Thunderstorm - what is it? Where do the lightning striking the whole sky and formidable peals of thunder come from? Thunderstorm is a natural phenomenon. Lightning, called electrical discharges, can form inside the clouds (cumulonimbus), or between the earth's surface and clouds. They are usually accompanied by thunder. Lightning is associated with heavy rains, a gale, and often hail.
Activity
Thunderstorm is one of the most dangerous natural phenomena. People struck by lightning survive only in isolated cases.
At the same time, approximately 1,500 thunderstorms act on the planet. The intensity of the discharges is estimated at a hundred lightning strikes per second.
The distribution of thunderstorms on Earth is uneven. For example, over continents there are 10 times more than over the ocean. Most (78%) of lightning discharges are concentrated in the equatorial and tropical zones. Especially often a thunderstorm is recorded in Central Africa. But the polar regions (Antarctica, Arctic) and lightning poles practically do not see. The intensity of the thunderstorm, it turns out, is associated with the celestial luminary. In middle latitudes, its peak occurs in the afternoon (afternoon) hours, in the summer. But the minimum is registered before sunrise. Geographical features are also important. The most powerful thunderstorm centers are in the Cordilleras and the Himalayas (mountainous regions). The annual number of “thunderstorm days” in Russia is different. In Murmansk, for example, there are only four, 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
How does it go? A thundercloud forms only 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 ice state, and the other in a liquid state. Convection, which will lead to the development of a thunderstorm, will arise in several cases.
Uneven heating of the surface layers. For example, above water at a significant temperature difference. Above large cities, thunderstorm intensity will be somewhat stronger than in the vicinity.
When forced out by warm cold air. The frontal convention often develops simultaneously with cover and layered rain clouds (clouds).
When air rises in the mountains. Even small elevations can lead to increased cloud formations. This is forced convection.
Any thunderstorm cloud, regardless of its type, necessarily passes through three stages: cumulus, maturity, and decay stage.
Classification
Thunderstorms for some time were classified 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 environments in which they develop. Ascending flows are formed due to the instability of the atmosphere. To create thunderclouds, this is a basic condition. The characteristics of such flows are very important. Depending on their thickness and magnitude, various types of thunderclouds are formed, respectively. How are they divided?
1. Cumulonimbus single cell, (local or intramass). Have hail or thunderstorm activity. The transverse dimensions are from 5 to 20 km, vertical - from 8 to 12 km. Such a cloud "lives" for up to an hour. After a thunderstorm, the weather remains virtually unchanged.
2. Multi-cell cluster. Here the scale is more impressive - up to 1000 km. A multi-cell cluster encompasses a group of thunderstorm cells located at various stages of formation and development and at the same time constituting 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 multi-cell thunderstorms “give” gusts of wind (heavy, but not strong), rainfall, hail. The existence of one mature cell is limited to half an hour, but the cluster itself can "live" for several hours.
3. Lines of squalls. It is also a multi-cell thunderstorm. They are also called linear. They can be either continuous or with gaps. Gusts of wind are longer here (on the leading front). The multi-cell line at approach seems to be a dark wall of clouds. The number of flows (both ascending and descending) is quite large. That is why such a complex of thunderstorms is classified as multi-cell, although the thunderstorm structure is different. The squall line is able to produce intense rainfall and large hail, but more often it is “limited” by strong condescending flows. Often she passes in front of a cold front. In the pictures, such a system has the shape of a bent 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 a single-cell, since both differ in the same upstream zone. But their sizes are different. Supercell cloud - huge - close to 50 km in radius, height - up to 15 km. Its boundaries can be in the stratosphere. The shape resembles a single semicircular anvil. The speed of the ascending flows 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 environmental conditions. This is a very strong convention with temperatures from +27 and wind with a variable direction. Such conditions arise during wind shears in the troposphere. Formed in ascending flows, precipitation is transferred to the downstream zone, which ensures long life to the cloud. Precipitation is unevenly distributed. Showers are near the upstream, and hail is closer to the northeast. The back of the thunderstorm may shift. Then the most dangerous zone will be next to the main upstream.
There is the concept of "dry thunderstorm". This phenomenon is quite rare, characteristic of monsoons. With such a thunderstorm, there is no precipitation (they simply do not fly, evaporating as a result of exposure to high temperature).
Movement speed
In an isolated thunderstorm, it is about 20 km / h, sometimes faster. If cold fronts are active, speed can be 80 km / h. Many thunderstorms replace old thunderstorm cells with new ones. Each of them passes a relatively small path (of the order of two kilometers), however, in aggregate, the distance increases.
Electrification mechanism
Where do the lightnings come from? Electric charges around and inside the clouds are constantly moving. This process is quite complicated. The easiest way to present a picture of the work of electric charges in mature clouds. A dipole positive structure dominates in them. How is it distributed? A positive charge is placed at the top, and a negative charge is below it, inside the cloud. According to the main hypothesis (this area of science can be considered little known so far), heavier and larger particles are negatively charged, while small and light particles have a positive charge. The former fall faster than the latter. This causes the spatial separation of space charges. Such a mechanism is confirmed by laboratory experiments. Pieces of ice croup or hail can have a strong charge transfer. The magnitude and sign will depend on the water content of the cloud, the temperature of the air (ambient), the speed of the collision (main factors). The impact of other mechanisms is not excluded. Discharges occur between the earth and the cloud (or neutral atmosphere, or ionosphere). It is at this moment that we observe flashes of the sky. Or lightning. This process is accompanied by loud peals (thunder).
Thunderstorm is a complex process. It can take decades to study, and possibly even centuries.