On the Importance of Air-Sea Coupling in Extended-Range Mesoscale Simulations of the Madden-Julian Oscillation and Tropical Cyclone 05

Three extended-range mesoscale simulations of the Madden-Julian Oscillation (MJO) and Tropical Cyclone 05 (TC05) that occurred in November 2011 during the DYNAMO/CINDY period are conducted and examined using the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS^®1) without the benefit of data assimilation. Three simulations are distinguished by using persistent SST, daily observed SST, and operating in a two-way coupled interactive mode using the Navy’s Coastal Ocean Model (NCOM). Evaluation of the model results shows that the persistent SST has a small impact on precipitation and wind biases for first 15 days, but a substantial impact for the second 15-day period. The observed SST reduces biases over the persistent SST, and two-way coupling reduces biases even further, indicating diurnal cycle of SST in two-way coupling is important in enhancing surface heat fluxes contributing to the buildup of the active phase of the MJO. The MJO is simulated starting 20 days into integration with observed SST and two-way coupling, but not with persistent SST. Only the two-way coupled model captures the two Kelvin waves and their interaction with TC05. The horizontal wind shear between the near-equatorial westerly and strong easterly around 10^oN are found to enhance the TC05 vortex, which the Kelvin waves increase the potential vorticity and further intensify the TC05 vortex.