Evaluation of the Added Value of Regional Ensemble Forecasts on Global Ensemble Forecasts

Abstract

The regional single-model-based Aire Limité e Adaptation Dynamique Dé veloppement InternationalLimited Area Ensemble Forecasting (ALADIN-LAEF) ensemble prediction system (EPS) is evaluated and compared with the global ECMWF-EPS to investigate the added value of regional to global EPS models. ALADIN-LAEF consists of 16 perturbed members at 18-km horizontal resolution, while ECMWF-EPS includes 50 perturbed members at 50-km horizontal resolution. In ALADIN-LAEF, the atmospheric initial condition uncertainty is quantified by using blending, which combines large-scale uncertainty generated by the ECMWF-EPS singular-vector approach with small-scale perturbations resolved by the ALADIN breeding technique. The surface initial condition perturbations are generated by use of the noncycling surface breeding (NCSB) technique, and different physics schemes are employed for different forecast members to account for model uncertainties. The verification and comparison have been carried out for a 2-month period during summer 2007 over central Europe. The results show a quite favorable level of performance for ALADIN-LAEF compared to ECMWF-EPS for surface weather variables. ALADIN-LAEF adds more value to precipitation forecasts and has greater skill for 10-m wind and mean sea level pressure results than does ECMWF-EPS. For 2-m temperature, ALADIN-LAEF forecasts have larger spread, are statistically more consistent, but also have less skill than ECMWF-EPS due to the strong cold bias in the ALADIN forecasts. For the upper-air weather parameters, the forecast of ALADIN-LAEF has a larger spread, but the forecast skill of ALADIN-LAEF is from neutral to slightly inferior compared to ECMWF-EPS. It may be concluded that a regional single-model-based EPS with fewer ensemble members could provide more added value in terms of greater skill for near-surface weather variables than the global EPS with larger ensemble size, whereas it may have limitations when applied to upper-air weather variables.

On the forecast skill of a convection-permitting ensemble

“…Wang et al (2012) demonstrated the added value of ALADIN-LAEF as a regional mesoscale EPS to the global ECMWF-EPS (European Centre for Medium-Range Weather Forecasts). Hence, the present study extends this research by addressing the step between regional mesoscale and CP ensembles.…”

27 Years of Regional Cooperation for Limited Area Modelling in Central Europe

“…The mesoscale ensemble prediction system ALADIN-LAEF has been in development since 2008 (Wang et al 2011). It provides a reliable short-range probabilistic forecast for members and probabilistic information for downstream applications such as civil warnings, hydrology, transportation, and the energy industry.…”

“…A strategy for perturbing surface ICs in a regional EPS, called noncycling surface breeding (NCSB), was proposed by Wang et al (2010). It uses short-range surface forecasts driven by perturbed atmospheric forcing.…”

“…Wang et al (2012) concluded that a regional single-model-based ensemble with fewer members could have better skill scores for screenlevel weather variables than the global EPS with a larger ensemble size, whereas it may have limitations when applied to upper-air weather variables. The performance of ALADIN-LAEF was also compared to other regional ensembles during the Beijing 2008 Olympic Summer Games and the Sochi 2014 Olympic and Paralympic Winter Games in the framework of the WMO research demonstration projects (Duan et al 2012;Kiktev et al 2017).…”

Towards an integrated probabilistic nowcasting system (En-INCA)

“…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). For En-INCA, the INCA blending algorithm is applied to all 17 members of the LAEF system individually.…”