Forecast Skill of Madden-Julian Oscillation Events in a Global Nonhydrostatic Model during the CINDY2011/DYNAMO Observation Period

抄録

Near real-time week-long forecasts of Madden-Julian Oscillation (MJO) events using a regionally stretched global nonhydrostatic model were executed for the intensive observation period of the Cooperative Indian Ocean experiment on intraseasonal variability in the year 2011 (CINDY2011)/Dynamics of the Madden-Julian Oscillation (DYNAMO) field program. Forecast skill was validated using a real-time multivariate MJO (RMM) index and the forecast skill scores. The scores indicated a dependency on the initial MJO amplitude and phase. The errors were smaller in forecasts initialized in the active period of the MJO. A tendency for over-amplification (under-amplification) in forecasts initialized at phases 2-6 (7-8, 1) and earlier (delayed) phase propagation in the forecasts initialized at phases 1-3 (5-6) was identified. This was related to systematic positive biases in RMM1 and RMM2. The RMM1 error dominated in wind fields without significant contributions from convection. The RMM2 error grew in both convection and wind anomalies after the 5-day lead time, causing reduction in the MJO skill score. These results suggest that improvement in the basic model fields, i.e., large-scale circulations and a link between convection and dynamics, should extend the predictability of MJO in this framework.