双路一维时变对流云数值模拟研究

EFFECT OF CLOUD-PRECIPITATION DEVELOPMENT ON THE FORMATION OF VERTICAL CIRCULATION IN A SUPERCELL STORM

中文摘要:

      超级单体风暴出现与一个独特的垂直环流的形成相关联着,其特点是一支强的云内上升气流与一支紧靠着它的湿下沉气流相伴。在条件不稳定大气中,一支强湿上升气流的形成是很容易理解的,但一支湿下沉气流的发生则比较复杂。看来在湿下沉气流发展中有二个因素是最为重要的,一是云体要有一个预发展过程,形成一个足够大的对流云体和产生大量的凝结水;二是在云的移向后侧有突发性的干冷空气的平流突入,而不是经常起阻尼作用的湍流和夹卷混合。为了试验这一设想,设计了一个双路一维时变对流云模式,一支描述云和降水发展过程,并供给水凝结物,另一支描述干冷环境气流的中层突入和下沉气流的发展。试验结果表明,这一设想原理上是合适的,说明云和降水发展过程在中尺度垂直环流形成中起重大作用,而且干冷空气突入量,水凝结物供应量,以及凝结物的微结构等影响着下沉气流的强度。

英文摘要:

      A supercell storm has a vertical circulation composed of a strong updraft and a downdraft. It is easier to understand the formation of the strong updraft in the case of an unstable stratification but it is more complex in describing the process of the downdraft inside the cloud. For this reason, two factors should be considered, one is that the ambient dry-cold airflow breaks into the rearpart of the cloud rather than slowly mixes by entrainment and turbulent processes; the other factor is the transport of liquid hydrometeors from the updraft region to the downdraft region. A one-dimensional time-dependent numerical model was designed which has two branches. The first branch is used to describe the cloud-precipitation developing process and to provide the liquid hydrometeors; the other one is used to simulate the development of the dowadraft. The calculation indicated that the dry-cold ambient airflow breaking into the rearpart of cloud plays a critical role in the occurrence of the downdraft while the transport of liquid hydrometeors satisfies the requirement for the persistance of moist adiabatic process otherwise the downdraft will be damped. In addition, the intensity of downdraft varies with the strength of the ambient air injection, with the amount of liquid hydrometeor transport, and with the microstructure of hydrometeors as well.