"Julian Scarfe" wrote in message news:rtvUb.17887
So where does the model above break down?

John, Mike, thanks for the replies.

To clarify, I'm sure the variation in wind speed within the boundary layer
is complex and depends on a multitude of factors. The main issue for me
is
the dependence of direction on speed. As far as I can see, provided the
only force acting, other than the coriolis and pressure gradient forces,
is
frictional (along the velocity vector) then the balance of forces
guarantees
the relationship

(Wind speed at surface) = (Geostrophic wind speed) * cos(veer)

I can imagine that tubulence introduces random errors, but empirically it
looks to me as if
(Wind speed at surface) is much less than (Geostrophic wind speed) *
cos(veer)
or putting it another way
veer is much less than arccos ((Wind speed at surface)/(Geostrophic wind
speed))

Julian Scarfe


I agree the simple model you suggest does give *wrong* answers for amount of
backing. Your equation suggests, for example, that given a Geostrophic wind
of 35 knots and a mean surface wind of about 23 knots ( a not unreasonable
value) the backing should be of the order of 48deg - which is certainly far
too large (20 to 30 deg is more likely).
So, as has been suggested, other forces are involved in the *real*
atmosphere.
John
--
York,
North Yorkshire.
(Norman Virus Protected)