The upper level dry and cold air with high moist potential vorticity value was superposed to the low-level disturbance, which was advantageous to instability stratification strength and precipitation.
高空具有高湿位势涡度值的干冷空气叠加在低层扰动上，有利于不稳定层结的加强和降水发生。
2
And the relationship of the oasis cold island and the stratification stability of the background field has been analyzed.
并且分析了背景场层结稳定度与冷岛的关系。
3
The result indicates that: density stratification in density lock formed by hot and cold fluid can prevent heat transfer downward in the vertical channel;