Why is there a snowstorm in China this time?

The global climate background this year is La Nina. We listen to and talk about El Nino almost every year, but we are still strangers to her sister La Nina.

La Nina is a climate phenomenon contrary to El Ni? o, which refers to the phenomenon that the sea water in the equatorial eastern Pacific (near Peru) continues to be unusually cold in a large range, and the surface temperature of the sea water is lower than the climate average by more than 0.5℃. A small 0.5 degree, as far away as South America, has a great influence on us.

1. How did the South Pacific issue spread to the whole world?

The ocean current movement on the ocean surface is mainly restricted by the sea surface wind. The existence of trade winds makes a lot of warm water blow from Peru in the eastern Pacific to China and Japan in the equatorial western Pacific. The warm water in the equatorial eastern Pacific was blown away, mainly supplemented by the cold water below the sea surface. The SST in the equatorial eastern Pacific is obviously lower than that in the western Pacific, which makes the airflow in the equatorial eastern Pacific sink, thus intensifying the upward movement of the airflow in the western Pacific. In fact, it weakens the subtropical high in the western Pacific, strengthens the trade winds and westerly winds, and further intensifies the development of cold water in the equatorial eastern Pacific, forming a vicious circle. Meanwhile, La Nina's influence has spread from Peru to the whole world, especially to China.

2. The influence of the rising movement in the western Pacific on China.

The intensification of the ascending movement in the western Pacific leads to the subtropical high that has been far away from Chinese mainland and entered the Pacific Ocean in winter and half a year, and further away from the mainland, further reducing its resistance to the cold air mass in the mainland. Obviously, without the obstruction of the subtropical high, the wind belts on both sides of the subtropical high, one is the strong cold westerly belt in the north and the other is the trade wind belt in the South Indian Ocean, can directly drive the mainland and sweep across Asia, and China is under the control of these two wind belts.

3. The influence of the strengthening of the wind belt on China

(1) westerlies

The influence of westerlies on China mainly comes from two directions. One is to add oil and vinegar to the strong cold air from Siberia in the north. The cold air mass comes from the polar direction. It's colder and stronger. Because the evaporation in the Arctic Ocean is small and the air is extremely dry, mainly due to strong winds and cooling processes, there will be no large-scale snowfall. It was this cold air that had the greatest influence on China in the past, and we were most impressed. There is little snowfall in the northeast this year, which is mainly affected by the northern air mass, as before. And he came from the marked army, which we seldom pay attention to, but with the help of the westerly belt, he came from the Atlantic Ocean in Iceland, crossed the Mediterranean Sea in Europe, and swept the whole Eurasia. As he came from the humid Atlantic Ocean, this cold air brought a lot of snowfall, which proved this. This year, because of this strong cold and humid air current, it snowed for the first time in a hundred years in an extremely dry place like Baghdad. The snow in Central Asia, especially in the mountainous areas of Afghanistan, exceeded two meters. The snowfall in relatively arid Gansu this year is more than twice that of normal years, the highest in 60 years. Interestingly, the snow in our sky actually comes from the Atlantic Ocean.

(2) Trade winds

As the direct point of the sun moved southward, the trade winds had little influence on China in the past.

However, due to the strengthening of La Nina and the gradually heated and humidified air mass diverted from the Qinghai-Tibet Plateau to the southern wing of the Himalayas, the southern part of China is affected by a large number of warm and humid air currents from the Indian Ocean, resulting in the temperature in the Yunnan-Guizhou Plateau being even higher than normal.

(3)*** The same influence

Due to the weakening of the Pacific subtropical high, the cold air in the north and south can directly drive the inland of China, and the warm and humid air flow brought by the trade winds controls the south, such as Shenzhen, where the humidity is as high as 90%. In the past, the cold air in the north went south, controlling the whole country, and the whole country was cold and dry. But this year La Nina led the trade wind to bring a lot of water vapor, which merged with the dry and cold air mass in the north in the middle and lower reaches of the Yangtze River, forming a large-scale blizzard. The principle of snowfall is the same as that of rainfall. Now, as soon as the temperature rises, it rains heavily, even rainstorm. From the scope of influence, the degree of disaster is decreasing from east to west, and the coastal provinces have little influence. It can be seen that the water vapor mainly comes from the Indian Ocean rather than the Pacific Ocean, and the trade winds have a great influence.

Two. Local analysis

1. The middle and lower reaches of the Yangtze River, Anhui and Hubei

This area is located near 30 degrees north latitude, where the westerlies and trade winds meet. The intersection of north and south air currents will definitely cause a lot of snowfall. Another reason is that there are many lakes in the middle and lower reaches of the Yangtze River, and a large amount of water vapor evaporated from the local water surface is also the source of snowfall.

1. Hunan

Hunan mainly concentrated the remaining cold air in Hengyang area of Chenzhou, that is, at the foot of Nanling Mountain. Because of the blocking of Nanling Mountain, all the last strength of cold air was vented to Hunan.

2. Guangxi and Guizhou

Yunnan-Guizhou Plateau used to be influenced by two air masses in the north and south, but this year it was extremely strong, too wet and too cold, causing severe freezing rain.

3. North

I was impressed by the scenery in the north before, and the snow in Wan Li remained unchanged. The northeast is mainly affected by the dry and cold air mass in the north, so the snowfall has not changed much. From the satellite cloud picture, it hardly snows these days. However, due to the strong westerly wind, the northwest region brought a lot of water vapor from the Atlantic Ocean, and the snowfall was more than normal.

The third is the impact of snowfall on the south.

Snow is a natural phenomenon, and it rains every year in the north. Even if there was a snowstorm, it didn't cause such a serious problem as this year. Why does snowfall in the south cause so many problems? This paper mainly makes a comparative analysis with the cold north.

1, freezing rain

Now the ground temperature in the north and south is below 0℃ for a long time. But the north is a steady cold air from low altitude to high altitude, so all the snow falls.

In the south, because the cold air force has weakened and the warm air force is strong, a warm air layer with a temperature higher than 0℃ is formed over 1500m to 3000m, and the temperature above 3000m is lower than 0℃. The vertical structure of the atmosphere is cold up and down and warm in the middle, that is, there is an inversion layer near the ground. The atmosphere is divided into ice crystal layer, warm layer and cold layer from top to bottom. In this way, the snow falling from the ice crystal layer in the sky melts into raindrops when passing through the warm layer, and then enters the cold air layer near the ground, and the raindrops quickly cool down and become supercooled raindrops. Before the raindrops turn into ice, the temperature drops below 0℃, forming freezing rain.

2. Freeze

It snows in the north, so it won't freeze, because the temperature is too low to melt. Even if the daytime temperature in Gao Xue melts, the north is completely controlled by extremely dry cold air masses. For example, the humidity in Lanzhou is only 15%, so the melted water will soon evaporate back into the air and the ground will be dry forever. It is very rare for trees and wires to freeze.

There is ice everywhere in the south. When freezing rain falls on the ground, branches, wires and other objects, it will gather and cover the surface of the object. Because the temperature of an object is below zero, it will immediately freeze into ice. When the temperature of snow falling during the day is above zero, the ice on the surface will melt, but the humidity is extremely high due to the control of warm moisture mass. For example, the humidity in Changsha is as high as 90% now, which can't be evaporated at all, and ice water remains on ground objects. At night, the temperature dropped below zero, and the water immediately became ice again.

3. Snowfall

It seems that the northern part of Wan Li is snowing thousands of miles, but in fact, the snow that is not so thick has accumulated for a winter. Because the cold air in Siberia is extremely dry, there is not much snow every time, and it always snows lightly, that is, only about 5 mm of snow per hour. There is only a few centimeters of snow in winter.

The humidity in the south is very high, and with the trade winds brought by La Nina, the snowfall is very heavy. In Anhui, Hunan, there are frequent snowstorms, that is, the snowfall exceeds 14 mm in one hour. At present, the snow in many places is more than 20 centimeters thick, far exceeding the annual snowfall in the north, so the snowstorm in the south is more serious.

4. Frostbite caused by overweight

Snow in the north is not easy to freeze, so although there is snow on the wire and the roof, once it is too big to maintain balance, it will automatically fall from the wire to the ground, so there will only be a small amount of snow on the upper surface of the wire, which has little effect on the strength of the wire, will not exceed the weight of the wire and will not collapse the roof.

Snowfall and rainfall in the south eventually turned into ice. Rain and snow fall on the wire, and when it freezes at night, the wire is wrapped tightly and the ice is fixed on the wire, so that the wire can be wrapped in ice layer by layer every day, forming a situation like tree rings. After several days of accumulation, the thickness can not be ignored. The news said that the thickness of ice on the wire is more than twice the diameter of the wire, the density of iron is 7, and the ice is 0.9, which is not small. The roofs and towers of high-voltage lines are like this. They were tightly wrapped in thick ice and eventually collapsed. This situation mainly occurs in Nanling, where the humidity is extremely high and the temperature is extremely low. Therefore, nearly one-third of more than 70 high-voltage towers in Hengyang, Chenzhou were crushed by ice. When it snows, the high-voltage tower will bear 2-3 times the weight. But if it is frozen, it will bear 10-20 times the weight of the wire. There is another problem with wires and water pipes, that is, because the temperature is unusually low, the wires contract beyond the design limit between towers due to thermal expansion and cold contraction, and the strength is greatly reduced.

This directly led to the serious paralysis of the power system. Chenzhou has been without water and electricity for five consecutive days, especially the Shaoguan-Chenzhou section of the Beijing-Guangzhou railway. The electric locomotive is out of power, so it can be replaced by diesel locomotive, but the signal lamp is out of power and the turnout is out of power. Therefore, even diesel locomotives have to rely on their eyes to see the manual command by the roadside and the turnout must be moved manually, which makes diesel locomotives unable to run at their usual speed on this section and increases the difficulty of railway transportation.

5. Freezing injury of highway

There will also be snow in northern expressway, but it will not melt, and the amount will not be great. Even if it melts, it will evaporate quickly, leaving no water on the ground and freezing into ice. The friction of snow compacted by cars is much greater than that of ice. Even if you want to climb a mountain, you can advance on the snow by installing snow chains.

The snow in the south is too thick, and it is too thick in many places. More importantly, snow will melt into water. Due to the extremely high humidity, Hunan is generally around 90%. Water will soon freeze into ice and cover the road layer by layer like wires. Some places are as thick as 10 cm. The friction of the car on the ice is very small, so it will naturally slip. For example, this morning, a bus in Guizhou fell off a 40-meter-high cliff due to road icing, killing 25 people. Therefore, the Beijing-Zhuhai Expressway is impassable only for people's safety, and the icing is totally irresistible. On the other hand, since ice is much harder than snow, it is useless to install snow chains on wheels. This most practical method in the north has lost its function in the south, but it will make friction less and driving more dangerous.

The above is my preliminary analysis of this snowstorm. When the cause of the problem was analyzed clearly, I felt the inevitability of this natural disaster and the smallness of human beings. Generally speaking, the probability of natural disasters is not great, but for this thousand, human beings have to pay 10 thousand to prevent it, and not every disaster can be accurately predicted. This year, there are too many irresistible factors, such as the low-temperature snowstorm once in 50 years or even once in a hundred years in some places. I see that there are still many ignorant commentators on the Internet, including People's Daily, who attack institutional problems everywhere when there is a disaster and always compare the so-called developed countries. He may not know how high the latitude of developed countries is. Is it meaningful to compare the number of snow sweepers in Hunan at 25 degrees north latitude and Canada at 45 degrees north latitude, and to compare the snow disaster emergency plan? It is better to let Saudi Arabia make a super perfect flood control plan. Specific analysis of specific problems, if there were no Nanling mountains and the north and south were as smooth as the United States, there would not be such a serious low temperature. Similarly, because we have the Qinghai-Tibet Plateau, we can leave a lot of snow brought by the west wind in Afghanistan instead of Sichuan. China is China. We have a unique climate and terrain in the world, and we have our own unique problems and our China characteristics. It is really touching to see so many fighting workers repairing cables, water pipes and cleaning roads, and even three electric workers fell from the iron tower and died. China is not without an emergency plan, and the whole society is united in fighting the snowstorm. Whenever there is a snowstorm and the American super hurricane floods New Orleans, we all hate our government. Why not say that the US government is not good? Some people even wonder, what if there is a war, will it freeze to death like Hitler and Napoleon? If there had been a war, China soldiers would have got off and crossed Nanling on foot. Guangzhou Railway clearly stated that it can't be repaired within a week, which seems to be the incompetence of the government, but after careful analysis, this is the fact that the realistic government is the real government, and the comprehensive and perfect government is the deceptive government. Marx said that productivity is the ability to transform nature, and human beings can only constantly improve productivity to survive, but nature will never be completely transformed by human beings. Respect and fear nature, people can never conquer nature, we can only make our thoughts stronger, and don't lose too badly in the confrontation with nature.