1. Results of semi realistic and realistic simulations performed
with new compressible dynamical core of COSMO-EULAG
Bogdan Rosa, Damian K. Wójcik,
Michał Z. Ziemiański
Institute of Meteorology and Water Management
National Research Institute
Warsaw, Poland
Podleśna, 61
COSMO General Meeting, 11 – 14 September 2017, Jerusalem, Israel

2. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
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 ( ).
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3. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
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).
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4. 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
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5. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Experiment settings
Dynamics:
Numerical and Smagorinsky diffusion are turned off for Cosmo-Eulag and on for Cosmo Runge-Kutta
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)
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)
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6. Wind [m/s] at 10 m – Forecast verification (before pressure correction)CE
mixing length = 150 m RK
mixing length = 150 m
<|RMSE|> = 2.250
<|ME|> =
<|RMSE|> = 2.211
<|ME|> = CE
mixing length (default) = 500 m RK
mixing length (default) = 500 m
<|RMSE|> = 2.242
<|ME|> =
<|RMSE|> = 2.216
<|ME|> =
There is notable overestimation of surface wind in CE. It may be related to different implicit diffusion of CE dynamical core and may need a dedicated tuning. All suggestions are very welcomed.
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7. Temperature (C) at 2 m – Forecast verification (before pressure correction)CE
mixing length = 150 m RK
mixing length = 150 m
<|RMSE|> = 2.216
<|ME|> =
<|RMSE|> = 2.310
<|ME|> = CE
mixing length (default) = 500 m RK
mixing length (default) = 500 m
<|RMSE|> = 2.196
<|ME|> =
<|RMSE|> = 2.241
<|ME|> =
Results computed using CE are closer to observations than those computed with RK. Interestingly, better agreement between numerical simulations (both RK and CE) and observations has been obtained for larger mixing length.
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8. Dew point temperature (C) at 2 m – Forecast verification (before pressure correction)CE
mixing length = 150 m RK
mixing length = 150 m
<|RMSE|> = 2.686
<|ME|> = 0.842
<|RMSE|> = 2.657
<|ME|> = 0.845 CE
mixing length (default) = 500 m RK
mixing length (default) = 500 m
<|RMSE|> = 2.678
<|ME|> = 0.847
<|RMSE|> = 2.628
<|ME|> = 0.855
Results from both models are similar. The effect of varying mixing length is almost negligible.
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9. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Diagnosis of pressure bias
Task 5: Integration and consolidation of the EULAG compressible DC with COSMO framework
Optimal formulation for the flows with the open boundary conditions: pressure bias diagnostics
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10. Semi-realistic simulations: setup
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 (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. 10

11. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Semi-realistic simulations: results without absorber for pressure CE RK
Default version of COSMO Runge-Kutta dynamical core is equipped with absorbers for:
The compressible implicit EULAG solver employs absorbers only for:
Pressure
U- and V-velocity components
Temperature
W (towards 0)
Potential Temperature
U- and V-velocity components
W (towards 0)
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12. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Semi-realistic simulations: results with absorber for pressure CE RK
Disabling the pressure absorber in RK results in the development of a pressure bias similar to that observed in CE results.
Conversely, adding of a simple linear absorber to the compressible implicit CE results in significant reduction of the pressure bias for CE.
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13. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
A 72 hour realistic simulation with the linear pressure absorber
Realistic simulation using COSMO Runge-Kutta (RK) and compressible COSMO-EULAG (CE) was run for 72 hours in order to check pressure fluctuations in a long-term simulation.
Configuration:
Turbulence parameterization is turned on
Moist microphysics and saturation adjustment are turned on
Soil processes are turned on
dt = 15 s (RK), dt = 10 s (CE)
Computational domain:
COSMO-2 domain of MeteoSwiss
dx = 2.2 km,
ie_tot – 582, je_tot = 390, ke_tot = 60
Test case :
21 July 2017
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14. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
A 72 hour simulation with compressible CE at 2.2 km grid resolution
Time evolution of horizontally averaged pressure perturbations. The perturbations were computed with respect to the time-evolving boundary data pressure from the simulations-driving COSMO-7 simulation. CE RK
Pressure perturbations within the both models have a similar magnitude also after 72 hours long integration time.
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15. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Pressure (hPa) – forecast verification with pressure absorber CE
wichfakt = 0.5
tkmmin = 0 RK
<|RMSE|> = 1.122
<|ME|> = 0.160
<|RMSE|> = 1.123
<|ME|> = 0.164 CE
wichfakt = 0
tkmmin = 0.4 RK
<|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.
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16. Before pressure correction With pressure absorber
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|> = 2.226
<|ME|> = 0.213
<|RMSE|> = 2.225
<|ME|> = 0.212
<|RMSE|> = 2.192
<|ME|> = 0.158 CE
wichfakt = 0
tkmmin = 0.4 CE RK
<|RMSE|> = 2.222
<|ME|> = 0.214
<|RMSE|> = 2.223
<|ME|> = 0.210
<|RMSE|> = 2.186
<|ME|> = 0.158
Little effect of pressure absorber on horizontal wind. Pressure absorber makes CE results more closer to both RK results and observations.
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17. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Temperature at 2 m – forecast verification with pressure absorber CE
wichfakt = 0.5
tkmmin = 0 RK
<|RMSE|> = 2.174
<|ME|> = 0.656
<|RMSE|> = 2.238
<|ME|> = 0.902 CE
wichfakt = 0
tkmmin = 0.4 RK
<|RMSE|> = 2.165
<|ME|> = 0.643
<|RMSE|> = 2.213
<|ME|> = 0.875
Results computed using CE are closer to observations than those computed with RK. No effect resulting from different values of parameters wichfakt and tkmmin.
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18. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Dew point temperature at 2 m – verification with pressure absorber CE
wichfakt = 0.5
tkmmin = 0 RK
<|RMSE|> = 2.664
<|ME|> = 0.856
<|RMSE|> = 2.639
<|ME|> = 0.884 CE
wichfakt = 0
tkmmin = 0.4 RK
<|RMSE|> = 2.644
<|ME|> = 0.850
<|RMSE|> = 2.628
<|ME|> = 0.875
Results from both models are in good quantitative agreement. Low sensitivity to different settings of vertical smoothing factor and minimal diffusion coefficients.
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19. Precipitation – forecast verification (wichfakt = 0.5, tkmmin = 0)CE RK
Probability of Detection
Probability of Detection CE RK
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.
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20. Precipitation cntd. – forecast verification (wichfakt = 0
Precipitation cntd. – forecast verification (wichfakt = 0.5, tkmmin = 0) CE RK
Probability of Detection
Probability of Detection CE RK
Probability of Detection
Probability of Detection
Success Ratio
Success Ratio
Also for larger precipitation the differences are in the range of statistical uncertainty.
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21. Precipitation – forecast verification (wichfakt = 0, tkmmin = 0.4)CE RK
Probability of Detection
Probability of Detection CE RK
Probability of Detection
Probability of Detection
Success Ratio
Success Ratio
Low sensitivity to different numerical parameters. Simulations performed with pressure absorber.
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22. Precipitation cntd. – forecast verification (wichfakt = 0, tkmmin = 0CE RK
Probability of Detection
Probability of Detection CE RK
Probability of Detection
Probability of Detection
Success Ratio
Success Ratio
Precipitation statistics evolve (in time) in a similar manner. For precipitation 16 mm and more results CE and RK are in qualitative agreement.
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23. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
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
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24. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
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 km. The four black markers (dots) in the right panel indicate corners of the averaging area for statistics.
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25. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Weather conditions – analysis of satellite data
Cloud cover (grayscale) derived from the albedo product of the HRV channel of Meteosat and underlying topographic map (brown to copper colors). Two images correspond to two different time instants (12 UTC and 15 UTC). The area matches to the computational domain of simulations at resolution 2.2 km.
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26. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Cloud cover
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.
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27. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
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.
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28. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Cross-section through vertical velocity
The vertical cross sections at 15:00 showing instantaneous vertical velocity and liquid water content (contours every 0.25 g / kg starting from 0.25 g / kg).
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29. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Comparison of numerical simulations performed using CE and RK at different resolutions with the satellite data.
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30. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Comparison of numerical simulations performed using CE and RK at different resolutions with the satellite data.
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31. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
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
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32. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Conclusions
CE results computed at grid resolutions 2.2 and 1.1 km and the results from reference RK simulation (2.2km) are generally similar for large scale cloud fields, precipitation and their evolution.
A robustness of CE numerics allowed for additional simulations of Alpine convective weather with horizontal grid sizes of 0.55 and 0.28 km.
The CE results show generally similar development of large-scale cloud fields for all model resolutions.
On the other hand, the CE simulations indicate significant influence of orographic forcing, strongly varying with underlying topography, on the model solutions (especially vertical wind component) 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. The difference concern e. g. the initial rate of precipitation growth (slower for higher resolutions) and timing and intensity of peak precipitation (later for higher resolutions and more intense especially for the grid size of 0.55 km).
The differences between the CRK simulations employing 2.2 and 1.1 km grid sizes are smaller comparing with CE ones.
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33. 19th COSMO General Meeting, 11-14 September 2017, Jerusalem, Israel
Documentation
Extended abstract - 34th International Conference on Alpine Meteorology, Reykjavík, Iceland, June 2017:
Compressible EULAG solver for limited-area numerical Alpine weather prediction in the COSMO consortium
Damian K. Wójcik, Bogdan Rosa, Michał Z. Ziemiański
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34. THANK YOU
FOR YOUR
ATENTION 34