Towards an Optimal Configuration of Dynamics and Physics for GEFS v12

With successful implementation of FV3-GFS (GFS v15) on June 12, 2019, the FV3-based GEFS (FV3-GEFS, aka GEFS v12) is scheduled to be implemented in 2020. GEFS v12 is substantially different from GEFS v11 because of its new FV3 dynamical core. In addition, a couple of new stochastic physics schemes, namely SPPT (stochastic physics perturbed tendency) and SKEB (stochastic kinetic energy backscatter), are employed to replace original STTP (stochastic total tendency perturbation) scheme, and a more advanced GFDL 6-class microphysics scheme is adopted to replace original Zhao-Carr 3-class microphysics. Besides these additions, several other physical parameterizations have been updated including the convection and boundary layer schemes and the land-surface model, each contributing to further improvements in the model performance.

In this study, several experiments were carried out to test various dynamical and physics options, aiming to obtain an optimal configuration for the ensemble forecast system. Some sensitivity tests are also conducted to better understand the contributions from the stochastic physics scheme. The model results are evaluated in terms of anomaly correlation, RMSE/ensemble spread relationship, bias etc. As GEFS provides crucial model guidance for 5-7 day hurricane forecasts in support of the National Hurricane Center and other customers, model capability in predicting tropical cyclone track and intensity is also examined from the experiments.