2.3. Dry stable boundary layer
2.3.1. Background
This is the stable boundary layer scenario described by Sauer and Munoz-Esparza (2020). This the stable boundary layer scenario outlined in Kosovic and Curry (2000).
2.3.2. Input parameters
Number of grid points: \([N_x,N_y,N_z]=[128,126,122]\)
Isotropic grid spacings: \([dx,dy,dz]=[3.125,3.125,3.125]\) m
Domain size: \([0.40 \times 0.39 \times 0.38]\) km
Model time step: \(0.005\) s
Geostrophic wind: \([U_g,V_g]=[8,0]\) m/s
Advection scheme: 5th-order upwind
Time scheme: 3rd-order Runge Kutta
Latitude: \(73^{\circ}\) N
Surface potential temperature: \(265\) K
Potential temperature profile:
Surface heat flux: \(-0.25\) K/h
Surface roughness length: \(z_0=0.1\) m
Rayleigh damping layer: uppermost \(75\) m of the domain
Initial perturbations: \(\pm 0.25\) K
Top boundary condition: free slip
Lateral boundary conditions: periodic
Time period: \(12\) h
2.3.3. Execute FastEddy
Run FastEddy using the input parameters file /examples/Example03_SBL.in. To execute FastEddy, follow the instructions here: https://github.com/NCAR/FastEddy-model/blob/main/README.md.
2.3.4. Visualize the output
Open the Jupyter notebook entitled “MAKE_FE_TUTORIAL_PLOTS.ipynb” and execute it using setting: case = ‘stable’.
XY-plane views of instantaneous velocity components at \(t=12\) h (FE_SBL.8640000):
XZ-plane views of instantaneous velocity components at \(t=12\) h (FE_SBL.8640000):
Mean (domain horizontal average) vertical profiles of state variables at \(t=12\) h (FE_SBL.8640000):
Horizontally-averaged vertical profiles of turbulence quantities at \(t=11-12\) h (FE_TEST.8640000) [perturbations are computed at each point relative to the previous 1-hour mean, and then horizontally averaged]:
2.3.5. Analyze the output
Using the XY and XZ cross sections, discuss the characteristics (scale and magnitude) of the resolved turbulence.
What is the boundary layer height in the stable case?
Using the vertical profile plots, explain why the boundary layer is stable.