Bogdan Rosa , Damian K. Wójcik, Michał Z. Ziemiański

1. Progress on new dynamical core of COSMO PP "COSMO-EULAG operationalization (CELO) Bogdan Rosa, Damian K. Wójcik, Michał Z. Ziemiański Institute of Meteorology and Water Management National Research Institute Warsaw, Poland Podleśna, 61 Email: bogdan.rosa@imgw.pl COSMO General Meeting, 11 – 14 September 2017, Jerusalem, Israel

2. Overview of project tasks Task 1: Integration of EULAG DC with COSMO framework The EULAG model has been successfully coupled to the COSMO framework from technical point of view. Coupling of the EULAG DC code with fully implemented ICON physics parameterizations will be performed in the framework of Task 5 of the project (postponed - due to unavailability of the official implementation of COSMO with ICON parameterizations). The task aimed at investigation and implementation of the strategy regarding lowest level of EULAG dynamical core on the surface will be carried out within COSMO Priority Project EX-CELO (In current implementation there is no additional surface layer). Task 2: Consolidation and optimization of the EULAG DC formulation This task has been completed. Task 3: Eulag DC code restructuring and engineering The remaining task, namely, implementation of a basic restart subroutine in the CE has been postponed for the next COSMO year (11.2017 - 03.2018). 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

3. Overview of project tasks • Task 4: Optimization and testing of COSMO with EULAG DC • Efforts aimed at tuning of the current COSMO-EULAG model have been already initiated. • Once the COSMO-EULAG with fully implemented ICON physics is available (Task 5) optimization and testing of the model will be performed. Task 5: Integration and consolidation of the EULAG compressible DC with COSMO framework • Implementation of ICON physics parameterizations to COSMO-EULAG (currently postponed). Our recent efforts have been focused on removing an observed pressure bias (successful). 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

4. Diagnosis of problem related to the pressure bias development Semi-realistic simulations using COSMO Runge-Kutta (RK) and compressible COSMO-EULAG (CE) were performed to diagnose for the problem of pressure bias development. Configuration: • Turbulence parameterization is turned on • Moist microphysics and saturation adjustment are turned off • Soil (sea) processes are turned off • Water vapour enters buoyancy and there are no sources / sinks of water vapour • dt = 15 s Computational domain: • Bay of Biscay (flat) • dx = 2.2 km Test case: • 15 November 2013 (Azoren High) Figures in following slides show time evolution of horizontally averaged pressure perturbations. The perturbations are calculated with respect to the time-evolving pressure from the driving COSMO-7 simulation.

5. Semi-realistic simulations: results without absorber for pressure RK CE Disabling the pressure absorber in RK results in the development of a pressure bias similar to that observed in CE results. Semi-realistic simulations: results with absorber for pressure CE RK Pressure bias is tremendously reduced in simulations with pressure absorber Pa Pa 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

6. Verification of CE forecasts computed for Nov 2013 (24h forecast) • Verification of the CE forecast concerns the whole month – November 2013 • Realistic simulations were performed for each day separately (24h forecast) • Horizontal step of the computational mesh is 2.2 km • Domain corresponds to the standard operational COSMO-2 domain of Meteo-Swiss. • The simulations were performed using both CE and RK – for comparison • Sensitivity of the results to different values of mixing length (150m and 500m), vertical smoothing factor for explicit vertical diffusion (wichfakt) and diffusion coefficient for momentum (tkmmin) is also analyzed Topographical map of the domain Station network for surface verification 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

7. Experiment settings Dynamics: • In Cosmo Runge-Kutta setup moist quantities are advected using the „Bott2Strang” scheme • In Cosmo-Eulag setup moist quantities are advected using the MPDATA A scheme • For Cosmo Runge-Kutta irunge_kutta=1 and itype_fast_waves=2 • dt = 10 s (RK), dt = 10 s (CE) • Numerical and Smagorinsky diffusion are turned off for Cosmo-Eulag and on for Cosmo Runge-Kutta • Microphysics: • Standard one-moment COSMO microphysics parameterization including ice, rain, snow and graupel precipitation (igsp=4) • Radiation: • Calculated every 6 minutes • Topographical corrections to radiation are turned off (lradtopo=F) Turbulence and convection scheme : • Default turbulence setup for high-resolution NWP (itype_turb=3, limpltkediff=T) • Shallow convection parameterization is turned off (lconv=F) Soil model: • Multi-layer soil model is used (lsoil= T,lmulti_layer=T, lforest=T) 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

8. Pressure (hPa) – forecast verification with pressure absorber RK CE wichfakt = 0.5 tkmmin= 0 <|RMSE|> = 1.122 <|ME|> = 0.160 <|RMSE|> = 1.123 <|ME|> = 0.164 CE RK wichfakt = 0 tkmmin= 0.4 <|RMSE|> = 1.112 <|ME|> = 0.155 <|RMSE|> = 1.122 <|ME|> = 0.162 Mean error is relatively small for both CE and RK. Before 18:00 simulations performed with RK are slightly more in line with observations than those performed with CE. After 18:00, the forecast computed using CE is in better agreement with observations. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

9. Horizontal wind (m/s) at 10 m (with pressure absorber) Before pressure correction With pressure absorber CE wichfakt = 0.5 tkmmin= 0 CE RK <|RMSE|> = 2.192 <|ME|> = 0.158 <|RMSE|> = 2.225 <|ME|> = 0.212 <|RMSE|> = 2.226 <|ME|> = 0.213 RK CE wichfakt = 0 tkmmin= 0.4 CE <|RMSE|> = 2.186 <|ME|> = 0.158 <|RMSE|> = 2.223 <|ME|> = 0.210 <|RMSE|> = 2.222 <|ME|> = 0.214 Little effect of pressure absorber on horizontal wind. Pressure absorber makes CE results more closer to both RK results and observations. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

10. Temperature at 2 m – forecast verification with pressure absorber RK CE wichfakt = 0.5 tkmmin= 0 <|RMSE|> = 2.238 <|ME|> = 0.902 <|RMSE|> = 2.174 <|ME|> = 0.656 CE RK wichfakt = 0 tkmmin= 0.4 <|RMSE|> = 2.213 <|ME|> = 0.875 <|RMSE|> = 2.165 <|ME|> = 0.643 Results computed using CE are closer to observations than those computed with RK. No effectresulting from differentvalues of parameterswichfakt and tkmmin. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

11. Dew point temperature at 2 m – verification with pressure absorber RK CE wichfakt = 0.5 tkmmin= 0 <|RMSE|> = 2.639 <|ME|> = 0.884 <|RMSE|> = 2.664 <|ME|> = 0.856 CE RK wichfakt = 0 tkmmin= 0.4 <|RMSE|> = 2.628 <|ME|> = 0.875 <|RMSE|> = 2.644 <|ME|> = 0.850 Results from both models are in good quantitative agreement. Low sensitivity to different settings of vertical smoothing factor and minimal diffusion coefficients. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

12. Precipitation – forecast verification (wichfakt = 0.5, tkmmin= 0) RK CE Probability of Detection Probability of Detection RK CE Probability of Detection Probability of Detection Success Ratio Success Ratio Numerical results computed using CE and RK (with pressure absorber) are in good quantitative agreement. The differences are in the range of statistical uncertainty. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

13. Precipitation cntd. – forecast verification (wichfakt = 0.5, tkmmin= 0) RK CE Probability of Detection Probability of Detection RK CE Probability of Detection Probability of Detection Success Ratio Success Ratio Also for larger precipitation the differences are in the range of statistical uncertainty. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

14. Conclusions • Problem related to pressure bias development has been diagnosed and solved by employing linear absorber at the lateral boundary condition • Verification of 24h forecast for the whole month (Nov. 2013) was performed. • We compared horizontal wind, temperature, dew point temperature, pressure and precipitation both with observations and numerical results obtained from simulations performed with RK dynamical core • There is overestimation of surface wind in CE. It may be related to different implicit diffusion of CE dynamical core and may need a dedicated tuning. • Temperature at (2m) computed using CE is closer to observations than temperature computed with RK DC. • Dew point temperature and precipitation computed using both models are in good quantitative agreement and weakly sensitive to different settings of vertical smoothing factor and minimal diffusion coefficients. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

15. Modeling of Alpine convection from the 19 July 2013 • Here we present results of simulations of Alpine convection performed with the new CE model (the most recent version with pressure absorber) • The simulations have been performed using four one-way nested domains having the horizontal grid size of 2.2, 1.1, 0.55 and 0.28 km • The simulations are compared with benchmark simulations of COSMO-Runge-Kutta with grid sizes of 2.2 and 1.1 km and satellite data 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

16. Realistic prognostic simulations of convective Alpine weather Computational domains employed in this study. The left panel shows domain corresponding to 2.2 km grid resolution. Analogously, the right panel - domain with finer grid resolution i.e. 0.55 km. The four black markers (dots) in the right panel indicate corners of the averaging area for statistics. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

17. Cloudcover Cloud cover (grayscale) derived from the albedo product of the HRV channel of Meteosat and underlying topographic map (brown to copper colors). Distribution of cloud cover (grayscale) from numerical simulations with 2 different models RK (top) and CE (bottom) at grid resolution 2.2 km. The cloud cover was evaluated based on the total liquid and ice water products of the COSMO framework. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

18. Cloud cover – results from numerical simulations Cloud cover (grayscale) at 15 UTC derived from simulation results of RK and CE. Different panels correspond to different grid resolution i.e. 1.1, 0.55 and 0.28 km. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

19. Cross-section through vertical velocity The vertical cross sections at 15:00 showing instantaneous vertical velocity and liquidwater content (contours every 0.25 g / kg starting from 0.25 g / kg). 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

20. Horizontally averaged cloud cover and precipitation Time series of horizontally averaged total cloud cover for different model setups. Data dumped every 15 min. Time series of horizontally averaged precipitation rates for different model setups 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

21. Documentation Extended abstract - 34th International Conference on Alpine Meteorology, Reykjavík, Iceland, 18-23 June 2017: Compressible EULAG solver for limited-area numerical Alpine weather prediction in the COSMO consortium Damian K. Wójcik, Bogdan Rosa, Michał Z. Ziemiański 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

22. Final conclusions and future work • From technical point of view EULAG model has been successfully coupled to the COSMO framework • Performed verification leads to conclusion that the CE results are close to observations • A robustness of CE numerics allows to perform simulations with horizontal grid sizes below 1km (0.28 km) • CE simulations indicate significant influence of orographic forcing on the model solutions so that no general grid convergence is obtained. • CE results indicate a dependence of the evolution of model representation of precipitation on the grid size. • Request to extend PP CELO until 8.2018 has been submitted • The additional time is needed to complete Tasks 3, 4 and 5 • The project will be finalized with delivery of fully operational weather prediction package without data assimilation. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel

23. THANK YOU FOR YOUR ATENTION