[gradsusr] NAM 12km vs. NAM Conus Nest Wind Direction

[Sam Wilson]

Just to add some detail here on how I’m processing the data from both the NAM 12km and the NAM conus nest:

After downloading the grib2 files, I run the following:

Wgrib2 grib2file –grib tmpgrib2file
Cnvgrib –g21 tmpgrib2file grib1file

I then run the grib2ctl program on the grib1 file to produce the ctl file.

The wgrib2 version I’m using is v0.1.9.7a.

Thanks
Sam


From: <gradsusr-bounces at gradsusr.org> on behalf of Sam Wilson <sam at surfline.com>
Reply-To: GrADS Users Forum <gradsusr at gradsusr.org>
Date: Thursday, March 23, 2017 at 8:05 AM
To: "gradsusr at gradsusr.org" <gradsusr at gradsusr.org>
Subject: [gradsusr] NAM 12km vs. NAM Conus Nest Wind Direction


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Hi all,

After the recent upgrade of the high resolution NAM conus nest, the wind direction in the wind plots I make appears to be wrong.

I also plot wind data from the NAM 12km data – below are the PDEF, XDEF, and YDEF lines from a NAM 12km ctl file and a NAM conus nest ctl file:

NAM 12km:

pdef 614 428 lccr 12.190000 226.541000 1 1 25.000000 25.000000 265.000000 12191 12191
xdef 614 linear -133.459 0.113383763365335
ydef 428 linear 12.190000 0.110827272727273

NAM conus nest:

pdef 1799 1059 lccr 21.138000 237.280000 1 1 38.500000 38.500000 262.500000 3000 3000
xdef 1799 linear -122.72 0.0292401642786411
ydef 1059 linear 21.138000 0.0272727272727273

The NAM conus nest wind directions appear to be about 90 degrees offset from those of the NAM 12km.  I initially thought it may be an issue where one is using grid relative where another is using earth relative, but now I’m second guessing that – I ran wgrib2 on a single file from each with the -vector_dir option and both appear to show grid relative.. and as you can see above, both have “lccr” in the PDEF.

What I’m after is being able to plot wind barbs in the meteorological convention from both and I’m curious why I’m getting different results between the above two datasets when plotting the same way.

Many thanks!

Sam Wilson

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