Dangerous atmospheric phenomena associated with water. Dangerous atmospheric processes. Natural hazards

Dangerous atmospheric processes include: cyclones, tornadoes, heavy rains, snowfalls, etc. Countries located near ocean coasts often suffer from destructive cyclones. IN Western Hemisphere cyclones are called hurricanes, and in the northwestern sector of the Pacific Ocean - typhoons.

The formation of cyclones is associated with intense heating (above 26-27°) of air above the ocean surface compared to its temperature above the continent. This leads to the formation of spiral-shaped updrafts of air, bringing heavy rain and destruction to the coast.

The most destructive are tropical cyclones, which hit the coasts of continents with hurricane air currents at speeds of more than 350 km/h, rainfall reaching 1000 mm for several days and storm waves up to 8 m high.

The conditions for the formation of tropical cyclones have been studied quite well. Seven areas of their origin have been identified in the World Ocean. All of them are located near the equator. Periodically, in these areas, the water warms up above the critical temperature (26.8°C), which leads to sudden atmospheric disturbances and the formation of a cyclone.

Every year, on average, about 80 tropical cyclones occur around the globe. The most vulnerable to them are the coasts of the south of the Asian continent and the equatorial zone of North and South America (Caribbean region) (Table 3). Thus, in Bangladesh over the past 30 years, more than 700 thousand people have died from cyclones. The most destructive cyclone occurred in November 1970, when more than 300 thousand inhabitants of this country died and 3.6 million people were left homeless. Another cyclone in 1991 killed 140,000 people.

Japan experiences more than 30 cyclones annually. The most powerful cyclone in the history of Japan (Ise-wan, 1953) killed more than 5 thousand, injured 39 thousand people, destroyed about 150 thousand residential buildings, washed away or buried under sediments more than 30 thousand hectares of arable land, damaged 12 thousand damages on roads, about 7 thousand landslides occurred. The total economic damage amounted to about $50 billion.

In September 1991, the mighty Typhoon Mireille swept over Japan, killing 62 people and destroying 700 thousand houses. Total damage amounted to $5.2 billion.

Very often, cyclones bring catastrophic rainfall to the shores of Japan. One of these showers hit the flat part in 1979

Federal Agency for Education Russian Federation

Far Eastern State Technical University

(FEPI named after V.V. Kuibyshev)

Institute of economics and management

discipline: BJD

on the topic: Atmospheric hazards

Completed:

Student of group U-2612

Vladivostok 2005

1. Phenomena occurring in the atmosphere

The gaseous environment around the Earth, rotating with it, is called the atmosphere.

Its composition at the surface of the Earth: 78.1% nitrogen, 21% oxygen, 0.9% argon, in small fractions of a percent carbon dioxide, hydrogen, helium, neon and other gases. The lower 20 km contains water vapor (3% in the tropics, 2 x 10-5% in Antarctica). At an altitude of 20-25 km there is a layer of ozone, which protects living organisms on Earth from harmful short-wave radiation. Above 100 km, gas molecules decompose into atoms and ions, forming the ionosphere.

Depending on the temperature distribution, the atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

Uneven heating contributes to the general circulation of the atmosphere, which affects the weather and climate of the Earth. The strength of the wind at the earth's surface is measured on the Beaufort scale.

Atmospheric pressure is distributed unevenly, which leads to the movement of air relative to the Earth from high pressure to low pressure. This movement is called wind. Region low blood pressure in the atmosphere with a minimum in the center is called a cyclone.

The cyclone reaches several thousand kilometers across. In the Northern Hemisphere, the winds in a cyclone blow counterclockwise, and in the Southern Hemisphere they blow clockwise. The weather during a cyclone is predominantly cloudy with strong winds.

An anticyclone is an area high blood pressure in an atmosphere with a maximum in the center. The diameter of the anticyclone is several thousand kilometers. An anticyclone is characterized by a system of winds blowing clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, partly cloudy and dry weather and weak winds.

The following electrical phenomena take place in the atmosphere: air ionization, atmospheric electric field, electric charges clouds, currents and discharges.

As a result of natural processes occurring in the atmosphere, phenomena are observed on Earth that pose an immediate danger or impede the functioning of human systems. To such atmospheric hazards include fog, ice, lightning, hurricanes, storms, tornadoes, hail, blizzards, tornadoes, downpours, etc.

Ice is a layer of dense ice that forms on the surface of the earth and on objects (wires, structures) when supercooled drops of fog or rain freeze on them.

Ice usually occurs at air temperatures from 0 to -3°C, but sometimes even lower. The crust of frozen ice can reach a thickness of several centimeters. Under the influence of the weight of ice, structures can collapse and branches break off. Ice increases the danger to traffic and people.

Fog is an accumulation of small water drops or ice crystals, or both, in the ground layer of the atmosphere (sometimes up to a height of several hundred meters), reducing horizontal visibility to 1 km or less.

In very dense fogs, visibility can be reduced to several meters. Fogs are formed as a result of condensation or sublimation of water vapor on aerosol (liquid or solid) particles contained in the air (so-called condensation nuclei). Most fog droplets have a radius of 5-15 microns at positive air temperatures and 2-5 microns at negative temperatures. The number of drops per 1 cm3 of air ranges from 50-100 in light fogs and up to 500-600 in dense fogs. Fogs, according to their physical genesis, are divided into cooling fogs and evaporation fogs.

According to the synoptic conditions of formation, intramass fogs are distinguished, forming in homogeneous air masses, and frontal fogs, the appearance of which is associated with atmospheric fronts. Intramass fogs predominate.

In most cases, these are cooling fogs, and they are divided into radiation and advection. Radiation fogs form over land when the temperature drops due to radiation cooling of the earth's surface, and from it the air. They most often form in anticyclones. Advection fogs are formed due to the cooling of warm, moist air as it moves over a colder surface of land or water. Advective fogs develop both over land and sea, most often in the warm sectors of cyclones. Advection fogs are more stable than radiation fogs.

Frontal fogs form near atmospheric fronts and move with them. Fogs prevent the normal operation of all types of transport. Fog forecast is important for safety.

Hail - view atmospheric precipitation, consisting of spherical particles or pieces of ice (hailstones) ranging in size from 5 to 55 mm, there are hailstones measuring 130 mm and weighing about 1 kg. The density of hailstones is 0.5-0.9 g/cm3. In 1 minute, 500-1000 hailstones fall per 1 m2. The duration of hail is usually 5-10 minutes, very rarely up to 1 hour.

Radiological methods for determining the hail content and hail hazard of clouds have been developed and operational services for combating hail have been created. The fight against hail is based on the principle of introduction using rockets or. projectiles into a cloud of reagent (usually lead iodide or silver iodide) that promotes freezing of supercooled droplets. As a result, a huge number of artificial crystallization centers appear. Therefore, hailstones are smaller in size and they have time to melt before falling to the ground.

2. Lightning

Lightning is a giant electrical spark discharge in the atmosphere, usually manifested by a bright flash of light and accompanying thunder.

Thunder is the sound in the atmosphere that accompanies a lightning strike. Caused by air vibrations under the influence of an instantaneous increase in pressure along the path of lightning.

Lightning most often occurs in cumulonimbus clouds. The American physicist B. Franklin (1706-1790), Russian scientists M.V. Lomonosov (1711-1765) and G. Richman (1711-1753), who died from a lightning strike while researching atmospheric electricity, contributed to the discovery of the nature of lightning.

Lightning is divided into intracloud, i.e., passing in the thunderclouds themselves, and ground, i.e., striking the ground. The development process of ground lightning consists of several stages.

At the first stage, in the zone where the electric field reaches a critical value, impact ionization begins, initially created by free electrons, always present in small quantities in the air, which, under the influence of the electric field, acquire significant speeds towards the ground and, colliding with air atoms, ionize their. In this way, electron avalanches arise, turning into threads of electrical discharges - streamers, which are well-conducting channels, which, when connected, give rise to a bright thermally ionized channel with high conductivity - a stepped leader. The movement of the leader towards the earth's surface occurs in steps of several tens of meters at a speed of 5 x 107 m/s, after which its movement stops for several tens of microseconds, and the glow greatly weakens. In the next stage, the leader again advances several tens of meters, while a bright glow covers all the passed steps. Then the glow stops and weakens again. These processes are repeated when the leader moves to the surface of the earth at an average speed of 2 x 105 m/sec. As the leader moves toward the ground, the field intensity at its end increases and, under its action, a response streamer is ejected from objects protruding on the surface of the earth, connecting to the leader. The creation of a lightning rod is based on this phenomenon. In the final stage, the reverse or main lightning discharge follows along the channel ionized by the leader, characterized by currents from tens to hundreds of thousands of amperes, strong brightness and high speed advancement 1O7..1O8 m/s. The temperature of the channel during the main discharge can exceed 25,000°C, the length of the lightning channel is 1-10 km, and the diameter is several centimeters. Such lightning is called prolonged lightning. They are the most common cause of fires. Typically, lightning consists of several repeated discharges, the total duration of which can exceed 1 s. Intracloud lightning includes only leader stages; their length ranges from 1 to 150 km. The probability of a ground object being struck by lightning increases as its height increases and the electrical conductivity of the soil increases. These circumstances are taken into account when installing a lightning rod. Unlike dangerous lightning, called linear, there are ball lightning, which often form after a linear lightning strike. Lightning, both line and ball, can cause serious injury and death. Lightning strikes can be accompanied by destruction caused by its thermal and electrodynamic effects. The greatest destruction is caused by lightning strikes on ground objects in the absence of good conductive paths between the strike site and the ground. From an electrical breakdown, narrow channels are formed in the material, in which a very high temperature is created, and part of the material evaporates with an explosion and subsequent ignition. Along with this, large potential differences may arise between individual items inside a structure, which may cause electric shock to people. Direct lightning strikes into overhead communication lines with wooden supports are very dangerous, as this can cause discharges from wires and equipment (telephones, switches) to the ground and other objects, which can lead to fires and electric shock to people. Direct lightning strikes on high-voltage power lines can cause short circuits. Lightning strikes on airplanes are dangerous. When lightning strikes a tree, people nearby can be struck.

3. Lightning protection

Discharges of atmospheric electricity can cause explosions, fires and destruction of buildings and structures, which led to the need to develop a special lightning protection system.

Lightning protection is a set of protective devices designed to ensure the safety of people, the safety of buildings and structures, equipment and materials from lightning strikes.

Lightning can affect buildings and structures with direct impacts (primary impact), which cause direct damage and destruction, and secondary impacts - through the phenomena of electrostatic and electromagnetic induction. The high potential created by lightning discharges can also be carried into buildings through overhead lines and various communications. The main lightning discharge channel has a temperature of 20,000°C and above, causing fires and explosions in buildings and structures.

Buildings and structures are subject to lightning protection in accordance with SN 305-77. The choice of protection depends on the purpose of the building or structure, the intensity of lightning activity in the area in question and the expected number of lightning strikes per year.

The intensity of thunderstorm activity is characterized by the average number of thunderstorm hours per year pc or the number of thunderstorm days per year pd. It is determined using the appropriate map given in CH 305-77 for a specific area.

A more general indicator is also used - the average number of lightning strikes per year (n) per 1 km2 of the earth's surface, which depends on the intensity of thunderstorm activity.

Table 19. Intensity of thunderstorm activity

The expected number of lightning strikes per year N of buildings and structures not equipped with lightning protection is determined by the formula:

N = (S + 6hx) (L+ 6hx) n 10"6,

where S and L are, respectively, the width and length of the protected building (structure), which has a rectangular shape in plan, m; for buildings of complex configuration, when calculating N, the width and length of the smallest rectangle into which the building can be inscribed in plan are taken as S and L; hx is the greatest height of the building (structure), m; p. - the average annual number of lightning strikes per 1 km2 of the earth's surface at the location of the building. For chimneys, water towers, masts, trees, the expected number of lightning strikes per year is determined by the formula:

In a power line unprotected from lightning with a length of Lkm with an average wire suspension height hcp, the number of lightning strikes per year will be, assuming that the danger zone extends from the line axis in both directions by 3 hcp,

N = 0.42 x K)"3 xLhcpnch

Depending on the likelihood of a fire or explosion caused by lightning, and based on the scale of possible destruction or damage, the standards establish three categories of lightning protection devices.

In buildings and structures classified as lightning protection category I, explosive mixtures of gases, vapors and dust are stored for a long time and systematically arise, explosives are processed or stored. Explosions in such buildings are usually accompanied by significant destruction and casualties.

In buildings and structures of lightning protection category II, the above-mentioned explosive mixtures can occur only at the time of an industrial accident or malfunction technological equipment, explosives are stored in secure packaging. Lightning strikes in such buildings, as a rule, are accompanied by significantly less destruction and casualties.

In buildings and structures of category III, a direct lightning strike can cause fire, mechanical damage and injury to people. This category includes public buildings, chimneys, water towers, etc.

Buildings and structures classified as Category I according to lightning protection must be protected from direct lightning strikes, electrostatic and electromagnetic induction, and the introduction of high potentials through above-ground and underground metal communications throughout Russia.

Buildings and structures of lightning protection category II must be protected from direct lightning strikes, its secondary effects and the introduction of high potentials through communications only in areas with an average intensity of thunderstorm activity lch = 10.

Buildings and structures classified as category III according to lightning protection must be protected from direct lightning strikes and the introduction of high potentials through ground-based metal communications in areas with thunderstorm activity for 20 hours or more per year.

Buildings are protected from direct lightning strikes by lightning rods. The lightning rod protection zone is the part of the space adjacent to the lightning rod, inside which a building or structure is protected from direct lightning strikes with a certain degree of reliability. Protection zone A has a reliability level of 99.5% or higher, and protection zone B has a reliability level of 95% or higher.

Lightning rods consist of lightning rods (receiving lightning discharge), grounding conductors, which serve to drain lightning current into the ground, and down conductors connecting lightning rods to grounding rods.

Lightning rods can be free-standing or installed directly on a building or structure. Based on the type of lightning rod, they are divided into rod, cable and combined. Depending on the number of lightning rods operating on one structure, they are divided into single, double and multiple.

Lightning rod lightning rods are made from steel rods of various sizes and cross-sectional shapes. The minimum cross-sectional area of ​​the lightning rod is 100 mm2, which corresponds to a round cross-section of a rod with a diameter of 12 mm, strip steel 35 x 3 mm or a gas pipe with a flattened end.

Lightning rods of cable lightning rods are made of steel multi-wire cables with a cross-section of at least 35 mm2 (diameter 7 mm).

Metal structures of protected structures can also be used as lightning rods - chimneys and other pipes, deflectors (if they do not emit flammable vapors and gases), metal roofing and other metal structures rising above the building or structure.

Down conductors are made with a cross section of 25-35 mm2 from steel wire with a diameter of at least 6 mm or steel strip, square or other profile. Metal structures of protected buildings and structures (columns, trusses, fire escapes, metal elevator guides, etc.) can be used as down conductors, except for prestressed reinforcement of reinforced concrete structures. Down conductors should be laid along the shortest paths to grounding conductors. The connection of down conductors with lightning rods and grounding conductors must ensure continuity of electrical communication in the structures being connected, which is usually ensured by welding. Down conductors must be located at such a distance from the entrances to buildings that people cannot touch them in order to avoid being struck by lightning current.

Grounding rods of lightning rods serve to divert lightning current into the ground, and the effective operation of lightning protection depends on their correct and high-quality design.

The design of the ground electrode is adopted depending on the required impulse resistance, taking into account the resistivity of the soil and the convenience of its installation in the ground. To ensure safety, it is recommended to fence the grounding electrodes or, during a thunderstorm, not to allow people to approach the grounding electrodes at a distance of less than 5-6 m. Grounding electrodes should be located away from roads, sidewalks, etc.

Hurricanes are a marine phenomenon and the greatest destruction from them occurs near the coast. But they can also penetrate far onto land. Hurricanes may be accompanied heavy rains, floods, in the open sea form waves more than 10 m high, storm surges. Tropical hurricanes are especially powerful, the radius of their winds can exceed 300 km (Fig. 22).

Hurricanes are a seasonal phenomenon. An average of 70 tropical cyclones develop on Earth every year. Average duration hurricane duration is about 9 days, maximum - 4 weeks.

4. Storm

The storm is very strong wind, leading to great roughness at sea and destruction on land. A storm can be observed during the passage of a cyclone or tornado.

Wind speed at the earth's surface exceeds 20 m/s and can reach 100 m/s. In meteorology, the term “storm” is used, and when the wind speed is more than 30 m/s - hurricane. Short-term wind increases up to speeds of 20-30 m/s are called squalls.

5. Tornadoes

A tornado is atmospheric vortex, arising in a thundercloud and then spreading in the form of a dark sleeve or trunk towards the surface of land or sea (Fig. 23).

At the top, the tornado has a funnel-shaped expansion that merges with the clouds. When a tornado descends to the earth's surface, its lower part also sometimes becomes expanded, resembling an overturned funnel. The height of a tornado can reach 800-1500 m. The air in a tornado rotates and at the same time rises in a spiral upward, drawing in dust or dust. The rotation speed can reach 330 m/s. Due to the fact that the pressure inside the vortex decreases, condensation of water vapor occurs. In the presence of dust and water, the tornado becomes visible.

The diameter of a tornado over the sea is measured in tens of meters, over land - hundreds of meters.

A tornado usually occurs in the warm sector of a cyclone and moves instead< циклоном со скоростью 10-20 м/с.

A tornado travels a path ranging from 1 to 40-60 km. A tornado is accompanied by a thunderstorm, rain, hail and, if it reaches the surface of the earth, it almost always causes great destruction, sucks in water and objects encountered on its path, lifts them high up and carries them over long distances. Objects weighing several hundred kilograms are easily lifted by a tornado and transported tens of kilometers. A tornado at sea poses a danger to ships.

Waterspouts over land are called blood clots; in the United States they are called tornadoes.

Like hurricanes, tornadoes are identified from weather satellites.

To visually assess the strength (speed) of the wind in points based on its effect on ground objects or on sea waves, the English admiral F. Beaufort in 1806 developed a conventional scale, which, after changes and clarifications in 1963, was adopted by the World Meteorological Organization and widely used in synoptic practice (Table 20).

Table. Wind force at the earth's surface according to the Beaufort scale (at a standard height of 10 m above an open, level surface)

6. The influence of atmospheric phenomena on transport

atmosphere fog lightning hail danger

Transport is one of the most weather-dependent industries National economy. This is especially true for air transport, which requires the most complete, detailed information about the weather, both actually observed and expected according to the forecast. The specificity of transport requirements for meteorological information lies in the scale of weather information - the routes of aircraft, ships and road cargo transportation have a length measured in many hundreds and thousands of kilometers; in addition, meteorological conditions have a decisive influence not only on the economic performance of vehicles, but also on traffic safety; The life and health of people often depend on the weather conditions and the quality of information about it.

To meet the needs of transport for meteorological information, it turned out to be necessary not only to create special meteorological services (aviation and sea - everywhere, and in some countries also railway, road), but also to develop new branches of applied meteorology: aviation and marine meteorology.

Many atmospheric phenomena pose a danger to air and sea transport, but some meteorological quantities must be measured with particular accuracy to ensure the safety of the flights of modern aircraft and the navigation of modern ships. For the needs of aviation and navy, new information was needed that climatologists did not have before. All this required the restructuring of what was already established and had become<классической>science of climate science.

The influence of transport needs on the development of meteorology over the past half century has become decisive; it has entailed the technical re-equipment of meteorological stations, and the use in meteorology of the achievements of radio engineering, electronics, telemechanics, etc., as well as the improvement of weather forecasting methods, the introduction of means and methods of pre-calculation future state of meteorological quantities (atmospheric pressure, wind, air temperature) and calculation of the movement and evolution of the most important synoptic objects, such as cyclones and their troughs with atmospheric fronts, anticyclones, ridges, etc.

It is an applied scientific discipline that studies the influence meteorological factors on the safety, regularity and economic efficiency of airplane and helicopter flights, as well as developing theoretical foundations and practical methods for their meteorological support.

Figuratively speaking, aviation meteorology begins with choosing the location of the airport, determining the direction and required length of the runway at the airfield and sequentially, step by step, explores a whole range of issues about the state of the air environment that determines flight conditions.

At the same time, she also pays considerable attention to purely applied issues, such as drawing up a flight schedule, which should optimally take into account weather conditions, or the content and form of transmitting information on the characteristics of the surface layer of air, which are crucial for the safety of landing, to board an aircraft approaching to land. airplane.

According to International organization civil aviation - ICAO, over the past 25 years, adverse meteorological conditions have been officially recognized as the cause of 6 to 20% aviation accidents; in addition, in an even greater (one and a half times) number of cases they were an indirect or concomitant cause of such incidents. Thus, in approximately a third of all cases of unsuccessful flight completion, weather conditions played a direct or indirect role.

According to ICAO, flight disruptions due to weather over the past ten years, depending on the time of year and climate of the area, occur on average in 1-5% of cases. More than half of these disruptions are flight cancellations due to adverse weather conditions at departure or destination airports. Statistics recent years shows that the lack of required weather conditions at destination airports accounts for up to 60% of flight cancellations, delays and aircraft landings. Of course, these are average numbers. They may not coincide with the actual picture in individual months and seasons, as well as in individual geographic areas.

Cancellation of flights and return of tickets purchased by passengers, changes in routes and additional costs arising from this, increase in flight duration and additional fuel costs, consumption of motor resources, payment for services and flight support, depreciation of equipment. Thus, in the USA and Great Britain, airline losses due to weather annually amount to 2.5 to 5% of total annual income. In addition, disruption of regular flights brings moral damage to airlines, which ultimately also results in a decrease in revenue.

Improving the on-board and ground equipment of aircraft landing systems makes it possible to reduce the so-called landing minimums and thereby reduce the percentage of violations of the regularity of departures and landings due to adverse meteorological conditions at destination airports.

These are, first of all, the conditions of the so-called weather minimums - visibility range, cloud base height, wind speed and direction, established for pilots (depending on their qualifications), aircraft (depending on their type) and airfields (depending on their technical equipment and terrain characteristics). When actual weather conditions are below the established minimums, flights are prohibited for safety reasons. In addition, there are meteorological phenomena dangerous for flights that complicate or severely limit flight operations (they are partially discussed in Chapters 4 and 5). This is air turbulence that causes loose aircraft, thunderstorms, hail, icing of aircraft in clouds and precipitation, dusty and sandstorms, squalls, tornadoes, fog, snowstorms and blizzards, as well as heavy downpours that sharply impair visibility. Also worth mentioning are the dangers of static electricity discharges in the clouds, snow drifts, slush and ice on the runway (runway) and treacherous changes in the wind in the ground layer above the airfield, called vertical wind shear.

Among large quantity minimums established depending on the qualifications of pilots, equipment of airfields and aircraft, as well as the geography of the area, three categories of ICAO international minima can be distinguished in terms of cloud height and visibility range at the airfield, according to which aircraft are allowed to take off and land at difficult conditions weather:

In civil aviation of our country, according to current regulations, the following meteorological conditions are considered difficult: cloud height of 200 m or less (even though they cover at least half of the sky) and visibility range of 2 km or less. Difficult weather conditions are also considered when there are one or more meteorological phenomena classified as dangerous for flights.

The standards for difficult weather conditions are not standard: there are crews who are allowed to fly under significantly worse weather conditions. In particular, all crews flying under ICAO category 1, 2 and 3 minimums can fly in difficult weather conditions, if there are no dangerous meteorological phenomena that directly interfere with flights.

IN military aviation restrictions on difficult weather conditions are somewhat less stringent. There are even so-called<всепогодные>aircraft equipped to fly in very difficult weather conditions. However, they also have weather restrictions. There is practically no complete independence of flights from weather conditions.

Thus,<сложные метеоусловия>- a conditional concept, its standards are related to the qualifications of flight personnel, the technical equipment of aircraft and airfield equipment.

Wind shear is the change in wind vector (wind speed and direction) per unit distance. There is a distinction between vertical and horizontal wind shear. Vertical shear is usually defined as the change in wind vector in meters per second per 30 m height; depending on the direction of the wind change relative to the movement of the aircraft, the vertical shift can be longitudinal (tailwind - positive or headwind - negative) or lateral (left or right). Horizontal wind shear is measured in meters per second per 100 km distance. Wind shear is an indicator of the instability of the state of the atmosphere, which can cause the aircraft to bump, interfere with flights, and even - at certain specific values ​​of its magnitude - threaten flight safety. Vertical wind shear of more than 4 m/s at 60 m altitude is considered a meteorological phenomenon dangerous for flights.

Vertical wind shear also affects the landing accuracy of the landing aircraft (Fig. 58). If the pilot of the aircraft does not counteract its impact by operating the engine or rudders, then when the descending aircraft passes through the wind shear line (from the upper layer with one wind value to the lower layer with another value), due to a change in the airspeed of the aircraft and its lift, the aircraft will leave the calculated descent trajectory (glide path) and land not in given point the runway and further or closer to it, to the left or to the right of the runway axis.

Icing of an aircraft, that is, the deposition of ice on its surface or on individual structural parts at the inlets of some instruments, occurs most often during flight in clouds or rain, when supercooled drops of water contained in the cloud or precipitation, colliding with the aircraft, freeze. Less commonly, there are cases of ice or frost deposits on the surface of an aircraft outside of clouds and precipitation, so to speak, in<чистом небе>. This phenomenon can occur in humid air that is warmer than the outside surface of the aircraft.

For modern aircraft, icing no longer poses a serious danger, since they are equipped with reliable anti-icing agents (electric heating of vulnerable areas, mechanical chipping of ice and chemical protection of surfaces). In addition, the frontal surfaces of aircraft flying at speeds of more than 600 km/h become very hot due to braking and compression of the air flow around the aircraft. This is the so-called kinetic heating of aircraft parts, due to which the surface temperature of the aircraft remains above the freezing point of water even when flying in cloudy air with a significant negative temperature.

However, intense icing of an aircraft during a forced long flight in supercooled rain or in clouds with high water content poses a real danger for modern aircraft. The formation of a dense crust of ice on the fuselage and tail of an aircraft disrupts the aerodynamic qualities of the aircraft, as the air flow around the surface of the aircraft is distorted. This deprives the aircraft of flight stability and reduces its controllability. Ice on the inlet openings of the engine air intake reduces the thrust of the engine, and on the air pressure receiver it distorts the readings of airspeed instruments, etc. All this is very dangerous if the anti-icing agents are not turned on in a timely manner or if the latter fails.

According to ICAO statistics, about 7% of all aviation accidents related to meteorological conditions occur annually due to icing. This is slightly less than 1% of all plane crashes in general.

In the air, no areas of space with a vacuum, or air pockets, can exist. But vertical gusts in a restless, turbulently disturbed flow cause the aircraft to throw, creating the impression of it falling into the void. They gave birth to this term, which is now falling out of use. Airplane roughness, associated with air turbulence, causes discomfort for passengers and crew of the aircraft, makes flying difficult, and, if excessively intense, can pose a danger to the flight.

Since ancient times, navigation has been closely connected with the weather. The most important meteorological quantities that determine the navigation conditions of sea vessels have always been the wind and the condition of the sea surface caused by it - waves, horizontal visibility range and phenomena that worsen it (fog, precipitation), the state of the sky - cloudiness, sunshine, visibility of stars, sun, moon . In addition, sailors are interested in air and water temperatures, as well as the presence of sea ice in high latitudes and icebergs penetrating water areas of temperate latitudes. Not the least important role for assessing navigation conditions is played by information about such phenomena as thunderstorms and cumulonimbus clouds, which are fraught with waterspouts and strong squalls that are dangerous for seagoing vessels. In low latitudes, navigation is also associated with the danger that tropical cyclones bring with them - typhoons, hurricanes, etc.

For sailors, weather is, first of all, a factor that determines the safety of navigation, then an economic factor, and finally, as for all people, a factor of comfort, well-being and health.

Weather information—weather forecasts that include estimates of wind, waves, and the position of cyclonic eddies, both low-latitude and extratropical—is crucial for maritime navigation, that is, for plotting routes that provide the fastest, most cost-effective navigation with minimal risk for ships and cargo and with maximum safety for passengers and crews.

Climatic data, that is, weather information accumulated over many previous years, serves as the basis for laying sea trade routes connecting continents. They are also used in scheduling passenger ships and for planning maritime transport. Weather conditions must also be taken into account when organizing loading and unloading operations (when it comes to cargo, influenced atmospheric conditions, for example tea, forest, fruit, etc.), fishing, tourism and excursion business, sports navigation.

Icing of sea vessels is the scourge of navigation in high latitudes, but at air temperatures below zero it can also occur in mid-latitudes, especially in strong winds and waves, when there is a lot of spray in the air. The main danger of icing is the increase in the ship's center of gravity due to the build-up of ice on its surface. Intense icing makes the vessel unstable and creates a real risk of capsizing.

The rate of ice deposition when splashes of supercooled water freeze on fishing trawlers in the North Atlantic can reach 0.54 t/h, which means that after 8-10 hours of sailing in conditions of intense icing, the trawler will capsize. A slightly lower rate of ice deposition in snowfalls and supercooled fog: for a trawler it is 0.19 and 0.22 t/h, respectively.

Icing reaches its greatest intensity in cases where the ship was previously in an area with an air temperature significantly below 0°C. Example hazardous conditions icing in temperate latitudes may serve as Tsemes Bay on the Black Sea, where during strong north-eastern winds, with the so-called Novorossiysk bora, in winter the freezing of the water sheet and splashes of sea water on the hulls and deck superstructures of ships occurs so intensely that the only effective way to save the ship is to go into open sea, beyond the influence of bora.

According to special studies conducted in the 50s and 60s, a tailwind increases the speed of a vessel by about 1%, while a headwind can reduce it, depending on the size of the vessel and its load, by 3-13%. Even more significant is the effect of sea waves caused by wind on a ship: the speed of the ship is an elliptical function of the height and direction of the waves. In Fig. Figure 60 shows this dependence. When the wave height is more than 4 m, sea vessels are forced to slow down or change course. In conditions of high seas, the duration of the voyage, fuel consumption and the risk of cargo damage increase sharply, therefore, based on meteorological information, the route is laid to bypass such areas.

Poor visibility, fluctuations in water levels in rivers and lakes, freezing of reservoirs - all this affects both the safety and regularity of vessel navigation, as well as the economic indicators of their operation. Early freeze-ups on rivers, as well as later opening of rivers from ice, shorten the navigation period. The use of icebreaking means lengthens navigation times, but increases the cost of transportation.

Decreased visibility due to fog and precipitation, snow drifts, icy conditions, rainfall, floods and strong winds make it difficult for road and rail transport, not to mention motorcycles and bicycles. Open modes of transport are more than twice as sensitive to adverse weather as closed modes. On days with fog and heavy precipitation, the flow of cars on the roads is reduced by 25-50% compared to the flow on clear days. The number of private cars on the roads decreases most sharply on rainy days. For this reason, it is difficult to establish an exact quantitative relationship between meteorological conditions and road accidents, although such a relationship undoubtedly exists. Despite the decrease in traffic flow in bad weather, the number of accidents during icy conditions increases by 25% compared to dry weather; Accidents are especially common when there is ice on curves in roads with heavy traffic.

IN winter months In temperate latitudes, the main difficulties for land transport are associated with snow and ice. Snow drifts require the clearing of roads, which complicates traffic, and the installation of barrier shields on sections of roads that do not have snow-protected plantings.

A shield placed vertically and oriented perpendicular to the air flow with which it is transferred (resists behind it a zone of turbulence, that is, disordered vortex movement of air (Fig. 61). Within the turbulent zone, instead of transfer it's snowing the process of its deposition - a snowdrift grows, the height of which, in the limit, coincides with the thickness of the turbulence zone, and the length - with the extent of this zone, which, as established experimentally, is approximately equal to fifteen times the height of the shield. The snowdrift created behind the shield is shaped like a fish.

The formation of an ice crust on roads is determined not only by the temperature regime, but also by humidity and the presence of precipitation (in the form of supercooled rain or drizzle falling on a previously very cold surface). Therefore, it is risky to draw a conclusion about icy conditions on roads based on air temperature alone, but the temperature regime remains the most important indicator of the danger of icing on roads: the minimum road surface temperature can be 3°C lower than the minimum air temperature.

Salt, which is scattered on roads and sidewalks, actually prevents the formation of an ice crust by melting the snow. A mixture of snow and salt remains a liquid, non-freezing mass at temperatures down to -8°C; melting of ice with salt can be achieved even at a temperature of -20°C, although the melting process will be much less efficient than at temperatures close to 0°C . In practice, clearing roads of snow using salt is effective when the snow cover is up to 5 cm thick.

However, using salt to clear roads of snow has a negative side: salt causes corrosion of cars and pollutes water bodies with chlorides, and pollutes the soil near roads with excess sodium (see also 13.10). Therefore, in a number of cities this method of combating road icing is prohibited.

Fluctuations in air temperature in winter can cause icing of rails and communication lines, as well as rolling stock when it is on sidings; There are, although relatively rare, cases of icing of pantographs on electric trains. All these features of the influence of meteorological conditions on the operation of railway transport require the use of special equipment and are associated with additional costs of labor and money in the amount of 1-2% of the cost of operational operating costs. In general, railway transport is less dependent on weather conditions than other modes of transport, which is why advertising brochures railways it is often stated that<железная дорога работает и тогда, когда все другие виды транспорта бездействуют>. Although this is an exaggeration, it is not too far from the truth. However, railways are not insured against natural disasters caused by weather anomalies in the same way as other sectors of the national economy: strong storms, floods, landslides, mudflows, and snow avalanches destroy railway tracks, like roads; Ice, intensively deposited on the contact wires of electric railways, breaks them in the same way as the wires of power lines or conventional communication lines. It should be added that the increase in train speed to 200-240 km/h created the threat of the train overturning under the influence of wind.

In hilly areas, to reduce snow drifts, barrier shields are installed, the slope of the road surface is changed, which helps to weaken the surface vortex, or low embankments are built. The embankment should not be too steep, otherwise it will create a noticeable leeward vortex, which will cause snow to accumulate on the leeward side of the embankment.

Bibliography

1. Mankov V.D.: BZD, part II, BE EVT: tutorial for higher educational institutions - St. Petersburg: VIKU, 2001.

2. Kosmin G.V., Mankov V.D. Guide to the civil law for the discipline “BZhD”, part 5. On the conduct of hazardous work and ET of Gostekhnadzor in the Armed Forces of the Russian Federation - VIKU - 2001

3. O. Rusak, K. Malayan, N. Zanko. “Life Safety” textbook

The science

The earth's atmosphere is a source of amazing and amazing phenomena. In ancient times, atmospheric phenomena were considered a manifestation of God's will, today someone takes them for aliens. Nowadays, scientists have uncovered many secrets of nature, including optical phenomena.

In this article we will tell you about amazing natural phenomena, some of them are very beautiful, others are deadly, but all of them are an integral part of our planet.

Atmospheric phenomena

© manfredxy

A lunar rainbow, also known as a night rainbow, is a phenomenon created by the Moon. Always located on the opposite side of the sky from the Moon. For a lunar rainbow to appear, the sky must be dark and rain must be falling on the opposite side of the moon (except for those rainbows caused by a waterfall). Such a rainbow is best seen when the moon phase is close to the full moon. A lunar rainbow is paler and thinner than a regular solar rainbow. But this phenomenon is also rarer.

© Jyliana

Bishop's Ring is a brown-red circle around the Sun that occurs during and after volcanic eruptions. Light is refracted by volcanic gases and dust. The sky inside the ring becomes light with a blue tint. This atmospheric phenomenon was discovered by Edward Bishop in 1883, after the famous eruption of the Krakatoa volcano.

© Aliaksei Skreidzeleu

A halo is an optical phenomenon, a ring of light around a light source, usually the Sun and Moon. There are many types of halos and they are caused mainly by ice crystals in cirrus clouds at an altitude of 5-10 km in upper layers atmosphere. Sometimes the light through them is refracted so strangely that so-called false suns appear, which in ancient times were considered a bad omen.

© Lunamarina

Belt of Venus - atmospheric optical phenomenon. Appears as a pink to orange band between the dark night sky below and the blue sky above. Appears before sunrise or after sunset and runs parallel to the horizon in the opposite direction from the Sun.

© Aleksandr Kichigin

Noctilucent clouds are the highest clouds in the atmosphere and are rare a natural phenomenon. They are formed at an altitude of 70-95 km. Noctilucent clouds can only be observed in summer months. In the northern hemisphere in June-July, in southern hemisphere at the end of December - beginning of January. The time of appearance of such clouds is evening and early evening twilight.

© Juhku/Getty Images Pro

Northern lights, aurora (Aurora Borealis) are the sudden appearance of colored lights in the night sky, usually green. Caused by the interaction of charged particles arriving from space and interacting with atoms and molecules of air in the upper layers earth's atmosphere. The aurora is observed mainly at high latitudes of both hemispheres in oval zones - belts surrounding the Earth's magnetic belts.

© David Baileys/Getty Images Pro

The Moon itself does not emit light. What we see is only the reflection of the sun's rays from its surface. Due to changes in the composition of the atmosphere, the Moon changes its usual color to red, orange, green or blue. The rarest color of the Moon is blue. It is usually caused by ash in the atmosphere.

© Minerva Studio/Getty Images

Mammatus clouds are one of the varieties of cumulus clouds that have a cellular structure. Rarely found, mainly in tropical latitudes, and are associated with the formation of tropical cyclones. Mammatus are located under the main cluster of powerful cumulus clouds. Their color is usually gray-blue, but due to direct rays of the Sun or the backlight of other clouds, they may appear golden or reddish.

© acmanley/Getty Images Pro

A fire rainbow is one of the types of halo, which is the appearance of a horizontal rainbow against the background of light, high clouds. This rare weather phenomenon occurs when light passing through cirrus clouds is refracted through flat ice crystals. The rays enter through the vertical side wall of the hexagonal crystal, exiting from the bottom horizontal side. The rarity of the phenomenon is explained by the fact that the ice crystals in the cloud must be oriented horizontally to refract the sun's rays.

Diamond dust is solid precipitation in the form of tiny ice crystals floating in the air, formed in frosty weather. Diamond dust usually forms under clear or nearly clear skies and resembles fog. However, unlike fog, it does not consist of water droplets, but of ice crystals and in rare cases slightly reduces visibility. Most often this phenomenon can be observed in the Arctic and Antarctic, but can occur anywhere at an air temperature of -10, -15.

© Sergey Nivens

Zodiacal light is a faint glow of the sky, visible in the tropics at any time of the year, extending along the ecliptic, i.e. in the area of ​​the Zodiac. This is the result of dispersion sunlight in dust accumulations in the region of the Earth's rotation around the Sun. It can be observed either in the evening over western part horizon, or in the morning above the eastern one. It has the appearance of a cone, narrowing with distance from the horizon, gradually losing brightness and turning into the zodiacal stripe.

© Pixabay / Pexels

Sometimes during sunset or sunrise you can see a vertical stripe of light stretching from the sun. Solar pillars are formed by the reflection of sunlight from flat ice crystals in the Earth's atmosphere. Usually the pillars are formed due to the sun, but the light source can be the Moon and artificial light sources.

Natural hazards

A firespout or tornado is a rare natural phenomenon. For its formation, several large fires are required, as well as strong winds. Next, these several fires combine to form a huge bonfire. The air rotation speed inside the tornado is over 400 km/h, and the temperature reaches 1000 degrees Celsius. The main danger of such a fire is that it will not stop until it burns everything in its path.

© Ablestock.com/Getty Images

A mirage is a natural phenomenon that results in the appearance of imaginary images. various items. This happens due to the refraction of light flows at the boundary between layers of air that are sharply different in density and temperature. Mirages are divided into upper - visible above the object, lower - visible under the object, and lateral.

A rare complex optical phenomenon consisting of several forms of mirages, in which distant objects are visible repeatedly and with various distortions, is called Fata Morgana. Travelers in the Al-er-Rawi desert often become victims of mirages. In front of people, in the vicinity, oases appear, which are actually 700 km away.

Federal Agency for Education of the Russian Federation

Far Eastern State Technical University

(FEPI named after V.V. Kuibyshev)

Institute of economics and management

discipline: BJD

on the topic: Atmospheric hazards

Completed:

Student of group U-2612

Vladivostok 2005

1. Phenomena occurring in the atmosphere

The gaseous environment around the Earth, rotating with it, is called the atmosphere.

Its composition at the surface of the Earth: 78.1% nitrogen, 21% oxygen, 0.9% argon, in small fractions of a percent carbon dioxide, hydrogen, helium, neon and other gases. The lower 20 km contains water vapor (3% in the tropics, 2 x 10-5% in Antarctica). At an altitude of 20-25 km there is a layer of ozone, which protects living organisms on Earth from harmful short-wave radiation. Above 100 km, gas molecules decompose into atoms and ions, forming the ionosphere.

Depending on the temperature distribution, the atmosphere is divided into the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

Uneven heating contributes to the general circulation of the atmosphere, which affects the weather and climate of the Earth. The strength of the wind at the earth's surface is measured on the Beaufort scale.

Atmospheric pressure is distributed unevenly, which leads to the movement of air relative to the Earth from high pressure to low pressure. This movement is called wind. An area of ​​low pressure in the atmosphere with a minimum in the center is called a cyclone.

The cyclone reaches several thousand kilometers across. In the Northern Hemisphere, the winds in a cyclone blow counterclockwise, and in the Southern Hemisphere they blow clockwise. The weather during a cyclone is predominantly cloudy with strong winds.

An anticyclone is an area of ​​high pressure in the atmosphere with a maximum in the center. The diameter of the anticyclone is several thousand kilometers. An anticyclone is characterized by a system of winds blowing clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, partly cloudy and dry weather and weak winds.

The following electrical phenomena take place in the atmosphere: air ionization, atmospheric electric field, electrical charges of clouds, currents and discharges.

As a result of natural processes occurring in the atmosphere, phenomena are observed on Earth that pose an immediate danger or impede the functioning of human systems. Such atmospheric hazards include fog, ice, lightning, hurricanes, storms, tornadoes, hail, blizzards, tornadoes, downpours, etc.

Ice is a layer of dense ice that forms on the surface of the earth and on objects (wires, structures) when supercooled drops of fog or rain freeze on them.

Ice usually occurs at air temperatures from 0 to -3°C, but sometimes even lower. The crust of frozen ice can reach a thickness of several centimeters. Under the influence of the weight of ice, structures can collapse and branches break off. Ice increases the danger to traffic and people.

Fog is an accumulation of small water drops or ice crystals, or both, in the ground layer of the atmosphere (sometimes up to a height of several hundred meters), reducing horizontal visibility to 1 km or less.

In very dense fogs, visibility can be reduced to several meters. Fogs are formed as a result of condensation or sublimation of water vapor on aerosol (liquid or solid) particles contained in the air (so-called condensation nuclei). Most fog droplets have a radius of 5-15 microns at positive air temperatures and 2-5 microns at negative temperatures. The number of drops per 1 cm3 of air ranges from 50-100 in light fogs and up to 500-600 in dense fogs. Fogs, according to their physical genesis, are divided into cooling fogs and evaporation fogs.

According to the synoptic conditions of formation, a distinction is made between intramass fogs, which form in homogeneous air masses, and frontal fogs, the appearance of which is associated with atmospheric fronts. Intramass fogs predominate.

In most cases, these are cooling fogs, and they are divided into radiation and advection. Radiation fogs form over land when the temperature drops due to radiation cooling of the earth's surface, and from it the air. They most often form in anticyclones. Advection fogs are formed due to the cooling of warm, moist air as it moves over a colder surface of land or water. Advective fogs develop both over land and sea, most often in the warm sectors of cyclones. Advection fogs are more stable than radiation fogs.

Frontal fogs form near atmospheric fronts and move with them. Fogs prevent the normal operation of all types of transport. Fog forecast is important for safety.

Hail is a type of atmospheric precipitation consisting of spherical particles or pieces of ice (hailstones) ranging in size from 5 to 55 mm; there are hailstones measuring 130 mm and weighing about 1 kg. The density of hailstones is 0.5-0.9 g/cm3. In 1 minute, 500-1000 hailstones fall per 1 m2. The duration of hail is usually 5-10 minutes, very rarely up to 1 hour.

Radiological methods for determining the hail content and hail hazard of clouds have been developed and operational services for combating hail have been created. The fight against hail is based on the principle of introduction using rockets or. projectiles into a cloud of reagent (usually lead iodide or silver iodide) that promotes freezing of supercooled droplets. As a result, a huge number of artificial crystallization centers appear. Therefore, hailstones are smaller in size and they have time to melt before falling to the ground.

2. Lightning

Lightning is a giant electrical spark discharge in the atmosphere, usually manifested by a bright flash of light and accompanying thunder.

Thunder is the sound in the atmosphere that accompanies a lightning strike. Caused by air vibrations under the influence of an instantaneous increase in pressure along the path of lightning.

Lightning most often occurs in cumulonimbus clouds. The American physicist B. Franklin (1706-1790), Russian scientists M.V. Lomonosov (1711-1765) and G. Richman (1711-1753), who died from a lightning strike while researching atmospheric electricity, contributed to the discovery of the nature of lightning.

Lightning is divided into intracloud, i.e., passing in the thunderclouds themselves, and ground, i.e., striking the ground. The development process of ground lightning consists of several stages.

At the first stage, in the zone where the electric field reaches a critical value, impact ionization begins, initially created by free electrons, always present in small quantities in the air, which, under the influence of the electric field, acquire significant speeds towards the ground and, colliding with air atoms, ionize their. In this way, electron avalanches arise, turning into threads of electrical discharges - streamers, which are well-conducting channels, which, when connected, give rise to a bright thermally ionized channel with high conductivity - a stepped leader. The movement of the leader towards the earth's surface occurs in steps of several tens of meters at a speed of 5 x 107 m/s, after which its movement stops for several tens of microseconds, and the glow greatly weakens. In the next stage, the leader again advances several tens of meters, while a bright glow covers all the passed steps. Then the glow stops and weakens again. These processes are repeated when the leader moves to the surface of the earth at an average speed of 2 x 105 m/sec. As the leader moves toward the ground, the field intensity at its end increases and, under its action, a response streamer is ejected from objects protruding on the surface of the earth, connecting to the leader. The creation of a lightning rod is based on this phenomenon. In the final stage, a reverse or main lightning discharge follows along the ionized leader channel, characterized by currents from tens to hundreds of thousands of amperes, strong brightness and high speed of movement of 1O7..1O8 m/s. The temperature of the channel during the main discharge can exceed 25,000°C, the length of the lightning channel is 1-10 km, and the diameter is several centimeters. Such lightning is called prolonged lightning. They are the most common cause of fires. Typically, lightning consists of several repeated discharges, the total duration of which can exceed 1 s. Intracloud lightning includes only leader stages; their length ranges from 1 to 150 km. The probability of a ground object being struck by lightning increases as its height increases and the electrical conductivity of the soil increases. These circumstances are taken into account when installing a lightning rod. In contrast to dangerous lightning, called linear lightning, there are ball lightning, which often form after a linear lightning strike. Lightning, both line and ball, can cause serious injury and death. Lightning strikes can be accompanied by destruction caused by its thermal and electrodynamic effects. The greatest destruction is caused by lightning strikes on ground objects in the absence of good conductive paths between the strike site and the ground. From an electrical breakdown, narrow channels are formed in the material, in which a very high temperature is created, and part of the material evaporates with an explosion and subsequent ignition. Along with this, large potential differences may occur between individual objects inside the building, which can cause electric shock to people. Direct lightning strikes into overhead communication lines with wooden supports are very dangerous, as this can cause discharges from wires and equipment (telephones, switches) to the ground and other objects, which can lead to fires and electric shock to people. Direct lightning strikes on high-voltage power lines can cause short circuits. Lightning strikes on airplanes are dangerous. When lightning strikes a tree, people nearby can be struck.

3. Lightning protection

Discharges of atmospheric electricity can cause explosions, fires and destruction of buildings and structures, which led to the need to develop a special lightning protection system.

The end of the century and the beginning of the century were associated with an increase in the number of hydrometeorological manifestations of natural disasters on human life, which is largely due to the recorded warming on our planet. The number of extreme rainfall events, floods, droughts and fires has increased by 2-4% over the past 50 years. Interdecadal to multidecadal fluctuations dominate the frequency and intensity of tropical storms, especially in tropical zone North Atlantic and western North Pacific region. The areas of mountain glaciers and ice masses are decreasing almost everywhere, the area and thickness are decreasing sea ​​ice in the Arctic during spring and summer is consistent with a widespread increase in surface temperatures. An increase in the concentration of greenhouse gases, natural and anthropogenic aerosols, the amount of clouds and precipitation, and the increasing role of El Niño manifestations cause a change in the global energy distribution of the Earth-atmosphere system. The heat content of the world's oceans has increased and the average sea level is rising at a rate of about 1-3 mm/ year. Tens of thousands of people become victims of hydrometeorological disasters every year, and material damage reaches tens of thousands of dollars.

Water plays great value for life on Earth. It cannot be replaced by anything. Everyone always needs it. But water can also be the cause of great trouble. Of these, floods occupy a special place. According to the UN, over the past 10 years, 150 million people have been affected by floods around the world. Statistics show that in terms of area of ​​distribution, total average annual damage and frequency of occurrence throughout our country, floods rank first among other natural disasters. As for human casualties and specific material damage, that is, damage per unit of affected area, in this regard, floods occupy second place after earthquakes.

Flood is a significant inundation of an area caused by rising water levels in a river, lake, or coastal area of ​​the sea. For reasons that cause a rise in water levels, the following types of floods are distinguished: flood, high water, retaining flood, breakthrough flood, surge, under the action of an underwater source of high energy.

High water and flood are associated with the passage of a large flow of water for a particular river.

A flood is a relatively long-term significant increase in the water content of a river that occurs annually in the same season. The cause of the flood is the increasing influx of water into the river bed caused by the spring melting of snow on the plains, the melting of snow and glaciers in the mountains in the summer, and prolonged monsoon rains. During spring floods, the water level on small and medium-sized lowland rivers rises by 2-5 meters, on large ones, for example, on Siberian rivers, by 10-20 meters. At the same time, rivers can overflow up to 10-30 km wide. and more. The greatest known rise in water level, up to 60 meters, was observed in 1876. in China on the Yangtze River in the Igang region. On small lowland rivers, the spring flood lasts 15-20 days, on large rivers - up to 2-3 months.

A flood is a relatively short-term (1-2 days) rise of water in a river caused by heavy rainfall or rapid melting of snow cover. Floods can occur several times a year. Sometimes they pass one after another, in waves, depending on the amount of heavy rainfall.

Backwater flooding occurs as a result of an increase in resistance to water flow during congestion and ice jams at the beginning or end of winter, during congestion on timber-rafting rivers, and during partial or complete blocking of the riverbed due to landslides during earthquakes and landslides.

Surge floods are created by wind surges of water in bays and bays on sea ​​coast and the shores of large lakes. They can occur at the mouths of large rivers due to the backing up of runoff by a surge wind wave. In our country, surge floods are observed in the Caspian and Seas of Azov, as well as at the mouths of the Neva rivers, Western Dvina and Northern Dvina. Thus, in the city of St. Petersburg, such floods occur almost every year; there were especially large ones in 1824. and in 1924

Outbreak flooding is one of the most dangerous. It occurs when there is destruction or damage hydraulic structures(dams, dikes) and the formation of a breakthrough wave. Destruction or damage to a structure is possible due to poor quality construction, improper operation, the use of explosive weapons, and also during an earthquake.

Floods caused by powerful pulsed sources in water basins also pose a serious danger. Natural sources are underwater earthquakes and volcanic eruptions, as a result of these phenomena tsunami waves are formed in the sea; technical sources - underwater nuclear explosions, at which surface gravity waves are formed. When coming ashore, these waves not only flood the area, but also transform into a powerful hydroflow, washing ships ashore, destroying buildings, bridges, and roads. For example, during the invasion of 1896. The tsunami on the northeastern coast of Honshu Island (Japan) washed away over 10 thousand buildings, killing about 26 thousand people. Floods caused by powerful pulsed sources in water basins also pose a serious danger. Natural sources are underwater earthquakes and volcanic eruptions; as a result of these phenomena, tsunami waves are formed in the sea; technical sources - underwater nuclear explosions, which generate surface gravitational waves. When coming ashore, these waves not only flood the area, but also transform into a powerful hydroflow, washing ships ashore, destroying buildings, bridges, and roads. For example, during the invasion of 1896. The tsunami on the northeastern coast of Honshu Island (Japan) washed away over 10 thousand buildings, killing about 26 thousand people.

The danger of flash floods is that they can occur unexpectedly, such as during heavy rainfall at night. During a flood, a relatively short-term rise in water occurs, caused by heavy rains or rapid melting of snow.

In case of accidents accompanied by the destruction of the dam, the stored potential energy of the reservoir is released in the form of a breakthrough wave (such as a powerful flood), formed when water flows through a hole (gap) in the body of the dam. The breakthrough wave spreads along the river valley for hundreds of kilometers or more. The propagation of a breakthrough wave leads to flooding of the river valley below the dam along the river, as was the case on the rivers of the North Caucasus in 2002. In addition, the breakthrough wave has a powerful damaging effect.

Surge floods are usually observed during the passage of powerful cyclones.

A cyclone is a giant atmospheric vortex. A type of cyclone is a typhoon, translated from Chinese typhoon is a very strong wind, in America it is called a hurricane. It is an atmospheric vortex with a diameter of several hundred kilometers. The pressure at the center of the typhoon can reach 900 mbar. The strong decrease in pressure in the center and the relatively small dimensions lead to the formation of a significant pressure gradient in the radial direction. The wind in the typhoon reaches 3050 m/s, sometimes more than 50 m/s. Tangentially blowing winds usually surround a calm area called the eye of a typhoon. It has a diameter of 1525 km, sometimes up to 5060 km. A cloud wall forms along its border, resembling the wall of a vertical circular well. Typhoons are associated with particularly high surge floods. As a cyclone passes through the sea, the water level in its central part rises

Mudflows are mud or mud-stone flows that suddenly appear in riverbeds mountain rivers at large bottom slopes as a result of intense and prolonged rainfall, rapid melting of glaciers and snow cover, as well as collapse into the riverbed large quantities loose clastic materials. According to the composition of the mudflow mass, mudflows are distinguished: mud, mud-stone, water-stone, and according to physical properties - non-cohesive and coherent. In non-cohesive mudflows, the transport medium for solid inclusions is water, and in cohesive mudflows it is a water-soil mixture in which the bulk of water is bound by finely dispersed particles. Content of solid material (destruction products rocks) in a mudflow can range from 10% to 75%.

Unlike ordinary water flows, mudflows, as a rule, do not move continuously, but in separate shafts (waves), which is due to their formation mechanism and the jammed nature of the movement - the formation of accumulations of solid material in narrowings and at turns in the channel, followed by their breakthrough. Mudflows move at speeds of up to 10 m/s or more. The thickness (height) of a mudflow can reach up to 30 m. The volume of debris is hundreds of thousands, sometimes millions of m3, and the size of the transported debris is up to 3-4 m in diameter and weighs up to 100-200 tons.

Possessing a large mass and speed of movement, mudflows destroy industrial and residential buildings, engineering structures, roads, power lines and communications.

Lightning is a giant electrical spark discharge in the atmosphere, usually manifested by a bright flash of light and accompanying thunder. Thunder is the sound in the atmosphere that accompanies a lightning strike. Caused by air vibrations under the influence of an instantaneous increase in pressure along the path of lightning. Lightning most often occurs in cumulonimbus clouds.

Lightning is divided into intracloud, i.e., passing in the thunderclouds themselves, and ground, i.e., striking the ground. The development process of ground lightning consists of several stages.

At the first stage, in the zone where the electric field reaches a critical value, impact ionization begins, initially created by free electrons, always present in small quantities in the air, which, under the influence of the electric field, acquire significant speeds towards the ground and, colliding with air atoms, ionize their. In this way, electron avalanches arise, turning into threads of electrical discharges - streamers, which are well-conducting channels, which, when connected, give rise to a bright thermally ionized channel with high conductivity - a stepped leader. The movement of the leader towards the earth's surface occurs in steps of several tens of meters at a speed of 5 x 107 m/s, after which its movement stops for several tens of microseconds, and the glow greatly weakens. In the next stage, the leader again advances several tens of meters, while a bright glow covers all the passed steps. Then the glow stops and weakens again. These processes are repeated when the leader moves to the surface of the earth at an average speed of 2 x 105 m/sec. As the leader moves toward the ground, the field intensity at its end increases and, under its action, a response streamer is ejected from objects protruding on the surface of the earth, connecting to the leader. The creation of a lightning rod is based on this phenomenon. In the final stage, a reverse or main lightning discharge follows along the ionized leader channel, characterized by currents from tens to hundreds of thousands of amperes, strong brightness and high speed of movement of 1O7..1O8 m/s. The temperature of the channel during the main discharge can exceed 25,000°C, the length of the lightning channel is 1-10 km, and the diameter is several centimeters. Such lightning is called prolonged lightning. They are the most common cause of fires. Typically, lightning consists of several repeated discharges, the total duration of which can exceed 1 s. Intracloud lightning includes only leader stages; their length ranges from 1 to 150 km. The probability of a ground object being struck by lightning increases as its height increases and the electrical conductivity of the soil increases. These circumstances are taken into account when installing a lightning rod. In contrast to dangerous lightning, called linear lightning, there are ball lightning, which often form after a linear lightning strike. Lightning, both line and ball, can cause serious injury and death. Lightning strikes can be accompanied by destruction caused by its thermal and electrodynamic effects. The greatest destruction is caused by lightning strikes on ground objects in the absence of good conductive paths between the strike site and the ground. From an electrical breakdown, narrow channels are formed in the material, in which a very high temperature is created, and part of the material evaporates with an explosion and subsequent ignition. Along with this, large potential differences may occur between individual objects inside the building, which can cause electric shock to people. Direct lightning strikes into overhead communication lines with wooden supports are very dangerous, as this can cause discharges from wires and equipment (telephones, switches) to the ground and other objects, which can lead to fires and electric shock to people. Direct lightning strikes on high-voltage power lines can cause short circuits. Lightning strikes on airplanes are dangerous. When lightning strikes a tree, people nearby can be struck.

Atmospheric hazards also include fog, ice, lightning, hurricanes, storms, tornadoes, hail, blizzards, tornadoes, downpours, etc.

Ice is a layer of dense ice that forms on the surface of the earth and on objects (wires, structures) when supercooled drops of fog or rain freeze on them.

Ice usually occurs at air temperatures from 0 to -3°C, but sometimes even lower. The crust of frozen ice can reach a thickness of several centimeters. Under the influence of the weight of ice, structures can collapse and branches break off. Ice increases the danger to traffic and people.

Fog is an accumulation of small water drops or ice crystals, or both, in the ground layer of the atmosphere (sometimes up to a height of several hundred meters), reducing horizontal visibility to 1 km or less.

In very dense fogs, visibility can be reduced to several meters. Fogs are formed as a result of condensation or sublimation of water vapor on aerosol (liquid or solid) particles contained in the air (so-called condensation nuclei). Most fog droplets have a radius of 5-15 microns at positive air temperatures and 2-5 microns at negative temperatures. The number of drops per 1 cm3 of air ranges from 50-100 in light fogs and up to 500-600 in dense fogs. Fogs, according to their physical genesis, are divided into cooling fogs and evaporation fogs.

According to the synoptic conditions of formation, a distinction is made between intramass fogs, which form in homogeneous air masses, and frontal fogs, the appearance of which is associated with atmospheric fronts. Intramass fogs predominate.

In most cases, these are cooling fogs, and they are divided into radiation and advection. Radiation fogs form over land when the temperature drops due to radiation cooling of the earth's surface, and from it the air. They most often form in anticyclones. Advection fogs are formed due to the cooling of warm, moist air as it moves over a colder surface of land or water. Advective fogs develop both over land and sea, most often in the warm sectors of cyclones. Advection fogs are more stable than radiation fogs.

Frontal fogs form near atmospheric fronts and move with them. Fogs prevent the normal operation of all types of transport. Fog forecast is important for safety.

Hail is a type of atmospheric precipitation consisting of spherical particles or pieces of ice (hailstones) ranging in size from 5 to 55 mm; there are hailstones measuring 130 mm and weighing about 1 kg. The density of hailstones is 0.5-0.9 g/cm3. In 1 minute, 500-1000 hailstones fall per 1 m2. The duration of hail is usually 5-10 minutes, very rarely up to 1 hour.

Radiological methods for determining the hail content and hail hazard of clouds have been developed and operational services for combating hail have been created. The fight against hail is based on the principle of introduction using rockets or. projectiles into a cloud of reagent (usually lead iodide or silver iodide) that promotes freezing of supercooled droplets. As a result, a huge number of artificial crystallization centers appear. Therefore, hailstones are smaller in size and they have time to melt before falling to the ground.

A tornado is an atmospheric vortex that arises in a thundercloud and then spreads in the form of a dark arm or trunk towards the surface of land or sea (Fig. 23).

At the top, the tornado has a funnel-shaped expansion that merges with the clouds. When a tornado descends to the earth's surface, its lower part also sometimes becomes expanded, resembling an overturned funnel. The height of a tornado can reach 800-1500 m. The air in a tornado rotates and at the same time rises in a spiral upward, drawing in dust or dust. The rotation speed can reach 330 m/s. Due to the fact that the pressure inside the vortex decreases, condensation of water vapor occurs. In the presence of dust and water, the tornado becomes visible.

The diameter of a tornado over the sea is measured in tens of meters, over land - hundreds of meters.

A tornado usually occurs in the warm sector of a cyclone and moves instead<* циклоном со скоростью 10-20 м/с.

A tornado travels a path ranging from 1 to 40-60 km. A tornado is accompanied by a thunderstorm, rain, hail and, if it reaches the surface of the earth, it almost always causes great destruction, sucks in water and objects encountered on its path, lifts them high up and carries them over long distances. Objects weighing several hundred kilograms are easily lifted by a tornado and transported tens of kilometers. A tornado at sea poses a danger to ships.

Waterspouts over land are called blood clots; in the United States they are called tornadoes.

Like hurricanes, tornadoes are identified from weather satellites.