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[IDV #ENY-716795]: IDV - true wind vectors

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  • Subject: [IDV #ENY-716795]: IDV - true wind vectors
  • Date: Thu, 18 Jan 2007 06:40:25 -0700
Greetings HP-

> Institution: EUMETSAT
> Package Version: 2.2b1
> Operating System: Windows XP
> Hardware Information: Java: home: C:\\Program Files\\IDV_2.2b1\\jre version: 
> 1.5.0_06 j3d:1.3.2 fcs (build12)
> Inquiry: Hi
> 
> This is something I always wanted to ask, but never did/dared so far. What 
> are the true
> wind vectors for. I know that e.g. in sailing one speaks of true and apparant 
> wind. I must
> miss something here. Can you enlighten me, please

Excellent question.  I should probably add this to the FAQ.

Many times the wind components are sent out as grid relative instead of 
relative to 
the earth.  The true wind vectors are rotated from the grid projection to actual
wind direction.  For global lat/lon grids, the grid relative is the same as 
true.
It's not always clear from a netCDF file whether the components are grid 
relative
or true.  In GRIB, there is a flag, but we are not taking advantage of that yet.

P.S. Jeff and I are out at the AMS meeting this week which accounts for our
lack of response.  We'll get back to your other questions next week.

Don

Ticket Details
===================
Ticket ID: ENY-716795
Department: Support IDV
Priority: Normal
Status: Open