On Thu, 5 Feb 2004 09:14:31 -0000, Julian Scarfe wrote in


So where does the model above break down?

"Mike Tullett" wrote in message
...

As John Whitby suggests, stability may well be a factor, but is not built
into that simple model. Another factor, related I think, is the model,
being so simple, is probably based on laminar flow theory - to make
understanding easier. Introduce turbulent flow, which we have to in the
real atmosphere to varying degrees, and the simplicity of that model is
seen to introduce errors when it comes to making any calculations.

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