日本近海における低氣壓の發生とその進行

抄録

The original data were obtained from the weather maps analysed by the Central Meteorological Observatory, Tôkyô. First, the locations where 4014 cyclones originate were determined carefully and were tabulated during the 8-year period extending 1933-1940. The frequencies were written for each 2° square of latitude and longitude (see Fig. 1). The place of origin of storms seems to be influenced to some extent by the distribution of land and water. The principal areas of origin may be roughly summed up as four groups (see Fig. 2) including storms which originate
(1) in the sea to northeast of Formosa, passing ovor Loochoo Islands and thence move to Japan proper or to the Pacific'
(2) in the sea to east of Korea, passing over the Sea of Japan and Northern Japan and thence move to the Pacific or the Okhotsk sea,
(3) in the sea to south of Sikoku Island, advancing along the southern coast of Japan proper and thence move to the Pacific, and
(4) in the sea to south of Kwanto district advancing to the Pacific.
Next, the cyclones which originate during the 9-year period (1932-1940) in Japanese area (including China Eastern Sea, Yellow Sea. Sea of Japan, Sea to East, Southeast and South of Japan) have been enumerated and their seasonal distribution is Winter 614, Spring 556, Summer 499, Autumn 529. The frequency of the depressions which appeare in our weather chart is rather high in Spring and Autumn, but the frequency of the cyclones which originate in Japanese area is highest in Winter and lowest in Summer.
Next the total number of storms that traversed each square, two degrees longitude in width and two degrees latitude in length, during the 8-year period 1933-1940 were enumerated. Chart 3 and 4 were constructed according to this plan. The location of the composite tracks is determined on the ground that the axis of the region of greatese cyclone frequency indicates the mean position of the storm path, which lays usually over sea along the Japanese Archeperago and tends to passing through strait or channel.
Lastly, the average movements of Japanese storms that originated during the 3-year period 1935-1937, inclusive, are shown graphically in Figures 5 and 6. Recause the computations were highly troublesome, the smoothed averages were obtained by taking the average of all observations in each 10° square for which data were available. From these figures, we find that in winter cyclones advance to the east with high speed, while in summer cyclones move to the northeast or east in the middle latitudes (>30°N) and advance to the west in the tropical regions (<20°N) with relatively low velocity.