Thermal wind

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Thermal wind

The thermal wind is a vertical

Vertical

vetical means up and downAn object is in a vertical position when it is aligned in an "up-down" direction, roughly speaking perpendicular to the horizon or horizontal plane....
shear

Shearing (physics)

Shearing in continuum mechanics refers to the occurrence of a shear Strain , which is a deformation of a material substance in which parallel internal surfaces slide past one another....
in the geostrophic wind

Geostrophic wind

The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis effect and the pressure gradient force....
caused

Causality

Causality denotes a necessary relationship between one event and another event which is the direct consequence of the first.While this informal understanding suffices in everyday use, the Philosophy analysis of how best to characterize causality extends over millennia....
by a horizontal

Horizontal

Horizontal may refer*Horizontal plane, in astronomy, geography, geometry and other sciences and contexts*Horizontal coordinate system, in astronomy...
temperature gradient

Temperature gradient

A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location....
. Its name is a misnomer

Misnomer

A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derived their names because of the form, action, or origin of the subject?becoming named popularly or widely referenced?long before their true natures were known....
, because the thermal wind is not actually a wind

WIND

The Global Geospace Science WIND satellite is a NASA science spacecraft launched at 04:31:00 EST on November 1, 1994 from launch pad 17B at Cape Canaveral Air Force Station in Merritt_Island%2C_Florida, Florida aboard a McDonnell Douglas Delta II 7925-10 rocket....
, but rather a wind gradient

Wind shear

Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind wind speed and wind direction over a relatively short distance in the Earth's atmosphere....
.

geostrophic wind is proportional to the slope of geopotential

Geopotential

Geopotential is the potential of the Earth's gravity field. For convenience it is often defined as minus the potential energy per unit mass, so that the gravity vector is obtained as the gradient of this potential, without the minus....
on a surface of constant pressure

Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
.

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Encyclopedia

The thermal wind is a vertical

Vertical

vetical means up and downAn object is in a vertical position when it is aligned in an "up-down" direction, roughly speaking perpendicular to the horizon or horizontal plane....
shear

Shearing (physics)

Geostrophic wind

The geostrophic wind is the theoretical wind that would result from an exact balance between the Coriolis effect and the pressure gradient force....
caused

Causality

Horizontal

Horizontal may refer*Horizontal plane, in astronomy, geography, geometry and other sciences and contexts*Horizontal coordinate system, in astronomy...
temperature gradient

Temperature gradient

A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location....
. Its name is a misnomer

Misnomer

WIND

Wind shear

Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind wind speed and wind direction over a relatively short distance in the Earth's atmosphere....
.

Description

Physical Intuition

The geostrophic wind is proportional to the slope of geopotential

Geopotential

Pressure

Barotropic

In meteorology, a barotropic atmosphere is one in which the pressure depends only on the density and vice versa, so that Isobaric process surfaces are also isopycnic surfaces ....
atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low....
, one where density

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ....
is a function only of pressure, the slope of isobaric

Isobaric

Isobaric may refer to:*in thermodynamics, an isobaric process, i.e. one that is carried out at constant pressure;*in mass spectrometry, ions with the same mass, e.g....
surfaces is independent of temperature

Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
, so geostrophic wind does not increase with height.

This does not hold true in a baroclinic atmosphere, one where density is a function of both pressure and temperature. Horizontal temperature gradients cause the thickness of gas

Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
layers between isobaric surfaces to increase with higher temperatures. When multiple atmospheric layers are stacked upon each other, the slope of isobaric surfaces increases with height. This also causes the magnitude

Magnitude (mathematics)

The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs....
of the geostrophic wind to increase with height.

Mathematical Formalism

The thickness of an atmospheric layer is described by the hypsometric equation

Hypsometric equation

The hypsometric equation relates the atmospheric pressure ratio to the thickness of an atmospheric layer under the assumptions of constant temperature and gravity....
:

which shows the thickness is proportional to the temperature. When there is a horizontal temperature gradient, the thickness of the layer would be greatest where the temperature is greatest.

If we differentiate the geostrophic wind, d with respect to pressure, and integrate from pressure level p₀ to p₁, we obtain the thermal wind equation:

.

Examples

Advection Turning

If a component of the geostrophic wind is parallel to the temperature gradient, the thermal wind will cause the geostrophic wind to rotate with height. If the geostrophic wind blows from cold air to warm air (cold advection

Advection

Advection, in mechanical and chemical engineering, is a transport mechanism of a substance or a conserved property with a moving fluid. The fluid motion in advection is described mathematically as a vector field, and the material transported is typically described as a scalar concentration of substance, which is contained in the fluid....
) the geostrophic wind will turn counterclockwise with height, a phenomenon

Phenomenon

A phenomenon is any observation occurrence. In popular usage, a phenomenon often refers to an extraordinary event. In physics, a phenomenon may be a feature of matter, energy, or spacetime....
known as wind backing. Otherwise, if the geostrophic wind blows from warm air to cold air (warm advection) the wind will turn clockwise

Clockwise

A 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....
with height, also known as wind veering.

Wind backing and veering allow us to estimate the horizontal temperature gradient with data from an atmospheric sounding

Atmospheric sounding

An atmospheric sounding is a measurement of vertical distribution of physical properties of the atmosphere column such as atmospheric pressure, temperature, wind speed and wind direction , liquid water content, ozone concentration, pollution, and other properties....
.

Frontogenesis

As in the case of advection turning, when there is a cross-isothermal component of the geostrophic wind, a sharpening of the temperature gradient results. The thermal wind causes a deformation field and frontogenesis

Frontogenesis

Frontogenesis, in meteorology, refers to the formation or strengthening of an atmospheric front.See also*Frontolysis...
may occur.

Jet Stream

A horizontal temperature gradient exists while moving North

North

North is one of the four cardinal directions, specifically the direction that, in Western culture, is treated as the fundamental direction:...
-South

South

South is one of the cardinal directions and is opposite to the north.By Western world Norm , the bottom side of a map is south; the southern direction has azimuth or bearing of 180?....
along a meridian

Meridian

Meridian, or a meridian line may refer to:...
because the curvature of the Earth allows for more solar heating

Insolation

Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day ....
at the equator

Equator

The equator is the intersection of the Earth's surface with the Plane perpendicular to the Earth's rotation and containing the Earth's center of mass....
than at the poles. This creates a westerly

Westerlies

The Westerlies or the Prevailing Westerlies are the Prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the Geographical poles....
geostrophic wind pattern to form in the mid-latitudes. Because thermal wind causes an increase in wind velocity

Velocity

In physics, velocity is defined as the Derivative of Position vector. It is a vector physical quantity; both speed and direction are required to define it....
with height, the westerly pattern increases in intensity up until the tropopause

Tropopause

The tropopause is the boundary in the Earth's atmosphere between the troposphere and the stratosphere. Going upward from the surface, it is the point where air ceases to cool with height, and becomes almost completely dry....
, creating a strong wind current known as the jet stream

Jet stream

Jet streams are fast flowing, narrow thermal winds found at the tropopause, the transition between the troposphere and the stratosphere ,and are located at 10-15 kilometers above the surface of the Earth....
. The Northern

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of the equator?the word sphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator....
and Southern

Southern Hemisphere

The Southern Hemisphere is the half of a planet that is south of the equator?the word sphere literally means 'half ball'. It is also that half of the celestial sphere south of the celestial equator....
Hemisphere

Hemisphere

Hemisphere may refer to:*half of a sphereAs half of the Earth:*Any half of the Earth or other planetary or stellar body*New World*Old World...
s exhibit similar jet stream patterns in the mid-latitudes.

Thermal wind

Description

Physical Intuition

Mathematical Formalism

Examples

Advection Turning

Frontogenesis

Jet Stream

Further reading