Geostrophic winds cannot be exactly parallel to isobars
In article ers.com,
"Icebound" wrote:
"Lawrence DčOliveiro" wrote in message
...
... Which I took to mean, that component of the
pressure gradient force perpendicular to the direction of the wind.
As long as the drag is nonzero, there must be a component of the
pressure gradient force in the direction of the motion of the wind, to
offset the drag. So the wind can never be exactly parallel to the
isobars.
Why?
The fact that the air is moving at all, is determined by the pressure
gradient force (PGF). The fact that it's direction is 90 degrees offset to
the PGF is a function of the coriolis effect... you cannot ask for *more*
PGF in that direction.
The work done by a force is the dot product of the force and the
displacement of the object it's pushing on. In particular, if the two
vectors (force and displacement) are at right angles, then the dot
product is zero. Which means if the wind is moving at right angles to
the pressure gradient force, then the pressure gradient force cannot
transfer any kinetic energy to the wind, so it cannot cause the wind to
blow.
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