Moisture Sources Of Extreme Precipitation Events In The First Rainy Season Of South China And Related Dynamic Processes

The research in extreme precipitation events is attracting more and more attention due to their catastrophic impacts on the social economy,human life,property,and ecosystems.The first rainy season(hereafter as,FRS)over South China,which is occurred in April-May-June,contributes more than 40% to the local annual total precipitation amount.Thus,understanding the moisture source and dynamic processes responsible for the FRS extreme precipitation over South China is of great importance for both scientifically and for the societal impact.We conduct the weather pattern classifications in this work by using “K-means ” algorithm on the circulation of selected extreme precipitation events over South China based on the CN05.1 grid point precipitation datasets and the ERA-Interim reanalysis datasets.The Lagrangian model FLEXPART was employed to address the moisture pathways and moisture sources that are associated with extreme precipitation in South China based on circulation classification.In addition,the moisture source of FRS extreme precipitation differences between wet and dry years are also well reproduced by the synthetic analysis method of dry and wet years.The main results include the following four aspects:(1)The circulation associated with the FRS extreme precipitation over South China are classified into three typical weather patterns,Type Ⅰ(30.3%),Type Ⅱ(42.5%)and Type Ⅲ(27.2%).The distribution of geopotential height anomaly for Type Ⅰ is characterized the low trough extending from Japan to South China,while Type Ⅱ and Type Ⅲ are characterized by “west negative-east positive”and “north positive-south negative” patterns over East Asia with anomalous cyclone over South China,respectively.Type Ⅱ accounts for the largest proportion and mainly occur in May-June after the onset of South China Sea summer monsoon.The extreme precipitation events from Type Ⅰ mainly concentrate in April and May,and the events from Type Ⅲ are nearly evenly seen over the whole FRS.(2)The main moisture source areas for extreme precipitation in FRS over South China are Southeast Asia,South China,the South China Sea and the Bay of Bengal,the contribution of land regions is larger than that from ocean regions.The contribution of ocean regions for Type Ⅱ is larger than the other two types,which is resulted from the more moisture contributed by the Indian Ocean(the Bay of Bengal and Arabian Sea)associated with the onset of South China Sea summer monsoon.The contribution of land regions to the extreme events of Type Ⅰ is much larger than the other patterns,which mainly attributed to the contribution of Southeast Asia,this is related to the large moisture content in Southeast Asia and the small loss during the transportation process because closely to South China.(3)The South China sea,Southeast Asia,South China and the Bay of Bengal are the main moisture contributors to the FRS extreme precipitation of dry and wet years,the contribution of land source area is larger than ocean source area in dry and wet years,the moisture contribution of land source area in wet years is larger than that in dry years.The moisture contribution of the Indian Ocean(Bay of Bengal and Arabian Sea)to Type Ⅱ events in dry and wet years is greater than the other two types,which is related to the onset of the South China Sea summer monsoon,and the contribution difference with the other two extreme events in wet years is greater than that of the dry years.