A New Method for Generating Initial Condition Perturbations in a Regional Ensemble Prediction System: Blending

Abstract

A blending method for generating initial condition (IC) perturbations in a regional ensemble prediction system is proposed. The blending is to combine the large-scale IC perturbations from a global ensemble prediction system (EPS) with the small-scale IC perturbations from a regional EPS by using a digital filter and the spectral analysis technique. The IC perturbations generated by blending can well represent both largescale and small-scale uncertainties in the analysis, and are more consistent with the lateral boundary condition (LBC) perturbations provided by global EPS. The blending method is implemented in the regional ensemble system Aire Limit ee Adaptation Dynamique D eveloppement International-Limited Area Ensemble Forecasting (ALADIN-LAEF), in which the large-scale IC perturbations are provided by the European Centre for Medium-Range Weather Forecasts (ECMWF-EPS), and the small-scale IC perturbations are generated by breeding in ALADIN-LAEF. Blending is compared with dynamical downscaling and breeding over a 2-month period in summer 2007. The comparison clearly shows impact on the growth of forecast spread if the regional IC perturbations are not consistent with the perturbations coming through LBC provided by the global EPS. Blending can cure the problem largely, and it performs better than dynamical downscaling and breeding.

Practical and Intrinsic Predictability of a Warm‐Sector Torrential Rainfall Event in the South China Monsoon Region

“…The accurate prediction of CI is a problem that is highly sensitive to the interactions between the surface and free atmosphere that occur within the PBL (Stensrud, ). Previous mesoscale studies have also shown that low‐level jet, land‐sea breeze, mountain‐valley wind, and terrain effects within the PBL play important roles in the occurrence of warm‐sector heavy rainfall (Wang, Luo, et al, ; Wu & Luo, ; Wu et al, ). Thus, the practical predictability analysis of warm‐sector torrential rainfall in this section focuses mainly on the uncertainties in the PBL.…”

A Comparison of ETKF and Downscaling in a Regional Ensemble Prediction System

“…Although the above results are mixed, these comparisons may shed some light on further improvement in present system. A practical way to take advantages of both ensemble perturbations is developing a blending technique, which has been primarily investigated by Caron [33] and Wang et al [34]. This technique can obtain blended perturbations that contain large-scale component from downscaling perturbations and small-scale component from ETKF perturbations.…”

Towards an integrated probabilistic nowcasting system (En-INCA)

“…But the INCA system is also able to improve the pure NWP forecasts up to +48 h using topographical downscaling and error correction (through a rather The second component of En-INCA is ALADIN-LAEF, the limited area ensemble forecasting system developed at ZAMG in cooperation with LACE members. The latest ensemble specifications are summarized in Table 1, the overall method is described in detail in Wang et al (2011), and some of its components in Wang et al (2010Wang et al ( , 2014. A comprehensive validation of LAEF compared to a global ensemble prediction system is given by Wang et al (2012).…”

“…Focusing on regional and local patterns one can see considerable differences in frost probabilities, especially in the southern and eastern low lying areas of Austria, in the Waldviertel as well as in the far West of Austria (marked with colored polygons). Wang et al, 2014) In order to show the added value of En-INCA during the nowcasting period, Fig. 3c shows the INCA analysis of 2 m temperature for 31 December 2012, 05:00 UTC.…”