Experimental Dynamical Forecast of an MJO Event Observed during TOGA-COARE Period

Abstract

With a hybrid atmosphere-ocean coupled model we carried out an experimental forecast of a well documented Madden-Julian Oscillation (MJO) event that was observed during the period of Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). The observed event, orig- inated in the western Indian Ocean around 6 January 1993, moved eastward with a phase speed of about 6.2 m s −1 and reached the dateline around February 1. The hybrid coupled model reasonably forecasts the MJO initiation in the western Indian Ocean, but the predicted MJO event propagates too slow (~ 4.4 m s −1 ). Results from previous observational studies using unprecedented humidity profiles obtained by NASA Aqua/AIRS satellite sugg- ested that two potential physical processes may be responsible for this model caveat. After improving the cumulus parameterization scheme based on the observa- tions, the model is able to forecast the same event one month ahead. Further sensitivity experiment confirms that the speed-up of model MJO propagation is primarily due to the improved convective scheme. Further, air-sea coupling plays an important role in maintaining the intensity of the predicted MJO. The results here suggest that MJO prediction skill is sensitive to model cumulus