The Variation Characteristics Of Heavy Rainfall In South China In The Past 40 Years And The Reasons For The Significant Increase Of Heavy Rainfall In Summer And Autumn

Base on the daily precipitation data from 824 stations in China from 1979 to 2018.And ERA5 and NCEP/NCAR reanalysis data.The temporal and spatial variation characteristics and causes of heavy rain in South China were studied,the main circulation patterns affecting heavy rain in South China were found,and the causes of the changes of heavy rain in summer and autumn were revealed.The results are as follows:(1)Using the hybrid clustering algorithm of REOF and K-Means,the rainstorm area in China is divided into 11 regions,and the obliquely rotated T-mode principle component analysis(PCT)algorithm is used to classify the atmospheric circulation to obtain 10 circulation patterns.Among them,South China is the main area of the study.The circulation pattern that most affects regional rainstorms is type 7(cyclonic type),the subtropical high at 500 h Pa shows a meridional extension,and there is a cyclonic water vapor transport at 850 h Pa.In the past 40 years,the total amount of heavy rainfall has shown a significant upward trend.(2)In the past 40 years,the significant increase in autumn rainstorm rainfall in South China is related to the increase in precipitation caused by the slower decay rate and longer duration of tropical cyclones in South China.Among them,the increase of near-surface temperature in autumn in South China is conducive to the increase of surface enthalpy flux,which leads to the slowdown of cyclone attenuation,while the vertical shear of the lower wind field weakens,the upward movement of the middle layer is strengthened,and the increase of the upper layer divergence is also conducive to the development of the cyclone and the maintain.The numerical model conclusion proves that the rise of the sea temperature at the cyclone generation place enables the cyclone to carry more water,the attenuation slows down after landfall,and the duration is longer,which brings more water vapor to the heavy rain.On the other hand,the precipitable amount of atmospheric precipitation in autumn in South China increases significantly,and the apparent water vapor sink and apparent heat source increase significantly,which means that the atmosphere is heated,the atmosphere can store more water,and provides sufficient water vapor conditions for the increase of rainstorms.In addition,the atmosphere Instability increases,which is conducive to the increase of heavy rain.(3)In the past 40 years,the summer torrential rainfall in South China has increased significantly,and there was a significant mutation in 1993,and it increased significantly after the mutation year.After the abrupt year,the subtropical northwestern Pacific has an abnormal subsidence movement,which is beneficial to the enhancement of the subtropical high and the enhanced water vapor transport on the south and southwest sides of the subtropical high.In addition,the latent heat flux in the Western Pacific Warm Pool and the South China Sea region increased abnormally after the abrupt year,the evaporation was enhanced,and the moisture over the region increased.The average input water vapor at the boundary increased,the north wind water vapor transport was abnormal in the north of South China,and the average output water vapor at the northern boundary decreased,water vapor increase.The abnormal convergence and rise of water vapor in South China led to an increase in the summer rainstorm in South China.