The Characteristic Structure of the Occluded Frontal Typhoon in the Late Fall other than the Occlusion of Wave-shaped Frontal Perturbations

摘要

Palmén (2) has shown that many “occluded” cyclones on surface maps have never gone through a real process of occlusion although they show the same characteristic structure as really occluded polar-front perturbations. Here a well-marked surface front is not so essential for the development as was generally assumed formerly.On October 8, 1951, the Central Meteorological Observatory, Tokyo, discovered evidence of a tropical disturbance in the formative stage south of the Guam Island. The disturbance soon developed into a typhoon whose center crossed Japan in the mature stage of development. Surface maps, as well as charts for the 500- and 700-mb surfaces are shown in Figs. 1 and 2, which are reproductions of charts prepared by the Central Meteorological Observatory, Tokyo.Fig. 1 presents six surface maps for October 14, 15 and 16. At the beginning of the period there is no surface front connected with this typhoon RUTH. There is one eastern front corresponding to the northern boundary of the moist warm Tropical Maritme air. On the chart for October 14, 1500 JMT a surface cold front extending to the southwest from the center is drawn, while the eastern front corresponding to the northern boundary of the Tropical air remains nearly stationary. On the chart for October 14, 2100 JMT two surface fronts have already been brought so near each other that a separation is almost impossible. At that time a structure corresponding to the classical picture of wave-shaped frontal cyclone has already started to develop. The surface typhoon of October 15, 1500 JMT has all the characteristics of a polar-front cyclone in spite of the fact that it did not develop from a wave cyclone.By comparison of the consecutive 500- and 700-mb charts in Fig. 2 it can be seen that the area of warm air at these level increases during the developement of the “occluded” surface typhoon. Therefore, in the upper atmosphere the warm air gains area over Japan, while in the lower atmosphere the cold air gains area.