- Pressure-gradient force
The pressure gradient force is not actually a 'force' but the acceleration of air due to pressure difference (a force per unit mass). It is usually responsible for accelerating a parcel of
airfrom a high atmospheric pressureregion to a low pressure region, resulting in wind. In meteorology, pressure gradient force refers to the horizontal movement of air according to the equation:
The term is equal to the acceleration because this is an expression of Newton's law . is the component of the pressure gradient along the x-axis. is the mass density and shows that as the mass density increases, the acceleration due to the pressure gradient becomes smaller.
The pressure gradient force acts at right angles to
isobars in the direction from high to low pressure. The greater the pressure difference over a given horizontal distance, the greater the force and hence the stronger the wind.
The pressure gradient force, however, is not the only force that acts on a moving parcel of air — if it were, then low and high pressure regions would eventually disappear. Other forces acting on a horizontally moving parcel of air include; surface
friction, coriolis force, centrifugal force. In large-scale atmospheric flows, the coriolis force generally balances the pressure gradient force, producing winds blowing largely along the isobars; however, near the surface the friction term is also important, generally giving a resulting net wind direction diagonal to the isobars (with a component blowing towards the low pressure center).
* Roland B. Stull (2000) "Meteorology for Scientists and Engineers", Second Edition, Ed. Brooks/Cole, ISBN 0-534-37214-7.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Pressure gradient — In atmospheric sciences (meteorology, climatology and related fields), the pressure gradient (typically of air, more generally of any fluid) is a physical quantity that describes in which direction and at what rate the pressure changes the most… … Wikipedia
gradient wind — /wind/ a wind with a velocity and direction that are mathematically defined by the balanced relationship of the pressure gradient force to the centrifugal force and the Coriolis force: conceived as blowing parallel to isobars. Cf. geostrophic… … Universalium
gradient wind — Any horizontal wind velocity tangent to the contour line of a constant pressure surface or an isobar. This movement of air is to the result of a combination of three forces: pressure gradient force, geostrophic force, and cyclostrophic force. In… … Aviation dictionary
gradient wind — noun see gradient velocity * * * /wind/ a wind with a velocity and direction that are mathematically defined by the balanced relationship of the pressure gradient force to the centrifugal force and the Coriolis force: conceived as blowing… … Useful english dictionary
Force — For other uses, see Force (disambiguation). See also: Forcing (disambiguation) Forces are also described as a push or pull on an object. They can be due to phenomena such as gravity, magnetism, or anything that might cause a mass to accelerate … Wikipedia
Pressure — This article is about pressure in the physical sciences. For other uses, see Pressure (disambiguation). Pressure as exerted by particle collisions inside a closed container … Wikipedia
Force-free magnetic field — A force free magnetic field is a type of field which arises as a special case from the magnetostatic equation in plasmas. This special case arises when the plasma pressure is so small, relative to the magnetic pressure, that the plasma pressure… … Wikipedia
pressure — 1. A stress or force acting in any direction against resistance. 2. (P, frequently followed by a subscript indicating location)In physics and physiology, the force per unit area exerted by a gas or liquid against the walls of its container or… … Medical dictionary
Low-pressure area — This depiction of the Hadley cell shows the process which sustains low pressure areas. Diverging winds aloft allow for lower pressure and convergence at the Earth s surface, which leads to upward motion. A low pressure area, or low , is a region… … Wikipedia
Low pressure area — A low pressure area, or low , is a region where the atmospheric pressure is lower in relation to the surrounding area. Tropical storms, extratropical cyclones, subpolar cyclones, and subarctic cyclones are called low pressure cells.Lows are… … Wikipedia