The size distribution of fog droplets in and around model woods was studied at Ochiishi, Hokkaidô to investigate the mechanism of the dissipation of fog by forest. The results indicate that the effect of capture by trees in the wood is predominant for large droplets with diameters above 10 μ and that in the daytime the evaporation of droplets becomes intence in and behind the wood, the latter being predominant for small droplets with diameters less than 10 μ We then placed a plate glass coated with ceder oil on the, ground and measured the number of fog droplets that fell in the oil. The result shows that even if the air is gusty the droplets are captured on the flat ground only by the action of gravity as in the case when there is no wind. The amount of fog captured on the ground was 5_??_8×10-7g/cm2 sec. The vertical change in the size distribution of fog droplets in the daytime was studied. The results show that nearer to the ground the proportion of small droplets in the distribution becomes smaller and that the amount of fog water increases linearly with height.
The monthly mean vertical cross sections drawn throughout a year show seasonal variations of the tropical, middle latitude and polar tropopauses in the middle latitudes. Mean geostrophic jet streams which are found between two tropopauses are associated with relatively dry areas under them.