Intrinsic Limit of Atmospheric Predictability for Mid-Latitude Jet/front Systems

            Atmospheric predictability can be intrinsically limited due to rapid upscale growth of small and unresolvable initial errors.  Using a regional idealized model, Zhang et al. proposed a three-stage conceptual model that describes the upscale error growth dynamics within the moist baroclinic waves. In their convection-permitting experiments, error starting from small random noise grows upscale and contaminates the large-scale forecast after a relative short period (36 h simulation).  

            This study aims to further extend Zhang et al. by examining the intrinsic predictability limit of the mid-latitude jet/front systems using the European Centre for Medium-Range Weather Forecasts (ECMWF) state-of-the-art ensemble. The detailed evolution of the perturbation kinetic energy in the ensemble is investigated, to see how closely it resembles the three-stage error model of Zhang et al. in short term. It is found that after two days the intrinsic error, evolved from two simulations with the same initial condition yet different resolutions (16km and 9km), is comparable with operational 12h forecast error, which is consistent with Zhang et al. The saturation time of the perturbation kinetic energy will also be examined closely and compared with what is expected from the turbulent models. Moreover, utilizing the global ensembles, the potential connections between the mid-latitudes and the tropics will also be investigated.

 

Zhang, F., N. Bei, R. Rotunno, C. Snyder, and C. C. Epifanio, 2007: Mesoscale Predictability of Moist Baroclinic Waves: Convection-Permitting Experiments and Multistage Error Growth Dynamics. Journal of the Atmospheric Sciences, 64, 3579-3594.