Abstract

In July 1961 an artificial fog dissipation experiment was carried out, using a helicopter. The experiment was based on the idea that fog will be dissipated by downward air current caused by fall of water drops sprinkled from the helicopter. The preliminary experiment showed that the effective width of distribution area of water drops was about 20 m under the sprinkling condition used. The vertical distributions of air temperature and humidity in sea fog were observed at the sea side near where the fog dissipation experiment was made. According to the observation, it was seen to be general in the sea fog in the daytime that strong temperature inversion existed near the fog top and that the air layer under the fog base was unstable with respect to the dry adiabatic. The sprinkling of water drops was carried out on the top of the advected sea fog, a smooth and flat area being selected; it was found that a few minutes after the sprinkling treatment, the flat and smooth fog layer changed to fracto-cumulus, then was dissipated if the fog was not dense. The dimensions of area of the modified fog were much larger than the effective width estimated in the preliminary experiment. This suggests that the water sprinkling served as only a trigger action causing vertical convection to occur in the lower unstable part of the fog.

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