New PP: Consolidation of COSMO ensemble (CONSENS)

1. Chiara Marsigli ARPA-SIM, Bologna, Italy New PP: Consolidation of COSMO ensemble (CONSENS)

2. Aim of the Project Consolidating the ensemble forecasting systems for the mesoscale built within COSMO in the past years • COSMO-LEPS and COSMO-SREPS have been designed for different forecast ranges (day 3-5 and 1-3, respectively) and with different perturbation strategies • The aim of the project is to build a unique “multi-perturbation-strategy” COSMO ensemble system, benefiting of perturbations able to produce appropriate spread for the entire forecast range (i.e., day 1-5)‏ • The ensemble should have a wide set of model perturbations to guarantee a good description of the COSMO model error • A calibration strategy should also be developed, to be applied to the ensemble output

3. Actions (I)‏ 1.COSMO-SREPS suite availability: COSMO-SREPS will be maintained as a system running regularly, also providing initial and boundary conditions to the COSMO-DE-EPS system 2.Model perturbations: Testing of perturbations of parameters of the COSMO model physics will be carried on, analysing also the impact of combining perturbations (positive impact?). It will be studied a methodology to perturb also the model lower boundary. This could be done by switching among fields obtained with different methodologies or by applying perturbations directly to the fields (define how!)‏ 3.Ensemble merging: Define the “multi-perturbation-strategy” to be used in the COSMO ensemble system, which perturbations appropriate for both the short and medium range (from day 1 to 5) -> comparison of the multi-model approach with the single-model ensemble or even multi-model ensemble ones for the different forecast ranges

4. Actions (II)‏ 4.Calibration: Development and testing of a calibration strategy for the high-resolution precipitation output. The reforecasts run by MeteoSwiss for the COSMO-LEPS system will be used for this action. Different methodologies should be compared: • CDF calibration using model climatology (following Fundel et al., 2008), which is the technique already applied by MeteoSwiss to COSMO-LEPS precipitation forecasts • standard bias correction as described in Hamill and Whitaker (2006)‏ • logistic regression • analog technique (Hamill and Whitaker, 2006)‏ collection of precipitation data on the whole domain is essential to perform a complete ensemble calibration

5. Links • Link with TIGGE-LAM and with the SRNWP Programme Interoperability as regards the possibility of nesting the COSMO model on other global models • Link with model development for getting new tunable parameters or meaningful combinations of the existing ones in the parametrisation schemes, or even for obtaining new alternative schemes • PP COLOBOC for obtaining reasonably perturbed lower boundary fields or techniques for perturbing them • COSMO-DE-EPS • PP KENDA

6. Main risks • Lack of Billing Units for running at ECMWF. Since a robust statistical analysis of the alternative options is needed in order to decide about the future ensemble set-up, it is necessary to run COSMO-SREPS for the whole period and parallel runs on some periods (already accounted for in the BU request)‏ • Difficulty of calibrating high-resolution precipitation forecasts. Most of the works found in literature deal with lower resolution systems. Furthermore, a dense and homogeneous precipitation network providing data over a very long period is needed for calibration and it seems difficult to obtain this over the whole COSMO ensemble area

7. People and FTEs • 2-year Project • Estimated resources needed in total: 5.0 FTEs • Estimated resources needed for 2009: 2.45 FTEs • Estimated resources needed for 2010: 2.55 FTEs • Institution/People involved: • ARPA-SIM (Cesari, Diomede, Marsigli, Montani: 3.4 FTE)‏ • HNMS (Gofa, Louka: 1.4 FTE)‏ • MeteoSwiss (Fundel: 0.2 FTE)‏