Ageostrophy or (ageostrophic flow) is the difference between the ''actual'' wind or current and the
geostrophic wind or
geostrophic current
A geostrophic current is an oceanic current in which the pressure gradient force is balanced by the Coriolis effect. The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern ...
. Since geostrophy is an exact balance between the
Coriolis force
In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...
and the
pressure gradient
In atmospheric science, the pressure gradient (typically of Earth's atmosphere, air but more generally of any fluid) is a physical quantity that describes in which direction and at what rate the pressure increases the most rapidly around a particu ...
force, ageostrophic flow reflects an imbalance, and thus is often implicated in disturbances, vertical motions (important for
weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
), and rapid changes with time. Ageostrophic flow reflects the existence of all the other terms in the
momentum equation neglected in that idealization, including
friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of t ...
and material acceleration
Dv/Dt, which includes the
centrifugal force
In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is paralle ...
in curved flow.
See also
*
geostrophic
A geostrophic current is an oceanic current in which the pressure gradient force is balanced by the Coriolis effect. The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern ...
*
geostrophic wind
References
External links
Meteo 422 – Lecture 17 – The Omega Equation Aloft
Oceanography
{{ocean-stub
fr:Vent géostrophique#Vent agéostrophique