accompanied with increased vertical advection. The MSE heat source is able to maintain the convection during the MJO by positive anomalies. Results from fixed SST show that the lack of MJO initiation is due to a small increase in the MSE tendency prior to the MJO. The experiment that use daily observed SST showed improved MSE buildup than that use fixed SST. However, the phase between precipitation and MSE tendency is offset, which may be attributed to the lack of SST diurnal variability. The coupled simulations have better phasing, especially for 27-km case, which shows the best phase coherence among all the simulations.

1The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) is a registered trademark of the Naval Research laboratory.