1 / 30

COSMO General Meeting 7 September 200 9 , Offenbach, Germany

Analyzing the TKE budget of the COSMO model for the LITFASS-2003 convective case: comparison with turbulence measurements and LES data. Balázs Szintai MeteoSwiss Daniel Nadeau EPFL, Switzerland. COSMO General Meeting 7 September 200 9 , Offenbach, Germany. Outline. Goal of the work

maxine-ross
Télécharger la présentation

COSMO General Meeting 7 September 200 9 , Offenbach, Germany

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Analyzing the TKE budget of the COSMO model for the LITFASS-2003 convective case: comparison with turbulence measurements and LES data Balázs Szintai MeteoSwiss Daniel Nadeau EPFL, Switzerland COSMO General Meeting 7September 2009, Offenbach, Germany

  2. 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. 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. LITFASS-2003 • Measurement campaign conducted in the area of Lindenberg • Main goal: measurement of turbulent fluxes in an inhomogeneous terrain • Case study: 2003-05-30 : convective day, calm winds, no clouds • Simulation of the whole diurnal cycle • Measurementsused: • Radiosoundings • Micrometeorological stations  all land cover types • Tower turbulence measurements (at 50 and 90 m) 20 km 20 km

  5. 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. LES – ideal cases Neutral Stable Unstable Velocity variances Velocity spectra Daniel Nadeau, EPFL

  7. 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. COSMO-3D at 1 km COSMO-1 COSMO-7

  9. COSMO-3D runs • Horizontal resolution: 0.0089° ~ 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 • In the following the control run is presented: • no horizontal diffusion • explicit TKE diffusion • oper. 60 levels

  10. Wind COSMO LES Wind speed [m/s] Wind dir. [deg]

  11. Wind profiles at 12 UTC Wind direction Wind speed • Wind direction is simulated accurately • Wind speed is overestimated by LES • Problem in LES above the PBL – wave pattern

  12. Potential temperature LES COSMO • COSMO simulates a too warm and too shallow PBL • LES background stratification is too stable 12 UTC

  13. TKE LES COSMO • 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) 12 UTC

  14. Component testing Prognostic equation for TKE: • Budget terms: • I. : Local tendency • II. : Buoyancy production term • III. : Shear production term • IV. : Turbulent transport of TKE and pressure correlation term • V. : Dissipation I. II. III. IV. V.

  15. TKE budget terms I. LES COSMO Buoyancy Shear

  16. TKE budget terms II. LES COSMO Transport Dissipation Budget imbalance

  17. 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 Buoyancy Transport Shear TKE Dissipation Budget imbalance

  18. 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

  19. Thank you for your attention!

  20. Reserve slides

  21. TERRA standalone run • Upper levels of the produced soil analysis are colder and moister than measurements

  22. COSMO-3D: Mean Vertical Velocity 2003-05-30 12 UTC, 800 m AGL Without horiz. Diffusion CTRL-60 With horiz. Diffusion HDIFF-60 300 km 100 km

  23. COSMO-3D: Turbulent Kinetic Energy2003-05-30 12 UTC, 800 m AGL Without horiz. Diffusion CTRL-60 With horiz. Diffusion HDIFF-60 • 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

  24. Validation of COSMO-3D – 10 m wind CTRL-60 IMPL-60 -3D -3D [m/s] [m/s] • Too strong wind in analysis – vanishes after 2 hours • Small maximum in the morning hours not present in measurement HDIFF-60 -3D IMPL-74 [m/s] -3D [m/s]

  25. Validation of COSMO-3D – Surface sens. heat flux -3D -3D • 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 -3D -3D HDIFF-60 IMPL-74

  26. Validation of COSMO-3D – Temperature and humidity profiles 2003-05-30 12 UTC • 60 level runs are very similar  to diffusive in the entrainment zone • 74 levels bring improvement in the PBL CTRL-60 IMPL-60 Specific hum. [kg/kg] Potential temp. [K] Potential temp. [K] Specific hum. [kg/kg] HDIFF-60 IMPL-74

  27. Validation of COSMO-3D – TKE timeseries at 90 m CTRL-60 IMPL-60 • 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? IMPL-74 HDIFF-60

  28. 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 IMPL-60 CTRL-60 IMPL-74 HDIFF-60

  29. LES – TKE budget profile

More Related