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Re: Overlaying gridded winds on satellite data [message #44919 is a reply to message #44816]

Thu, 21 July 2005 08:03

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Christopher Lee writes:

> Wind barbs point in the direction the wind is coming FROM. Hence the
> terms westward (winds coming from the west) and eastward (winds coming
> from the east) etc.
>
> http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/sfcobs/wnd.rxml
> http://www.rap.ucar.edu/weather/info/about_windbarb.html
> http://sanangelo.tamu.edu/bookmark/wind_dir.htm
> http://www.al.noaa.gov/WWWHD/pubdocs/windbarb.html
> (this one sounds `wrong' at first, but it really is correct, the feathers
> are on the back of the `arrow', also tells you which way the feathers
> point)
>
> Of course, if the users wind vectors are wrong, there's no convincing
> them otherwise. Wind vectors are usually northerly(to the north) and
> easterly(to the east), but I've seen westerly data (you could
> obviously use keywords like /WESTERLY and /EASTERLY).

In light of this information I have reverted to my original
notion of how to draw the wind arrow. I have also improved
the documentation so that it is clear what direction I assume
the positive wind vectors are pointing in. In the northern
hemisphere, the "feathers" on the arrow shaft are drawn in
the clockwise direction (which is what I was doing previously),
but I have added a SOUTHERN_HEMISPHERE keyword to draw the
feathers in a counterclockwise direction, which is apparently
the norm for our friends down under.

And while I was hacking around, I also fixed a small problem
with the CLIP keyword.

So, I expect this to be the definitive word on the subject. :-)

You can find the updated program here:

http://www.dfanning.com/programs/windbarb.pro

> I've never used the stationplot/windbarb programs. Can the STATIONPLOT
> function show the cloud coverage (in the circle)? Or is the 3/4 filled
> circle the symbol for a weatherstation?

It could be made to show the cloud coverage, I'm sure, but
currently is is the 3/4 filled circle symbol for a weather
station.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Overlaying gridded winds on satellite data By: Chris[3] on Tue, 19 July 2005 21:17
		Re: Overlaying gridded winds on satellite data By: K. Bowman on Fri, 22 July 2005 09:56
		Re: Overlaying gridded winds on satellite data By: Chris Lee on Fri, 22 July 2005 00:33
		Re: Overlaying gridded winds on satellite data By: Chris Lee on Fri, 22 July 2005 00:31
		Re: Overlaying gridded winds on satellite data By: Mark Hadfield on Thu, 21 July 2005 16:00
		Re: Overlaying gridded winds on satellite data By: David Fanning on Thu, 21 July 2005 08:03
		Re: Overlaying gridded winds on satellite data By: R.G. Stockwell on Thu, 21 July 2005 07:53
		Re: Overlaying gridded winds on satellite data By: Chris Lee on Thu, 21 July 2005 00:28
		Re: Overlaying gridded winds on satellite data By: Chris[3] on Wed, 20 July 2005 14:52
		Re: Overlaying gridded winds on satellite data By: David Fanning on Wed, 20 July 2005 14:44

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