High-level Cyclones South of the Subtropical Jet Stream

[摘要] An example of a high-level cyclone to the south of the maximum westerlies, with its entire life within the network of aerological observations of the Far East, is investigated. The conditions for the formation of such a high-level cyclone are found firstly to be a rapid intrusion, of cold air into the upper westerlies from the north and to lie in the dynamic instability of the upper tropospheric westerlies. The observational occurrence of negative absolute vorticity south of pronounced jet streams, in connection with the cutting-off process of a low, is illustrated in the cross section and is reasoned by aa perceptible influence of the vertical motion in changing the vorticity about the vertical. It is also presented in terms of the height profiles of selected isobaric surface that in that case the upper low does not extend down to the lower level.The westerly displacement of the high-level cyclone is mainly dependent on the easterlies prevailing over the Japanese Islands above the level of the tropical tropopause. The thermal structure is studied in the vertical west-east cross section through the center of high-level cyclone. The outstanding example is the formation of an isolated island of warm air below the tropical tropopause through the descent over a cold cyclonic vortex. A new “false” tropopause is seen to form as the lower limit of such descent.

[学科分类] 大气科学