Differences And Characteristics Of Multi-scale Cyclones In The Changjiang River-Huaihe River Valleys Between April And June

Based on ERA-Interim 6h reanalysis data from 1986 to 2015,characteristics of development rate and movement of multi-scale cyclones from April to June over the past 30 years in the Changjiang River-Huaihe River valleys(CHV)are investigated by using improved extratropical cyclone objective recognition method.The diameter of middle-scale cyclones is between 4 deg.lat.and 10 deg.lat.,and the diameter of bigger-scale cyclones is greater than or equal to 11 deg.lat..The climatic characteristics of extratropical cyclones in different scales affecting the CHV were studied by the scale classification of the development cyclone.And the circulation configuration and dynamic factors in favor of different scale cyclones were analyzed.Finally,the typical examples were extracted to compare the dynamic process of cyclones in different scales.The results show that:(1)The development rates of cyclones upgrade firstly and then descend,while the bigger-scale cyclones rise significantly and the middle-scale cyclones nearly stay the same.As for the source of cyclones,the bigger-scale cyclones are focused on the border of Hunan-Hubei,while that of middle scale is located in eastern CHV.Each scale cyclone source is distributed in the large value region of the whole atmospheric non-adiabatic heating element.There are shear line with the smaller speed in the northern CHV during the primary stage of cyclongenesis.Besides,geopotential height anomaly is negative in the lower troposphere and positive at high level,so cyclones in the CHV are shallow systems.No matter what scale cyclones,there are east and northeast moving paths,but the proportion of northeast moving path in the larger-scale cyclones increased.(2)Based on the data set of multi-scale developed cyclones from April to June over the past 30 years in the CHV,the intensities of cyclones in the CHV are defined.The differences and causes of the precipitation and intensity of multi-scale cyclones in the CHV are investigated.The results show that the strength of bigger-scale cyclone is on the decline with a quasi three-year cycle variation,consistent with the tendency of the overall cyclone.However,the intensity of middle-scale cyclone shows a rising trend with no obvious cycle period.As for the correlation,the intensity of bigger-scale cyclone is more relevant with overall cyclone intensity than that of middle-scale cyclone,while the middle-scale cyclone occurs more frequently and is more correlated with the total frequency.The intensity of both-scale cyclones has significant positive correlation with precipitation,and the intensity of the larger cyclones is stronger with the precipitation.The precipitation caused by the middle-scale cyclone is non-negligible.Besides,the latitude distance between the center of the bigger-scale cyclone and high jet axis is less than which of middle-scale cyclone.The vertical movement and the vapor transportation of the bigger-scale cyclone are stronger than which of middle-scale cyclone.The more extensive and stronger precipitation will happen.(3)Comparing the typical example of different-scale cyclones which produce extreme precipitation,the strength and area of large-scale cyclone are greater than which of middle-scale cyclone.In addition,the two scale cyclones are both eastward.They are controlled by the strong Western Pacific Subtropical High which is zonal distribution,and are affected by the eastward of short wave trough over the Plateau.The precipitation of large-scale cyclone is formed by the intersection of moist air and cold air from the outer cold eddy.And the transport of warm moist air by strong southeast airflow leads to the precipitation of middle-scale cyclone,characterized by warm area precipitation.