两类低空急流的流量学诊断

DIAGNOSES OF TWO KINDS OF LOW-LEVEL JETS AS VIEWED FROM ENERGETICS

根据ＫＲ和ＫＤ方程的各项水平分布，着重讨论伴有暴雨和不伴有暴雨两类低空急流维持的动力过程，指出主要差异在于维持机理不同，尤其是能量转换方向相反，从ＫＤ向ＫＲ的正转换似乎是暴雨发生的必要但非充分的条件，同时能量转换的强度和方向不仅决定于涡度场和散度场的相对配置，还与急流的垂直分布形式直接有关。

Coupled equations of rotational and divergent Kinetic energy are used to study the mechanisms for generating and maintaining low-level jets in two real cases with and without heavy rain. As they are accountable by the relative height at which upper and lower jets are lying, individual terms in the equations are analysed with respect to their horizontal distribution. Particularly, it is the direction of enetgy converted between the rotational and divergent components rather than the intensity of the jet that detemines whether it will be acconipanied by heavy rain. A positive Conversion from divergent to rotational kinetic energy appears to be the neceseary but not sufficient condition for the heavy rain to take place. The intensity and direction of energy conversion depends not only on the relative position of vorticity and diversity feild, but also the vertical profile of the jet.