Summary
A two-dimensional nonhydrostatic numerical model was used to investigate the behaviour of a cold air gravity current, moving along complex terrain. It is found, that the model with a high horizontal and vertical resolution and with a closure scheme, using the turbulent kinetic energy, is suitable to simulate currents, which have the main features of those found in laboratory experiments.
Simulations are presented for different orographic structures (mountain and valley), for varying thermal stratification of the environmental atmosphere (neutral, stable and stable with an elevated inversion) and for different heights of the cold air reservoir.
The major effect of a hill on the advance of a gravity current is a reduction of the front speed upstream as well as (even stronger) downstream of the obstacle, where the amount of this decrease depends on thermal stratification. Near surface blocking of the air flow on the windward side occurs for all simulations. However, for small depths of the oncoming cold air, the current cannot surmount the hill and remains on the lee side.
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Bischoff-Gauss, I., Gross, G. & Wippermann, F. Numerical studies on cold fronts Part II: Orographic effects on gravity flows. Meteorl. Atmos. Phys. 40, 159–169 (1989). https://doi.org/10.1007/BF01032456
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DOI: https://doi.org/10.1007/BF01032456