What kind of clouds does hail come from? See what "Grad" is in other dictionaries. How the hail gets big
Forms when tiny pieces of ice, held aloft by strong updrafts, are blown through supercooled thunderclouds until they become heavy enough to fall to the ground. Most large thunderstorms produce some amount of small hailstones, but the proper conditions must be present for the hailstone to grow to freeze several solid layers of ice on it so that it can "survive" until it reaches the Earth's surface.
Internal structure of a hailstone.
Ideal conditions for hail are created by high clouds that are high in the atmosphere, as well as many updrafts such as tornadoes and cold temperatures within and below the storm.
Hailstone
A hailstone begins to form as a kernel of ice, a small accumulation of supercooled drops of water or clots of snow. This center may continue to accumulate ice, melt into a thundercloud and turn into rain, or be broken by other hailstones. If dust, sand, small seeds or other small particles become trapped in a thundercloud, this will create another opportunity for additional ice and hailstones to form.
Diagram of hailstone formation.
Hail can grow into a large number of layers when it is carried upward by the air current through all the thunderstorm layers. Even heavy hailstones can be held aloft by fairly strong updrafts. When the hail falls back through the storm due to gravity, it grows back into even more layers until it becomes so heavy that it falls as precipitation. Hailstones form in the highest, cumulonimbus clouds that reach the colder upper atmosphere, but not all hail survives once it falls from a thundercloud. The outer few layers often melt when hail mixes with other precipitation such as snow and rain.
Fully formed hailstones can range in size from pinheads to a hen's egg. There are official hail size categories that are useful for estimating the damage they can cause. Some hailstones have measured more than 6 inches (15.24 cm) in diameter and more than 1 pound (0.45 kg) in weight. Most hailstones, however, are smaller than 0.5 inches (1.27 cm) across.
Back in the Middle Ages, people noticed that after a loud sound, rain and hail either did not fall at all, or hailstones fell to the ground much smaller than usual. Not knowing why and how hail forms, in order to avoid disaster, to save crops, at the slightest suspicion of the possibility of huge ice balls, they rang bells, and if possible, even fired cannons.
Hail is a type of rainfall that forms in large cumulonimbus clouds that are ashy or dark gray in color with white ragged tops. After this, it falls to the ground in the form of small spherical or irregularly shaped particles of opaque ice.
The size of such ice floes may well vary from a few millimeters to several centimeters (for example, the size of the largest peas that were recorded by scientists was 130 mm, and their weight turned out to be about 1 kg).
This precipitation is quite dangerous: studies have shown that every year about 1% of the vegetation on Earth is killed by hail, and the damage they cause to the economies of different countries of the world is about $1 billion. They also cause trouble for residents of the region where the hail has occurred: large hailstones are quite capable of destroying not only crops, but also breaking through the roof of a car, the roof of a house, and in some cases, even killing a person.
How is it formed?
Precipitation of this type occurs mainly in hot weather, during the day, and is accompanied by lightning, thunder, downpours, and is also closely associated with tornadoes and tornadoes. This phenomenon can be observed either before or during rain, but almost never after. Despite the fact that such weather lasts relatively short time (on average about 5-10 minutes), the layer of precipitation that falls on the ground can sometimes be several centimeters.
Each cloud that carries summer hail consists of several clouds: the lower one is located low above the surface of the earth (and can sometimes stretch out in the form of a funnel), the upper one is at an altitude significantly exceeding five kilometers.
When the weather is hot outside, the air heats up extremely strongly and, together with the water vapor contained in it, rises, gradually cooling. At a great height, the steam condenses and forms a cloud that contains drops of water, which may well fall onto the earth's surface in the form of rain.
Due to the incredible heat, the updraft can be so strong that it can carry steam to a height of 2.4 km, where temperatures are much below zero, as a result of which water droplets become supercooled, and if they rise higher (at an altitude of 5 km) they begin to form hailstones (At the same time, it usually takes about a million tiny supercooled drops to form one such piece of ice).
For hail to form, it is necessary that the air flow speed exceeds 10 m/s, and the air temperature is not lower than -20°, -25°C.
Along with water droplets, tiny particles of sand, salt, bacteria, etc. rise into the air, onto which frozen steam adheres, and causes hail to form. Once formed, the ice ball is quite capable of rising several times on the updraft to the upper layers of the atmosphere and falling back into the cloud.
If an ice pellet is cut open, it can be seen to consist of layers of transparent ice alternating with translucent layers, thus resembling an onion. To determine exactly how many times it rose and fell in the middle of a cumulonimbus cloud, you just need to count the number of rings;
The longer such a hailstone flies through the air, the larger it becomes, collecting not only droplets of water, but in some cases even snowflakes along the way. Thus, a hailstone with a diameter of about 10 cm and a weight of almost half a kilogram may well form.
The higher the speed of the air currents, the longer the ice ball flies through the cloud and the larger it becomes.
A hailstone flies across a cloud as long as the air currents are able to hold it. After the piece of ice gains a certain weight, it begins to fall. For example, if the speed of the upward flow in a cloud is about 40 km/h, it is not able to hold hailstones for a long time - and they fall down quite quickly.
The answer to the question why ice balls formed in a small cumulonimbus cloud do not always reach the earth's surface is simple: if they fall from a relatively small height, they manage to melt, resulting in showers falling on the ground. The thicker the cloud, the greater the likelihood of freezing precipitation. Therefore, if the cloud thickness is:
- 12 km – the probability of occurrence of this type of precipitation is 50%;
- 14 km – chances of hail – 75%;
- 18 km – heavy hail will definitely fall.
Where is ice precipitation most likely to be seen?
This kind of weather can't be seen everywhere. For example, in tropical countries and polar latitudes this is a rather rare phenomenon, and icy precipitation occurs mainly either in the mountains or on high plateaus. There are lowlands here where hail can be observed quite often. For example, in Senegal it not only falls frequently, but often the layer of ice precipitation is several centimeters deep.
The regions of Northern India suffer quite heavily from this natural phenomenon (especially during the summer monsoons), where, according to statistics, every fourth hailstone is more than 2.5 cm.
The largest hail was recorded here by scientists at the end of the 19th century: the ice peas were so huge that 250 people were beaten to death.
Most often, hail falls in temperate latitudes - why this happens largely depends on the sea. Moreover, if it occurs much less frequently over expanses of water (upward air currents occur more often over the earth’s surface than over the sea), then hail and rain fall much more often close to the shore than far from it.
Unlike tropical latitudes, in temperate latitudes there is much more ice precipitation in lowlands than in mountainous areas, and they can be seen more often on more uneven ground surfaces.
If hail does fall in mountainous or foothill areas, it turns out to be dangerous, and the hailstones themselves are extremely large in size. Why is that? This happens primarily because in hot weather the relief here warms up unevenly, very powerful upward currents arise, raising steam to a height of up to 10 km (it is there that the air temperature can reach -40 degrees and is the cause of the largest hail flying to the ground from speed of 160 km/h and bringing with it trouble).
What to do if you find yourself under heavy precipitation
If you are in a car when the weather turns bad and hail falls, then you need to stop the car near the side of the road, but without driving off the road, since the ground may simply wash away and you will not get out. If possible, it is advisable to hide it under a bridge, put it in a garage or covered parking lot.
If it is not possible to protect your car from precipitation during such weather, you need to move away from the windows (or better yet, turn your back to them) and cover your eyes with your hands or clothes. If the car is large enough and its dimensions allow, you can even lie on the floor.
It’s absolutely forbidden to leave the car when it’s raining and hailing! Moreover, you won’t have to wait long, since this phenomenon rarely lasts longer than 15 minutes. If you are indoors during a rainstorm, you need to move away from the windows and turn off electrical appliances, since this phenomenon is usually accompanied by a thunderstorm with lightning.
If such weather finds you outside, you need to find shelter, but if there is none, you definitely need to protect your head from hailstones falling at great speed. It is advisable not to hide under trees during such a downpour, since large hailstones can break branches, which can seriously injure you if they fall.
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. In a short time, such heavy hail can fall that it completely covers 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”. The different shapes are caused by the wind blowing the resulting hailstone high in the air.
The largest hailstone
The largest 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.
How does hail occur?
Thunderclouds are real hail factories. Powerful air currents carry dust, sand and other small particles inside a thundercloud. A hailstone is formed when pieces of ice stick to particles floating through the air inside a cloud. In some hailstones, such particles may be dead insects.
Interesting:
What is the "greenhouse effect"?
The hailstone grows larger and larger as more and more ice sticks to the wind-born ice “ship”, rushing without a rudder or sails across 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.
Interesting fact: a hailstone weighing about 800 grams fell in 1970.
What causes the difference in the structure of hailstone layers?
When the ice on a hailstone freezes quickly (at a very low temperature). In order to carry a hailstone with a diameter of about 10 centimeters through the air, the rising air currents in a thundercloud must have a speed of at least 200 kilometers, which includes snowflakes and air bubbles. This layer looks cloudy. But if the temperature is higher, then the ice freezes more slowly, and the included snowflakes have time to melt and the air evaporates. Therefore, such a layer of ice is transparent. Using the rings, you can trace which layers of the cloud the hailstone visited before falling to the ground.
How does hail get big?
A hailstone grows, flying up and down across the cloud. During this time it becomes heavier and heavier. It is clear that in order for a hailstone to become significantly heavier, the wind in the cloud must be very strong. For example, for a hailstone to grow to 10 centimeters in diameter, the wind speed must be at least 200 kilometers per hour. These powerful air currents carry the hailstone until its weight becomes such that the wind is no longer able to support it in a suspended state. Now the hailstone is falling to the ground.
Hail is precipitation in the form of spherical particles or pieces of ice (hailstones) with a diameter of 5 to 50 mm, sometimes more, falling isolated or in the form of irregular complexes. Hailstones consist only of transparent ice or a series of layers of ice at least 1 mm thick, alternating with translucent layers. Hail usually occurs during severe thunderstorms.
Hail formation.
What is the mechanism of hail formation? Descartes built hypotheses on this matter in the first half of the 17th century. However, the scientific theory of hail processes and methods of influencing them was created by physicists together with meteorologists only in the middle of the last century.
Warm air rising from the earth's surface on a hot summer day cools with height, and the moisture it contains condenses, forming a cloud. Passing the zero isotherm at a certain height, the smallest drops of water become supercooled. Supercooled drops in clouds are found even at temperatures of minus 40°.
Hail forms in a powerful cumulus cloud with strong upward air currents. Their speed usually exceeds 15 m/sec (average speed of a passenger train). These flows support large supercooled (up to -10...-20°C) drops of water. The higher, the lower the speed of air flows, the more difficult it is for them to hold drops. But these drops are very unstable. Tiny particles of sand, salt, combustion products and even bacteria lifted from the earth's surface collide with supercooled drops and upset the delicate balance. Supercooled drops that come into contact with solid condensation nuclei turn into an icy hailstone embryo.
Small hailstones exist in the upper half of almost every cumulonimbus cloud, but most often such hailstones melt as they fall towards the earth's surface. So, if the speed of ascending currents in a cumulonimbus cloud reaches 40 km/h, then they are not able to contain the emerging hailstones, therefore, passing through the warm layer of air between the zero isotherm (an average height of 2.4 to 3.6 km) and the earth's surface, they fall out of the cloud in the form 
small “soft” hail, or even in the form of rain. Otherwise, rising air currents lift small hailstones to layers of air with a temperature of -10 to -40 degrees (altitude between 3 and 9 km), the diameter of the hailstones begins to grow, sometimes reaching a diameter of several centimeters.
At an altitude of 8-10 km, where the temperature reaches -35...-40°C, the drops freeze and ice particles are formed - hailstone embryos. Hitting each other, colliding with supercooled drops that have not yet had time to freeze, they freeze them to themselves, get thicker, heavier and fall into lower clouds, where there are even more supercooled drops. To "gain" a diameter of 1 cm, each hailstone must experience approximately 100 million collisions with cloud droplets.
It is worth noting that in exceptional cases, the speed of upward and downward flows in the cloud can reach 300 km/h! And the higher the speed of updrafts in a cumulonimbus cloud, the larger the hail. It would take more than 10 billion supercooled water droplets to form a hailstone the size of a golf ball, and the hailstone itself would have to remain in the cloud for at least 5 to 10 minutes to reach such a large size. It is worth noting that it takes approximately a million of these small supercooled drops to form one raindrop. Hailstones larger than 5 cm in diameter occur in supercellular cumulonimbus clouds, which contain very powerful updrafts. It is supercell thunderstorms that generate tornadoes, heavy rainfall and intense squalls.
When a hailstone reaches such a mass that the upward flow is unable to hold it, it rushes to the surface of the earth, and we observe the fall of large hail. When observing hail, if you carefully cut the hailstone, you will notice that matte layers of ice will alternate in the form of rings with layers of transparent ice. Thus, by the number of such rings, one can determine how many times the hailstone was lifted by rising air currents in the cloud.
The falling speed of a hailstone with a diameter of 4 cm can reach 100, and larger hailstones rush to the ground at a speed of 160 km/h. It is not difficult to guess what destruction hailstorms can cause. But not every large hailstone will reach the ground: falling in a cloud, the hailstones collide with each other, collapsing and turning into smaller hailstones that melt in the warm air. On average, 40 - 70% of the formed hailstones never reach the surface of the earth, melting in the warm air. Hail usually falls during strong thunderstorms in the warm season, when the temperature at the surface of the earth is not lower than 20°C.
Hail falls like an avalanche. Sometimes, in a matter of minutes, hail covers the ground with ice balls with a layer of 5-7 cm. In the Kislovodsk region in 1965, hail fell, covering the ground with a layer of 75 cm! Most often, hail falls in a narrow (no more than 10 kilometers) but long (sometimes hundreds of kilometers) stripe. The area of the hail zone can vary from one hectare to several tens of kilometers. In the latter case, the hail zones correspond to the squall line.
Hail is a less terrible disaster than a hurricane or earthquake, but it, both in the old days and now, often causes huge losses. Hail breaks grape vines and branches of fruit trees, knocks off fruits from them, destroys grain crops, breaks stems of sunflowers and corn, knocks out tobacco and melon plantations. Poultry, small and sometimes cattle often die from hail strikes.
In 1593 “...on Sunday the eleventh day of June, on the day of the Holy Trinity, at seven o'clock in the evening there was such a strong thunderstorm with thunder, lightning, rain and hail, which people had not heard of until then. Some hailstones... weighed from 18 to 20 pounds each. As a result of this, great damage was caused to crops and many churches, castles, houses and other buildings were destroyed. The vineyards did not bear fruit after this for 5-6 years; the forest was uprooted and thrown to the ground. Such horror gripped the people that there was no "A man, no matter how brave he was, who would not prepare for death. Many were killed and wounded, others lost their minds. Many livestock, both domestic and wild, died." This is an excerpt from chronological records kept in one of the southern departments of France. Perhaps there is some exaggeration here; it is known that “fear has big eyes.” Such a large weight of hailstones is doubtful, but it must be taken into account that in those days the pound as a unit of weight had several meanings. However, it is clear that this was a terrible natural disaster, one of the most catastrophic hailstorms to hit France.
In the eastern part of Colorado (USA), about six hailstorms occur annually, each of them causing huge losses. In our country, hailstorms most often occur in the North Caucasus, Georgia, Armenia, and in the mountainous regions of Central Asia. Here is one of the laconic messages from the Nalchik weather station: “From June 9 to 10, 1939... hail the size of a chicken egg fell, accompanied by heavy rain. As a result, over 60 thousand hectares of wheat and about 4 thousand hectares of other crops were killed; about 2 thousand sheep."
It has long been noted that there are areas that suffer from hail from year to year. Some farmers are even convinced that hail will certainly destroy the crops in some fields, while the neighboring area will not be damaged. For residents of England, hail is a great rarity, and French winegrowers living on the other side of the English Channel curse it several times a year. In the tropics, hail almost never occurs, although thunderstorms occur frequently there. Thus, in Brazzaville there are up to 60 thunderstorms per year, but in the entire history of the city, hail has never been recorded there.
When talking about hail, the first thing to note is the size of the hailstones. They are usually all different in size. The largest ones attract attention. And now we learn about absolutely fantastic hailstones. In India and China, there are known cases of ice blocks weighing 2-3 kilograms falling from the sky. They even talk about such a sad incident: in 1961, a heavy hailstone killed an elephant in Northern India. In our temperate latitudes, hailstones weighing about a kilogram were observed. There is a known case when hail broke the tiles on the roof of a house in Voronezh and pierced the metal roof of a bus. These are indirect signs by which the size of hailstones is also judged. Sometimes it is possible to take photographs with a scale - an object of well-known dimensions (a coin, a watch, a matchbox, or even better - a ruler) is placed next to the hailstone.
One of the hailstones, photographed in the USA, had a diameter of 12 cm, 40 cm in circumference, and weighed 700 g. In France, elongated hailstones were recorded approximately the size of a palm (15 X 9 cm). The weight of individual hailstones reached 1200 g! And 5-8 such hailstones fell per square meter. So the ancient chroniclers may not have exaggerated what they saw.
But these are all exceptional cases. Typically, even hailstones with a diameter of 25 mm or more are rare. Not every old-timer can remember hail the size of a chicken egg...
Hail control:
At all times, hail caused the greatest damage to agriculture. Therefore, from very ancient times, people began to look for ways to combat this natural disaster. Herodotus talks about how the Thracians shot arrows into hail clouds. Of course, it was a gesture of despair. And in later centuries they shot at the clouds from rifles and cannons. But the shooters had no idea what the projectile was actually supposed to do with the cloud. And even in our century, attempts to use modern technology - aviation and missiles - to combat a hail cloud ended in vain. It is known that in Italy in the 1955 season, about one hundred thousand rockets were fired at clouds carrying hail.
It is estimated that nature “spends” millions of kilowatts to create a summer cumulus cloud. One inevitably wonders: is there a force capable of destroying it? Fortunately, as meteorologists have found, there is no need to destroy clouds. Atmospheric processes are sometimes in such an unstable state that with relatively little intervention their course can be pushed in the desired direction.
This is exactly what meteorologists achieve when they storm the clouds. The size of hail clouds is enormous, sometimes several thousand square kilometers; it is not difficult to hit such a target with a shell, but the result is insignificant - nothing more than a pellet to an elephant. It was necessary to find a weak spot - the “Achilles heel” of the giant cloud. Calculations and experiments by meteorologists and physicists have shown that hail originates in a relatively small (20-30 cubic kilometers), the so-called large-drop cloud zone, and it is on this zone that “pressure” must be applied. But how to do that?
The most effective way is to artificially create a large number of hail nuclei. Each “newborn” will intercept droplets of supercooled water, and its reserves in the cloud are limited. Each of the embryos interferes with the growth of the other, so the hailstones are small. Such hail, falling on the ground, will not cause serious damage, and it is very possible that instead of hail it will rain. This is already a victory!
Artificial hail nuclei are created when dry carbon dioxide or silver iodide or lead are added to the supercooled part of the cloud. One gram creates 1012 (trillion) ice crystals.
The difficulty is to determine the hail zone in the cloud and spray reagents there in time. In general, the entire fight against hail resembles air defense.
Radars detect a hail cloud almost 40 km before the protected areas. Hail clouds develop very quickly. The entire process of hail formation takes 30-40 minutes, so it is necessary to influence the cloud no later than 15-20 minutes after the start of its rapid development. The coordinates of the large-droplet zone are clarified and anti-aircraft guns equipped with special shells or missiles are launched.
The large anti-hail rocket "Cloud" carries approximately 3 kg of a special reagent. In the head and tail of the rocket there are remote mechanisms that, at the required height and in a certain section of the rocket’s flight path, ignite the pyrotechnic composition and eject the parachute. The rocket descends by parachute, releasing smoke containing tiny particles of lead iodide. The rocket's flight passes through supercooled parts of the cloud, where myriads of ice crystals form on aerosol particles. They become artificial embryos of hailstones.
Having done its job, the rocket slowly falls to the ground and usually becomes the prey of the children. It is completely safe, which allows you to work in densely populated areas. The range of the "Cloud" is 10 km.
What is hail and how is it formed?
Very often in the summer there is an unusual type of 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 a chicken egg. Such hail can cause catastrophic consequences - 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 type of precipitation consists of pieces of ice of different sizes. The structure of a hailstone can consist of several alternating layers of ice - transparent and translucent.
How do ice floes form?
The formation of hail is a complex atmospheric process based on the water cycle in nature. Warm air, which contains moisture vapor, rises 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 of 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 of impressive size - 8-10 cm in diameter and weighing 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.