What are the beneficial effects of the cold wave on agriculture? What is the structure of the cold wave?

Lead: Under the background of global warming, there will be more and more extreme cold events around the world, such as the cold wave in winter in China. So, what are the beneficial effects of the cold wave on agriculture? What is the composition of the cold wave? Let's have a look.

The favorable influence of cold wave on agriculture

1, cold wave brings cooling, which may bring snowfall. Snow has a certain thermal insulation effect on crops to prevent frostbite of crops;

2. Cold wave can freeze some pests to death and reduce pests and diseases;

3. The snow brought by the cold wave can form snow water after melting in the following spring, which can help crops to survive the spring drought and make the water source of crops grow more abundant in spring.

Other effects of cold wave weather on agricultural production

The cold wave is a large-scale cold air activity, so when the cold wave strikes, the weather changes dramatically. However, due to the different seasons, geographical conditions and cold wave intensity, the weather changes in different places are also different. Generally speaking, the most prominent thing in winter is that the temperature drops and the wind direction changes dramatically when the cold front passes through. There is often a strong northerly wind behind the front, sandstorms in northwest and Inner Mongolia, and occasional snowfall north of Huaihe River. As soon as the cold front passed the weather, the eyes lit up. After the cold front crosses the Huaihe River, the precipitation opportunities increase, especially when the cold front is slow or static in the south of the Yangtze River, the precipitation time will last for a long time.

Cold wave weather has the greatest impact on agriculture. The temperature drop caused by cold wave can reach 10℃ or even above 20℃, which usually exceeds the cold tolerance of crops and causes freezing damage to crops.

The physiological temperature of cold tolerance of different crops in different regions also has certain limits. For example, spring wheat, beans and oil crops in the north are all cold-tolerant crops, which can tolerate the low temperature of -7 ~- 10℃, radish can tolerate the low temperature of -6℃, Chinese cabbage can tolerate the low temperature of -4℃, and corn and potato can only tolerate the low temperature of -3 ~-2℃. Moreover, the cold tolerance of various plants at different growth and development stages is also different. For most plants, when the temperature drops to about 0℃, it will obviously suffer. Almost every cold wave process in history will cause crops to be affected in a large area, and the degree of disaster will vary greatly due to the different invasion range of cold air.

After the cold wave crosses the border, the temperature drops sharply, and the cooling can last for one to several days. The temperature drop in northwest and north China is large, and that in central and south China is small, but freezing frost may occur. For example, in 1955 and 1 two months, the extreme minimum temperature of-14.6℃ appeared in Wuhan,-19.2℃ appeared in Shanghai and -2. 1℃ appeared in Nanning. Among them, many areas in Jiangsu, Anhui, Hubei, Hunan, Jiangxi and other provinces experienced 10- 15 days of continuous heavy snow and freezing rain, which blocked traffic and telecommunications and caused heavy losses in agricultural and animal husbandry production. In spring and autumn, in addition to strong winds and cooling in the south of the Yangtze River basin, there are often rain and snow in cold wave weather. Sometimes there will be severe weather such as thunderstorm and hail, especially the frost caused by the last frost, the first frost and the cold wave, which is more threatening to crops in North China and Central China and often leads to serious production reduction.

Composition structure of cold wave

the polar vortex

In winter in the northern hemisphere, the cyclone vortex around the polar region at 500hPa in the upper troposphere is called polar vortex. It is a sign of a wide range of extremely cold air, with a shallow cold high pressure on the ground and a low pressure circulation of 700 hectopascals.

Polar high

① There is a complete anticyclone circulation on the 500 HPA map, and at least a closed isoline can be analyzed; (2) There is a considerable range of independent warm centers cooperating with the geopotential height field; ③ The main body of warm and high pressure is in the north of 70 N; (4) high pressure for more than three days.

Cold wave ground high pressure

In the whole process of cold wave, the ground high pressure behind the cold front is mostly a thermodynamic asymmetric system, and there is a strong cold advection in front of the high pressure; The back is warm advection, the temperature advection in the central area tends to zero, and a few high pressures are always cold. It can indicate the strength of cold air, and the central moving path can be used as the moving path of cold air.

cold front

There is a strong cold front on the high pressure front of the cold wave ground, which inclines to the cold air side with the height, and there is a strong front area on the high altitude isobaric surface. The front area is wide and narrow in structure, and there are obvious cold troughs and front areas on the isobaric surface below 300hPa.