Squall Lines: Moderate Shear

Squall line experiments: moderate-shear results

Run n95E: 300-km along-front domain - Mpeg / QT movie

Shortcuts: Latest images | Movies/first case | Higher-RH case | Some low-shear images | Run history

A series of simulations were carried out in which a two-dimensional front (modeled previously) is used to initiate convection in a 3D cloud model. Given the lineal form of the forcing, a squall line develops. Simulations were performed with:

Frontal forcing, random perturbations (only) - most realistic
Frontal forcing, random + 5 thermals - isolate cell-cell interaction
No frontal forcing, random + 5 thermals - isolate role of the front

The results shown here represent simulations currently being made. As such, the content of this page will be changing frequently.

Random/frontal results (vertical scale magnification factor: 3)
Looking nw	Looking nnw

Explanation of images | movie (mpeg, 3 MB) | movie (QuickTime, 12 MB)

5-thermal/frontal-forcing evolution (vertical scale magnification: 7)
Cloud+Rainwater at 4 hrs Vorticity contours, Qc+Qr

Movie (mpeg, 3MB)
Movie (mpeg, 590k)

Meridional vorticity > .005/s Vorticity surface > .002/s

Movie (mpeg, 3.4 MB)
Movie (mpeg, 3.5 MB)

5-thermal/frontal-forcing evolution (vertical scale magnification: 7)
Cloud+Rainwater at 4 hrs	Vorticity contours, Qc+Qr
Movie (mpeg, 3MB)	Movie (mpeg, 590k)
Meridional vorticity > .005/s	Vorticity surface > .002/s
Movie (mpeg, 3.4 MB)	Movie (mpeg, 3.5 MB)

The low-shear results were presented at the Mesoscale Processes conference (Reading, England, Sept. 9-13). From results available to date, the higher shear environments produce longer-lived and more distinct cells, as expected. The storms are supercellular in that they maintain low level rotation even as continuous updraft growth occurs on the south side of each cell.

3D simulations in a more moist environment

The above results were taken from a specific time in the evolution of the 2D simulation. 3D results from a later (2D run) time (though still prior to convective initiation) are shown below. These simulations are still underway.

60 minutes

120 minutes

240 minutes

Cloud+rain movie available (1.9 MB).

Comparison - lower shear simulation

Most of the lower-shear simulation data may be found here. A few images and a movie (also with vertical exaggeration=3) are here for comparison.

60 minutes

120 minutes

225 minutes

Cloud+rain movie available (1.5 MB).

Experimental design

Slab-symmetric frontal simulations
- nested: horiz. resolutions 16, 5.3, 1.8 km
- used to simulate cold front at high resolution
- repeated until desired (1D) along-front conditions reproduced by model
- final state represents more complete initial state for the convection.
3D simulations
- 2D frontal simulation (see above) expanded in N-S direction
- Random perturbations introduced to allow 3D structures to develop
- Experiments made with and without the presence of the front to isolate the role of the front on the convection.

Simulation details

Go to: Observations | Low-shear simulations | Moderate-shear simulations | Top simulation page

Further information regarding this work may be found (for now) in the conference preprint for the 1996 Severe Local Storms conference (San Francisco) and the corresponding preprint for the 1996 Mesoscale Processes conference (Reading).

Credit

Thanks go to Crystal Shaw of the Atmospheric Sciences Dept. & NCSA for her assistance with Iris Explorer and with cleaning up the figures. Thanks also to David Wojtowicz of Atmospheric Sciences for Explorer help and for use of and help with his trajectory package.

Brian F. Jewett | bjewett@ncsa.uiuc.edu | homepage