Recently, rain, sleet, snow, freezing rain, ice particles ...... can often be seen in the weather forecastIt is not difficult to see the complexity of the precipitation phase this time. Affected by this round of cold wave, the daily maximum temperature dropped to 0 or below in most parts of North China, most of the Huanghuai, western Jianghuai, Jianghan and central and northern Hunan. Why is it around 0, where it rains, somewhere it snows, and somewhere it freezes? Let's take a look at the introduction of meteorologists
*Zhang Feng, Senior Engineer of the Meteorological Observatory: In the process of precipitation in winter, there may be a variety of different precipitation phases such as rain, snow, ice particles, freezing rain, etc., and different precipitation phases may be converted to each other. What causes the different phases? The most important thing is the vertical distribution and variation of temperature at different altitudes in the atmosphere, which is the single most important factor in determining whether it rains or snows.
Vertical distribution of temperature.
How does it affect the phase change of rain and snow?
If there is a relatively cold layer of air less than 0 from the ground to the sky, the snowflakes will not melt as they fall, and they will eventually fall to the ground and it will be snow. If there is a warm layer near the ground, the snowflakes will gradually melt into raindrops as they enter the warm layer as they fall. The last thing I saw was the rain.
In another more complicated situation, the snowflakes of the cold layer enter a thin warm layer in the process of falling, at this time, the surface of the snowflakes partially melts, forming a state of liquid surrounding the middle snowflakes. As it continues to fall, it enters a cold layer, at which point the liquid on the surface freezes again. That's when ice grains come in.
If the warm layer in the middle is thicker, then the snowflakes will completely melt into raindrops after entering the warm layer, and the raindrops will fall further, and after entering the cold layer, they will not freeze again, but become a supercooled raindrop. When a supercooled raindrop falls on the ground, it will freeze quickly if it encounters an object below 0, which is freezing rain.
There is another mechanism for the formation of freezing rain, without the participation of ice particles and snowflakes, it is the state of raindrops when it is formed, and it will continue to become supercooled in the process of growth and development in the cold layer, and finally fall to the ground to freeze, which is also a mechanism for the formation of freezing rain.
The formation mechanism of hail is completely different from that of several different phases of precipitation mentioned above. Hail is mainly in the clouds, due to the strong upward movement, pushing small ice crystals to grow and grow in the process of rising, becoming larger and larger, when the hail becomes large enough, and the updraft cannot support it, it will fall to the ground, forming hail.
The actual atmosphere will be more complex and changeable, so phase forecasting has always been one of the difficulties faced by forecasters in winter precipitation forecasting. Remind everyone that at present, most of the central and eastern parts of China have a wide range of rain, snow and freezing weather, and the public should try to pay attention to the condition of roads and traffic when going out, and pay attention to cold and warmth.