Large, Synoptic and Meso Scale Variations of the Baiu Front, during July 1982

[摘要] In part I of this study, cloud variations in/around the Baiu front in July 1982 were studied. The purpose of Part II is to clarify inclusively the structure of the Baiu frontal zone and features of the Baiu frontal disturbances which would be related to the cloud variations studied in Part I, analyzing relative vorticity fields in July 1982. Attention is focused on the relationship and interaction between the upper westerly jet (W-jet) in 40°N-50°N and the Baiu low-level jet (B-jet) in 30°N-40°N.In monthly mean, the Baiu frontal cloud zone, which was formed in 30°N-40°N, coincided with a low-level positive vorticity zone associated with a B-jet. Over the continent, the positive vorticity zone was confined to the lower layer. The zone merged with the positive vorticity zone associated with the W-jet around the east coast (-120°E) of the continent. Over the region east of 120°E (Japan-the northwestern Pacific), the deep positive vorticity zone of a baroclinic structure was formed in the Baiu frontal zone. This will account for the difference in cloud features of the Baiu frontal mesoscale systems between the continent and the Japan-northwestern Pacific region described in Part I.With the change of large-scale circulation in East Asia, the relationship between the W-jet and the B-jet changed during the analysis period. Concurrently, the frontal structure, features of disturbances and cloud amounts in the Baiu front, also changed significantly in the 120°E-140°E region. Three situations of the Baiu front ((1) active-deep, (2) active-shallow and (3) inactive phases) are classified. The vertical structure of the Baiu front and features of the disturbances in these three phases are studied in detail. Over 120°E-140°°E, the Baiu frontal mesoscale disturbances showed a deep-baroclinic structure in the active-deep phase, while in the active-shallow phases they showed a shallow structure and located to south of the deep mesoscale disturbances in the northern frontal zone of the W-jet. In both active phases, the mesoscale disturbances in the Baiu frontal zone began to develop around the east coast (-120°E) of the continent under the influence of the upper-level disturbances in the W-jet propagated from Central Asia.

[学科分类] 大气科学