wind

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Passers-by in the wind, 1990

As wind ( althochdeutsch wint ; as synonymous Latin ventus to indogermanisch ue , blow, blow ') is in meteorology a directional, greater air movement in the Earth's atmosphere called. The Astronomy knows beyond winds on planets and moons with a sufficiently dense atmosphere blow.

Head wind and the apparent wind resulting from it are not winds, but are perceived as such. Air movements within closed rooms or systems (e.g. chimneys) are referred to as drafts .

Phenomena such as the solar wind or the electric wind have nothing to do with wind in the meteorological sense.

Emergence

The pressure-gradient force following, the air moves from the high altitude above the equator to the height above the low Pol
The Coriolis force diverts the air movement to westerly winds ( westerly wind drift )
Wind at a topographic obstacle (in the Alpine region as a foehn )

The main cause of wind are spatial differences in the air pressure distribution . Air particles move from the area with a higher air pressure - the high pressure area - into the area with the lower air pressure - the low pressure area - until the air pressure is balanced . Wind is therefore a mass flow which , according to the second law of thermodynamics, aims for a uniform distribution of the particles in space and thus a maximum entropy . The associated force is called the pressure gradient force .

The greater the difference between the air pressures, the more violently the air masses flow into the area with the lower air pressure and the stronger the wind resulting from the air movement.

Wind direction

The wind direction is usually given in the form of a compass direction from which the wind comes. They are measured with weather vanes (wind socks). North and south winds are also referred to as meridional winds , east and west winds as zonal winds . Each wind direction can be broken down into a meridional and a zonal component.

The wind direction is determined by the location of the low pressure area and the high pressure area. In doing so, however, it is deflected by the Coriolis force : in the northern hemisphere in the direction of movement to the right, in the southern hemisphere to the left ( Baric wind law ).

Below the free atmosphere , the wind is also influenced by friction and can also vary greatly due to morphological structures such as mountains, valleys and canyons (example: foehn or downwind , updraft , valley wind , mountain wind ). In rotating systems such as hurricanes , centrifugal force also plays a decisive role.

Wind strength and wind speed

The windsock is one of the oldest tools for estimating wind speed and direction

The speed of the wind is measured in meters per second (m / s), in kilometers per hour (km / h) or in seafaring and aviation in knots (1 kt = 1.852 km / h) with an anemometer. The highest ever measured wind speeds of 500–650 km / h have so far only occurred at great heights in the so-called jet streams .

The strength of a wind - according to the very popular Beaufort scale - is expressed in the unit Beaufort (Bft).

  • Winds between 2 and 5 Bft are called breezes .
  • Winds with wind strengths between 6 and 8 Bft are called wind with the gradations of strong , stiff and stormy wind.
  • When the wind force is 9 Bft or more, it is called a storm .
  • Wind force 12 is called a hurricane .

A violent movement of air of short duration is called a gust .

The power of the wind

The force ( wind pressure ) that the wind exerts on objects (e.g. on a valley bridge) increases quadratically with the wind speed: twice the wind speed means four times the force. The force of the wind acting on structures and components is called wind load . The wind can also exert a suction effect, see wind suction .

The kinetic energy of the wind is used as renewable energy , see wind energy .

Types of winches

Classification according to the driving forces

Euler winch :

  • Direct pressure gradient wind
  • No Coriolis, centrifugal or frictional force
  • Close to the equator (low Coriolis force)

Geostrophic winds or quasi- geostrophic winds:

  • Balance between pressure gradient and Coriolis force
  • Isobars parallel (without curvatures)
  • Above the ground friction layer (free atmosphere)
  • Depends only on the horizontal pressure gradient
  • ageostrophic wind component ( isallobaric wind ):
    • Real compensation component for the idealized geostrophic wind
    • Based on fluctuations that lead to mass balancing

Gradient winds :

  • Balance between pressure gradient, centrifugal and Coriolis force
  • Isobars parallel (with curvatures)
  • Above the ground friction layer (free atmosphere)
  • Depends only on the horizontal pressure gradient

Cyclostrophic winds :

Classification according to the magnitude of the air movements

A distinction based on the spatial and temporal magnitude of the winds is also common. There are essentially three groups:

  • synoptic winds - includes all of the above winds except geostrophic wind components; large-scale winds, usually persistent over long periods of time
  • Local winds that were barely predictable
  • Strong local, unpredictable winds: expansion limited to a few thousand meters, duration only seconds to minutes

Regional winds and wind systems

See list of winds and wind systems (e.g. bora , monsoon , trade wind )

Winds on other planets

For the wind conditions on the other planets of the solar system see:

See also

About fluid mechanics:

Web links

Commons : Wind  album with pictures, videos and audio files
Wiktionary: Wind  - explanations of meanings, word origins, synonyms, translations
Wikiquote: Wind  Quotes

Individual evidence

  1. ^ Friedrich Kluge: Etymological dictionary of the German language. 20th edition. Berlin / New York 1967, pages 860 ( wind ) and 843 ( blow )