Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Analyzing the TKE budget of the COSMO model for the LITFASS-2003 convective case: comparison with turbulence measurements and LES data COSMO General Meeting 7 September 2009, Offenbach, Germany Balázs Szintai MeteoSwiss Daniel Nadeau EPFL, Switzerland

2 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Outline Goal of the work LITFASS-2003 campaign Large Eddy Simulation COSMO-3D simulations Mean variables (temperature, wind) TKE TKE budget terms Summary and Outlook

3 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Goal of the work Evaluate the current one-equation turbulence scheme of the COSMO model Investigation of both unstable and stable cases Comparison with measurements and LES data Eventually further tuning

4 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai LITFASS-2003 Measurement campaign conducted in the area of Lindenberg Main goal: measurement of turbulent fluxes in an inhomogeneous terrain Case study: : convective day, calm winds, no clouds Simulation of the whole diurnal cycle Measurements used: Radiosoundings Micrometeorological stations  all land cover types Tower turbulence measurements (at 50 and 90 m) 20 km

5 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Large Eddy Simulation Large Eddy Simulation runs were performed at the Environmental Fluid Mechanics Laboratory (EFLUM) at EPFL, Switzerland Model was developed at the Johs Hopkins University and was used several times previously to simulate the atmospheric boundary layer LES details: Solves the filtered incompressible N-S equations Lagrangian scale-dependent dynamic subgrid scale model Spectral representation in the horizontal directions Finite differences in the vertical direction Periodic lateral boundary conditions Stress-free lid as a top BC for unstable conditions Surface temperature is imposed Heat exchange using MOS

6 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai LES – ideal cases Neutral StableUnstable Daniel Nadeau, EPFL Velocity variances Velocity spectra

7 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai LES - LITFASS-2003 case Domain size 6 x 6 km horizontal (Δx = Δy = 94 m) 3 km vertical (Δz = 47 m) Time step: 0.2 s 3 hours of simulation from 9 to 12 UTC Geostrophic forcing calculated from COSMO-7 analysis (constant in time, vertically changing) Changing lower BC from measurements for each land cover type 10 minute averaging in output No space averaging Work in progress, preliminary results

8 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai COSMO-3D at 1 km COSMO-7 COSMO-1

9 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Horizontal resolution: ° ~ 1 km Timestep : 10 s Operational external parameters (soil type) are not accurate in the area  improved dataset from Felix Ament is used Soil analysis was produced with a one-month TERRA standalone run forced with COSMO-7 analyses Investigated: Numerical horiz. diffusion Implicit TKE diffusion Finer vertical resolution COSMO-3D runs In the following the control run is presented: no horizontal diffusion explicit TKE diffusion oper. 60 levels

10 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Wind COSMOLES Wind speed [m/s] Wind dir. [deg]

11 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Wind profiles at 12 UTC Wind direction is simulated accurately Wind speed is overestimated by LES Problem in LES above the PBL – wave pattern Wind speed Wind direction

12 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Potential temperature COSMO simulates a too warm and too shallow PBL LES background stratification is too stable COSMO LES 12 UTC

13 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai TKE COSMO gives higher values than LES in the lower half of the PBL Height of TKE maximum is too high in LES Double peak in the profiles of horizontal velocity variances in LES (not shown) COSMO LES 12 UTC

14 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Component testing Budget terms: I. : Local tendency II. : Buoyancy production term III. : Shear production term IV. : Turbulent transport of TKE and pressure correlation term V. : Dissipation Prognostic equation for TKE: I. II. III. IV. V.

15 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai TKE budget terms I. COSMO LES Buoyancy Shear

16 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai TKE budget terms II. COSMO LES Transport Dissipation Budget imbalance

17 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai TKE budget - measurements Average values computed from two sonic anemometers at 50 and 90 m Turbulent transport: triple correlations (M. Mauder, Research Centre Karlsruhe) Dissipation: turbulence spectrum (D. Michel, University Basel) Positive values of turbulent transport in COSMO Large negative imbalance in measurements Transport Dissipation Budget imbalance Buoyancy Shear TKE

18 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Summary and Outlook The diurnal cycle of a dry convective case has been simulated with the COSMO model at 1 km resolution TKE budget terms have been compared to preliminary LES data and measurements The shear production term shows vertical oscillations (in stable regimes) The transport term near the surface have different sign as compared to measurements and LES The TKE budget from turbulence measurements shows a large negative imbalance Outlook: More reliable LES data Stable case: GABLS-3

Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Thank you for your attention!

20 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai

21 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Reserve slides

22 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai TERRA standalone run Upper levels of the produced soil analysis are colder and moister than measurements

23 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai COSMO-3D: Mean Vertical Velocity UTC, 800 m AGL Without horiz. Diffusion CTRL km 100 km With horiz. Diffusion HDIFF-60

24 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai COSMO-3D: Turbulent Kinetic Energy UTC, 800 m AGL Without horizontal diffusion the results are not very realistic   wavelength is on the order of the mesh size Horizontal diffusion reduces the amplitude of waves and increases the wavelength Cellular updrafts on areas with low winds vanish with horizontal diffusion Without horiz. Diffusion CTRL-60 With horiz. Diffusion HDIFF-60

25 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Validation of COSMO-3D – 10 m wind Too strong wind in analysis – vanishes after 2 hours Small maximum in the morning hours not present in measurement CTRL-60 IMPL-60 HDIFF-60 IMPL-74 [m/s] -3D

26 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Validation of COSMO-3D – Surface sens. heat flux No significant differences between the experiments Surface sensible heat flux is overestimated during daytime Surface latent heat flux is underestimated, large horizontal variability (not shown) CTRL-60 IMPL-60 HDIFF-60 IMPL-74 -3D

27 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Validation of COSMO-3D – Temperature and humidity profiles UTC 60 level runs are very similar  to diffusive in the entrainment zone 74 levels bring improvement in the PBL CTRL-60 IMPL-60 HDIFF-60 IMPL-74 Potential temp. [K] Specific hum. [kg/kg]

28 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai Validation of COSMO-3D – TKE timeseries at 90 m Experiments give similar results Maximum of TKE is earlier in the model Night time TKE is overestimated by the model Fairly accurate results for TKE with „wrong” surface heat flux? CTRL-60 IMPL-60 HDIFF-60 IMPL-74

29 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai COSMO-3D: TKE budget terms Similar results to the idealized convective case Turbulent transport of TKE is too weak Negative buoyancy flux at PBL top is missing Higher vertical resolution in the entrainment zone and implicit formulation are improving the results CTRL-60 IMPL-60 HDIFF-60 IMPL-74

30 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data Balázs Szintai LES – TKE budget profile