Roll of the Tibetan Plateau concerning the formation of the Baiu front over China and the occurrence of the Baiu season

点击翻译按钮获取中文摘要

Though the Baiu (Mei-yu) front is considered to be a quasi-stationary subtropical front, rainfall zone or cloud band which corresponds to the Baiu front does not always appear over east Asia. Therefore, formation or renewal process of the Baiu front should exist in the day-to-day variation in the synoptic field. The purpose of this study is to detect the stmospheric circulation system around the Tibetan Plateau which contributes to the formation and/or evolution process of the Baiu front over China from intimate case analysis.Before the appearance of the renewed Baiu front, an east-west oriented high pressure system in the lower level is formed on the north of the Tibetan Plateau in accordance with the southeastward advancing of upper level trough to the Tibetan Plateau. This high pressure system and low pressure system to the northeast of the Tibetan Plateau are intensified when the upper level trough reaches just to the north of the Tibetan Plateau. Simultaneously, a shallow cold are … More a emerges between the low pressure system at the northeast corner of the Tibetan Plateau and a high pressure system around the North China Plain. In this time, a strong westerly-northerly wind is observed along the northern-eastern periphery of the Tibetan Plateau, and a north-south oriented wind shear line between the northerly and southerly wind appears to the east of the Tibetan Plateau. This lower level shear line or positive vorticity zone is established due to the emergence of ageostrophic northwesterly-northerly wind along the northeastern periphery of the Tibetan Plateau. In this time, plateau-trapped high pressure and low pressure systems are also observed. With the eastward migration of the cold air mass, the direction of the shear line becomes nearly an east-west orientation. It seems that the localized strong temperature gradient to the south of the cold air-mass and the water vapor supply due to the southerly wind could contribute to the evolution of the shear line to the Baiu front. Less