The Madden-Julian oscillation (MJO) is the leading source of global subseasonal predictability; however, many dynamical forecasting systems struggle to predict MJO propagation through the Maritime Continent. Better understanding the biases in simulated physical processes associated with MJO propagation is the key to improve MJO prediction. In this study, MJO prediction skill, propagation processes, and mean state biases are evaluated in reforecasts from models participating in the Subseasonal Experiment (SubX) and Subseasonal to Seasonal (S2S) prediction projects. SubX and S2S reforecasts show MJO prediction skill out to 4.5 weeks based on the Real-time Multivariate MJO index consistent with previous studies. However, a closer examination of these models' representation of MJO propagation through the Maritime Continent reveals that they fail to predict the MJO convection, associated circulations, and moisture advection processes beyond 10 days with most of models underestimating MJO amplitude. The biases in the MJO propagation can be partly associated with the following mean biases across the Indo-Pacific: a drier low troposphere, excess surface precipitation, more frequent occurrence of light precipitation rates, and a transition to stronger precipitation rates at lower humidity than in observations. This indicates that deep convection occurs too frequently in models and is not sufficiently inhibited when tropospheric moisture is low, which is likely due to the representation of entrainment.
Bibliographical noteFunding Information:
Constructive and valuable comments from three anonymous reviewers are greatly appreciated. H. K. was supported by NSF Grant AGS-1652289, NOAA Grant NA16OAR4310070, and the KMA R&D Program Grant KMI2018-03110. GloSea5 reforecast was provided by Dr. Myong-In Lee from UNIST. M. J. and the generation of the Navy-ESPC forecasts were supported by the Office of Naval Research and N2N6E through the Navy Earth System Prediction Capability Effort, and the Chief of Naval Research through the NRL Base Program (PE 0601153N). Navy-ESPC forecasts were performed as part of the NMME-SubX experiment funded by the NOAA-Modeling, Analysis, Predictions, and Projections (MAPP) Program (NOAA-OAR-CPO-2016-2004413). Computational resources were supported in part by a grant of time from the High-Performance Computing Modernization Program, and the Navy-ESPC forecasts were integrated at the Navy Department of Defense Supercomputing Resource Center, Stennis Space Center, Mississippi. The sources of data used in this study are as follows: http://cola.gmu.edu/kpegion/subx/ for SubX reforecasts, http://s2sprediction.net/ for S2S reforecasts, and http://apps.ecmwf.int/datasets/data/interim-full-daily for ERA-Interim.
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