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Re: A MISCONCEPTION ITEM



It would be quite proper to expect wind directions
parallel to isobars at heights exceeding 2000 ft above ground level
(in terms to which pilots are accustomed).

Closer than this to the ground, pilots expect the wind to back and
moderate in reaction to ground friction.
(This height can vary between 500 ft on nights with no thermal action
to 3000 ft on clear sunny days).

A value of 20 degrees angular difference and 40% speed change
is not unusual in this lowest layer during the day.
Oceanic surface is subject to smaller effects with its smoother
surface and more even temperature distributions disfavoring thermals.

Backing is a counterclockwise rotation of the wind vector
(which always describes the direction the wind is coming FROM)

The Southern hemisphere sees the wind veer (rather than back)
closer to the ground in classical bathtub style. :-)

(From IR notes)

Brian

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At 11:07 7/26/99 -0400, you wrote:
Would it be more proper to use "upper-level tropospheric wind velocities"
rather than "common wind velocities", or am I being too picky?


| Robert Cohen

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On Sat, 24 Jul 1999, Ludwik Kowalski wrote:

6) On our rotating planet common wind velocities
are more or less parallel to the isobaric lines,
not more or less perpendicular. Common winds
are due to regional pressure differences but
the directions of their flows are affected by
planetary rotation (Coriolis effect).


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brian whatcott <inet@intellisys.net>
Altus OK