水汽凝结过程与高低空急流对冷锋环流的作用

Effects of Both the Condensation Process of Moisture and Upper and Low-Level Jets on the Cold-Front Circulation

文中利用包括水汽凝结过程的湿大气原始方程模式，研究了高空西风急流和低空南风急流中冷锋环流和垂直运动场的演变，计算结果显示：水汽凝结过程的加入，使锋区垂直运动和锋面环流大大增强，上升运动随时间发生剧烈的变化；湿过程对锋面环流的作用发生在水汽饱和并发生凝结之后，未饱和水汽的存在对锋面环流没有什么作用；与干大气模式中高空西风急流是造成冷锋环流演变的主要因子情况不同，低空南风急流在湿大气中对锋面环流有极为重要的作用，其作用至少与高空西风急流相等；在激发锋区重力波上，低空南风急流的作用可能更加明显；水汽凝结湿过程的加入，不论是在高空西风急流下还是在低空南风急流中，都能在锋区激发出波长约为３００ｋｍ的重力波。

The evolutions of both the cold-front circulation and vertical motion fields in the upper-level westerly jet and low-level southerly jet are investigated by using a two-dimensional primitive equation model including moisture condensation process. The analysing results show that the moisture condensation enhances greatly the frontal circulation and vertical motion in the frontal zone, and causes a severe change of the upward motion with time. The effect of moist process on the frontal circulation occurs as the moist air saturated and condensation produced, and the presence of the unsaturated moist air is shown to have little effect on the frontal circulation. In moist case, the low-level southerly jet plays an extremely important role for the evolution of cold-front circulation which is very different compared to the dry case in which the upper westerly jet plays a main role. The effect of low-level jet in the moist case on exciting gravity wave in the frontal zone may be more important than that of the upper-level jet. The condensation process of moisture also plays an important role on the excitation of gravity wave which has wavelength 300 km and propagates into the warm sector with wave velocity greater than the frontal velocity.