How to classify stratiform cloud precipitation?
Second, the characteristics of precipitation
1. Macroscopic characteristics
Layered clouds spread out in the sky like a uniform curtain. Low-level clouds look blurred; High stratus clouds spread in the sky like silk, and sometimes they don't exist at all.
Generally, the horizontal scale of layered clouds is one or two orders of magnitude larger than the vertical scale; Life span is much longer than that of convective clouds, and the life history of stratiform clouds related to weather systems is often more than one week.
Large-scale stratiform clouds are mainly produced under the condition of relatively stable atmospheric stratification. Stratiform cloud formation process: (1) Frontal cyclone cloud system formed by large-scale regular updraft movement, including cirrus, cirrostratus, stratosphere and nimbostratus;
(2) The cloud systems formed by large-scale irregular disturbances include cumulus, stratocumulus and stratocumulus.
The characteristics of turbulent field in layered clouds are: generally, the turbulence under clouds is the strongest, and the Richardson number Ri is the lowest, which is 2040 times larger than that under clouds.
2. Characteristics of temperature field: there is an inversion layer in the upper or lower part of the cloud, and the temperature gradient in the cloud is close to the wet adiabatic cooling rate, while the stratification of cumulus clouds is often greater than the wet adiabatic cooling rate, which is different.
The water content in layered clouds is close to adiabatic water content, especially in colder layered clouds.
Three: precipitation characteristics
The macro-structure of stratiform clouds associated with low-value weather systems is layered, sometimes with two layers and sometimes with three layers. There is a cloud-free zone between the two clouds, and the ice crystal particles produced by the high-level cloud fall to the bottom cloud, which is a catalytic cloud; The ice crystal particles entering the low cloud continue to grow, and the water and environment needed for the growth of ice crystals in the low cloud are the replenishment clouds.
The precipitation mechanism of this "catalytic-replenishment" cloud is that in the glacier layer (catalytic cloud layer), ice crystals fall from the glacier layer (replenishment cloud layer) and begin to melt, and completely melt into raindrops before reaching the ground. In addition, the raindrops formed in this layer contact and cloud water grows.