一次梅雨锋暴雨的边界层热通量输送与湍流动能收支分析

Analysis of heat flux transfer and TKE budget in the boundary layer during a Meiyu rainstorm

利用中尺度WRF模式对于2007年7月一次典型的梅雨锋暴雨过程进行了高分辨率数值模拟,对于边界层内的热通量输送和湍流动能的时空变化特征,以及湍流动能各收支项的分布及变化特征进行了分析。结果表明,降水发生时段内边界层热通量和湍流动能的时空分布特征与晴空日变化特征表现出显著不同,潜热通量随高度自下而上呈现"正—负—正"的分布,感热通量以负值为主,负值中心高度与潜热通量由负转正的高度相对应,湍流动能的发展高度与持续时间都有所增加,降水区近地面湍流动能弱于其他区域,但是在468 m以上高度则显著强于其他区域。降水区湍流动能的来源主要是平均风切变所产生的机械湍流,浮力作用与粘性耗散在降水期间消耗湍流动能,湍流输送作用将低层的湍流动能输送至较高的高度,使低层减小而高层增大,临界高度与湍流动能的大值中心高度对应。

A heavy rainfall caused by Meiyu front during July,2007 is simulated by high-resolution mesoscale WRF model to analyze the characteristics of heat flux transportation and Turbulent Kinetic En- ergy （TKE） in the boundary layer during the event. Results show that the temporal and spatial distributionof heat flux and TKE are different from diurnal change characteristics during the rainstorm event. Latent heat flux appears to be positive-negative-positive as the height above ground grows, while sensible heat flux is mostly minus, with the height of negative center corresponding with that of latent heat changing from negative to positive. The height and duration of the development of TKE increased during the event, with the TKE in the precipitation zone is weaker than in other areas in the near-surface but stronger at 468 m or higher levels. The development of TKE in the precipitation zone transferred mainly from me- chanical turbulence generated by shear of the average wind, while buoyancy and viscidity dissipation make the consumption. Turbulent transportation transfers TKE from near-surface to higher levels, contrib- uting to the TKE at upper levels while decreasing TKE at lower levels. The critical height between the negative effect and the positive corresponds to the height of the maximum center of TKE.