Shanghai issued an orange warning for hail. What caused the hail?

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 grow in convective clouds by multiple collisions between hail embryos and supercooled water droplets, and fall to the ground when the updraft in the clouds can't support them. Strong hail is produced in thunderstorm clouds, with strong updraft and rich liquid water content. The scope of each hail is very small, ranging from several meters to several kilometers wide and 20-30 kilometers long. So there is such a saying among the people? Hail hit the line? . Hail mainly occurs in mid-latitude continental areas, usually more mountains than plains, and more inland than 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, eastern Gansu, 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 sudden hail in Shengzhou, Zhejiang Province is relatively small in scope and short in time, it is 3 cm in diameter and strong in intensity, and it is often accompanied by sudden disastrous weather processes such as strong wind, heavy precipitation and rapid cooling. China is a country with frequent hail disasters, which 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. Edit the introduction of hail formation in this section, which is usually called hail. Hail is formed in convective clouds. When water vapor cools with the rise of air flow, it will condense into small water droplets. If the temperature continues to decrease with the increase of height and reaches below 0, water droplets will condense into ice particles. In the process of ascending motion, it will absorb small ice particles or water droplets around it until its weight cannot be borne by the ascending airflow. When it falls to a higher temperature area, its surface will melt into water and absorb the small water droplets around it. At this time, if it is lifted by a strong updraft, its surface will condense into ice again, and it will grow bigger and bigger like a snowball until its weight is greater than the buoyancy of the air, that is, it will fall. If it reaches the ground, if it doesn't melt into water, it is still a solid ice particle, and it will be called hail. If it melts into water, it is the rain we usually see. Hail rained down from the clouds.

But hail clouds 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, its pressure drops and its 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 drop by about 1 degree due to adiabatic change. We know that there is a limit to the amount of water vapor contained in the air at a certain temperature. Is this the so-called? Saturation? . When the temperature decreases, the amount of water vapor that may be contained in the air will decrease.