Federal Department of Home Affairs FDHAFederal 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 SzintaiMeteoSwiss
Daniel Nadeau EPFL, Switzerland
2 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 ([email protected])
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 ([email protected])
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
• Measurements used:• Radiosoundings• Micrometeorological stations
all land cover types• Tower turbulence measurements
(at 50 and 90 m)
20 k
m
20 km
5 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 ([email protected])
LES – ideal cases
Neutral Stable Unstable
Daniel Nadeau, EPFL
Ve
loc
ity
va
ria
nc
es
Ve
loc
ity
sp
ec
tra
7 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 ([email protected])
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 ([email protected])
• 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
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 ([email protected])
Wind
COSMO LES
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 ([email protected])
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 ([email protected])
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 ([email protected])
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 ([email protected])
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.
3
212
13
3
232
3
1313
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x
puu
xU
uuxU
uuute
v
15 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 ([email protected])
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 ([email protected])
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 ([email protected])
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 FDHAFederal 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 ([email protected])
21 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
Reserve slides
22 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 ([email protected])
COSMO-3D: Mean Vertical Velocity 2003-05-30 12 UTC, 800 m AGL
Without horiz. DiffusionCTRL-60
300
km
100
km
With horiz. DiffusionHDIFF-60
24 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
COSMO-3D: Turbulent Kinetic Energy2003-05-30 12 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. DiffusionCTRL-60
With horiz. DiffusionHDIFF-60
25 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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
]
[m/s
][m
/s]
[m/s
]
-3D -3D
-3D -3D
26 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 -3D
-3D -3D
27 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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
HDIFF-60 IMPL-74
Potential temp. [K] Potential temp. [K]Specific hum. [kg/kg] Specific hum. [kg/kg]
28 Analyzing the TKE budget of the COSMO model: comparison with turbulence measurements and LES data
Balázs Szintai ([email protected])
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 ([email protected])
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 ([email protected])
LES – TKE budget profile