The goal of work package 3 (WP3), “Ensemble Generation” of objective C3 “Optimizing regional ensembles” is to produce a comprehensive set of dynamically downscaled regional decadal hindcast simulations from which recommendations for the optimum operational ensemble can be derived. For this purpose, the already existing ensemble from the first phase of MiKlip will be enlarged by new simulations with higher resolution (0.22° and 0.0625°) as well as by simulations with a different land surface scheme and perturbed physics. The simulations will be performed with the regional climate model (RCM) COSMO-CLM (CCLM). They will focus on the EURO CORDEX region (see Fig. 1) and cover the decades 1961 – 2015. The full MiKlip hindcast period from 1960 onward will be considered in order to account for inter-decadal variability and to assess the robustness of our analyses. The final result will be a robust and reliable moderate size ensemble for the operational system fulfilling a balance between scientific (reliability, accuracy) and practical (computational costs) criteria and proven added value compared to the global predictions. The work will be shared between IMK-TRO/KIT and the German Weather Service ( DWD).
The work package C3-WP3 is subdivided into five sub-tasks
Task C3-3.1: Generation of the basic regional hindcast ensemble
Extend the existing decadal ensembles a) by downscaling the MPI-ESM decadal hindcasts for an extended ensemble at a horizontal grid spacing of 0.22° (initial conditions perturbation) to analyse the impact of inter-decadal variability on the ensemble metrics, and b) by using advanced perturbed physics methods based on those developed in MiKlip I, in order to achieve a balanced spread.
Task C3-3.2: Provide ensemble members at high resolution
For selected decades and realizations high-resolution simulations at 0.0625° will be performed, followed by an analysis of the added value of the higher resolution and the impact on the ensemble metrics, especially for high/low quantiles.
Task C3-3.3: Provide ensemble members using a different SVAT and/or coupled ocean
In cooperation with the work package C1-WP2, “Soil vegetation processes”, simulations using the soil-vegetation-atmosphere transfer scheme (SVAT) Veg3d instead of the standard scheme TERRA will be performed for selected decades and realizations. Furthermore, coupled ocean simulations provided by C1-WP, “Regional ocean coupling”, will be integrated in the ensemble. The impact of the additional members on the ensemble metrics, especially for high/low quantiles, will be analysed.
Task C3-3.4: Very high-resolution simulations
Depending on the overall progress of this work package and the available computing power, very high-resolution simulations (0.0025°) will be carried out for a selected subregion of Central Europe, and their added value will be assessed.
Task C3-3.5: Overall ensemble assessment, analysis and optimization
This is the synthesis task of work package C3-WP3. The various ensemble compositions are analyzed over several decades to assess the inter-decadal and intra-ensemble variability in terms of ensemble size and quality criteria and. The aim is to derive recommendations for an optimum ensemble size and composition taking into account also technical and computing efficiency issues. This work will be done in cooperation with work packages C3-WP1, “Post-processing”, and C3-WP2, “Optimized ensemble characteristics”.
The CCLM model has been implemented and thoroughly tested on the new supercomputer “MISTRAL” at Deutsches Klimarechenzentrum (DKRZ). A comparison of recent results, achieved during the first phase of MiKlip and on the old computing system “BLIZZARD” at DKRZ, with those from the new machine showed a negligible impact of the new computing system on the results. This has been demonstrated by a repetition of previous ERA-Interim driven reference simulations performed during MiKlip I. Fig. 2 compares the mean annual cycles of mean monthly temperature at 2 m height and of mean monthly precipitation sum for the sub-region Mid-Europe (ME). Red lines depict the results from MiKlip I achieved on BLIZZARD, blue lines those of the simulation on MISTRAL. Also a comparison with observations, here E-OBS Version 11, did not reveal noteworthy changes, as shown in Fig. 3.
The existing members of the MiKlip II MPI-ESM-HR preop hindcast ensemble have been downscaled with CCLM for the starting years 1960 – 2016 as well as the decadal forecast 2017. In addition, the necessary reference simulations (ERA-driven and un-initialized MPI-ESM-HR driven) have been provided as well. A preliminary analysis showed comparable skill to baseline1 for most variables. The ensemble generation will be continued in line with the global hindcast system.
Karlsruher Institut für Technologie (KIT), Institut für Meteorologie und Klimaforschung – Bereich Troposphäre (IMK-TRO)
Dr. Hans-Jürgen Panitz
+49 (0)721 608 22802
Deutscher Wetterdienst - Klima- und Umweltberatung
Dr. Barbara Früh
+49 (0)69 8062-2968