The Climate Character Of Precipitation And A Case Numerical Study Of Typical Heavy Rainfall During The First Rainy Season In South China

The first rainy season in south China is an important period of annual typical rainfall variation in China, and usually results in flood in south China. Considering the severe weather evolution under global variation, the formation, evolution and its mechanism of heavy rainfall during the first rainy season in south China are shown in the paper with a couple of observation and analysis data after a general climate analysis of rainfall feature in May. The computational effect of some physical schemes is assessed in a heavy rainfall process via numerical simulation and sensitive experiments, so that to learn the capability of physical schemes and the numerical model for simulation of heavy rainfall in the first rainy season in south China.(1) Using fifty-year daily precipitation observation data during1961and2010, we summarized the climatic and synoptic character, and find that the heavy rainfall in middle west of Guang Dong province increased significantly in the first ten-day of May. The general tendency of heavy rainfall and total precipitation increased in southern China.(2) Analysis and diagnosis with NCEP/NCAR1°×1°Preanalysis data, FY2-E satellite remote sensing data, regular surface and sounding data, and composited reflectivity of Doppler radar network are shown in this paper, so that to learn the dynamical and thenno-dynamical structure of the convective systems and their evolution. Dynamical numerical simulation is carried out with WRF mesoscale model and effective micro-physics scheme. The possible mechanism of the cause and evolution of heavy rainfall is given in this study. The analysis shows that the heavy rainfall was a result of suitable overlapping of surface cold front, shear line on850-hPa and northwest cold wind following a trough on500-hPa. Control simulation displays a proper rainfall belt being simulated with the large-scale circulation being described. Mesoscale systems, such as low-level shear, lower and upper jets are well shown in the simulation in compare with the analysis. Overlapping of the lower and upper jets benefits the sustainment of heavy rainfall. Lower jet displays its importance in water vapor transportation. Some diagnosed variables, e.g. divergence, vapor flux and divergence of vapor flux, serve to indicate the heavy rainfall very well. Energy front of θse discontinuous region is corresponding with the location of convection and heavy rainfall. The simulation illustrates that the cold front, in addition with the squall line and meso-β-scale bow echo, is the major influence system when moved southward.(3) In comparison with the control simulation, several sensitive experiments with different micro-physics and cumulus schemes are carried out. The experiments show that simple micro-physics scheme with ice phase substance gives better simulation of precipitation than the complex scheme because of the worm rainfall in the first rainy season in south China. The result reveals relatively simple transformation process among micro-physics substance, and no need to pursue complex scheme with heavy computation of phase transformation.(4) For comparison and better understanding of the micro-physics effect, we show a snow case at middle of Yangtze river in spring. This is also a convective heavy rainfall case in concern with cold front in spring. In case of snowfall, the micro-physics Lin scheme with complex transformation among vapor, liquid and solid phase gives reasonable simulation to the precipitation and feedback to the mesoscale system. Even if according only a case study, the results reveal the importance of scheme selection of micro-physics and cumulus in different type of rainfall. The effect of a scheme may be quite different from case to case.