On the mechanism of hail formation. Why is there hail?

What is hail and how is it formed?

Very often in the summer it is observed unusual look precipitation in the form of small and sometimes large pieces of ice. Their shape can be different: from small grains to large hailstones the size of egg. Such hail can cause catastrophic consequences - roost material damage and harm to health, as well as damage to agriculture. But where and how does hail form? There is a scientific explanation for this.

Hail formation is facilitated by strong updrafts of air within a large cumulus cloud. This kind atmospheric precipitation consists of pieces of ice different sizes. The structure of a hailstone can consist of several alternating layers of ice - transparent and translucent.

How do ice floes form?

Hail formation is complex atmospheric process, based on the water cycle in nature. Warm air, which contains moisture vapor, rises upward on a hot summer day. As the altitude increases, these vapors cool and the water condenses, forming a cloud. It, in turn, becomes a source of rain.

But it also happens that during the day it is too hot, and the rising air flow is so strong that drops of water rise to a very high altitude, bypassing the region of the zero isotherm, and become supercooled. In this state, droplets can occur even at temperatures of -400C at an altitude of more than 8 kilometers. Supercooled drops collide in the air flow with tiny particles sand, combustion products, bacteria and dust, which become centers of moisture crystallization. This is how a piece of ice is born - more and more droplets of moisture stick to these small particles and, at an isothermal temperature, turn into real hail. The structure of a hailstone can tell the story of its origin through layers and peculiar rings. Their number indicates how many times the hailstone rose into the upper atmosphere and descended back into the cloud.

The speed of updrafts inside cumulus clouds can vary from 80 to 300 km/h. Therefore, newly formed pieces of ice can continuously move, also at high speed, along with air currents. And the greater the speed of their movement, the larger the size of the hailstones. Passing repeatedly through the layers of the atmosphere, where the temperature changes, at first small hailstones become overgrown with new layers of water and dust, sometimes forming hailstones impressive size– with a diameter of 8-10 cm and a weight of up to 500 grams.

One raindrop is formed from approximately a million supercooled water particles. Hailstones with a diameter exceeding 50 mm usually form in cellular cumulus clouds, where there are super-powerful updrafts of air. A thunderstorm involving such rain clouds can generate intense wind squalls, heavy downpours and tornadoes.

Hail is one of the most unusual and mysterious atmospheric phenomena. The nature of its occurrence is not fully understood and remains the subject of fierce scientific debate. Does it hail at night - the answer to this question is of interest to everyone who has never experienced it a rare event in the dark.

Brief information about the city

Hail is atmospheric precipitation in the form of pieces of ice. The shape and size of these deposits can vary greatly:

• Diameter from 0.5 to 15 cm;
• Weight from several grams to half a kilogram;
• The composition can also be very different: several layers clear ice, and alternating transparent and opaque layers;
• The form is very diverse - up to bizarre formations in the form of “flower buds”, etc.

Hailstones easily stick together, forming large particles the size of a fist. Precipitation of more than 2 cm in diameter is already sufficient to cause major damage to a farm. As soon as hail of this size is expected, a storm warning is issued.

Different states may have different size thresholds: it all depends on the specific agricultural area. For example, for grape plantations, even small hailstones will be enough to destroy the entire crop.

The necessary conditions

According to modern ideas about the nature of hail, for its occurrence it is necessary:

• Water drops;
• Condensation yard;
• Rising air currents;
• Low temperature.

Similar atmospheric phenomenon is formed in 99% of cases in temperate latitudes over large continental spaces. Most researchers believe that thunderstorm activity is a prerequisite.

In tropical and equatorial zones Hail is a fairly rare occurrence, despite the fact that thunderstorms occur quite often there. This happens because for the formation of ice, it is also necessary that at an altitude of approximately 11 km there is enough low temperature, which does not always happen in warm places globe. Hail occurs there only in mountainous areas.

In addition, the probability of hail becomes vanishingly small as soon as the air temperature drops below -30 °C. Supercooled water droplets in this case are located near and inside snow clouds.

How does hail occur?

The mechanism of formation of this type of precipitation can be described as follows:

1. An ascending air flow containing a significant number of water droplets encounters a cloud layer of low temperature on its path. It often happens that such an air flow is a strong tornado. A significant part of the cloud should be below the freezing point (0 ° C). The probability of hail formation increases a hundredfold when the air temperature at an altitude of 10 km is about -13 °.
2. Upon contact with condensation nuclei, pieces of ice are formed. As a result of alternating processes of raising and lowering, hailstones acquire a layered structure (transparent and white levels). If the wind blows in a direction where there are a lot of water droplets, a transparent layer is created. If water vapor blows into an area, the hailstones become covered with a crust of white ice.
3. When colliding with each other, the ice can stick together and seriously grow in size, forming irregular shapes.
4. Hail formation may last for at least half an hour. As soon as the wind stops supporting the increasingly heavy thunder cloud, hail will begin to fall on the earth's surface.
5. After the ice passes past the area with temperatures above 0 ° C, the slow process of melting begins.

Why doesn't there hail at night?

In order for ice particles of such a size to form in the sky that they do not have time to melt when they fall to the ground, sufficiently strong vertical forces are needed. air currents. In turn, for the upward flow to be powerful enough, strong heating is required earth's surface. That is why, in the vast majority of cases, hail falls in the evening and afternoon hours.

However, nothing prevents it from falling out at night, if there is a thundercloud of sufficient size in the sky. True, at night most people sleep, and small hail may go completely unnoticed. That's why the illusion is created that “freezing rain” only occurs during the day.

As for statistics, in most cases hail occurs in summer time at approximately 15:00. The possibility of precipitation is quite high until 22:00, after which the probability of this type of precipitation tends to zero.

Observational data from meteorologists

Among the most known cases loss " freezing rain» in the dark:

• One of the most powerful overnight hailstorms occurred on June 26, 1998 in the Illinois village of Hazel Crest. Then local Agriculture seriously damaged by hailstones measuring 5 cm in diameter that fell around 4 a.m.;
• On September 5, 2016, hail fell in the vicinity of Yekaterinburg, damaging local crops;
• In the Belarusian city of Dobrush on the night of August 26, 2016, ice floes the size of fists broke car windows;
• On the night of September 9, 2007, there was hail in the Stavropol region, which damaged 15 thousand private houses;
• On the night of July 1, 1991, Mineral water An icy downpour struck, not only causing damage to local households, but even damaging 18 aircraft. The average size icicles were about 2.5 cm, but there were also giant balls the size of a chicken egg.

Many people still don't know if it hails at night. Probability of occurrence this phenomenon at night it is vanishingly small, but still there. And for these rare cases There are many strong anomalies that cause serious harm to the economy.

hail

When it hails, the roof and gutters shake with a terrible roar and the hail can cause destruction. Hailstones can pierce the wing of an airplane, destroy wheat seedlings, and hail kills horses, cows and other domestic animals. Behind a short time Such heavy hail may fall that it will completely cover the earth.

After a strong hail storm, rushing streams carry out accumulations of ice up to two meters long and wide. Small hailstones are often round in shape . They fall to the ground like little billiard balls. But it happens that the shape of hailstones has unusual shapes: sometimes a sun with rays, sometimes a frozen letter “X”. Various shapes are caused by the wind blowing the formed hailstone high in the air.

The largest hailstone

The most big hailstone ever seen, fell in September 1970 near Coffeyville, Kansas. It was more than 40 centimeters in diameter, weighed about 800 grams, and ice spikes protruded from it in different directions. This shapeless piece of ice resembled a medieval deadly weapon.

The hailstone grows more and more as more and more more ice sticks to the ice “ship” born by the wind, rushing without a rudder and without sails on a thundercloud. If you split a hailstone, you can trace the history of its birth. Rings are visible on the fault, like rings on a tree stump, marking the stages of hailstone growth. One layer is transparent, another is milky, the next is transparent again, and so on.

: a hailstone weighing about 800 grams fell in 1970.

I'm always surprised when it hails. How is it that on a hot summer day during a thunderstorm, peas of ice fall to the ground? In this story I will tell you why it is hailing.

It turns out that hail forms when raindrops cool down, passing through the cold layers of the atmosphere. Single drops turn into tiny hailstones, but then amazing transformations happen to them! Falling down, such a hailstone collides with a counterflow of air from the ground. Then she rises up again. Unfrozen raindrops stick to it and it sinks again. A hailstone can make a lot of such movements from bottom to top and back and its size will increase. But there comes a time when it becomes so heavy that the rising air currents are no longer able to support it. That’s when the moment comes when the hailstone quickly rushes to the ground.

A large hailstone, cut in half, is like an onion: it consists of several layers of ice. Sometimes hailstones resemble layered cake, where ice and snow alternate. And there is an explanation for this - from such layers one can calculate how many times a piece of ice traveled from rain clouds to supercooled layers of the atmosphere.

Besides, hailstones can take the shape of a ball, cone, ellipse, or look like an apple. Their speed towards the ground can reach 160 kilometers per hour, so they are compared to a small projectile. Indeed, hail can destroy crops and vineyards, break glass and even pierce the metal trim of a car! The damage caused by hail across the planet is estimated at a billion dollars a year!

But everything, of course, depends on the size of the hailstones. So in 1961 in India, a hailstone weighing 3 kilograms outright killed... an elephant! In 1981, in Guangdong Province, China, hailstones weighing seven kilograms fell during a thunderstorm. Five people were killed and about ten thousand buildings were destroyed. But the most people - 92 people - died due to one-kilogram hailstones in 1882 in Bangladesh.

Today people learn to deal with hail. A special substance (called a reagent) is introduced into the cloud using rockets or projectiles. As a result, hailstones are smaller in size and have time to melt completely or largely in warm layers air before it hits the ground.

This is interesting:

Even in ancient times, people noticed that loud noise prevents hail or causes smaller hailstones. Therefore, to save the crops, they rang bells or fired cannons.

If hail catches you indoors, stay as far away from windows as possible and do not leave the house.

If hail catches you outside, try to find shelter. If you run far from it, be sure to protect your head from hail strikes.