The Environmental Conditions And Structure Characteristics Of Linear Convective Systems With No Stratiform In Dry And Moist Environmental Conditions Over Yangtze And Huaihe River Basin

The synoptic circulations and surface weather patterns of19linear convective systems with no stratiform(NS) occurred over the Yangtze and Huaihe River Basin from June to September during2007—2010were investigated. The environmental conditions related to them were classified as dry and moist environments according to precipitable water<50mm or≥50mm. The synoptic patterns of5(14) examples in dry (moist) environments could be classified into post-trough and the rim of subtropical high (pre-trough, post-trough and the rim of subtropical high) patterns. The post-trough pattern is the major type in dry environments, convection systems occurred frequently in dry and warm areas with low humidity. These systems in the dry environment develop vigorously and easy to produce high wind and hail. In moist environments, the pre-trough pattern is the major type that characterized various surface systems including: stationary front, inverted trough, cold front and warm front. The most unstable layer is relatively high and water vapor is sufficient. Heavy precipitation occurs in the moist environment with high frequency. The aforementioned analyses show that the significant differences exist between in dry and in moist environmental conditions while severe convective systems occur, the detail mechanism of convective system in dry and moist environment should be investigated in the future.Wet typical case of linear convective systems with no stratiform(NS) on July82007were analysised using high-resolution model data. The evolution process of the strong convection was divided into three stages:(1) the forming stage:7～8UTC;(2) the maturing stage:9～10UTC;(3) the weakening stage:11～12UTC. Characteristics of linear convective systems that were simulated were investigated at each stage, studies have shown that, thunderstorm high pressure was formated when systems matured, and the mesoscale low pressure were generated in front of meiyu front. Intensively variable pressure and temperature were concentrated in the convective zone, in addition, the heavy rainfall caused by the mesoscale convective systems on meiyu front is usually on the border of the systems. In maturing stage, comparing the internal structure of the NS case with the bow echoes(BE) convective systems occurred on June32009simulated by Liang Jianyu (2012), it revealed the structure characteristics of the example occurred on July82007and the reason why no or less of stratiform clouds were caused. In the convective zone of the NS systerms, there was a updraft in front of the systems guided by the front-to-rear inflow, in the process of ramping up, air flow met the rear-to-front inflow in the middle troposphere. Low temperature environmental air which was entrained into the convective zone reduced upward movement, thus it led to the formation of convective scale subsidence, and before the subsidence reached the ground, it had been shunted to the back of the system. Another part of the inclined airflow continued to upward and forward move clockwise with the rear-to-front inflow of middle and high troposphere together. The inhibition of the rear-to-front inflow above the middle troposphere may be the reason why no or less of stratiform clouds were caused.