What? Hail loves to check in at the Qinghai-Tibet Plateau?

Did you know?

Hail likes to "go mountain roads"

The more complex the terrain

The higher the altitude

More vulnerable to hail

therefore

Areas in my country where hail occurs most frequently

The Qinghai-Tibet Plateau

On average, it occurs 3 to 15 days per year.

In some areas, it may take more than 15 days

In provincial capital cities

vulnerable to hail

The first six cities are

Lhasa, Hohhot

Xining, Harbin

Changchun and Shenyang

The coastal areas of South China and the Sichuan Basin

The middle and lower reaches of the Yangtze River

The average number of hail days per year is often less than 0.1 day

hail

How it is formed

?

Although hail has the word "ice" in its name, it prefers warm seasons, and high temperature is a triggering condition for the formation of hail.

Image source: National Meteorological Information Center

Hail usually comes from strong cumulonimbus clouds, which are also called hail clouds. They only form under unstable atmospheric conditions. This is why hail only occurs in the warm seasons of spring and summer. In winter, the temperature near the ground is very low and there will be no strong and rapid updrafts, so hail is difficult to form in winter.

Usually, hail in various regions will arrive about one month earlier than the rain belt.

hail

How big can it be

?

When hailstones fall, people are usually more concerned about their size, because the bigger the hailstones are, the harder they usually hit, and the greater the damage they are likely to cause.

Photography: Xin Pingping

White or milky white solid precipitation with a diameter of about 3 mm is not considered hail in meteorology, but is called "sleet".

Only solid precipitation with a diameter of more than 5mm is called hail, which is basically the size of a soybean. Generally, the diameter of hail is between 5mm and 5cm, and 80% to 90% of hail is less than 3cm in diameter. Hail with a diameter greater than 5cm is rare, and hail reaching 10cm is considered very large.

Image source: National Meteorological Information Center

Hail Grade GB/T 27957-2011

Image source: CNR

hail

What determines size?

?

The more vigorously the hail cloud develops, the greater the water vapor content, the stronger the updraft, and the longer the hail rolls up and down in the cloud, the larger the hail that is eventually formed will be.

At present, the largest hailstone has a diameter of 11.5cm, which is slightly larger than an adult's fist. When the diameter of hailstone reaches 2cm, the landing speed is equivalent to about 70 kilometers per hour, which will damage crops, fruits and vegetables. When the diameter of hailstone reaches 6cm or more, the landing speed is equivalent to 100 kilometers per hour, at this time, cars, doors and windows, roof tiles will be "damaged", and even casualties of people and animals will be caused.

Image source: Miaodong Encyclopedia

Yuanxiao+Onion

=Hail

?

Hail is born in hail clouds. Hail clouds are rich in water and are composed of snowflakes, ice crystals, supercooled water droplets and water droplets. They are roughly divided into three layers. The upper layer is the coldest, with a temperature below -20℃, and is composed of snowflakes and ice crystals; the middle layer has a temperature between -20 and 0℃, and is composed of ice crystals, snowflakes and supercooled water droplets; the lower layer is the warmest, with a temperature above 0℃, and is composed of water droplets. Hail is constantly rolling up and down inside the hail cloud, just like rolling Lantern Festival dumplings.

Image source: China Weather Network Photographer: Li Qi

In a hail cloud, the updrafts are sometimes strong and sometimes weak. When the updrafts are strong, the water droplets in the lowest layer enter the middle layer first under the influence of the strong updrafts, collide with supercooled water droplets, ice crystals and snowflakes, and grow, then continue to rise to the coldest upper layer, condense into a solid state, fall down, and collide with supercooled water droplets during the descent, freezing a layer of opaque ice nuclei on the small ice crystals, thus forming hail embryos. Then, the hail embryos are lifted up by the updrafts and fall down again, rolling up and down again and again, attaching more supercooled water droplets, and so on, constantly wrapping themselves around in circles, becoming larger and heavier, until they are so heavy that the updrafts can no longer hold them up, and they fall from the sky and "come down" to earth as hail.

Image source: Changchun Evening News

Therefore, although hail looks like a "mound", it is actually formed layer by layer like an onion. Generally, the hail embryo includes 4 to 5 layers of transparent or opaque ice, and there can be more than 20 layers at most.

Intervention hail

Mounting guns

!!!

It is quite difficult to forecast hail. This is because hail usually comes and goes quickly, and the duration of its appearance is very short, only 2 to 10 minutes. In addition, the area where hail appears is not large, usually a narrow strip of land with a width of tens to thousands of meters and a length of hundreds to tens of thousands of meters. Therefore, accurate forecasting of hail has always been a problem.

Moreover, there are other factors that interfere with observation and judgment using high-tech means such as satellites and radars. There are often multiple thunderstorm clouds around the hail cloud that produces hail, and the characteristics of hail are easily obscured by other weather characteristics such as heavy rainfall, thunderstorms and strong winds.

Image source: Baidu Encyclopedia

However, people can still take some technical measures to suppress the formation of hail at various stages of its growth.

At present, meteorological departments generally use ground rockets or antiaircraft guns to launch rockets and shells containing silver iodide, launch them into appropriate locations in the clouds, produce excessive amounts of artificial ice nuclei, and achieve the purpose of hail prevention by snatching supercooled water droplets in the clouds. Simply put, it is to "disperse power." The amount of water vapor and supercooled water droplets in the clouds is certain. After a large number of artificial ice nuclei are spread, a large number of hail embryos may be produced, and the cold water droplets in the clouds will be consumed. At this time, the number of hail embryos is large but the volume is very small, and it is very likely that they will no longer fall as hail, and even if they fall, the size will be very small.

Image source: Fujian Meteorological Bureau

Source: China National Radio Producer: Ma Lian Editor: Wu Nan

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