COMPARATIVE STUDY OF CHARACTERISTICS AND THERMODYNAMICAL DEVELOPMENT MECHANISM ON TWO TYPES OF WARMSECTOR HEAVY RAINFALL IN SOUTH CHINACOAST
MIAO Chun-sheng
YANG Yi-ya
WANG Jian-hong
LI Ping
Abstract：Warm-sector heavy rainfalls in the South China coast during April to June in 2009-2014 can be mainly divided into two types according to low level circulations;one is the southern pattern with a meridional convergence line at the west of Pearl River Estuary,which is formed by the convergence of southeasterly,southerly and southwesterly,and the other is the southwesterly pattern with a zonal convergence line at the east of Pearl River Estuary,which is formed by convergence of westerly and southwesterly.Statistics on 6-hr heavy rainfall events indicate that,during the 6 years,there are on average 73.2 times of the southerly pattern and 50.3 times of the southwesterly pattern per year.After the onset of summer monsoon in the South China Sea,the occurrence frequencies of both patterns increase remarkably.The synthetic diagnosis of pattem circulation show that,at 500 hPa,there is a broad warm high ridge and a temperature ridge is behind the high ridge,which causes an obvious warm advection at the high ridge area.There is no frontal region for the southerly pattern;For the southwesterly pattern,the circulation is a weak trough with a temperature trough falling behind the height trough with weak perturbations,the position of frontal region is near Yangzi River,the South China coast is located in the warm-sctor of the frontal region.At the vertical cross-sections of both categories of heavy rainfall,each has a strong vertical motion center stretching to 400 hPa.The convergence layer in the rainfall region is deep and with several vertical convergence centers overlapping each other.Both types of heavy rainfalls are all with abundant water vapor,with deep convective instability energy layers,and with strong release of latent heat caused by condensation of water vapor.The release of latent heat leads to the warming-up and stretching of air column,thus strengthens deep convergence and vertical velocity upward.There is stronger latent heat release in the southwesterly pattern than in southerly,but there is a stronger warm advection at middle and upper layers which is larger than the latent heat release in the southerly pattern.For investigating in thermo-dynamical developing mechanisms,WRF numerical simulations are made and the results show that,latent heat release warms up the air column,and strengthens and maintains the depth and strength of vertical velocity upward effectively.Also,the release of latent heat strengthens convergent circulation at lower layers and weakens divergent circulation at middle layers over the strong rainfall regions.The influence power can be as strong as 30％～50％ of the wind.circulation strength of the two types of the warm-sector heavy rainfall over South China coast.The release of latent heat increases and maintains the deep convection and the warm-sector heavy rainfall development.
Keywords：warm-sector heavy rainfallthe convergence line at low levelthermo-dynamical developing mechanismnumerical simulationlatent heat
Publication Date：2017-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：11( 53-63 )