1. Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai MeteoSwiss, Zürich, Switzerland Advisors: Mathias Rotach, Pirmin Kaufmann Oliver Fuhrer, Matteo Buzzi MeteoSwiss COSMO General Meeting – UTCS Parallel Session 15 September 2008, Krakow, Poland

2. 2 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Outline PBL height determination Ideal convective case Real case study (LITFASS) Further plans

3. 3 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) PBL height: good indicator of the overall performance of the turbulence scheme Following methods were applied to COSMO model outputs to diagnose the PBL height: Gradient Richardson number Bulk Richardson number Turbulent Kinetic Energy (TKE) Turbulent fluxes (momentum and heat) Theoretical approaches Unstable  Slab model (prognostic) Stable  Zilitinkevich equation (diagnostic) Methods for diagnosing PBL height Mean variables Turbulence variables

4. 4 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – PBL heights Using radiosounding profiles (Bulk Ri method) Validation against 00 and 12 UTC soundings 4 stations (Payerne, Stuttgart, Munich, Milan) Verification periods:  10 ideal convective and stable case (in 2006-2007) Cloud free, low winds  Continuous period: 2008-02-20 – 2008-03-20 Both cyclonic and anticyclonic conditions are represented Operational setting: COSMO-7 and COSMO-2

5. 5 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Results – PBL heights Best results: Richardson number, Momentum flux, Theoretical approaches Problems: TKE  considerable overestimation Unstable Stable BIAS (relative) RMSE (relative)

6. 6 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Component testing Motivation: Better understand the behaviour of the one- equation turbulence scheme in different situations Method: component testing  analyse the TKE budget terms one by one Approach: inter-comparison of Measurements LES COSMO 3D COSMO 1D Case studies: Dry convective – Ideal case Dry convective – Real case (LITFASS)

7. 7 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Component testing Budget terms: I. : Local tendency II. : Advection by the mean wind III. : Buoyancy production term IV. : Shear production term V. : Turbulent transport of TKE VI. : Pressure correlation term VII. : Dissipation Prognostic equation for TKE: I. II. III. IV. V. VI. VII.

8. 8 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Ideal convective case Horizontally homogeneous and flat Dry case Constant heating rate Non-rotating Shear free Large Eddy Simulation (LES): Mironov et al., 2002 20 m mesh size Filtered Navier-Stokes equations Smagorinsky closure TKE

9. 9 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Ideal convective case Operational COSMO-2 levels First full level at 10 m dt=72 s TKE 10 m equidistant levels First full level at 5 m dt=72 s Transport vanishes due to numerical limiter in the explicit scheme LES

10. 10 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Ideal convective case - Solution I. Keep explicit formulation Deactivate numerical limiter Smaller timestep needed 10 m levels dt = 3.6 s TKE 20 m levels dt = 7.2 s 1 m levels: only stable with dt < 0.1s  memory problems

11. 11 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Ideal convective case - Solution II. Implement semi-implicit formulation for the transport term (O. Fuhrer) Results are not sensitive to timestep Same results for 20m, 10m, 1m levels TKE 1 m levels dt = 3.6 s 20 m levels dt = 3.6 s

12. 12 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Ideal convective case - Conclusions Solution independent of vertical resolution and timestep achieved Turbulent transport of TKE is too weak Negative buoyancy flux at PBL top is missing Horizontal portion of TKE is badly described at the PBL top and near the surface Implicit handling of the diffusion term in the TKE equation should be considered

13. 13 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) LITFASS-2003 Measurement campaign conducted in the area of Lindenberg, Germany Main goal: measurement of turbulent fluxes in an inhomogeneous terrain Measurement types: Micrometeorological stations Remote sensing 100 m tower Helicopter flights 20 km

14. 14 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) LITFASS-2003 Single column runs were made for the 8 land cover types Two types of runs: „Free run” initialized with mesurements „Forced run”: surface temperature and humidity Mean variables (wind, temp.) and surface fluxes were verified with micrometeorological stations TKE was compared to the tower measurements Humidity profile

15. 15 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) LITFASS-2003 – Wind problem All the single column runs showed strong diurnal cycle of 10 m windspeed This maximum was not present in the measurements Assumption: local winds due to surface heterogeneity suppress the mean wind at midday Solution: initialize with lower wind speed (2 m/s instead of 6 m/s)

16. 16 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) LITFASS-2003 TKE Budget

17. 17 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Outlook High resolution LES runs (<10m) for the real convective case Investigation of both ideal and real stable cases

18. 18 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch)

19. Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Reserve slides – PBL height

20. 20 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Methodology - TKE Relative threshold is used: TKE crit = TKE max * T Different thresholds for stable/unstable situations: T unstable = 0.1 T stable = 0.3 Typical profile of TKE during daytime TKE max

21. 21 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Ideal cases Unstable - Scatter plot diagrams TKE Mom. flux Slab model Bulk Ri Shallower PBLs are overestimated High PBLs are underestimated Only exception: Bulk Ri method

22. 22 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period 30 days: 2008-02-20 – 2008-03-20 First half: anticyclone Second half: cyclones 4 radiosounding stations Operational runs: COSMO-7: 6.6 km, 60 vertical levels 72 hour forecasts COSMO-2: 2.2 km, 60 vertical levels 24 hour forecasts Validation against 00 and 12 UTC soundings T_2m_max Sunshine Precip. Wind speed

23. 23 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period Unstable + 12 h Ri number methods improved, compared to other methods Possible cause: on average smaller observed PBL heights TKE method: considerable overestimation

24. 24 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period Unstable + 12 h Slab model often gets unstable and gives unrealistically high values Max. cases: COSMO-7: 99 COSMO-2: 93

25. 25 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period Unstable No significant dependency of the errors on lead time

26. 26 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period Stable + 24 h TKE method: overestimation, especially with COSMO-2 Best methods: Ri numbers, Zil., Momentum flux

27. 27 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period Stable + 24 h Gradient Ri method only successful in half of the cases Max. cases: COSMO-7: 114 COSMO-2: 117

28. 28 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation – Continuous period Stable Dependency on lead time: only by TKE and heat flux Using analysis  no improvement

29. 29 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) PBL height horizontal variability Gradient Ri and Bulk Ri methods give the smoothest fields TKE: very strong variability Gradient Ri TKE Momentum flux COSMO-2 2008-02-24 12 UTC

30. 30 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) PBL height – TKE method – Convective cases

31. 31 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Dependency of observed PBL heights on wind speed in stable cases

32. 32 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) TKE method - overestimation 2006-07-18 14 UTC COSMO-7 Level 28 1800 m AGL Unsuccessful grid points TKE method

33. 33 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) TKE method – overestimation Case study: 2008-02-28 00 UTC COSMO-7 - Stuttgart Bulk Ri (0.33) 153 TKE_rel (0.3) 924 Mom. Flux (0.3) 313 Heat flux (0.3) 319 Zil.121 TEMP142 PBL height [m]

34. 34 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch)

35. Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Reserve slides – UTCS, LITFASS

36. 36 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) LITFASS-2003 Selected day: 30 May 2003 Dry convective day, no precipitation Low easterly winds Radiosounding

37. 37 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) LITFASS-2003 Considerable differences between the surface fluxes of the different land cover types Measured fluxes of „grass” agree quite well with „farmland” 30 May 2003

38. 38 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) 3D COSMO runs Model version used: 4.0.4. Horizontal resolution: 0.0625° ~ 7 km 45 vertical levels Problems with external parameters: Soil type LAI Root depth Problem with soil model initialization: Assimilation cycle only with old soil model Multi layer soil model: cold start Too moist soil

39. 39 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Possible solutions: Change analysis file manually according to the observations Run new soil analysis cycle (TERRA standalone)

40. 40 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Same vertical level distribution as in the 3D model (45 levels, first main level at 30 m) First experiments: 1)Reproduce the 3D run Initialize from 3D analysis OK Geostriphic forcing 2)Free run with modified externals and soil moisture 3)Force the model with measured surface temperature and humidity Single Column runs

41. 41 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) SC run with modified externals and soil moisture 3D runSC run Root depth50 cm5 cm Soil moisture19%5% For the modification, the values of the main measurement site (GM Falkenberg) were used  grass 3D 1D

42. 42 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) SC run with modified externals and soil moisture 12 UTC Humidity profile agrees better with sounding than that of the 3D run

43. 43 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) SC run with modified externals and soil moisture

44. 44 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation of diagnosed turbulence characteristics Ideal dry-convective case Homogeneous terrain, constant heating LES from Mironov et al. (2000)

45. 45 Component testing of the COSMO model’s turbulent diffusion scheme Balázs Szintai (balazs.szintai@meteoswiss.ch) Validation of diagnosed turbulence characteristics LITFASS-2003 campaign Tower measurements at 50 and 90 m