The ice falling in the air is mostly accompanied by thunderstorms in late spring and early summer.
Hail is a kind of solid precipitation. It is a spherical or conical ice block, which consists of transparent layers and opaque layers alternately. The diameter is generally 5 ~ 50 mm, and the maximum can reach 10 cm. The greater the diameter of hail, the greater the destructive power. Hail often destroys crops and threatens the safety of people and animals. This is a serious natural disaster. Many countries with severe hail disasters have carried out artificial hail suppression experiments.
Hail comes from strong convective convective clouds (cumulonimbus clouds). The updraft in the cloud is stronger than that in the general thunderstorm cloud. Small hailstones are formed by hail embryos colliding with supercooled water droplets several times up and down in convective clouds, and fall to the ground when the updraft in the clouds can't support them. Heavy hail is produced in a thunderstorm cloud with strong updraft and rich liquid water. The scope of each hail is very small, usually several meters to several kilometers wide and 20-30 kilometers long, so there is a folk saying that "hail hits a line". Hail mainly occurs in mid-latitude continental areas, usually more in mountainous areas than in plains, and more in inland areas than in coastal areas. Hail in China mostly occurs in spring, summer and autumn, accounting for about 70% of the total from April to July. Severe hail disaster areas include southern Gansu, Longdong, the yinshan mountains, Taihang Mountain, western Sichuan and Yunnan Province.
Hail disaster is a serious meteorological disaster caused by strong convective weather system. Although it appears in a small range and in a short time, it is fierce and strong, and is often accompanied by sudden disastrous weather processes such as strong winds, heavy precipitation and sharp cooling. China is a country with frequent hail disasters. Hail brings huge losses to agriculture, construction, communication, electricity, transportation and people's lives and property every year. According to relevant statistics, the economic losses caused by hail in China reach hundreds of millions or even billions of yuan every year. Therefore, it is necessary for us to understand the temporal and spatial turbulence pattern of hail disaster and the losses caused by hail disaster, so as to better prevent hail disaster and reduce economic losses.
Hail falls from the clouds like rain and snow. But the clouds that hail are very strong cumulonimbus clouds, and only very strong cumulonimbus clouds can hail.
Cumulonimbus clouds, like all kinds of clouds, are formed by the rising and condensation of air near the ground. When air rises from the ground, the air pressure decreases and the volume expands. If there is no heat exchange between the rising air and its surroundings, the air temperature will decrease, because expansion consumes energy. This temperature change is called adiabatic cooling. According to the calculation, every time the air in the atmosphere rises 100 m, the temperature will decrease by about 1 degree due to the adiabatic change. We know that at a given temperature, there is a limit to the amount of water vapor contained in the air, and reaching this limit is called "saturation". When the temperature is lowered, the amount of water vapor that may be contained in the air will decrease. Therefore, the originally unsaturated air may reach saturation due to adiabatic cooling in the upward movement. After the air reaches saturation, excess water vapor will attach to the floating condensation nuclei in the air and form water droplets. When the temperature is below zero degrees Celsius, excess water vapor will condense into fine ice crystals. These water droplets and ice crystals gather together and float in the air to become clouds.
There are different forms of air movement in the atmosphere, forming different forms of clouds. Clouds formed by convection include light cumulus, thick cumulus and cumulonimbus. People call it cumulus clouds. They are isolated and upward-developing clouds, because there are upward and downward movements in convection, which often form clouds in the updraft area, become gaps in the downdraft area, and sometimes you can see the blue sky.
Cumulative clouds are different because of different convective intensities, and the sizes of clouds are also very different. If the convective movement in the cloud is weak and the updraft can't reach the condensation height, there will be no cloud, only dry convection. If the convection is strong, it can develop into cumulus clouds. The top of cumulus clouds, like cauliflower, consists of many well-defined convex clouds, and the thickness of clouds can reach 4-5 kilometers. If the convection is intense, a cumulonimbus cloud can be formed, the cloud bottom is dark, the cloud top develops very high, reaching about 10 km, the edge of the cloud top becomes blurred, and the cloud top often expands to form an anvil. Generally, cumulonimbus clouds may produce thunderstorms, but only when they are particularly strong, the clouds are very high, there is a strong rising gas in the clouds, and there is a lot of water in the clouds, will hail be produced. This kind of cloud is usually called hail cloud.
Hail clouds consist of water droplets, ice crystals and snowflakes. Generally, there are three layers: the bottom layer is above 0℃ and consists of water droplets; The middle layer has a temperature of 0℃ to -20℃ and consists of supercooled water droplets, ice crystals and snowflakes. The temperature of the top layer is lower than -20℃, which is basically composed of ice crystals and snowflakes.
In the hail cloud, the airflow is very strong. Usually in the direction of the cloud, a strong updraft enters from the bottom of the cloud and flows out from the top of the cloud. There is also a downward airflow flowing in from the middle behind the cloud and out from the bottom of the cloud. This is also the precipitation area where hail usually occurs. These two organized updrafts are connected with the airflow between the downdraft and the environment, so the airflow structure in the heavy hail cloud is relatively continuous. The strong updraft not only delivers enough water vapor to the hail cloud, but also supports the hail particles to stay in the cloud and grow to a considerable size before landing.
Hail falls from the clouds like rain and snow. It is a kind of solid precipitation falling from cumulonimbus clouds.
The formation of hail requires the following conditions.
There must be a fairly thick unstable layer in the atmosphere.
(2) Cumulonimbus clouds must develop to a height that can freeze a single large water droplet (generally, the temperature is-12 ~- 16℃).
③ There should be strong wind shear.
④ The vertical thickness of cloud should not be less than 6 ~ 8km.
⑤ Cumulonimbus clouds are rich in water content. Generally, it is 3 ~ 8 g/m3, and there is an accumulation area of liquid supercooled water above the maximum rising speed.
⑥ There should be inclined, strong and uneven updraft in the cloud, generally above10 ~ 20m/s. ..
How does hail grow in hail clouds?
In the hail cloud, the strong updraft carries many large and small water droplets and ice crystals, some of which fuse with ice crystals and freeze into larger ice particles. These particles and supercooled water droplets are transported by the updraft to the water content accumulation area, which can become the hail core. The initial growth core of these hailstones has good growth conditions in the water content accumulation area. After the hail enters the growth area with the updraft, it collides with supercooled water droplets in the area with large water volume and low temperature, and grows into a transparent ice layer, and then enters the low temperature area with small water volume, where it is mainly composed of ice crystals, snowflakes and a small amount of supercooled water droplets, and the hail adheres to them and freezes to form an opaque ice layer. At this time, the hail has grown up and the updraft there is weak. When it can't support the growing hail, the hail will fall in the updraft and continue to grow through the fusion of ice crystals, snowflakes and water droplets in autumn. When it falls to a higher temperature area, the supercooled water droplets that hit it will form a transparent ice layer. At this time, if it falls into another stronger updraft area, the hail will rise again and repeat the above growth process. In this way, hail grows in transparent layer and opaque layer; Due to the differences in growth time and water content, the thickness and other characteristics of each layer are also different. Finally, when the updraft couldn't support the hail, it fell from the clouds and became the hail we saw.
Generally speaking, hail has the following characteristics:
(1) has strong locality, and the impact range of each hail is generally about tens of meters to thousands of meters wide and hundreds of meters to tens of kilometers long;
② The duration is short, a storm or hail usually lasts only 2 ~ 10 minutes, and a few last more than 30 minutes;
(3) It is significantly affected by the terrain, and the more complex the terrain, the greater the possibility of hail;
(4) The interannual change is great. In the same area, some years occur several times in a row, and some years occur several times or even do not occur;
⑤ The occurrence area is wide, and it can occur in a wide range of climatic zones from subtropical zone to temperate zone, but the frequency of occurrence is mostly in temperate zone.
According to the maximum hail (general hail) diameter, hail accumulation time and hail accumulation thickness in a hail process, the hail is divided into three grades.
1. light hail: most hailstones are less than 0.5cm in diameter, the cumulative hail falling time is less than10min, and the hail thickness in the area is less than 2cm;
2. Moderate hail: The diameter of most hail is 0.5 ~ 2.0 cm, the cumulative hail falling time is 10 ~ 30 minutes, and the hail thickness is 2 ~ 5 cm;
3. Heavy Hail: Most hailstones have a diameter greater than 2.0 cm, the cumulative hail time is greater than 30 minutes, and the hail thickness is greater than 5 cm.
Hail disaster is a serious meteorological disaster caused by strong convective weather system. Although it appears in a small range and in a short time, it is fierce and strong, and is often accompanied by sudden disastrous weather processes such as strong winds, heavy precipitation and sharp cooling. China is a country with frequent hail disasters. Hail brings huge losses to agriculture, construction, communication, electricity, transportation and people's lives and property every year. According to relevant statistics, the economic losses caused by hail in China reach hundreds of millions or even billions of yuan every year.
Many people have encountered hail in thunderstorm weather. Usually, these hailstones will not exceed the size of softball, they fall from the storm clouds. However, sometimes the hail is very heavy. Once 80 kg of hail fell from the sky and broke into many small pieces when it landed on the ground. The most mysterious thing is that when the sky is cloudless, huge hail falls from the sky. There have been many incidents that confirmed that the wing of the plane was hit by hail, and scientists still can't explain why there was such a huge hail.
Hail is a disastrous weather that harms agricultural production in spring and summer. When hail appears, it is often accompanied by human wind, severe cooling and strong lightning. A hail attack, light yield reduction, heavy refusal to harvest. So how to predict hail and prevent hail? According to the weather map, satellite cloud image analysis and radar monitoring, meteorological stations can make forecasts in advance, but the accuracy is still not ideal. After long-term practice, the working people in China have accumulated rich experience in hail forecasting. Although the forecast time limit is not long, these experiences are still relatively easy to use, and a few are summarized for reference.
Feeling hot and cold: If the morning in the hail season is cool and humid, and the sun radiation is strong at noon, resulting in strong air convection, it will easily develop into cumulonimbus clouds and form hail. Therefore, there are sayings that "it's chilly in the morning, and the blood is broken in the afternoon" and "the dew is heavy in the morning, and then the hail is fierce".
Identify the wind direction: there is often strong wind before hail, but the wind direction changes sharply. There are some agricultural proverbs, such as "evil clouds see the wind grow, hail falls with the wind", "wind twists clouds, hail flakes" and so on. In addition, if the south wind continues to blow, the wind direction becomes northwest or north wind, and when the wind increases, hail often follows, so there is a saying that "no east wind blows, no rain blows, no south wind blows, no hail falls".
Yunzhou: There are many proverbs all over the country to explain the omen of hail from the color of clouds, such as "I'm not afraid of dark clouds, but I'm afraid that dark clouds are red, and I'm afraid that white worms will grow in red Huang Yun", and "The tail of dark clouds and Huang Yun's head kill sheep and cattle". Because of the color of hail, there are white characters on a black background, and then red in the middle, forming a white, black and red cloud. There are also sayings that clouds are a precursor to hail, such as "the dark clouds rolled into a ball in the afternoon, and the wind, rain and hail came together" and "the sky was yellow and sultry, and the Tianhe water roared to prevent hail", indicating that the air convection was extremely strong at that time, and the clouds developed rapidly, like smoke going straight up and down, and the clouds rolled up and down, which made it easy to hail.
Listen to the thunder: the thunder is dull. In succession, the masses called this kind of thunder "Remore". Therefore, there is a saying that there is nothing wrong with thunder, and it is boring to lay an egg. This is because the frequency of horizontal flash in hail cloud is higher than that of vertical flash, and the range is wide The thunder and echoes emitted by various parts of lightning are mixed together and sound continuous.
Understanding lightning: lightning in hail clouds is mostly inter-cloud lightning, that is, "horizontal lightning", which shows that the process of forming hail in clouds is very intense. Therefore, there is a saying that "vertical lightning can come, and horizontal lightning can prevent hail disasters".
Look at the image: I have a lot of experience in measuring hail by looking at the image. For example, there is a proverb in Guizhou that "the geese fly low, and the hail comes quickly", "the willow leaves fly, and it hails in the sky", and there is a proverb in Shanxi that "cattle and sheep don't lie on the beam at noon, but beware of the hail in the afternoon" and "the grass is white, and the hail falls steadily". It should be noted that the above experience can not be judged by only one article, but should be comprehensively analyzed and applied.
1. forecast
Since 1980s, with the wide application of advanced equipment such as weather radar, satellite cloud image receiving, computer and communication transmission in meteorological services, the ability to track and monitor hail activities has been greatly improved. When the local meteorological observatory (station) finds hail weather, it shall immediately notify the meteorological observatory (station) that may be affected. Meteorological departments at all levels combine modern meteorological science and technology with long-term accumulated forecasting experience to comprehensively forecast the occurrence, development, intensity, scope and harm of hail, and continuously improve the forecasting accuracy. In order to transmit the hail warning information to government leaders and the masses at all levels as soon as possible, meteorological departments at all levels issued "alerts" and "emergency alerts" through local radio stations, television stations, telephones, computer service terminals and severe weather warning systems, which enabled all sectors of society and the broad masses of the people to take defensive measures in advance, avoided and alleviated disaster losses, and achieved obvious social and economic benefits.
2. Prevention and control
China is one of the countries with early artificial hail suppression. Due to the serious hail disaster in China, the hail suppression work has received the attention and support of the government. At present, many provinces have established long-term experimental fields, conducted rigorous experiments and achieved many valuable scientific research results. Artificial hail suppression is carried out to make it develop in the direction people expect and achieve the purpose of disaster reduction. At present, the commonly used methods are as follows: ① using rockets, anti-aircraft guns or planes to send catalysts such as silver iodide, lead iodide and dry ice directly into the cloud; (2) On the ground, before the formation of cumulonimbus clouds, catalysts such as silver iodide, lead iodide and dry ice are sent into the free atmosphere to make these substances play the role of hail embryos in the hail clouds, so that the hail embryos are enlarged and the hail becomes smaller; (3) Launching rockets and anti-aircraft guns at hail clouds on the ground, or launching rockets and bombs at hail clouds on airplanes, thus disrupting water transport to hail clouds; (4) Sprinkle condensation nuclei on warm clouds with rockets and anti-aircraft guns to make the clouds form precipitation, so as to reduce the water in the clouds; In the cold cloud, some ice cores are scattered to inhibit the growth of hail embryos.
3. Agricultural hail suppression measures
The common methods are as follows: ① Planting grass and trees in hail-prone areas, increasing forest area, improving landform environment and destroying hail cloud conditions, so as to reduce hail disasters; (2) Planting more crops with strong hail resistance and resilience; ③ timely harvest mature crops; (4) In the hail season in hail-stricken areas, farmers carry hail suppression tools with them in the fields, such as bamboo baskets and wicker baskets, to reduce personal injuries.
Geographical Distribution of Hail Disaster in China
Hail activity is not only related to weather system, but also greatly influenced by topography. China has a vast territory, complex topography and great differences in landforms, and China has the largest plateau in the world with complex atmospheric circulation. Therefore, the hail weather in China is wide and the hail disaster area is large. According to the relevant data, the spatial pattern of hail disasters in China is compared and analyzed, and the following four aspects are obtained. (1) Hail disaster has a wide range. Although the hail disaster is a small-scale disaster event, there are hail disasters in most areas of China, and almost all provinces have different degrees of hail disaster records. The number of counties affected by the disaster is close to half of the number of counties in China, which fully shows that hail disasters are widely distributed. (2) The distribution of hail disasters is discrete. Most hail falls in individual counties. (3) The local distribution of hail disaster is obvious. Hail disasters often occur in some specific areas, especially in the piedmont and agricultural areas east of the Qinghai-Tibet Plateau, which is closely related to the formation conditions of hail disasters. (4) The overall distribution pattern of hail disasters in China is that there are many hail disasters in the central and eastern regions and few hail disasters in the western regions, and the spatial distribution presents a pattern of one area, two belts and seven centers (Figure 3). The first area refers to the area north of the Yangtze River, south of the Yanshan Line and east of the Qinghai-Tibet Plateau, which is a hail disaster-prone area in China. The two zones refer to the hail-prone zones on the outer edge of the first step (especially in the east) and the hail-prone zones on the eastern edge and east of the second step, which are hail-prone zones in China. Seven centers refer to several hail-prone centers scattered in two hail-prone areas: Northeast High Value Area, North High Value Area, Hubei-Henan High Value Area, Nanling High Value Area, East Sichuan-West Hubei-West Hunan High Value Area, Gansu-East High Value Area and Kashi-Aksu High Value Area.
Time Distribution of Hail Disaster in China
Generally speaking, the time distribution of hail disasters in China is very extensive. Although there is hail at any time of the day, there is a relatively concentrated hail period all over the country. According to the analysis of relevant data, 70% of hail time in most areas of China is concentrated in local time 13 ~ 19, and the most is between 14 ~ 16. Hail usually falls at night in western Hunan, Sichuan Basin and western Hubei, and at noon in some places on the Qinghai-Tibet Plateau. In addition, there is obvious monthly variation of hail in various parts of China, which is consistent with the monthly variation of atmospheric circulation and monsoon climate characteristics. The hail area moved northward with the northward movement of the south branch jet, and the arrival of hail in various places was about one month ahead of the rain belt. Generally speaking, Fujian, Guangdong, Guangxi, Hainan and Taiwan Province provinces are in March-April, Jiangxi, Zhejiang, Jiangsu and Shanghai are in March-August, parts of Hunan, Guizhou, Yunnan and Xinjiang are in April-May, most of the Qinling Mountains and Huaihe River are in April-August, parts of North China and Tibet are in May-September, and Shanxi, Shaanxi and Xinjiang. In addition, due to the strong regionality of hail, the annual changes in various regions and even the whole country are great.
Analysis on the disaster-causing environment and factors of hail in China
From the perspective of regional natural disaster system theory, hail disaster is a disaster formed by the interaction of hail disaster-prone environment, disaster-causing factors and affected bodies. Hail and rainstorm are both strong convective weather processes, often accompanied by terrain constraints, so heavy rain and terrain have become the main factors that breed hail disasters. The intensity and regional differentiation of hail disaster first depend on the characteristics of hail. Judging from the regional differentiation of hail in China, the hail high-value area presents the characteristics of one area and two zones: the first area refers to the hail-prone area on the Qinghai-Tibet Plateau; These two belts refer to the southern hail belt and the northern hail belt. The former is mainly distributed in the Yunnan-Guizhou Plateau at an altitude of1000 ~ 2000m, extending eastward to the junction of Xiangxi and Sichuan and Hubei, while the latter is connected with the Inner Mongolia Plateau from the northern part of the Qinghai-Tibet Plateau via Qilian Mountain and Liupanshan Mountain. Compared with the regional differentiation of hail disasters (hail) in China, the regional differentiation of hail disasters has an obvious trend of expanding eastward, southward and westward, with the following three obvious differences. First, from a large area, the hail disaster-prone area and the highest frequency area are completely different. The former is densely populated in the middle and lower reaches of North China-Yangtze River, while the latter is sparsely populated in Qinghai-Tibet Plateau. Secondly, there are two hail disaster-prone areas, but the former is located further east than the latter, especially in the east, forming a north-south hail disaster area. Thirdly, the hail-prone areas are all located in the hail-prone areas, which are distributed in a lump. It can be seen that the regional differentiation of hail disasters in China is deeply influenced by the scope of human activities, showing the spatial pattern characteristics of more central and eastern regions and less western regions. From the comparison of regional hail and hail disaster spatial differentiation, it is only a natural process, and the change of the nature of the affected body makes the hail disaster high-value area not necessarily a disaster high-value area. Although the affected body is not the direct driving force of the disaster, it makes the hail disaster relatively expand or shrink.
Analysis on the main body of hail disaster in China
The regional differentiation of hail disasters in China is deeply influenced by the affected bodies. Through the classification analysis of the existing hail cases in China, the results show that there are 6 categories and 20 subtypes of hail disasters in China, among which food crops are the most frequently affected. From the perspective of dynamic changes, there are four subcategories worthy of attention: First, the number of corn disasters (relative to other crops) has increased, which is related to the universality of corn planting in China and the development of plastic film corn planting. Using plastic film to advance the growth period of crops will undoubtedly increase the time period of hail disaster. Second, cotton, the number of disasters has increased significantly, especially in some major cotton-producing areas. It can be seen that the change of crop variety and crop area directly affects the amplification or reduction of disaster situation. Third, vegetables, fruits and flowers have been seriously affected. With the improvement of urbanization, the development of vegetables, melons and fruits, especially flowers, and the wide application of greenhouse technology, the probability of hail disaster increases. It can be seen that the change of land cash crop yield directly affects the vulnerability of the affected bodies. Fourth, the number of communication disasters has soared. With the rapid development of national communication, especially the rise of network in recent years, the vulnerability of hail victims has been amplified.
The area with the most hail in China
The area with the most hail in China is the Qinghai-Tibet Plateau, such as Heihe (Naqu) in the northeast of Tibet, with an average annual hail of 35.9 days (53 days in the most years and at least 23 days in the least); Followed by Bango 3 1.4 days, Shenzha 28.0 days, Amdo 27.9 days, Suoxian 27.6 days, all appeared in the Qinghai-Tibet Plateau.