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[GEMPAK #YKO-952227]: Wind decoding problem for grib2 grid 227
- Subject: [GEMPAK #YKO-952227]: Wind decoding problem for grib2 grid 227
- Date: Thu, 05 Feb 2015 12:40:43 -0700
Hi Art,
I decoded the file and am plotting it with GDSTREAM, I see the odd contouring
that you mention, and after playing with IJSKIP and STREAM values I can produce
a streamline plot that looks "okay".
from "phelp stream"
STREAM lines/arrows/stop/slow/scale
The STREAM parameter controls several parameters dealing with
the overall streamline calculation and display. "Lines" is a
real number multiplier which controls the number (density) of
streamlines drawn (default 1.0); "arrows" is a real number
multiplier which controls the number of arrowheads displayed
(default 1.5*lines); "stop" is a real number multiplier which
controls how close a streamline comes to another streamline
before drawing is discontinued (default 0.5); "slow" is a
real number multiplier which controls the minimum vector speed
threshold for stopping a streamline (default 0.67); "scale" is
a real number multiplier which controls how much the input vector
field is scaled prior to streamline calculation (default 0.33).
I tried IJSKIP=10 and STREAM=1////2 and that seemed to minimize the unusual
contouring, but did not eliminate it entirely. It may be that you need to play
with these values yourself to find a visually coherent plot.
Checking the values in GDLIST and plotting them with GDPLOT2, it seems that the
contouring is due to the relatively small wind speeds in the area, a lot of sub
5 knot winds at 10 meter height make it difficult to produce a visually
appealing streamline field.
So I think the data are correct, and the odd contouring a result of the low
wind speeds and dense grid spacing.
What do you think?
-Michael
> We're trying to use ARW and NMM winds from NCEP grids that appear to be on an
> equivalent
> of the 227 grid but they seem to not be properly decoded. Attached is an
> example ARW grib2
> wind field and gif streamline display (decoded with gempak 7.0.3 and
> displayed with gempak 6.6.0).
> Any ideas what might be wrong?
>
> Thanks... Art
>
> --
> Arthur A. Person
> Research Assistant, System Administrator
> Penn State Department of Meteorology
> email: address@hidden, phone: 814-863-1563
>
>
>
Ticket Details
===================
Ticket ID: YKO-952227
Department: Support GEMPAK
Priority: Normal
Status: Open