Thunderstorm - what is it? Where do the lightnings that cut through the whole sky and the menacing peals of thunder come from? Thunderstorm is a natural phenomenon. Lightning, called electrical discharges, can form inside clouds (cumulonimbus), or between the earth's surface and clouds. They are usually accompanied by thunder. Lightning is associated with heavy rains, heavy winds, and often with hail.
Activity
Thunderstorm is one of the most dangerous natural phenomena. People struck by lightning rarely survive.
At the same time, approximately 1500 thunderstorms operate on the planet. The intensity of the discharges is estimated at a hundred lightning per second.
The distribution of thunderstorms on Earth is uneven. For example, there are 10 times more of them over the continents than over the ocean. Most (78%) of lightning discharges are concentrated in the equatorial and tropical zones. Thunderstorms are especially frequent in Central Africa. But the polar regions (Antarctica, Arctic) and lightning polespractically do not see. The intensity of a thunderstorm, it turns out, is associated with a heavenly body. In middle latitudes, its peak occurs in the afternoon (daytime) hours, in the summer. But the minimum was registered before sunrise. Geographic features are also important. The most powerful thunderstorm centers are in the Cordillera and the Himalayas (mountainous regions). The annual number of "stormy days" is also different in Russia. In Murmansk, for example, there are only four of them, in Arkhangelsk - fifteen, Kaliningrad - eighteen, St. Petersburg - 16, in Moscow - 24, Bryansk - 28, Voronezh - 26, Rostov - 31, Sochi - 50, Samara - 25, Kazan and Yekaterinburg - 28, Ufa - 31, Novosibirsk - 20, Barnaul - 32, Chita - 27, Irkutsk and Yakutsk - 12, Blagoveshchensk - 28, Vladivostok - 13, Khabarovsk - 25, Yuzhno-Sakhalinsk - 7, Petropavlovsk-Kamchatsky - 1.
Thunderstorm development
How is it going? Thunderclouds only form under certain conditions. The presence of ascending moisture flows is mandatory, while there must be a structure where one fraction of the particles is in an icy state, the other in a liquid state. Convection, which will lead to the development of thunderstorms, will occur in several cases.
- Uneven heating of surface layers. For example, over water with a significant temperature difference. Over large cities, thunderstorm intensity will be somewhat stronger than in the surrounding area.
- When cold air displaces warm air. The frontal convention often develops simultaneously with obstructive and nimbostratus clouds (clouds).
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When air rises in mountain ranges. Even small elevations can lead to increased cloud formations. This is forced convection.
Any storm cloud, regardless of its type, must go through three stages: cumulus, maturity, decay.
Classification
Thunderstorms were classified for some time only at the place of observation. They were divided, for example, into spelling, local, frontal. Thunderstorms are now classified according to characteristics that depend on the meteorological environment in which they develop. Updrafts are formed due to the instability of the atmosphere. For the creation of thunderclouds, this is the main condition. The characteristics of such flows are very important. Depending on their power and size, various types of thunderclouds are formed, respectively. How are they subdivided?
1. Cumulonimbus single-cell, (local or intramass). Have hail or thunderstorm activity. Transverse dimensions from 5 to 20 km, vertical - from 8 to 12 km. Such a cloud "lives" up to an hour. After a thunderstorm, the weather hardly changes.
2. Multicell cluster. Here the scale is more impressive - up to 1000 km. A multi-cell cluster covers a group of thunderstorm cells that are at different stages of formation and development and at the same time form a single whole. How are they arranged? Mature thunderstorm cells are located in the center, decaying - on the leeward side. Their transverse dimensions can reach 40 km. Cluster multicell thunderstorms "give"gusts of wind (heavy, but not strong), downpour, hail. The existence of one mature cell is limited to half an hour, but the cluster itself can "live" for several hours.
3. Squall lines. These are also multicell thunderstorms. They are also called linear. They can be either solid or with gaps. Wind gusts are longer here (on the leading front). The multicell line appears as a dark wall of clouds when approached. The number of streams (both upstream and downstream) is quite large here. That is why such a complex of thunderstorms is classified as multi-cell, although the thunderstorm structure is different. The squall line is capable of producing intense downpour and large hail, but is more often “limited” by strong downdrafts. It often passes ahead of a cold front. In the pictures, such a system has the shape of a curved bow.
4. Supercell thunderstorms. Such thunderstorms are rare. They are especially dangerous for property and human life. The cloud of this system is similar to the single-cell cloud, since both differ in one upstream zone. But they have different sizes. Supercell cloud - huge - close to 50 km in radius, height - up to 15 km. Its boundaries may lie in the stratosphere. The shape resembles a single semicircular anvil. The speed of ascending streams is much higher (up to 60 m/s). A characteristic feature is the presence of rotation. It is it that creates dangerous, extreme phenomena (large hail (more than 5 cm), destructive tornadoes). The main factor for the formation of such a cloud is the environmental conditions. We are talking about a very strong convention with a temperature of +27 and wind with variabledirection. Such conditions arise during wind shear in the troposphere. Formed in the updrafts, precipitation is transferred to the downdraft zone, which ensures a long cloud life. Precipitation is unevenly distributed. Showers go near the updraft, and hail - closer to the northeast. The rear of the thunderstorm may shift. Then the most dangerous zone will be near the main updraft.
There is also the concept of "dry thunderstorm". This phenomenon is quite rare, characteristic of the monsoons. With such a thunderstorm, there is no precipitation (they simply do not reach, evaporating as a result of exposure to high temperatures).
Movement Speed
In an isolated thunderstorm it is about 20 km/h, sometimes faster. If cold fronts are active, the speed can be 80 km/h. In many thunderstorms, old thunderstorm cells are replaced by new ones. Each of them covers a relatively short distance (on the order of two kilometers), but in the aggregate the distance increases.
Electrification mechanism
Where do lightning come from? Electric charges around clouds and inside them are constantly moving. This process is rather complicated. It is easiest to imagine how electric charges work in mature clouds. The dipole positive structure dominates in them. How is it distributed? The positive charge is placed at the top, and the negative charge is placed below it, inside the cloud. According to the main hypothesis (this area of science can still be considered little explored), heavier and larger particles are negatively charged, while small and light ones havepositive charge. The former fall faster than the latter. This becomes the reason for the spatial separation of space charges. This mechanism is confirmed by laboratory experiments. Particles of ice pellets or hail can have a strong charge transfer. The magnitude and sign will depend on the water content of the cloud, the (ambient) air temperature, and the collision velocity (the main factors). The influence of other mechanisms cannot be excluded. Discharges occur between the earth and the cloud (or the neutral atmosphere or the ionosphere). It is at this moment that we observe flashes dissecting the sky. Or lightning. This process is accompanied by loud peals (thunder).
Thunderstorm is a complex process. It may take many decades, and perhaps even centuries, to study it.
