[Urgent] The influence of the cold wave on all aspects of our country (ask for 2000 words! )

Causes of cold wave and its main harm to China

Because the sun's altitude angle in the Arctic is extremely small, the ground and the atmosphere absorb very little heat, and it is covered with ice and snow all year round. In winter, due to the oblique sunlight, the days are shorter and the nights are longer, so the solar radiation energy obtained on the ground is less, and the heat released far exceeds the absorbed heat, thus gradually strengthening the cold degree and expanding the scope. In winter, the temperature is generally between MINUS 40-50℃, and even in some places there has been a low temperature of MINUS 60-70℃. These large-scale cold air masses gather to a certain extent and go south on a large scale under the guidance of favorable atmospheric circulation. It is also the main disastrous weather that the cold wave becomes a kind of strong cold air activity with large intensity and wide range, which attacks from polar regions or cold zones to mid-latitude or low-latitude regions and harms the production and life of the national economy, especially the safety of civil aviation. This paper briefly introduces the causes, hazards and early warning signals of cold wave, hoping to provide some reference for this disastrous weather, so as to have a clearer understanding of it and better prevent the hazards caused by cold wave.

Cold wave disaster; Early warning signal; Genetic path

introduce

Cold wave is a kind of strong cold air activity with large intensity and wide range, which attacks middle and low latitudes from polar regions or cold zones. Because of its rapid arrival, the temperature drops sharply in a short period of time, accompanied by strong winds, frequent rain and snow and sharp cooling, freezing will occur. Generally speaking, the influence of cold wave is stronger in the north than in the south, and the northwest, north China and northeast China are the areas with strong influence of cold wave, and the average process cooling value is12 ~14℃; However, from the south of Jiangnan to Nanling in the north of South China, the cold wave cooling reached the same intensity as that in the north of the Three North, with an average of 12 ~ 13℃. According to statistics, from the autumn of 1955 to the spring of 1975, the Qinghai-Tibet Plateau and its peripheral areas were weakly affected by the cold wave, especially on the leeward slope in the southeast of the plateau, with an average cooling range of only 4 ~ 6℃, while the far north, east and southeast of the Qinghai-Tibet Plateau were strongly affected. Beijing, Baoding and Shijiazhuang, located in the plain area east of Taihang Mountain and south of Yanshan Mountain, have obviously cooled down.

1. Definition and frequency of cold wave in China.

At present, China's regulations on cold wave are: under the influence of strong cold air, the temperature in the middle and lower reaches of the Yangtze River and its northern area will drop to above 10℃( 14℃) within 48 hours, and the minimum temperature will reach below 4℃. There are strong winds of magnitude 5-7 in the land equivalent to three (three or four) administrative regions, and there are three (all) strong winds above magnitude 7 in the coastal areas. For example, because China has a vast territory and the climate varies greatly from place to place, strong cold air has different effects on industrial and agricultural production. Therefore, from a nationwide perspective, the China Central Meteorological Observatory takes the daily average total temperature drop 10℃ or above, the absolute value of negative temperature anomaly (below average) above 5℃, or the total temperature drop above 7℃ and the absolute value of negative temperature anomaly above 3℃ as the standard, and according to the size of the affected area of cold wave,

The average number of cold waves in China is about 6 times a year, but there is a big difference every year. The year with the most cold waves is 10, and the year with the least cold waves is only 2 times. The cold wave affecting China mainly occurs from June 10 to April of the following year, and rarely occurs in September and May. The total number of cold waves in each month is 165438+ 10, with 25 times, accounting for 1/6, that is, once a year on average; 65438+22 times in February; 10 65438+ 18 times; February 2 1 time; 20 times in March and April; 10, 15 times; Six times in May and four times in September. A cold wave cannot form in summer.

2. Causes of cold wave

The reason why the Arctic is covered with ice and snow all the year round is that the altitude angle of the sun is very small, and the heat absorbed by the ground and the atmosphere is also very small. In winter, due to the oblique sunlight, the days are shorter and the nights are longer, so the solar radiation energy obtained on the ground is less, and the heat released far exceeds the absorbed heat, thus gradually strengthening the cold degree and expanding the scope. In winter, the temperature is generally between MINUS 40-50℃, and even in some places there has been a low temperature of MINUS 60-70℃. These large-scale cold air masses gather to a certain extent and go south on a large scale under the guidance of favorable atmospheric circulation. This is the cold wave outbreak. When the cold wave moves south on a large scale, the warm air will also "retreat one after another", so the area it passes through will be affected by the warm air first, and the temperature will increase obviously. If the passing area is already under the control of the warm air mass, there will also be weather in which the temperature rises sharply under the continuous delivery of warm air before the cold wave. So it tends to be warm for a day or two before the cold wave comes.

2. 1 Three cold wave sources and their invasion paths in China:

2. 1. 1 Three main sources of cold wave

(1) The cold ocean west of Xindi Island. Cold air enters our country through Barents Sea and Soviet Union and Europe. The frequency of occurrence is the most, and the intensity of cold wave is the most. (2) the cold ocean surface east of Xindi Island. Cold air enters China through the Kara Sea, the Taiwan Strait Peninsula and the Soviet Union. Although it appears several times, the temperature is low and can reach the intensity of cold wave. (3) The ocean surface south of Iceland. Cold air enters our country through the former Soviet Union's southern Europe or Mediterranean Sea, Black Sea and Caspian Sea. It often appears, but the temperature is not very low, and generally it can't reach the cold wave intensity, but it can also reach the cold wave intensity if it is combined with cold air from other sources. The above three sources of cold air are the statistical results of 1970 ~ 1973,1~ April and10 ~ 65438+February by the Central Meteorological Observatory. Among them, 95% cold air passes through central Siberia (70 ~ 90 E, 43 ~ 65 N) and accumulates there. This area is called the key area of cold wave.

2. 1.2 cold wave path

When the cold wave invades, the moving route of its main body is called the cold wave path. Due to the different sources of the cold wave invading China and the influence of the terrain, its path is different every time, but it is not chaotic. Statistical analysis shows that cold waves often invade China in four ways. (1) The cold wave from the northwest starts from the icy ocean near Xindi Island, crosses western Siberia, enters northern Xinjiang or the People's Republic of Mongolia, and sweeps across the Hetao area of the Yellow River to the North China Plain and the middle and lower reaches of the Yangtze River; Sometimes it is more common to cross Nanling to affect the southern coast, also known as the middle road. (2) the cold wave comes from the north, starting from the Arctic Ocean in northern Asia, passing through the far east part of the Soviet Union and the Mongolian people, and going straight south, which is called East Road. (3) The cold wave from the west starts from the Arctic Ocean in northern Europe, crosses the whole European continent, goes south to the Mediterranean Sea, then turns east and comes in from the west of China, also called West Road. (4) East Road and West Road, the cold air in East Road goes south from the lower reaches of Hetao, and the cold air in West Road goes south from the southeast of Qinghai. Two cold air often meet on the east side of the Loess Plateau, between the Yellow River and the Yangtze River.

2.2 Main circulation characteristics when cold wave occurs

The circulation situation during the cold wave can be roughly divided into five categories: small trough development type, low trough moving eastward type, horizontal trough turning vertical type, zonal circulation type and low trough rotating type.

(1) Small trough development type: the unstable small trough that appeared in the western part of Xindi Island and the eastern part of Greenland developed in the process of moving eastward, and finally evolved into the East Asian trough. This cold wave is caused by the unstable trough moving eastward and southward along the northwest airflow in front of the high-pressure ridge in Ural Mountain. Under the specific circulation situation, it quickly deepens into a large trough in the north-south direction, leading to the large-scale southward movement of cold air. The most remarkable feature of this cold wave is its high speed and the sharp increase in the intensity of each system.

(2) The trough moves eastward: During the eastward movement of the European trough, fresh cold air from the north meets, which makes the trough develop and leads to the cold wave process. This cold wave is caused by a pair of ridges moving from west to east in the westerly belt, which drives the cold air to move southward in a large range. During the cold wave, there is always a radial circulation over Europe and Asia, which directly connects the trough with the polar vortex and has a strong cold source. In the first 48 hours, the low trough is generally located in the Ural Mountains, and the central part of Mongolia is a high-pressure ridge. The low latitude circulation in Asia is flat, with many south branches moving eastward, and the low trough is located in the west of Hetao in the first 24 hours. Whether you can go south in a big way at this time depends on whether there is a ridge of high pressure on the Qinghai-Tibet Plateau, and if there is an outbreak, there is no general cold air activity.

(3) The transverse trough turns to the vertical type: when the inverted ω flow pattern in East Asia is established, the polar vortex extends westward as an east-west trough, and there are shear of northerly wind (340 ~ 20) and westerly wind (300 ~ 250) before and after the trough. When it turns vertical, there are two troughs and a ridge over Europe and Asia, a high-pressure ridge over Urals Mountain or Eastern Europe or Western Asia, and a low trough over Europe or Western Europe. Compared with the south profile, the low pressure center connected with the transverse trough is east to north, generally east of105 E and north of 60° N, and the trough line is southwest to northeast, and the position is also between 50 and 70 N. Whether the transverse trough can vertically turn south depends on whether the high pressure ridge around Ural Mountain can continue to develop in the eastward movement. If it is, turn it vertical, otherwise, it will not be easy to turn it vertical in a short time.

(4) zonal circulation pattern: The characteristics of this kind of cold wave are that the radial degree of atmospheric circulation over Europe and Asia increases, and the ridges are almost strengthened in situ or superimposed from north to south to form large ridges.

(5) Low pressure rotary type: it is a special case of transverse groove type. Different from the transverse trough, the cold wave outbreak is not caused by the south pressure or vertical rotation of a trough line, but by the reversal of the polar low pressure in Temel, and one small transverse trough after another continues to go south after the low pressure, driving the cold air to go south and forming a continuous low temperature. The long wave ridge behind the low pressure is stable and less moving, which is the remarkable feature of this kind of cold wave.

For example, the circulation background of a nationwide cold wave weather process in 2005 10 ~ 13, the main factors affecting the weather system are (1) the formation of Siberian blocking high caused by strong warm advection over western Europe and the establishment of horizontal trough. The northeast airflow on the north side of the horizontal trough guides the ultra-polar cold air and the west cold air to merge and strengthen; An unusually strong cold high pressure, front area, cold temperature center and cold temperature advection are formed. (2) Two short-wave troughs moved eastward, invading and blocking the high pressure, so that the horizontal trough was established twice and turned into a vertical trough, which led to the massive invasion of strong cold air to the south. (3) The cold wave brought a large range of strong cooling, and the southwest jet at 700hPa met the cold air. The temperature above 1000hPa was vertically distributed below 0℃, which provided the conditions of power, water vapor and condensation temperature for the snowstorm in the south.

3. The main hazards and early warning signals of cold wave in China.

Cold wave is the main disastrous weather in China. In places hit by cold waves, the wind direction often changes quickly, the wind speed increases, the air pressure suddenly rises, the temperature drops sharply, and there may be rain, snow and frost. The cold wave goes south, and windy and dusty weather often occurs in northwest, Inner Mongolia and North China. In the area north of Huaihe River, there is generally little rain and occasional snowfall. After crossing the Huaihe River, the chances of precipitation increase. Different weather can also be formed in different seasons, and several kinds of weather are harmful to the national economy. The sharp cooling caused by the cold wave in winter will freeze and crack all kinds of pipelines and valves in industrial and mining areas, and also cause fires and floods, resulting in shutdown and production stoppage. Rain, snow and freezing weather bring great harm to transportation. For example, 1987 1 1 A cold wave process in the last ten days caused the turnouts of several stations under the jurisdiction of Harbin, Shenyang, Beijing and Urumqi to freeze, the tracks were buried by snow, the communication signals failed, and the train operation was blocked. After the rain and snow, the roads were frozen and skidded, and traffic accidents increased obviously. The cash crops in the south are also most afraid of freezing injury. When the temperature of rubber tree is lower than 5℃, the trunk will burst or even dry up. Citrus will be frostbitten when it meets the low temperature below -9℃.

In spring, the cold wave moves south, confronting the warm and humid air flow in the south of the Yangtze River, resulting in continuous low temperature and rainy weather. It has the greatest impact on early rice. As long as the daily average temperature is lower than 12℃ and the minimum temperature is lower than 8℃ for more than three days, accompanied by rainy weather, chilling injury will occur, causing mildew or rotten seedlings. Freezing rain is formed in the cold wave in winter and spring and autumn, and there are more mountains than plains. The biggest harm of freezing rain is to break the power line and push down the pole, resulting in the interruption of telecommunications and transmission; Traffic jams and frequent accidents; Even the female animals in pastoral areas who eat the grass in freezing rain will also cause miscarriage.

A cold wave will lead to a snowstorm. For example, from June1983 65438+February 2 1-28, it snowed continuously for nearly 30 hours in Kunming, setting a 500-year record, and the Southwest Railway was interrupted by heavy snow for two days. In the northern pastoral areas, snowstorms often lead to "white disasters", causing a large number of livestock deaths.

The cold wave also has a great influence on the flight safety of civil aviation. Generally, the average wind speed of cold wave and gale can reach more than15m/s, the gust can reach more than 25m/s, and the wind direction is mostly from northwest to west wind, which lasts for a long time, usually for several hours to more than ten hours, and sometimes for more than 2 days. Especially in the Capital Airport, the strong wind forms an angle of more than 45 degrees with the runway, and the crosswind angle is large, which makes the take-off and landing of aircraft very complicated. When taxiing in the crosswind, the forces on the two wings of the aircraft are different. The lift of windward wing increases, while that of leeward wing decreases, resulting in the tilting moment. In addition, because the crosswind pressure center does not coincide with the center of gravity of the aircraft, it will also produce a turning moment that makes the aircraft rotate in the headwind direction. When the crosswind is very strong, and the reaction force of the runway to the wheels is opposite to the turning moment, which is not enough to keep the plane balanced, the nose will deflect to the crosswind direction. Therefore, when the plane is running in the crosswind, the captain always presses the joystick in the crosswind direction to eliminate the tilting moment, and boards the rudder in the opposite direction to eliminate the turning moment. It is more difficult for an airplane to land in a crosswind than to take off. At this time, the captain must pay attention to correct the drift. If it is not corrected properly, the plane will be grounded in different places. When an airplane lands in a strong crosswind, accidents such as tire breakage and landing gear breakage are likely to occur, which seriously endanger the safety of the airplane and passengers. Cold wave precipitation makes the humidity in the lower layer increase sharply, which is easy to produce low-broken clouds, sometimes only tens of meters, and the height of the cloud bottom fluctuates greatly, which seriously affects the take-off and landing of aircraft.

Cold wave cold air is brewing and developing on the cold continent at high latitudes. Under the specific atmospheric circulation pattern, it is guided by the strong northerly airflow in the troposphere and enters China through Novosibirsk, Mongolian People's Republic or Soviet Central Asia. The cold air mass can reach several dry kilometers in diameter and extend to 6 or 7 kilometers in thickness. However, due to the influence of geographical environment and climatic conditions, the cold wave standards are also different. Its early warning signal is divided into three levels, which are represented by blue, yellow and orange respectively.

-Cold wave blue warning signal

Meaning: within 24 hours, the minimum temperature drops by more than 8℃, the minimum temperature is less than or equal to 4℃, the average wind force reaches above 6, or the gust is above 7; Or it has dropped by more than 8℃, the lowest temperature is less than or equal to 4℃, the average wind force is above 6, or the gust is above 7, and it may continue.

-Cold wave yellow warning signal

Meaning: within 24 hours, the minimum temperature drops 12℃ or above, the minimum temperature is less than or equal to 4℃, the average wind force reaches 6 or above, or the gust is 7 or above; Or it has dropped above 12℃, the lowest temperature is less than or equal to 4℃, the average wind force is above 6, or the gust is above 7, and it may continue.

-Cold wave orange warning signal

Meaning: within 24 hours, the minimum temperature drops 16℃ or above, the minimum temperature is less than or equal to 0℃, and the average wind force reaches 6 or above or the gust is 7 or above; Or it has dropped above 16℃, the lowest temperature is less than or equal to 0℃, the average wind force is above 6, or the gust is above 7, and it may continue.

4. Summary

(1) Cold wave is a strong cold air activity with large intensity and wide range, which comes from polar regions or cold zones and invades middle and low latitudes. In China, the frequency of occurrence is about 6 times a year, and the impact on the south is generally less than that on the north. In summer, a cold wave cannot be formed.

(2) There are four paths and three main sources of cold wave in China. Its circulation situation can be roughly divided into five categories: small trough development type, low trough moving eastward type, horizontal trough turning vertical type, zonal circulation type and low trough rotating type.

(3) Cold wave is the main disastrous weather in China. In the affected areas, the wind direction often changes quickly, the wind speed increases, the air pressure suddenly rises, the temperature drops sharply, and there may be rain, snow, frost and freezing. Therefore, it has great influence on road traffic, agricultural production, power transmission and civil aviation.

References:

[1] Meteorology and Climatology Zhang Zhiming and Fan Zhongxiu China Water Conservancy and Hydropower Press.

[2] Principles and Methods of Meteorology translated by Zhu Ganggen, Lin, Shou Shaowen and Tang Dongsheng.

[3] Countless Weather-Cold Wave Jin Chuanqi Meteorological Publishing House

[4] China Meteorological News March 3, 2007 (Meng Jiachuan)

Fan Ming, Jean. Analysis on the Formation Process of "200 1 4 9" Cold Wave Weather. Meteorology, 28, 2002 (3): 54 ~ 57.