Investigating the Dual-MJO Events of November 2011 in 30-Day Regional COAMPS Simulations. Part II: Surface Fluxes and Moisture Convergence

The dual MJO events of November 2011 are simulated in 30-day regional coupled COAMPS-NCOM forecasts, using NAVGEM forecasts for lateral boundary conditions (BCs). Earlier results demonstrated the need for ocean coupling in the NAVGEM forecasts in order to obtain accurate BCs for the COAMPS runs. COAMPS produces a skillful forecast for both MJO waves when using BCs from the skillful, coupled NAVGEM-HYCOM. However, even when using poor BCs from NAVGEM with fixed SSTs, COAMPS is able to correctly predict the onset of the second MJO (hereafter MJO2) in late November.

New results indicate that MJO1 excites a westward-propagating atmospheric Rossby wave over the Maritime Continent. This Rossby wave eventually contributes to the development of MJO2 over the western Indian Ocean. We hypothesize that the fact that the Rossby wave develops and propagates entirely within the COAMPS domain, and is well-predicted in COAMPS, adds skill to the forecast, even when using the lower-skill BCs.

While the COAMPS forecast performs well in predicting the timing and location of MJO2, the magnitude of the MJO is strong biased. We investigate the role of surface heat fluxes, radiation, and the horizontal and vertical advection of moisture in the initiation of MJO2, and how errors in each of these fields may contribute to this bias.