The movement of air above the Earth's surface in a horizontal direction is called by the wind. The wind always blows from the area high pressure to the low area.

Wind characterized by speed, force and direction.

Wind speed and strength

Wind speed measured in meters per second or points (one point is approximately equal to 2 m/s). The speed depends on the pressure gradient: the greater the pressure gradient, the higher the wind speed.

The strength of the wind depends on the speed (Table 1). The greater the difference between neighboring areas earth's surface, the stronger the wind.

Beaufort scale— conditional scale for visual assessment wind strength (speed) in points based on its effect on ground objects or on sea waves. It was developed by the English admiral F. Beaufort in 1806 and at first was used only by him. In 1874, the Standing Committee of the First Meteorological Congress adopted the Beaufort scale for use in International Synoptic Practice. In subsequent years, the scale was changed and refined. The Beaufort scale is widely used in maritime navigation.

Direction of the wind

Direction of the wind is determined by the side of the horizon from which it blows, for example, the wind blowing from the south is south. The direction of the wind depends on the pressure distribution and the deflecting effect of the Earth's rotation.

On climate map the prevailing winds are shown by arrows (Fig. 1). The winds observed at the earth's surface are very diverse.

You already know that the surface of land and water heats up differently. On a summer day, the land surface heats up more. When heated, the air over land expands and becomes lighter. At this time, the air above the reservoir is colder and, therefore, heavier. If the body of water is relatively large, on a quiet hot summer day on the shore you can feel a light breeze blowing from the water, above which it is higher than above the land. Such a light breeze is called a daytime breeze breeze(from the French brise - light wind) (Fig. 2, a). The night breeze (Fig. 2, b), on the contrary, blows from land, since the water cools much more slowly and the air above it is warmer. Breezes can also occur at the edge of the forest. The breeze diagram is shown in Fig. 3.

Rice. 1. Distribution diagram of the prevailing winds on the globe

Local winds can occur not only on the coast, but also in the mountains.

Föhn- a warm and dry wind blowing from the mountains to the valley.

Bora- gusty, cold and strong wind, appearing when cold air moves over low ridges to the warm sea.

Monsoon

If the breeze changes direction twice a day - day and night, then seasonal winds - monsoons- change their direction twice a year (Fig. 4). In summer, the land quickly warms up, and the air pressure above its surface increases. At this time, cooler air begins to move inland. In winter, the opposite is true, so the monsoon blows from land to sea. With the change from the winter monsoon to the summer monsoon, there is a change from dry, partly cloudy weather to rainy.

The effect of monsoons is strongly manifested in the eastern parts of the continents, where they are adjacent to vast expanses of oceans, so such winds often bring heavy precipitation to the continents.

The unequal nature of atmospheric circulation in different regions of the globe determines differences in the causes and nature of monsoons. As a result, a distinction is made between extratropical and tropical monsoons.

Rice. 2. Breeze: a - daytime; b - night

Rice. 3. Breeze pattern: a - during the day; b - at night

Rice. 4. Monsoons: a - in summer; b - in winter

Extratropical monsoons - monsoons of temperate and polar latitudes. They are formed as a result of seasonal pressure fluctuations over the sea and land. The most typical zone of their distribution is Far East, Northeast China, Korea, and to a lesser extent Japan and the northeast coast of Eurasia.

Tropical monsoons - monsoons of tropical latitudes. They are caused by seasonal differences in heating and cooling of the Northern and Southern hemispheres. As a result, pressure zones shift seasonally relative to the equator to the hemisphere in which given time summer. Tropical monsoons are most typical and persistent in the northern part of the basin Indian Ocean. This is greatly facilitated by the seasonal change in atmospheric pressure over the Asian continent. The fundamental features of the climate of this region are associated with the South Asian monsoons.

The formation of tropical monsoons in other areas of the globe occurs less characteristically, when one of them is more clearly expressed - the winter or summer monsoon. Such monsoons are observed in Tropical Africa, in northern Australia and in the equatorial regions of South America.

Constant winds of the Earth - trade winds And westerly winds- depend on the position of the atmospheric pressure belts. Since in equatorial belt Low pressure prevails, and near 30° N. w. and Yu. w. - high, at the surface of the Earth throughout the year the winds blow from the thirties latitudes to the equator. These are trade winds. Under the influence of the Earth's rotation around its axis, trade winds deviate to the west in the Northern Hemisphere and blow from northeast to southwest, and in the Southern Hemisphere they are directed from southeast to northwest.

From high pressure belts (25-30° N and S latitude), winds blow not only towards the equator, but also towards the poles, since at 65° N. w. and Yu. w. low pressure prevails. However, due to the rotation of the Earth, they gradually deviate to the east and create air currents moving from west to east. Therefore, in temperate latitudes, westerly winds predominate.

Wind speed can be assessed visually by its effect on objects surrounding the observer. In 1805 Francis Beaufort(Francis Beaufort), a sailor of the British Navy, developed a 12-point scale to characterize the strength of the wind at sea. allows you to estimate wind speed without using any instruments. In 1926, land wind speed estimates were added to this scale. To distinguish between hurricane winds different strengths, The US Weather Bureau expanded the scale to 17 points in 1955.

Today, the 12-point scale is adopted by the World Meteorological Organization for an approximate estimate of wind speed by its effect on ground objects or by waves in the open sea. average speed wind is indicated at a standard height of 10 meters above an open, level surface. Sea roughness is also characterized by points, but different; the anxiety scale has nine points. The table below compares wave scores with wind scores. The wave parameters are given for open waters; in the coastal zone the waves are less.

Beaufort scale table

Meteorological hazards are natural processes and phenomena that occur in the atmosphere under the influence of various natural factors or their combinations, which have or may have a damaging effect on people, farm animals and plants, economic objects and the natural environment.

Wind - This is the movement of air parallel to the earth's surface, resulting from the uneven distribution of heat and atmospheric pressure and directed from a high pressure zone to a low pressure zone.

Wind is characterized by:
1. Wind direction - determined by the azimuth of the side of the horizon from where
it blows, and is measured in degrees.
2. Wind speed - measured in meters per second (m/s; km/h; miles/hour)
(1 mile = 1609 km; 1 nautical mile = 1853 km).
3. Wind force - measured by the pressure it exerts on 1 m2 of surface. The strength of the wind varies almost proportionally to the speed,
therefore, wind force is often measured not by pressure, but by speed, which simplifies the perception and understanding of these quantities.

Many words are used to denote the movement of wind: tornado, storm, hurricane, gale, typhoon, cyclone and many local names. To systematize them, people all over the world use Beaufort scale, which allows you to very accurately estimate the strength of the wind in points (from 0 to 12) by its effect on ground objects or on waves at sea. This scale is also convenient because it allows you to quite accurately determine the wind speed without instruments based on the characteristics described in it.

Beaufort scale (Table 1)

Breeze (light to strong breeze) sailors call winds that have a speed of 4 to 31 mph. In terms of kilometers (coefficient 1.6) it will be 6.4-50 km/h

Wind speed and direction determine weather and climate.

Strong winds, significant changes in atmospheric pressure and a large number of precipitation causes dangerous atmospheric vortices(cyclones, storms, squalls, hurricanes) that can cause destruction and loss of life.

Cyclone is the general name for vortices with low blood pressure in the center.

An anticyclone is an area high blood pressure in an atmosphere with a maximum in the center. In the Northern Hemisphere, the winds in an anticyclone blow counterclockwise, and in the Southern Hemisphere they blow clockwise; in a cyclone the wind movement is reversed.

Hurricane - wind destructive force and a significant duration, the speed of which is equal to or exceeds 32.7 m/s (12 points on the Beaufort scale), which is equivalent to 117 km/h (Table 1).
In half of the cases, the wind speed during a hurricane exceeds 35 m/sec, reaching 40-60 m/sec, and sometimes up to 100 m/sec.

Hurricanes are classified into three types based on wind speed:
- Hurricane (32 m/s or more),
- strong hurricane (39.2 m/s or more)
- violent hurricane (48.6 m/s or more).

The reason for such hurricane winds is the occurrence, as a rule, on the line of collision of warm and cold fronts air masses, powerful cyclones with a sharp pressure drop from the periphery to the center and with the creation of a vortex air flow moving in the lower layers (3-5 km) in a spiral to the middle and upward, in the northern hemisphere - counterclockwise.

Such cyclones, depending on the place of their origin and structure, are usually divided into:
- tropical cyclones found over warm tropical oceans, during the formation stage they usually move to the west, and after formation ends they bend towards the poles.
A tropical cyclone that has reached unusual strength is called hurricane, if he is born in Atlantic Ocean and the adjacent seas; typhoon - V Pacific Ocean or its seas; cyclone – in the Indian Ocean region.
mid-latitude cyclones can form both over land and over water. They usually move from west to east. Characteristic feature Such cyclones are characterized by their great “dryness”. The amount of precipitation during their passage is significantly less than in the zone of tropical cyclones.
The European continent is affected by both tropical hurricanes originating in the central Atlantic and cyclones of temperate latitudes.
Storm – a type of hurricane, but has a lower wind speed of 15-31
m/sec.

The duration of storms is from several hours to several days, the width is from tens to several hundred kilometers.
Storms are divided:

2. Stream storms – These are local phenomena of small distribution. They are weaker than vortex storms. They are divided:
- stock – the air flow moves down the slope from top to bottom.
- Jet – characterized by the fact that the air flow moves horizontally or up a slope.
Stream storms most often occur between chains of mountains connecting valleys.
Depending on the color of the particles involved in the movement, black, red, yellow-red and white storms are distinguished.
Depending on the wind speed, storms are classified:
- storm 20 m/sec or more
- strong storm 26 m/sec or more
- severe storm of 30.5 m/sec or more.

Squall – a sharp short-term increase in wind up to 20–30 m/s and higher, accompanied by a change in its direction associated with convective processes. Despite the short duration of squalls, they can lead to catastrophic consequences. Squalls are most often associated with cumulonimbus (thunderstorm) clouds of either local convection or a cold front. A squall is usually associated with showers and thunderstorms, sometimes with hail. Atmosphere pressure during a squall it rises sharply due to rapid precipitation, and then falls again.

If it is possible to limit the impact zone, all of the listed natural disasters are classified as non-localized.

Dangerous consequences of hurricanes and storms.

Hurricanes are one of the most powerful forces elements and in their harmful effects are not inferior to such terrible natural disasters like earthquakes. This is explained by the fact that hurricanes carry enormous energy. Its amount released by an average hurricane during 1 hour is equal to the energy nuclear explosion at 36 Mt. In one day, an amount of energy is released that would be enough to supply a country like the United States with electricity for six months. And in two weeks (the average duration of a hurricane’s existence), such a hurricane releases energy equal to the energy of the Bratsk hydroelectric power station, which it can produce in 26 thousand years. The pressure in the hurricane zone is also very high. It reaches several hundred kilograms per square meter a fixed surface located perpendicular to the direction of wind movement.

Hurricane wind destroys strong and demolishes light buildings, devastates sown fields, breaks wires and knocks down power and communication line poles, damages highways and bridges, breaks and uproots trees, damages and sinks ships, causes accidents in utility and energy networks, in production. There are known cases when hurricane winds destroyed dams and dams, which led to major floods, threw trains off the rails, tore bridges from their supports, knocked down factory chimneys, and threw ships onto land. Hurricanes are often accompanied by heavy downpours, which are more dangerous than the hurricane itself, as they cause mudflows and landslides.

Hurricane sizes vary. Usually, the width of the catastrophic destruction zone is taken as the width of a hurricane. Often this zone is supplemented with an area of ​​storm force winds with relatively little damage. Then the width of the hurricane is measured in hundreds of kilometers, sometimes reaching 1000 km. For typhoons, the destruction strip is usually 15-45 km. Average duration hurricane - 9-12 days. Hurricanes occur at any time of the year, but are most common from July to October. In the remaining 8 months they are rare, their paths are short.

The damage caused by a hurricane is determined by a whole complex of various factors, including the terrain, the degree of development and strength of buildings, the nature of vegetation, the presence of population and animals in its area of ​​effect, the time of year, preventive measures taken and a number of other circumstances, the main of which is speed pressure of air flow q, proportional to the product of atmospheric air density by the square of air flow speed q = 0.5pv 2.

According to building codes and regulations, the maximum standard value of wind pressure is q = 0.85 kPa, which, with an air density of r = 1.22 kg/m3, corresponds to wind speed.

For comparison, you can give the calculated values ​​of the velocity head used for the design nuclear power plants for the Caribbean region: for buildings of category I - 3.44 kPa, II and III - 1.75 kPa and for open installations - 1.15 kPa.

Every year, about a hundred powerful hurricanes sweep across the globe, causing destruction and often carrying away human lives(Table 2). On June 23, 1997, a hurricane swept over most of the Brest and Minsk regions, as a result of which 4 people were killed and 50 were injured. In the Brest region, 229 settlements were de-energized, 1,071 substations were disabled, roofs were torn off from 10-80% of residential buildings in more than 100 settlements, and up to 60% of agricultural buildings were destroyed. In the Minsk region, 1,410 settlements were cut off and hundreds of houses were damaged. Trees in forests and forest parks were broken and uprooted. At the end of December 1999 from hurricane wind, which swept across Europe, Belarus also suffered. Power lines were broken, and many settlements were without power. In total, 70 districts and more than 1,500 settlements were affected by the hurricane. In the Grodno region alone, 325 transformer substations were out of order, in the Mogilev region even more - 665.

table 2
Effects of some hurricanes

Tornado (tornado)- a vortex movement of air, spreading in the form of a giant black column with a diameter of up to hundreds of meters, inside of which there is a rarefaction of air, into which various objects are drawn.

Tornadoes occur both over the water surface and over land, much more often than hurricanes. Very often they are accompanied by thunderstorms, hail and downpours. The speed of air rotation in the dust column reaches 50-300 m/sec or more. During its existence, it can travel up to 600 km - along a strip of terrain several hundred meters wide, and sometimes up to several kilometers, where destruction occurs. The air in the column rises in a spiral and draws in dust, water, objects, and people.
Hazardous factors: buildings caught in a tornado due to vacuum in the air column are destroyed by air pressure from the inside. It uproots trees, overturns cars, trains, lifts houses into the air, etc.

Tornadoes occurred in the Republic of Belarus in 1859, 1927 and 1956.

Wind(the horizontal component of air movement relative to the earth's surface) is characterized by direction and speed.
Wind speed measured in meters per second (m/s), kilometers per hour (km/h), knots or Beaufort points (wind force). Knot is a maritime unit of speed, 1 nautical mile per hour, approximately 1 knot is equal to 0.5 m/s. The Beaufort scale (Francis Beaufort, 1774-1875) was created in 1805.

Direction of the wind(from where it blows) is indicated either in points (on a 16-point scale, for example, north wind - N, northeast - NE, etc.), or in angles (relative to the meridian, north - 360° or 0°, east - 90°, south – 180°, west – 270°), fig. 1.

Beaufort scale- a conventional scale for visually assessing the strength (speed) of the wind in points based on its effect on ground objects or on sea waves. It was developed by the English admiral F. Beaufort in 1806 and at first was used only by him. In 1874, the Standing Committee of the First Meteorological Congress adopted the Beaufort scale for use in international synoptic practice. In subsequent years, the scale was changed and refined. The Beaufort scale is widely used in maritime navigation.