Convective boundary layer with horizontally homogeneous heating

The following four sequences are showing different flow aspects and phenomena of the convective boundary layer. All simulations are driven by a constant and horizontally homogeneous surface sensible (and latent) heat flux. The initial state is an atmosphere at rest with neutral stratification, capped by an inversion at about 800m. Simulations differ in domain size and grid resolution.

First sequence: 3D view on moist convection (2001)

Project: none

Responsible: Siegfried Raasch

Description: Particles are released near the surface. The particle color reflects the buoyancy at the current particle position (red: positive, blue: negative). The particle size is proportional to the magnitude of the vertical velocity component. The isososurfaces display areas with a liquid water content larger than 0.2 g/kg, i.e. cumulus clouds. The horizontal domain size in this simulation is too small in order to allow the development of the typical near-surface hexagonal flow pattern (see next two sequences).

Model Setup
Total domain size (x|y|z):2000m x 2000m x 4638m
Grid spacing (x|y|z):25m x 25m x 25m
Number of grid points (x|y|z):80 x 80 x 80
Simulated time:1h
CPU-time:176h
Number of CPUs:32
Machine/ processor type:SGI Altix ICE at HLRN / Intel Xeon Gainestown
Visualization software:DSVR


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Video Format File size
Flash (.flv) 9.6mbDownload
MPEG (.avi) 9.7mbDownload



Second & Third sequence: horizontal cross-sections (2009)

Project: Numerical Simulation of the interaction between the atmosphere and the wing circulation

Responsible: Carolin Helmke

Description:
Second sequence:
Shown is the horizontal near-surface flow at z = 10m in a dry convective boundary layer. The particle color reflects the vertical velocity at the current particle position (red: upward, blue:downward). The near-surface flow is dominated by hexagonal cells with weak downdrafts in their centers and strong narrow updrafts within the lines of convergence between the cells. This flow pattern is sometimes called spoke-like pattern. Big plumes with cumulus clouds at their top can always be found at those centers where several spokes are merging. Although a very high grid resolution has been used, the pixel resolution used here does not allow to see any detailed small-scale flow structures. This sequence shows the last 15 minutes of a model run with 1.5 hours simulated time in total.

Third sequence:
The simulation and particle features are the same as for the second sequence, but here only a part of the horizontal domain with a size of 400 m x 400 m is shown. The fine grid spacing allows to resolve vortex-like structures which develop within the convergence lines. Some of them are part of dust-devil-like vortices (see next sequence).

Model Setup
Total domain size (x|y|z):4096.0m x 4096.0m x 1859.7m
Grid spacing (x|y|z):2m x 2m x 2m
Number of grid points (x|y|z):2048 x 2048 x 450
Simulated time:900s
CPU-time:4.8h
Number of CPUs:2048
Machine/ processor type:SGI Altix ICE at HLRN / Intel Xeon Gainestown
Visualization software:DSVR


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Video Format File size
Flash (.flv) 13.7mbDownload (2nd Sequence)
MPEG (.avi) 14.3mbDownload (2nd Sequence)
Flash (.flv) 3.1mbDownload (3nd Sequence)
MPEG (.avi) 3.1mbDownload (3rd Sequence)



Fourth sequence: dust devils (2006)

Project: LES of dust devils

Responsible: Theres Riechelmann

Description:
This animation displays 3d-views of the lower 150m of the same convective boundary layer as shown before. Particles are released near the surface in those areas, where the dynamic pressure is below a specified threshold of -2 Pa. This allows to visualize dust-devil like vortices, which always have a pressure minimum in their center. The particle color displays the magnitude of horizontal velocity (red: fast, blue: slow). At the end of the sequence, two dust devils with opposite rotation collide and cancel out each other due to conservation of angular momentum.

Model Setup
Total domain size (x|y|z):768m x 768m x 768m
Grid spacing (x|y|z):2m x 2m x 2m
Number of grid points (x|y|z):384 x 384 x 384
Simulated time:1h
CPU-time:
Number of CPUs:
Machine/ processor type:IBM Regatta / Power 4
Visualization software:DSVR


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Video Format File size
Flash (.flv) 9.6mbDownload
MPEG (.avi) 9.7mbDownload



Fifth sequence: dust devils in the convective boundary layer (2012)

Responsible: Fabian Hoffmann, Björn Maronga

Project: Numerical impacts on the strength of simulated dust devils

Description:
This sequence shows the development of a large dust devil during a time period of 10 minutes. The shown region has a horizontal extent of 350 m x 300 m and is about 300 m high. The dust devil is made visible by a passive scalar which is advected by the flow. The surface flux of the passive scalar is calculated by a simple parametrization of the saltation process which depends on the friction velocity (White, 1979). Due to uncertainties in the parametrization of the surface flux, the displayed concentrations of the passive scalar are in arbitrary units. Dust concentrations in the order of magnitude of 0.1 g/m3 have been found for dust devils in field measurements (Renno et al., 2004).

Model Setup
Total domain size (x|y|z):768m x 768m x 945m
Grid spacing (x|y|z):1m x 1m x 1m
Number of grid points (x|y|z):768 x 768 x 832
Simulated time:3h
CPU-time:24h
Number of CPUs:2048
Machine/ processor type:SGI Altix ICE at HLRN
Visualization software:VAPOR
DOI: 10.5446/9352


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Video Format File size
Flash (.flv) 5.0mbDownload
MPEG (.avi) 4.8mbDownload



Sixth sequence: structure parameter for temperature CT2 (2010)

Project: High-resolution LES studies of the turbulent structure of the lower atmospheric boundary layer over heterogeneous terrain and implications for the interpretation of scintillometer data

Responsible: Björn Maronga

Description:
This visualization shows the turbulent structure parameter CT2 in the surface layer of a convectively driven boundary layer. Dark colors match to high values up to 0.01, whereas white colors represent lower values down to 0.001. All values which are out of range are set to transparent. Shown is the last half an hour of the simulation. The movie shows, that CT2 is high near the surface, decreasing with height. High values, in comparison with their horizontal environment can be observed in regions where warm air rises upward (plumes). These regions organize in hexagonal cells, which can also be seen in this sequence. Please note that the capping inversion in this simulation was in a height of about 400m.

Model Setup
Total domain size (x|y|z):1280m x 1280m x 1080m
Grid spacing (x|y|z):5m x 5m x 5m
Number of grid points (x|y|z):256 x 256 x 256
Simulated time:1.5h
CPU-time:1.5h
Number of CPUs:64
Machine/ processor type:SGI Altix ICE at HLRN / Intel Xeon Gainestown
Visualization software:VAPOR