| In 2013, the onset of Meiyu is late and the outset is early in the Jianghuai valley. As the western Pacific subtropical high is to the south as compared with the normal, the rainfall had characteristics of intermittent, short-time and hard. Compare the hard rainfall on June23 with June25 by using the NCEP reanalysis data, there are significant differences in the generation of upper throuth, the source of cold air, the shear line, the location of the low-level jet and the transport path of vapor. In this study, the measured date of precipitation, objective analysis data and WRF numerical simulation fine data were used to analysis developing and maintaining mechanism of heavy rainfall on Meiyu front. The results show that, the heavy rain event was close related to the developing, maintaining and mergence of two meso-scale convective systerms. The configuration of Meiyu front, the coupling of upper and lower jet, the lower-level convergence, upper-level divergence and the short wave trough in middle level of troposphere is advantaged for causing strong convection and heavy rainfall. The cooperation with the pumping action of upper trough and the feedback of latent heating has two positive effects. On the one hand, transport water vapor to the middle troposphere to strengthen the low level positive vorticity. On the other hand, transport latent heat to the middle troposphere to avoid the accumulation of latent heat in the middle troposphere. All of these is advantageous to the unstable situation and upward movement, which affects the movement and development of the mesoscale convective system. At the end of this study, carry out a series of sensitivity tests of temperature and humidity to find out the different maintaining mechanism between the two MCS in Jianghuai valley. The results improve that the mechanism of the two MCS in June23 is different and the upper trough is in favor of the developing and maintaining of heavy rainfall. |
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