A two-dimensional axially symmetric computer model was used to study downwash-induced fog clearings. In order to produce a clearing the helicopter downwash must reach the ground while the helicopter hovers at or above the top of the fog. The major factors affecting the size and penetration of the downwash are the strength of the helicopter and the buoyancy of the downwash. The clearing can be enlarged beyond the size of the primary downwash by surface-induced divergence and by mixing of dry air into the fog.

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