Abstract
A one-dimensional hydrostatic and incompressible numerical model based upon the ‘shallow water wave’ equations is developed and used to simulate surface outflows from convective storms. Axial symmetry is employed to simulate surface outflows from storms in non-shearing environments, while slab symmetry is used to simulate unidirectional convective outflows.
The model is initialized with observed data from GATE and is found to be capable of simulating the slope, depth, overall shape, and propagation speed of the outflow of tropical squall-lines.
The model is used to construct a series of nomograms relating the depth of the head of the gust front to the origin and strength of the downdraft for various density differences and downdraft radii. The model predicts that convection which generates wide downdrafts originating deep within cumulonimbi and growing in strongly sheared environments (encouraging unidirectional outflows at the surface) produces the deepest gust fronts. To maintain these outflows requires the weakest downdraft velocities; when the downdrafts cease, such outflows do not decay rapidly. Conversely, the model predicts that narrow downdrafts originating near cloud base and growing in environments which encourage radial outflows, produce the shallowest gust fronts. To maintain radial outflows requires the strongest downdrafts; when the downdrafts cease, radial outflows decay most rapidly.
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Addis, R.P. A numerical model of surface outflows from convective storms. Boundary-Layer Meteorol 28, 121–160 (1984). https://doi.org/10.1007/BF00119460
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DOI: https://doi.org/10.1007/BF00119460