中尺度干、湿对流影响环境场的差异分析

THE DIFFERENCE OF INFLUENCE OF DRY AND MOIST CONVECTION ON CIRCUMSTANCE

用1999年6月一次梅雨锋大暴雨过程高分辨的敏感性数值模拟结果分析了对流活动对大尺度环境的反馈作用,共设计了两个敏感性方案:干绝热过程(干调整)和包含水汽及凝结潜热释放的湿过程(湿调整),两种调整过程包含的不稳定能量不同,对环境场造成的影响也不同。通过分析,得到以下几点结论:在对流强盛期间,湿调整比干调整更能增强底层辐合和高层辐散;当对流消失后即大气从不稳定调整到稳定状态后,两种调整过程对水平风场的影响基本相同;湿调整比干调整产生的垂直速度更大;湿调整比干调整更能使大气底层温度降低、高层温度升高。干、湿调整过程都是不稳定能量释放过程,当层结不稳定能量释放、产生强对流时,强上升运动中心的中下层辐合增加、高层辐散增加,当对称不稳定能量释放时,高层指向冷区一侧的水平风分量增强,底层指向暖区一侧的水平风分量增强。水平风场受对流影响后改变的量值与原有量值相当;不稳定能量释放可影响到对流中心周围5个经纬距以上的范围。

When it is forced to initiate by instability, convection can influence on wind, humidity and temperature and instability of circumstance by vertical transportation. To analyze the effect of convection, we design two cases: one is the dry process and the other is the moist process. The unstable energy is different in two processes, making different effects. From the study we draw some conclusions: When convection is strong, the moist adjustment can enhance the convergence in the bottom layer and the divergence in upper layer more than the dry adjustment. When the convection disappears, the two processes have the same effect on the wind. The moist adjustment has a greater vertical velocity. The moist adjustment can increase temperature more in the lower atmosphere and decrease it more in the bottom atmosphere than the dry adjustment. The dry and moist processes both release instability. When the conditional instability is released, the convergence in the middle and bottom layers and divergence in the upper layer will enhance at the center of the updraft motion; When the conditional symmetric instability is released, the south wind will increase in the bottom layer and weaken in the middle and upper layers at the center of the updraft motion. The change of horizonal wind by the effect of convection is comparable with its original quantity. The release of instability can affect the ambient within 500km around the center of the updraft convection. The release of instability can also change the temperature around the convection, which will increase the temperature in the upper layer and decrease the temperature in the lower layer.