关于暴雨和湿急流的讨论

湿急流是20世纪70年代末谢义炳在长期研究降水问题的基础上、在雷雨顺能量学方法对暴雨和强对流天气研究成果的启发下提出的一个科学猜想。近年来在多个暴雨实例的中尺度数值模拟结果都与湿急流猜想相符,即暴雨区中是存在将低空急流和高空急流在垂直方向上连接起来的湿急流,利用可视化技术还可将湿空气块在暴雨云团中的上升、加速和转向的轨迹清楚地展示出来。但是,湿空气块的加速并不仅仅是湿绝热上升过程中浮力的作用,动量收支的计算表明,中尺度水平气压梯度力对气块动量的增加也有贡献。文中还讨论了与暴雨和湿急流相关联的湿斜压平衡方程(湿热成风方程)等问题,指出从总能量收支平衡出发是不能解决暴雨过程中不同形式能量之间的转换过程是如何实现的。由于暴雨过程是高度非地转平衡的,也是非静力平衡的,同时还存在复杂的多尺度之间的相互作用,因此具有完善物理过程的高分辨率的数值模式是暴雨机理研究最有效的方法。

DISCUSSION ON HEAVY RAINFALL AND MOIST JET STREAM

The moist jet stream is a scientific imagination supposed by Y.B.Xie(i.e.Y.P.Hsieh) based on his long time research work of precipitation of China and animated by the static energetic method of heavy rainfall prediction supposed by Y. S.Lei.In recent year,a couple of meso-scale numerical simulations of heavy rainfall support the presence of the moist jet stream,which links the low level jet and the upper level jet in the heavy rainfall region.Using the modern visualization technology,trajectories of moist air parcels rising,acceleration and turning could be displayed on the computer screen.But,the calculation of momentum budget shows that the increasing of momentum caused not only by the buoyancy force,but also by the horizontal pressure gradient force on meso-scale.The moist baroclinic balance equation(i.e.moist thermal wind equation) was discussed,which indicated that the total energy conservation can not reveal the conversions between different energy forms.Since the process of heavy rainfall is highly non-geostrophic balance,also non-hydrostatic balance,and being multi-scale interactions,the numerical model with with fine resolution and complete physic processes is the most powerful tool for heavy rainfall research.