Over Moscow shone silvery clouds

For several nights in a row over Moscow appears bright and large field of Noctilucent clouds in the Northern part of the sky.

A beautiful phenomenon of course, these “noctilucent clouds”, just besides the beauty they raise questions, such as why they began to appear where before them was not, and that could. For example, in 2013, the anomalous appearance of these clouds is explained by a meteorite. The reason for the appearance of noctilucent clouds over Europe, according to experts, is connected with falling of the Chelyabinsk meteorite, which on power is 15 times inferior to the famous Tunguska meteorite. So, the night after the Tunguska catastrophe of 30 June 1908, noctilucent clouds were observed everywhere in Western Europe and Russia, becoming a source of optical anomalies. Read scientific works on the theme of “noctilucent clouds”:

M. minnaert Light and color in nature. Moscow, 1969
Bronshten V. A., Grishin N. And. Noctilucent clouds. Moscow, 1970
Bronshten V. A. Noctilucent clouds and their observation. M., 1984

Newer scientific papers on this topic, I have not included in the review specifically, that you could make an opinion on the account of “beautiful sky show” based on data collected during more or less the usual climate and without modern habits of meteorologists is not inappropriate to explain the emergence of such entities where they don’t belong, and drive to the head of the man in the street only thought – “It’s just a beautiful natural phenomenon,” but this is not a “simple” phenomenon, but a sign of more serious problems with our home – planet Earth.

NOCTILUCENT CLOUDS, the highest cloud formations in the earth’s atmosphere, formed at altitudes 70-95 km, and They are also called polar mesospheric clouds (polar mesospheric clouds, PMC), or night luminous clouds (noctilucent clouds, NLC). It is the latter name that most precisely meets their appearance and their conditions of observation, is accepted as the standard in international practice.

To observe noctilucent clouds is possible only in summer months: in the Northern hemisphere in June-July, usually mid-June to mid-July, and only in latitudes from 45° to 70°, and in most cases from 55° to 65°. In the southern hemisphere in late December and in January, at latitudes from 40° to 65°. This time of year and at these latitudes the Sun even at midnight dips are not very deep below the horizon, and sliding his rays illuminate the stratosphere, where at the height of an average of about 83 km appear noctilucent clouds. As a rule, they are visible low above the horizon, at a height of from 3° to 15° in the Northern part of the sky (for observers in the Northern hemisphere). Upon closer observation they notice annually, but high brightness they achieve not every year.

During the day, even against a pure blue sky, these clouds are not visible: they are very much subtle, etheric. Only deep twilight and the darkness of the night make them visible to the ground observer. However, using the apparatus raised to high altitudes, these clouds can be detected and in the daytime. It is easy to make the remarkable transparency of the silver clouds, through them you can clearly see the stars.

For geophysicists and astronomers noctilucent clouds are of great interest. Because these clouds are born in the region of the temperature minimum, where the atmosphere cooled to -70° C and sometimes down to -100° C. the Height from 50 to 150 km is little research as planes and balloons there can’t get up, and artificial satellites of the Earth are not able for a long time to go down there. Therefore, so far scientists argue as much about conditions at these heights and themselves on the nature of noctilucent clouds, which, in contrast to the low tropospheric clouds are in the area of active interaction of the Earth’s atmosphere from outer space. Interplanetary dust, meteoric matter, charged particles of solar and cosmic origin, magnetic fields are constantly involved in physical and chemical processes occurring in the upper atmosphere. The results of this interaction are observed in the form of auroras glow of the atmosphere, meteor phenomena and changes colors and duration of twilight. It remains to be seen what role these phenomena play in the development of noctilucent clouds.

Currently, noctilucent clouds are the only natural source of data on winds at high altitudes, the wave movements in menopause that significantly complements the study of its dynamics using other methods, such as radar meteor trails, missile and laser sensing. Large area and considerable time of the existence of such cloud fields provides a unique opportunity for direct determination of the parameters of atmospheric waves of various types and their temporal evolution.

Because of the geographic peculiarities of the phenomenon noctilucent clouds mainly in Northern Europe, Russia and Canada. Russian scientists have made and are making to this work a very important contribution and significant role played by skilled observations obtained by Amateurs of science.

The discovery of noctilucent clouds. Some mention of night shining clouds occur in the works of European scientists in the 17th-18th century, but they are fragmentary and vague. By the time of the opening of the silver cloud is considered to be June 1885, when they noticed dozens of observers in different countries. The discoverers of this phenomenon are considered to be T. Backhaus (T. W. Backhouse) who observed them on June 8 in Kissingen (Germany), and Moscow University astronomer Vitold Karlovich Zereski who discovered them independently and for the first time observed the evening of 12 June (new style). In the following days Zereski together with the well-known Pulkovo astrophysicist A. A. Belopolski then worked at the Moscow Observatory, has extensively studied noctilucent clouds and for the first time determined their altitude, having values of from 73 to 83 km, confirmed 3 years later by a German meteorologist Otto Jesse (O. Jesse).

Night shining clouds made a great impression Tsarskogo: “Clouds shone brightly in the night sky, white, silver rays, with a slight bluish tint, taking in the immediate vicinity of the horizon, yellow, Golden hue. There were cases that they were made of light, walls of buildings is very much enlightened and clear visible objects sharply acted. Sometimes clouds have formed layers or strata, sometimes their views were like a series of waves or resembled a sandbar covered with ripples or wavy irregularities… It’s so brilliant a phenomenon, that it is impossible to form an idea of it without drawings and detailed description. Some long, dazzling silver stripes, intersecting or parallel to the horizon, change rather slowly and so harsh that they can hold in the field of the telescope.

The observation of noctilucent clouds. It should be remembered that the surface of the Earth noctilucent clouds can be observed only in a period of deep twilight, on the background of the nearly black sky and, of course, in the absence of lower tropospheric clouds. It is necessary to distinguish the twilight sky from trivago sky. Zori observed during early civil twilight when the center of the solar disk falls below the observer’s horizon to a depth of from 0° to 6°. The sun’s rays thus illuminate the entire thickness of the layers of the lower atmosphere and the lower edge of tropospheric clouds. Dawn is typical of a rich variety of bright colors.

In the second half of civil twilight (sun depth of 3-6°) the Western part of the sky is still quite bright trevoe light, but in neighboring areas the sky becomes a deep dark blue and blue-green shades. High sky brightness in this period is called twilight segment.

The most favorable conditions for the detection of noctilucent clouds created during the period of nautical twilight, when the Sun dip below the horizon at 6-12° (at the end of June in the middle latitudes it is hours for 1.5–2 at the true midnight). At this time, earth’s shadow covers the lower, most dense, dusty layers of the atmosphere, and featured only sparse layers, starting from the mesosphere. In the mesosphere the ambient solar light forms a weak glow of the twilight sky; against this background is easily detected glow noctilucent clouds that attract the attention of even casual witnesses. Various observers determine their colors like pearl silver with a bluish tint or blue and white.

At twilight the color of noctilucent clouds seems unusual. Sometimes clouds like phosphorescent. Them moving barely noticeable shadow. Individual sections of the cloud fields are much brighter than others. In a few minutes more vivid could be neighboring areas.

Despite the fact that the wind speed in the stratosphere is 100-300 m/s, high altitude noctilucent clouds makes them almost immobile in a field of view of the telescope or camera. So the first photos of these clouds was Jesse in 1887. Several groups of researchers around the world systematically study noctilucent clouds in both Northern and southern hemispheres. The study of noctilucent clouds and other phenomena of uncertain nature, involves extensive involvement of the science lovers. Every scientist, regardless of his profession, can contribute to a collection of facts about this remarkable atmospheric phenomenon. High quality photo of noctilucent clouds can be obtained using a simple Amateur camera. For example, you can use the Zenit camera with the standard lens “Gelios-44”; at an aperture of 2.8 to 3.5 and a film sensitivity 100-200 units of GOST are recommended extract from 2-3 to 10-15 seconds. It is very important that during the exposure the camera trembling; for it is desirable to use a strong tripod, but in extreme cases it is enough to press the camera arm to the jamb of a window, tree or stone; when the shutter is released, be sure to use the cable.

To the images represented not only aesthetic interest, but also had a scientific meaning and would be given material for further analysis, you must accurately record the circumstances of the shooting (time, instrument parameters and photographs), and use the simplest of tools: filters, polarizing filters, a mirror for determining the velocity of the contrasting parts of the clouds.

In appearance noctilucent clouds have some similarities with high Cirrus clouds. To describe the structural forms of noctilucent clouds in their visual observation by the international morphological classification:

Type I. a Fleur, the most simple, smooth shape, filling the space between the more complex, contrasting parts and having vague structure and a weak pale white with a bluish tint glow.

Type II. Bands resembling the narrow streams, as if carried away by the flow of air. Often located in groups of several pieces parallel to each other or interwoven at a slight angle. Bands are divided into two groups – blurry (II-a) and crisp (II-b).

Type III. Waves are divided into three groups. Scallops (III-a) sites with frequent location of a narrow, sharply-defined parallel strips, similar to the light ripples on water when a small gust of wind. The ridges (III-b) are more visible signs of a wave nature; the distance between adjacent ridges 10-20 times more than the scallops. Wavy, (III-c) are formed as a result of the curvature of the surface of the clouds taken in other forms (strips, scallops).

Type IV. Vortices are also classified into three groups. Eddies with small radii (IV-a): from 0.1° to 0.5°, i.e. no more of the lunar disk. They completely bend or twist strips, scallops, and sometimes a veil, forming a ring with a dark area in the middle, reminiscent of a lunar crater. Turbulence in a simple bending of one or more lanes in the direction from the primary direction (IV-b). Powerful vortex emissions “luminous” matter in the direction from the main clouds of (IV-c) is a rare formation is characterized by rapid variability of its forms.

The zone of maximum frequency observations of noctilucent clouds in the Northern hemisphere is in latitude 55-58°. In this band fall in many big cities of Russia: Moscow, Yekaterinburg, Izhevsk, Kazan, Krasnoyarsk, Nizhny Novgorod, Novosibirsk, Chelyabinsk, etc., and only a few cities in Northern Europe and Canada.

Properties and nature of noctilucent clouds. The range of altitudes at which the formation of noctilucent clouds, generally very stable (73-95 km), but in some years narrows to 81-85 km, and sometimes expands to 60-118 km are Often cloud field consists of several fairly narrow altitude layers. The main reason for the glow of the clouds is scattering them sunlight, but it is possible that some role is played by the effect of luminescence under the action of ultraviolet rays of the Sun.

Transparency noctilucent clouds are extremely high: average cloud field holds only about 0.001% of the light passing through. It is the nature of the scattering of sunlight noctilucent clouds has allowed to establish that they are clusters of particles of 0.1–0.7 µm. The nature of these particles there were a variety of hypotheses: it was assumed that it could be ice crystals, fine particles of volcanic dust, salt crystals in ice “coat” the cosmic dust particles of meteoric or cometary origin.

Bright silver clouds, first observed in 1885-1892 and, apparently, not gone unnoticed so before, suggested that their occurrence was due to some huge catastrophic process. This phenomenon was the eruption of Krakatoa in Indonesia on 27 August 1883. In fact, it was a huge explosion with an energy equal to the explosion of twenty hydrogen bombs (20 MT of TNT). The atmosphere was thrown about 35 million tons of volcanic dust rose to a height of up to 30 km, and a huge mass of water vapor. After the explosion of Krakatoa was observed optical anomalies: the light dawns, a decrease in atmospheric transparency, polarization anomaly, ring of the Bishop (brown-red crown around the Sun with the outer angular radius of about 22° and a width of 10°; the sky inside the ring of light with a bluish tint). These anomalies lasted for about two years, gradually weakening, and noctilucent clouds appeared only towards the end of this term.

The hypothesis of the volcanic nature of noctilucent clouds first suggested by a German researcher V. Kohlraush in 1887; he thought them condensed water vapor, emitted during the eruption. Jesse 1888-1890 developed this idea, believing that it is not water, but an unknown gas (possibly hydrogen) was thrown out by the volcano and frozen in the form of small crystals. It was argued that the volcanic dust also plays a role in the formation of noctilucent clouds, because it represents the centers of crystallization of water vapor.

The gradual accumulation of observational data gave the facts spoke clearly in favor the volcanic hypothesis. Analysis of the light anomalies following major volcanic eruptions (of Mont Pelee, 1902; Katmai, 1912; Andes, 1932) showed that only in rare cases they are accompanied by the appearance of silvery clouds; most likely it was a coincidence. Currently, the volcanic hypothesis, which in the early 20th century, has been universally accepted and even entered the textbooks of meteorology, has only historical significance.

The occurrence of meteoric hypothesis of the origin of noctilucent clouds is also associated with a Grand natural phenomenon of the Tunguska catastrophe of 30 June 1908. From the point of view of observers, among whom were very experienced astronomers and meteorologists (V. Denning, F. Bush, E. Esclangon, M. wolf, F. Archenhold, D. O. class, etc.), this phenomenon manifested itself mainly various optical anomalies observed in many European countries, in the European part of Russia and Western Siberia up to Krasnoyarsk. Along with the bright sorami and “white nights”, the beginning where they usually even at the end of June is not the case, many observers have noted the appearance of noctilucent clouds. However, in 1908 one of the witnesses of the optical anomalies and the glowing clouds nothing knew about the Tunguska meteorite. Information about it appeared in print only about 15 years later.

In 1926 the idea of a connection between these two phenomena was independently made the first researcher of the place of the Tunguska catastrophe by L. A. Kulik and L. weatherman by Apostolovi. Leonid Alekseyevich Kulik detail has developed its hypothesis, proposing a definite mechanism of formation of noctilucent clouds. He believed that not only large meteorites, but the usual meteors, completely collapsing just at altitudes of 80-100 km, in the mesosphere deliver the products to their sublimation, which congenerous then the finest particles of dust, forming clouds.

In 1930, a famous American astronomer H. Shapley, and in 1934 independently by English meteorologist F. George.Whipple (not to be confused with the American astronomer F. L. Whipple) expressed the hypothesis that the Tunguska meteorite was the core of a comet with a dust tail. The penetration of the substance of the tail of the earth’s atmosphere has led, in their opinion, rise to the optical anomalies and the appearance of noctilucent clouds. However, the idea that the cause of optical anomalies of 1908 was the passage of the Earth through a cloud of space dust, made in 1908 one of the witnesses “light nights” of the period F. de Roy, of course, knew nothing about the Tunguska meteorite.

In subsequent years, the meteoric hypothesis was supported and developed by many astronomers, seeking to explain with its help, the observed feature of noctilucent clouds – their morphology, latitudinal and temporal distribution, optical properties, etc. But the meteor shower hypothesis in its purest form with this task have failed, and since 1960, its development has virtually stopped. But the role of meteoric particles as condensation nuclei and growth of ice crystals that make up noctilucent clouds, still remains indisputable.

Itself condensation (ice) the hypothesis was developed independently in 1917, but for a long time did not have a sufficient experimental basis. In 1925 the German geophysicist A. Wegener on the basis of this hypothesis, calculated that the condensation of vapor into ice crystals at an altitude of 80 km the temperature should be around -100° C; as it turned out during the rocket experiments, after 30 years, Wegener has been very far from the truth. Since 1950s in the works of V. A. Bronshten, I. A. khvostikova etc. was developed meteor-condensation hypothesis noctilucent clouds and meteoric particles act as condensation nuclei, without which education in the atmosphere of droplets and crystals from the vapor is extremely difficult. This hypothesis is partly based on the results of rocket experiments in which at altitudes 80-100 km has been collected microscopic particulates from the frozen ice on them “fur coat”; in the launching of rockets in the area of observed noctilucent clouds, the number of such particles was a hundred times more than in the absence of clouds.

In addition to the classic hypotheses have been other, less traditional; considered the relationship of noctilucent clouds to the solar activity, auroras, and other geophysical phenomena. For example, the source of water vapor in the mesosphere was considered the reaction of atmospheric oxygen with the protons of the solar wind (the hypothesis of “solar rain”).

One of the last hypothesis relates noctilucent clouds with the emergence of the ozone holes in the stratosphere. The region of formation of these clouds is being studied increasingly in relation to space and stratospheric transport: on the one hand, the launches of powerful rockets with acidity-oxygen engines are a major source of water vapor in the mesosphere and stimulate cloud formation, and with another – the appearance in this region of the cloud creates problems when returning spacecraft to Earth. It is necessary to create a reliable theory of noctilucent clouds, giving the opportunity to predict and even control this phenomenon of nature. But still many of the facts in this area is incomplete and contradictory.

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