Information about Thermal Wind
The thermal wind is not actually a wind, but a vector difference in the geostrophic wind between two pressure levels 
and 
, with 
. It is a wind shear. It is only present in an atmosphere with horizontal gradients of temperature (or in an ocean with horizontal gradients of density), i.e. baroclinicity. In a barotropic atmosphere the geostrophic wind is independent of height. The name stems from the fact that this wind flows around areas of low (and high) temperature in the same manner as the geostrophic wind flows around areas of low (and high) pressure.
The thermal wind equation is
where the
are geopotential height fields with 
, 
is the Coriolis parameter, and 
is the upward-pointing unit vector in the vertical direction. The thermal wind equation does not determine the wind in the tropics. Since f is small or zero there, the equation reduces to stating that 
is small.
is negative there, it yields the same result.)
In the Northern hemisphere, the polar region is cold (low temperature) while the equatorial region is warm (high temperature). Because the thermal wind circles the area of low temperature in the same manner as the geostrophic wind flows around a cyclone, namely counter-clockwise in the Northern hemisphere, the thermal wind in the northern hemisphere mid latitudes is westerly (i.e. is directed eastward). This can be seen by looking at a globe from above the North Pole — a westerly current flows counter-clockwise around the globe.
What does this mean for the vertical wind profile in the mid-latitude NH troposphere? If the thermal wind is westerly, the atmospheric flow will become more westerly with height, as the thermal wind describes the wind change with height. Therefore, if at a certain level, say, at the top of the boundary layer, the wind speed is close to zero, the wind speed will have a strong eastward component at higher levels.
This simple argument basically describes the jet stream, a westerly current of air with maximum wind speeds close to the tropopause which is basically (even though other factors are also important) a result of the temperature contrast between equator and pole.
The outcome is that a geostrophic wind that advects warm air into a region of colder air causes the wind to turn right (clockwise, veering) with height, while cold air advection into a region of warmer air results in the wind turning left (counter-clockwise, backing).
and , with . It is a wind shear. It is only present in an atmosphere with horizontal gradients of temperature (or in an ocean with horizontal gradients of density), i.e. baroclinicity. In a barotropic atmosphere the geostrophic wind is independent of height. The name stems from the fact that this wind flows around areas of low (and high) temperature in the same manner as the geostrophic wind flows around areas of low (and high) pressure.
The thermal wind equation is
,
where the
are geopotential height fields with , is the Coriolis parameter, and is the upward-pointing unit vector in the vertical direction. The thermal wind equation does not determine the wind in the tropics. Since f is small or zero there, the equation reduces to stating that is small.
Examples of thermal wind
Temperature contrast between equator and pole: Increasing westerlies with height
(This applies similarly to the Southern hemisphere, and because is negative there, it yields the same result.)
In the Northern hemisphere, the polar region is cold (low temperature) while the equatorial region is warm (high temperature). Because the thermal wind circles the area of low temperature in the same manner as the geostrophic wind flows around a cyclone, namely counter-clockwise in the Northern hemisphere, the thermal wind in the northern hemisphere mid latitudes is westerly (i.e. is directed eastward). This can be seen by looking at a globe from above the North Pole — a westerly current flows counter-clockwise around the globe.
What does this mean for the vertical wind profile in the mid-latitude NH troposphere? If the thermal wind is westerly, the atmospheric flow will become more westerly with height, as the thermal wind describes the wind change with height. Therefore, if at a certain level, say, at the top of the boundary layer, the wind speed is close to zero, the wind speed will have a strong eastward component at higher levels.
This simple argument basically describes the jet stream, a westerly current of air with maximum wind speeds close to the tropopause which is basically (even though other factors are also important) a result of the temperature contrast between equator and pole.
Advection of warm or cold air: Turning of the geostrophic wind with height
If the geostrophic wind at a level advects (i.e. transports) warm or cold air, the thermal wind causes a turning of wind direction with height. A similar argument as in the other example with regard to how the thermal wind is related to the temperature distribution can be made.The outcome is that a geostrophic wind that advects warm air into a region of colder air causes the wind to turn right (clockwise, veering) with height, while cold air advection into a region of warmer air results in the wind turning left (counter-clockwise, backing).
Further reading
- Holton, James R.: An Introduction to Dynamic Meteorology, 2004. ISBN 0-12-354015-1
- Vasquez, Tim: Weather Forecasting Handbook, 2002. ISBN 0-9706840-2-9
WIND (SOLARWIND) was a NASA spacecraft launched on November 1, 1994. It was deployed to study radio and plasma that occur in solar wind, in the Earth's magnetosphere. The spacecraft's original mission was to orbit the Sun at the L1
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The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient force. This condition is called geostrophic balance.
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Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height (elevation above mean sea level) using the variation of gravity with latitude and elevation. Thus it can be considered a "gravity-adjusted height.
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trillion fold).]]
Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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In physics, density is mass m per unit volume V—how heavy something is compared to its size. A small, heavy object, such as a rock or a lump of lead, is denser than a lighter object of the same size or a larger object of the same weight, such as pieces of
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baroclinity (sometimes called baroclinicity) is a measure of the stratification in a fluid. A baroclinic atmosphere is one for which the density depends on both the temperature and the pressure; contrast this with barotropic atmosphere, for which the density depends only on
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barotropic atmosphere is one in which the pressure depends only on the density and vise versa, so that isobaric surfaces (constant pressure surfaces) are also isopycnic surfaces (constant density surfaces).
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The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient force. This condition is called geostrophic balance.
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Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface.
Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height (elevation above mean sea level) using the variation of gravity with latitude and elevation. Thus it can be considered a "gravity-adjusted height.
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The Coriolis frequency, f, is equal to twice the rotation rate of the Earth multiplied by the sine of the latitude. Inertial oscillations on the surface of the earth have this frequency. These oscillations are the result of the Coriolis effect.
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In mathematics, a unit vector in a normed vector space is a vector (often a spatial vector) whose length, (or magnitude) is 1 (the unit length). A unit vector is often written with a superscribed caret or “hat”, like this (pronounced "i-hat").
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In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force (per unit mass) at that point.
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tropics are the geographic region of the Earth centered on the equator and limited in latitude by the Tropic of Cancer in the northern hemisphere, at approximately 23°30' (23.5°) N latitude, and the Tropic of Capricorn in the southern hemisphere at 23°30' (23.5°) S latitude.
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Northern Hemisphere or northern hemisphere[1] is the half of a planet that is north of the equator—the word hemisphere literally means 'half ball'. It is also that half of the celestial sphere north of the celestial equator.
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The CYCLONE, was an early computer built in 1959 by Iowa State University, was based on the Institute for Advanced Study (IAS) architecture developed by John von Neumann. As with all computers of its era, it was a one of a kind machine that could not exchange programs with other
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clockwise motion is one that proceeds 'like the clock's hands': from the top to the right, then down and then to the left, and back to the top. In a mathematical sense, a circle defined parametrically in a positive Cartesian plane by the equations x = sin t
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Westerly can refer to a number of things:
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- Westerly, Rhode Island, a town in the United States of America
- The Westerlies are the prevailing winds in the middle latitudes
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North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets the Earth's surface.
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Jet streams are fast flowing, relatively narrow air currents found in the atmosphere at around 11 kilometers (36,000 ft) above the surface of the Earth. They form at the boundaries of adjacent air masses with significant differences in temperature, such as of the polar region and
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The tropopause is a boundary region in the atmosphere between the troposphere and the stratosphere. Here the air ceases to cool at -50°C, and the air becomes almost completely dry.
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Wind direction is the direction from which the wind is blowing. It is usually reported in cardinal directions or in azimuth degrees.
There are a variety of instruments used to measure wind direction, such as the windsock and wind vane.
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There are a variety of instruments used to measure wind direction, such as the windsock and wind vane.
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