Prediction skill of the Madden and Julian Oscillation in dynamical extended range forecasts

The Madden and Julian Oscillation (MJO) is the most prominent mode of intra seasonal variations in the tropical region. It plays an important role in c limate variability and has a significant influence on medium-to-extended ra nges weather forecasting in the tropics. This study examines the forecast s kill of the oscillation in a set of recent dynamical extended range forecas ts (DERF) experiments performed by the National Centers for Environmental P rediction (NCEP). The present DERF experiments were done with the reanalysi s version of the medium range forecast (MRF) model and include 50-day forec asts, initialized once-a-day (0Z) with reanalyses fields, for the period be tween 1 January, 1985, and 31 December, 1989. The MRF model shows large mea n errors in representing intraseasonal variations of the large-scale circul ation, especially over the equatorial eastern Pacific Ocean. A diagnostic a nalysis has considered the different phases of the MJO and the associated f orecast skill of the MRF model. Anomaly correlations on the order of 0.3 to 0.4 indicate that skillful forecasts extend out to 5 to 7 days lead-time. Furthermore, the results show a slight increase in the forecast skill for p eriods when convective anomalies associated with the MJO ate intense. By re moving the mean errors, the analysis shows systematic errors in the represe ntation of the MJO with weaker than observed upper level zonal circulations . The examination of the climate run of the MRF model shows the existence o f an intraseasonal oscillation, although less intense (50-70%) and with fas ter (nearly twice as fast) eastward propagation than the observed MJO. The results indicate that the MRF model likely has difficulty maintaining the M JO, which impacts its forecast. A discussion of future work to improve the representation of the MJO in dynamical models and assess its prediction is presented.