Mei-Yu front is one of most important weather event in southeast China, which is strongly related with some kinds of severe weather, such as meso-scale storm, and mesoscale convection Clusters (MCCs) in summer season. During Mei-Yu season, the long-lasting of intense but fitful rainfall that is sometimes damaging Chinese societies can be contributed to the Mei-Yu frontogenesis. The mechanism of Mei-Yu frontogenesis so far is still a great challenge in meteorological dynamics. Recent synoptic investigation and field-observation have discovered some new aspects of Mei-Yu front, as well as its ambient airflow. Among others, the most distinguishing characteristics of Mei-Yu frontogenesis from typical front is the strong gradient of moisture or derived variables like potential temperature or equivalent potential temperature; the both sides of Mei-Yu front exist so-called easterly cold surge and southerly warm surge embedded respectively in cold/dry and warm/moist air mass; such surges intermittently influence the area of Yangtse River of southeast China during Mei-Yu season and could be considered as the unbalanced potential vorticity current that is of ageostrophic characteristics; since the long-term observation had depicted the quasi-stationary character of My-YU front, therefore, it is very rational to assume both the term of Mei-Yu front is just the interface zone of surges and which kept the front to be stationary; in other words, the theoretical research can be simplified so that the main concern is focused on the imbalanced mass and its characteristic contrast adjusted to the frontogenesis (the numerical sensitive tests had shown very clearly, neither stronger cold surge, nor stronger warm surge could make the stationary of front); Such consideration leads to the implementation of geostrophic adjustment theory under the influence of imbalanced PV surges, with the constraint of potential vorticity (PV) conservation. In addition, we should declare that in the following analytical approaches, the beginning point of frontogenesis mechanism always starts from the imbalanced mass, instead imbalanced momentum field in which it implies that the initial velocity should be set to zero in such analytical solutions and the imbalanced PV surges depicted through the imbalanced mass filed.
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