wind¹ • n. / wind/ 1. the perceptible natural movement of the air, esp. in the form of a current of air blowing from a particular direction: the wind howled about the building an easterly wind| gusts of wind. ∎  [as adj.] relating to or denoting energy obtained from harnessing the wind with windmills or wind turbines. ∎  used to suggest something very fast, unrestrained, or changeable: run like the wind she could be as free and easy as the wind. ∎  used in reference to an influence or tendency that cannot be resisted: a wind of change. ∎  used in reference to an impending situation: he had seen which way the wind was blowing. ∎  the rush of air caused by a fast-moving body. ∎  a scent carried by the wind, indicating the presence or proximity of an animal or person.2. breath as needed in physical exertion or in speech. ∎  the power of breathing without difficulty while running or making a similar continuous effort: he waited while Jerry got his wind back.See also second wind.3. empty, pompous, or boastful talk; meaningless rhetoric. ∎  air swallowed while eating or gas generated in the stomach and intestines by digestion.4. air or breath used for sounding an organ or a wind instrument. ∎  (also winds) [treated as sing. or pl.] wind instruments, or specifically woodwind instruments, forming a band or a section of an orchestra: concerto for piano, violin, and thirteen winds | [as adj.] wind players. • v. / wind/ [tr.] 1. (often be winded) cause (someone) to have difficulty breathing because of exertion or a blow to the stomach: the fall nearly winded him.2. detect the presence of (a person or animal) by scent: the birds could not have seen us or winded us.3. / wīnd/ (past and past part. wind·ed / ˈwīndid/ or wound / wound/ ) poetic/lit. sound (a bugle or call) by blowing: but scarce again his horn he wound.PHRASES: before the wind Sailing with the wind blowing more or less from astern.get wind of inf. begin to suspect that (something) is happening; hear a rumor of: Marty got wind of a plot being hatched.off the wind Sailing with the wind on either quarter.on a wind Sailing against a wind on either bow.sail close to (or near) the wind1. Sailing sail as nearly against the wind as possible while still making headway.2. inf. verge on indecency, dishonesty, or disaster.take the wind out of someone's sails frustrate someone by unexpectedly anticipating an action or remark.to the wind (s) (or the four winds) in all directions: my little flock scatters to the four winds. ∎  so as to be abandoned or neglected: I threw my friends' advice to the winds.DERIVATIVES: wind·less adj.wind² / wīnd/ • v. (past wound / wound/ ) 1. [intr.] move in or take a twisting or spiral course: the path wound among olive trees.2. [tr.] pass (something) around a thing or person so as to encircle or enfold: he wound a towel around his midriff. ∎  repeatedly twist or coil (a length of something) around itself or a core: Anne wound the wool into a ball. ∎  [intr.] be twisted or coiled in such a way: large vines wound around every tree. ∎  wrap or surround (a core) with a coiled length of something: devices wound with copper wire.3. [tr.] make (a clock or other device, typically one operated by clockwork) operate by turning a key or handle: he wound up the clock every Saturday night she was winding the gramophone. ∎  turn (a key or handle) repeatedly around and around: I wound the handle as fast as I could. ∎  [tr.] cause (an audio or videotape or a film) to move back or forward to a desired point: wind your tape back and listen to make sure everything is okay. ∎  [tr.] hoist or draw (something) with a windlass, winch, or similar device.• n. 1. a twist or turn in a course.2. a single turn made when winding.PHRASAL VERBS: wind down (of a mechanism, esp. one operated by clockwork) gradually lose power. ∎ inf. (of a person) relax after stress or excitement. ∎  (also wind something down) draw or bring gradually to a close: business began to wind down as people awaited the new regime.wind up inf. 1. arrive or end up in a specified state, situation, or place: Kevin winds up in New York.2. another way of saying wind something up (sense 2): he wound up by attacking Nonconformists.3. Baseball (of a pitcher) use the windup delivery.wind someone up (usu. be wound up) make tense or angry: he was clearly wound up and frantic about his daughter.wind something up1. arrange the affairs of and dissolve a company: the company has since been wound up.2. gradually or finally bring an activity to a conclusion: the experiments had to be wound up because the funding stopped.3. inf. increase the tension, intensity, or power of something: he wound up the engine.

Wind

Wind refers to any flow of air above Earth's surface in a roughly horizontal direction. A wind is always named according to the direction from which it blows. For example, a wind blowing from west to east is a west wind.

The ultimate cause of Earth's winds is solar energy. When sunlight strikes Earth's surface, it heats that surface differently. Newly turned soil, for example, absorbs more heat than does snow. Uneven heating of Earth's surface, in turn, causes differences in air pressure at various locations. Heated air rises, creating an area of low pressure beneath. Cooler air descends, creating an area of high pressure. Since the atmosphere constantly seeks to restore balance, air from areas of high pressure always flow into adjacent areas of low pressure. This flow of air is wind. The difference in air pressure between two adjacent air masses over a horizontal distance is called the pressure gradient force. The greater the difference in pressure, the greater the force and the stronger the wind.

The Coriolis effect and wind direction

An important factor affecting the direction in which winds actually blow is the Coriolis effect, named for French mathematician Gaspard-Gustave de Coriolis (1792–1843). In 1835, Coriolis discovered that a force appears to be operating on any moving object situated on a rotating body, such as a stream of air traveling on the surface of a rotating planet. Because of the spinning of Earth, any moving object above the planet's surface tends to drift sideways from its course of motion. Thus winds are deflected from their straightforward direction. In the Northern Hemisphere, the Coriolis effect tends to drive winds to the right. In the Southern Hemisphere, it tends to drive winds to the left.

Words to Know

Coriolis effect: A force exemplified by a moving object appearing to travel in a curved path over the surface of a spinning body.

Local winds: Small-scale winds that result from differences in temperature and pressure in localized areas.

Pressure gradient force: Difference in air pressure between two adjacent air masses over a horizontal distance.

Friction and wind movement

The Coriolis effect and pressure gradient forces are the only factors affecting the movement of winds in the upper atmosphere. Such is not the case near ground level, however. An additional factor affecting air movements near Earth's surface is friction. As winds pass over the surface, they encounter surface irregularities (hills, mountains, etc.) and slow down. The decrease in wind speed means that the Coriolis effect acting on the winds also decreases. Since the pressure gradient force remains constant, the wind direction is driven more strongly toward the lower air pressure, often resulting in gusts.

Local winds

Local winds are small-scale winds that result from differences in temperature and pressure in localized areas. Sea and land breezes are typical of such winds. Along coastal areas, winds tend to blow onshore during the day and offshore during the evening. This is because dry land heats up and cools down quicker than water. During the day, air over land heats up and rises. Cooler air over the water then moves onshore (sea breeze). At night, air over the water remains warm and rises. The nowcooler air over land is then pushed out to sea (land breeze).

The presence of mountains and valleys also produces specialized types of local winds. For example, Southern Californians are familiar with the warm, dry Santa Ana winds that regularly sweep down out of the San Gabriel and San Bernadino Mountains, through the San Fernando Valley, and into the Los Angeles Basin. As the air blows over the mountains and sinks down into the valleys, it creates high pressure. The high pressure, in turn, compresses the air and heats it. These warm winds often contribute to widespread and devastating wildfires.

Wind chill

Wind chill is the temperature felt by humans as a result of air blowing over exposed skin. The temperature that humans actually feel can be

quite different from the temperature measured in the same location with a thermometer. In still air, skin is normally covered with a thin layer of warm molecules that insulates the body, keeping it slightly warmer than the air around it. When the wind begins to blow, that layer of molecules is swept away, and body heat is lost to the surrounding atmosphere. An individual begins to feel colder than would be expected from the actual thermometer reading at the same location. The faster the wind blows, the more rapidly heat is lost and the colder the temperature appears to be.

The National Weather Service has published a wind chill chart that shows the relationship among actual temperature, wind speed, and wind chill factor. Wind chill factor is the temperature felt by a person at the given wind speed. According to this chart, individuals do not sense any change in temperature with wind speeds of 4 miles (6 kilometers) per hour or less. The colder the temperature, the more strongly the wind chill factor is felt. When the wind chill factor is below −58°F (−50°C), flesh will freeze in about one minute.

Wind shear

Wind shear occurs between two air currents in the atmosphere that are traveling at different speeds or in different directions. The friction that occurs at the boundary of these two currents is an indication of wind shear.

Wind shear is a crucial factor in the development of other atmospheric phenomena. For example, as the difference between adjacent wind currents increases, the wind shear also increases. At some point, the boundary between currents may break apart and form eddies (circular currents) that can develop into clear air turbulence or, in more drastic circumstances, tornadoes and other violent storms.

Under certain storm conditions, a wind shear will travel in a vertical direction. The phenomenon is known as a microburst, a strong downdraft or air which, when it reaches the ground, continues to spread out horizontally. An airplane that attempts to fly through a microburst feels, in rapid succession, an additional lift from headwinds and then a sudden loss of lift from tailwinds. In such a case, a pilot may not be able to maintain control of the aircraft in time to prevent a crash.

[See also Atmospheric circulation; Atmospheric pressure; Tornado ]

Wind

The coriolis effect and wind direction

Friction and wind movement

Local winds

Resources

The term wind refers to any flow of air relative to Earth’s surface in an approximately horizontal direction. Breezes that blow back and forth from a body of water to adjacent land areas—on-shore and off-shore breezes—are examples of wind.

The ultimate cause of Earth’s winds is solar energy. When sunlight strikes Earth’s surface, it heats that surface differently. Newly turned soil, for example, absorbs more heat than does snow.

Uneven heating of Earth’s surface, in turn, causes differences in air pressure at different locations. On a weather map, these pressure differences can be found by locating isobars, lines that connect points of equal pressure. The pressure at two points on two different isobars will be different. A pressure gradient is said to exist between these two points. It is this pressure gradient that provides the force that drives air from one point to the other, causing wind to blow from one point to the other. The magnitude of the winds blowing between any two points is determined by the pressure gradient between those two points.

The coriolis effect and wind direction

In an ideal situation, one could draw the direction of winds blowing over an area simply by looking at the isobars on a weather map. The Earth, however, is not an ideal situation. At least two important factors affect the direction in which winds actually blow: the Coriolis effect and friction. The Coriolis effect is a pseudoforce that appears to be operating on any moving object situated on a rotating body, such as a stream of air traveling on the surface of the rotating planet. The effect of the Coriolis force is to deflect winds from the straight-forward direction that we might expect them to take simply from an examination of isobars. In the Northern Hemisphere, the Coriolis effect tends to deflect winds to the right and in the Southern Hemisphere, it tends to drive winds to the left.

The Coriolis effect will determine the movement of winds in the Northern Hemisphere. Suppose that air initially begins to move from west to east as a result of pressure gradient forces. At once, the Coriolis effect will begin to drive the stream of air to the right, that is, to the south. The actual path followed by the wind, then, is a compromise between the pressure gradient force and the Coriolis force. Since each of these forces can range widely in value, the precise movement of wind in any one case is also variable.

At some point, the two forces driving the wind are likely to come into balance. At that point, the wind begins to move in a straight line that is perpendicular to the direction of the two forces. Such a wind is known as a geostrophic wind.

Friction and wind movement

The idealization described above applies to winds in the upper atmosphere. At distances of more than a kilometer or so above the ground, pressure gradient and Coriolis forces are the only factors affecting the movement of winds. Thus, air movements eventually reach an equilibrium point between pressure gradient forces and the Coriolis force, and geostrophic winds blow parallel to the isobars on a weather map.

Such is not the case near ground level, however. An additional factor affecting air movements near Earth’s surface is friction. As winds pass over Earth’s surface, they encounter surface irregularities and slow down. The decrease in wind speed means that the Coriolis effect acting on the winds also decreases. Because the pressure gradient force remains constant, the wind is driven more strongly toward the lower air pressure. Instead of developing into geostrophic winds, as is the case in the upper atmosphere, the winds tend to curve inward towards the center of a low pressure area or to spiral outward away from the center of a high pressure area.

Friction effects vary significantly with the nature of the terrain over which the wind is blowing. On very hilly land, winds may be deflected by 30 degrees or more, while on flat lands, the effects may be nearly negligible.

Local winds

In many locations, wind patterns exist that are not easily explained by the general principles outlined above. In most cases, unusual topographic or geographic features are responsible for such winds, known as local winds. Land and sea breezes are typical of such winds. Because water heats up and cools down more slowly than does dry land, the air along a shoreline is alternately warmer over the water and cooler over the land, and vice versa. These differences account for the fact that winds tend to blow offshore during the evening and on-shore during the day.

KEY TERMS

Coriolis effect —An apparent force experienced by any object that is moving across the face of a rotating body.

Geostrophic wind —A movement of air that results from the balance of pressure gradient and Coriolis forces and that travels across isobars.

Isobar —A line on a weather map connecting points of equal atmospheric pressure.

The presence of mountains and valleys also produces specialized types of local winds. For example, Southern Californians are familiar with the warm, dry Santa Ana winds that regularly sweep down out of the San Gabriel and San Bernadino Mountains, through the San Fernando Valley, and into the Los Angeles Basin, often bringing with them widespread and devastating wildfires. Large buildings in major cities constitute a topography of their own, sometimes causing strong winds to be funneled through urban canyons.

See also Atmospheric circulation; Atmospheric pressure.

Resources

BOOKS

Ahrens, Donald C. Meteorology Today. Pacific Grove, Calif.: Brooks Cole, 2006.

Palmer, Tim and Renate Hagedorn, ed. Predictability of Weather and Climate. New York: Cambridge University Press, 2006.

David E. Newton

Wind

The term wind refers to any flow of air relative to the Earth's surface in a roughly horizontal direction. Breezes that blow back and forth from a body of water to adjacent land areas—on-shore and off-shore breezes—are examples of wind.

The ultimate cause of Earth's winds is solar energy . When sunlight strikes Earth's surface, it heats that surface differently. Newly turned soil , for example, absorbs more heat than does snow.

Uneven heating of Earth's surface, in turn, causes differences in air pressure at various locations. On a weather map, these pressure differences can be found by locating isobars , lines that connect points of equal pressure. The pressure at two points on two different isobars will be different. A pressure gradient is said to exist between these two points. It is this pressure gradient that provides the force that drives air from one point to the other, causing wind to blow from one point to the other. The magnitude of the winds blowing between any two points is determined by the pressure gradient between those two points.

The Coriolis effect and wind direction

In an ideal situation, one could draw the direction of winds blowing over an area simply by looking at the isobars on a weather map. But the earth is not an ideal situation. At least two important factors affect the direction in which winds actually blow: the Coriolis effect and friction . The Coriolis effect is a pseudoforce that appears to be operating on any moving object situated on a rotating body, such as a stream of air traveling on the surface of the rotating planet . The effect of the Coriolis force is to deflect winds from the straight-forward direction that we might expect them to take simply from an examination of isobars. In the Northern Hemisphere, the Coriolis effect tends to deflect winds to the right and in the Southern Hemisphere, it tends to drive winds to the left.

Imagine how the Coriolis effect will determine the movement of winds in the Northern Hemisphere. Suppose that air initially begins to move from west to east as a result of pressure gradient forces. At once, the Coriolis effect will begin to drive the stream of air to the right, that is, to the south. The actual path followed by the wind, then, is a compromise between the pressure gradient force and the Coriolis force. Since each of these forces can range widely in value, the precise movement of wind in any one case is also variable.

At some point, the two forces driving the wind are likely to come into balance. At that point, the wind begins to move in a straight line that is perpendicular to the direction of the two forces. Such a wind is known as a geostrophic wind.

Friction and wind movement

The picture described above applies to winds that blow in the upper atmosphere. At distances of more than a kilometer or so above the ground, pressure gradient and Coriolis forces are the only factors affecting the movement of winds. Thus, air movements eventually reach an equilibrium point between pressure gradient forces and the Coriolis force, and geostrophic winds blow parallel to the isobars on a weather map.

Such is not the case near ground level, however. An additional factor affecting air movements near the earth's surface is friction. As winds pass over the earth's surface, they encounter surface irregularities and slow down. The decrease in wind speed means that the Coriolis effect acting on the winds also decreases. Since the pressure gradient force remains constant, the wind direction is driven more strongly toward the lower air pressure. Instead of developing into geostrophic winds, as is the case in the upper atmosphere, the winds tend to curve inward towards the center of a low pressure area or to spiral outward away from the center of a high pressure area.

Friction effects vary significantly with the nature of the terrain over which the wind is blowing. On very hilly land, winds may be deflected by 30 degrees or more, while on flat lands, the effects may be nearly negligible.

Local winds

In many locations, wind patterns exist that are not easily explained by the general principles outlined above. In most cases, unusual topographic or geographic features are responsible for such winds, known as local winds. Land and sea breezes are typical of such winds. Because water heats up and cools down more slowly than does dry land, the air along a shoreline is alternately warmer over the water and cooler over the land, and vice versa. These differences account for the fact that winds tend to blow offshore during the evening and on-shore during the day.

The presence of mountains and valleys also produces specialized types of local winds. For example, Southern Californians are familiar with the warm, dry Santa Ana winds that regularly sweep down out of the San Gabriel and San Bernadino Mountains, through the San Fernando Valley, and into the Los Angeles Basin , often bringing with them widespread and devastating wildfires.

See also Atmospheric circulation; Atmospheric pressure.

Resources

books

Ahrens, C. Donald. Meteorology Today. 2nd ed. St. Paul: West Publishing Company, 1985.

Battan, Louis J. Fundamentals of Meteorology. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1979.

Holton, James R. An Introduction to Dynamic Meteorology. 2nd ed. New York: Academic Press, 1979.

Lutgens, Frederick K., and Edward J. Tarbuck. The Atmosphere: An Introduction to Meteorology. 4th ed. Englewood Cliffs, NJ: Prentice Hall, 1989.

David E. Newton

KEY TERMS

Coriolis effect

—An apparent force experienced by any object that is moving across the face of a rotating body.

Geostrophic wind

—A movement of air that results from the balance of pressure gradient and Coriolis forces and that travels across isobars.

Isobar

—A line on a weather map connecting points of equal atmospheric pressure.

Wind

Wind refers to any flow of air relative to the earth's surface in a roughly horizontal direction. Breezes that blow back and forth from a body of water to adjacent land areas—on-shore and off-shore breezes, or land and sea breezes—are examples of local wind. Winds, driven by large pressure systems also exist in great wind belts that comprise the earth's atmospheric circulation .

The ultimate cause of Earth's winds is solar energy . When sunlight strikes Earth's surface, it heats that surface differently. Newly turned soil , for example, absorbs more heat than does snow.

Uneven heating of Earth's surface, in turn, causes differences in air pressure at various locations. On a weather map, these pressure differences can be found by locating isobars , lines that connect points of equal pressure. The pressure at two points on two different isobars will be different. A pressure gradient is said to exist between these two points. It is this pressure gradient that provides the force that drives air from one point to the other, causing wind to blow from one point to the other. The magnitude of the winds blowing between any two points is determined by the pressure gradient between those two points.

In an ideal situation, one could draw the direction of winds blowing over an area simply by looking at the isobars on a weather map. The earth, however, is not an ideal situation. At least two important factors affect the direction in which winds actually blow: the Coriolis effect and friction. The Coriolis effect is an apparent force that appears to be operating on any moving object situated on a rotating body, such as a stream of air traveling on the surface of the rotating planet. The Coriolis effect deflects winds from the straightforward direction across isobars. In the Northern Hemisphere, the Coriolis effect tends to deflect winds right of path and in the Southern Hemisphere, it tends to drive winds left of path.

For example, wind in the Northern Hemisphere initially begins to move from west to east as a result of pressure gradient forces. The Coriolis effect results in a deflection of the wind right of path. This results in air moving out of a high-pressure system (an area of divergence) to spin clockwise. Conversely, air moving into a low pressure area (an area of convergence) also deflected right of path, is spun counterclockwise.

The actual path followed by the wind is a compromise between the pressure gradient force and the Coriolis force. Since each of these forces can range widely in value, the precise movement of wind in any one case is also variable. At some point, the two forces driving the wind are likely to come into balance. At that point, the wind begins to move in a straight line that is perpendicular to the direction of the two forces. Such a wind is known as a geostrophic wind.

The Coriolis effect is most pronounced on winds farther from the surface of the earth. At distances of more than a half a mile or so above the ground pressure gradient and Coriolis forces are the only factors affecting the movement of winds. Thus, air movements eventually reach an equilibrium point between pressure gradient forces and the Coriolis force, and geostrophic winds blow parallel to the isobars on a weather map.

Such is not the case near ground level, however. An additional factor affecting air movements near the Earth's surface is friction. As winds pass over the earth's surface, they encounter surface irregularities and slow down. The decrease in wind speed means that the Coriolis effect acting on the winds also decreases. Since the pressure gradient force remains constant, the wind direction is driven more strongly toward the lower air pressure. Instead of developing into geostrophic winds, as is the case in the upper atmosphere, the winds tend to curve inward towards the center of a low pressure area or to spiral outward away from the center of a high pressure area.

Friction effects vary significantly with the nature of the terrain over which the wind is blowing. On very hilly land, winds may be deflected by 30 degrees or more, while on flat lands, the effects may be nearly negligible.

In many locations, wind patterns exist that are not easily explained by the general principles outlined above. In most cases, unusual topographic or geographic features are responsible for such winds, known as local winds. Land and sea breezes are typical of such winds. Because water heats up and cools down more slowly than does dry land, the air along a shoreline is alternately warmer over the water and cooler over the land, and vice versa. These differences account for the fact that winds tend to blow offshore during the evening and on-shore during the day.

The presence of mountains and valleys also produces specialized types of local winds. Annual changes in weather patterns produce seasonal winds such as the dry Santa Ana winds in Southern California.

See also Air masses and fronts; Atmospheric composition and structure; Atmospheric inversion layers; Jet stream; Weather forecasting methods; Wind chill; Wind shear