What caused the hail?

Hail pays attention to 6.24 hail disaster.

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 the scope is small and the time is short, the hail in Shengzhou, Zhejiang Province has a diameter of 3 cm.

, strong intensity, and often accompanied by strong winds, heavy precipitation, rapid cooling and other sudden disastrous weather processes. China is a country with frequent hailstorms, which bring huge losses to agriculture, construction, communication, electricity, transportation and people's lives and property every year (Figure 1.2). 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.

Edit this section of hail formation

brief introduction

Hail is often called hail. Hail is formed in convective clouds. Water vapor rises with the airflow and condenses into small water droplets after cooling. If the temperature continues to decrease with the increase of height and reaches below zero degrees Celsius, water droplets will condense into ice particles. In the process of its upward movement, it will absorb small ice particles or water droplets around it and grow up until its weight cannot be borne by the upward airflow. When it falls to a higher temperature area, its surface will melt into water and absorb the surrounding small water droplets. At this time, if it is lifted by a strong updraft, its surface will condense into ice and snowball until its weight is greater than the buoyancy of the air, that is, it will fall down. If it reaches the ground, it is called hail. If it melts into water, it is the rain we usually see. hail

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 certain 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. Heavy hail

There are different forms of air movement in the air, 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

① Short-term hail in the atmosphere.

There must be a fairly thick unstable layer in it. (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?

Drop short-term hail in hail cloud area

The strong updraft carries many large and small water droplets and ice crystals, some of which merge with the 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 hail nuclei. 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.