On the Development of Cyclones in the Neighbourhood of Japan

[摘要] By the investigation in the quickly developed 127 cyclones (typhoons are excluded) which appeared in the four years, 1933-36, the author obtained the statistical results as follows.1. The number of depressions appearing in Japan and its vicinity shows a maximum in spring and a minimum in summer, but developed cyclones appear from October to May and severe ones only from January to March.2. Cyclones which appear in Amur Region and enter in Okhotsk Sea passing Karahuto are found most frequently in December and January, ones passing Japan Sea in March and April, ones passing the sea to south of Japan Proper especially in January and February, nextly in spring, and ones forming and developing in the sea to east of Japan Proper in March.3. In winter, the region, where cyclones develop quickly, forms a belt extending northeastward from the sea to south of Japan Proper to the neighbouring sea of Tisima. This belt is the so-called climatological frontal zone. In spring the western part of this frontal zone moves northward, in summer it goes till farthest north (about 50°N) However, the eastern part of this zone is nearly stationary in the sea to east of Tisima. Thus the climatological frontal zone in the neighbourhood of Japan makes a seasonal periodic movement. And cyclones move between eastnortheastward and northnortheastward developing within the frontal zone.4. Developing cyclones which appeared in Japan, in general, become most vigorous after 48 hours since their appearance, while the deepening of their center is about 20mm.5. The rate of development is maximum in winter and minimum in summer.Collecting the data, the author found some interesting and remarkable facts as follows.a) Every severe cyclone has the distinct omen of the development in the early stage, that is the striking fall of the pressure around the center, the precipitation over a wide area, the rather vigorous cyclonic wind system in spite of the young shallow depression, and a line of discontinuity extending f_??_om south to north through the center.b) Every cyclone in active development has the distinct warm sector, whose intensity increases with the deepening of the center. But the form of the warm front is differ from the Bjerknes' model, and in general runs out to eastnortheast or northeastward far from the center.In the course of time the cold air in the rear side of the front pushes forward, but generally the occlusion does not take place, since the cyclone does not always move with warm current, but rather along the warm front.c) As the Fujiwhara's theory in 1923, the quick development of cyclones by amalgamation is found frequently.More detailed investigation about these remarks will be reported by the author in the near future.

[学科分类] 大气科学