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

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 Download Video Format File size Flash (.flv) 13.7mb Download (2nd Sequence) MPEG (.avi) 14.3mb Download (2nd Sequence) Flash (.flv) 3.1mb Download (3nd Sequence) MPEG (.avi) 3.1mb Download (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 Download Video Format File size Flash (.flv) 9.6mb Download MPEG (.avi) 9.7mb Download

Fifth 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