Assessment of Extended-Range Prediction Capability Based on CMA-GEPS
This study assessed the extended-range prediction capability of the CMA-Global Ensemble Prediction System(CMA-GEPS).Using this system,we conducted 35-day ensemble prediction experiments and evaluated the forecast capability.Results showed that,at the geopotential height of 500hPa,the ACC skills of the extended-range ensemble prediction system were 9 days and 8.7 days in the northern and southern hemispheres,respectively.The ACC skills in the northern hemisphere exhibited a seasonal cycle with higher prediction skills in winter and lower skills in summer,reflecting the inherent atmospheric properties.Quantitative analysis of the spread-root mean square error(RMSE)skill relations revealed that the ensemble forecasting system was more predictive than deterministic prediction on the extended scale.The potential forecast days in the northern and southern hemispheres were 18 and 16 days,respectively.In terms of 2m temperature,CMA-GEPS effectively captured the spatial distribution characteristics of the temperature field on the extended period scale.Further analysis showed that prediction errors for 2m temperature mainly occurred in desert or plateau areas with significant thermal forcing effects.Additionally,CMA-GEPS demonstrated skillful forecasting of the Madden-Julian Oscillation(MJO)with a lead time of 15 days,outperforming other general circulation models.This suggested that CMA-GEPS has the potential to develop extended-range ensemble predictions further.Moreover,analyses revealed that the predicted intensity of MJO was weaker than the analyses,possibly due to a weak tropical convective system.The predicted propagation speed for the first 1-8 days was slightly faster,while the predicted propagation speed of the 9-35 days was slower compared to the analyses.CMA-GEPS effectively predicted the eastward and northward signals of MJO.Furthermore,the prediction of circulation signal propagation characteristics was better than that of convective signal,and MJO eastward propagation characteristics were better predicted than northward propagation.
CMA-GEPSextended-range weatherensemble predictionMJOassessment of prediction capability
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