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Hello Grads users,<br>
<br>
I am a complete GRIB novice and I hope someone can help.<br>
<br>
I have GRIB2 files from NFDC and I need to extract the wind speed
and direction at a given lat/long/altitude point (interpolated to
closest lat/long). Or, in fact, a list of these 3D points if that
is possible in a single query. (Our GRIB2 contains only one 4 hour
time period, so time is not a factor at least initially.) The wind
speeds & directions will be used to alter the 4D coordinates for
large numbers of simulated aircraft. (My boss calls this "applying
the crab factor".)<br>
<br>
I've been trying to find a query in wgrib2 or degrib or grads (using
ctl and idx files) that will return either the wind speed &
direction OR the correct UGRD/VGRD values for one or more 3D points
(which means that I also need to understand how to transform
altitude into pressure). And I just can't seem to get a handle on
the structure of the idx file, i.e. what array dimensions to use and
etc. <br>
<br>
Oh and unfortunately I have to run on Windows, I'll be using C++.<br>
<br>
My ctl file looks like this:<br>
<small><font face="Courier New, Courier, monospace">dset ^als.grib2<br>
index ^als.grib2.idx<br>
undef 9.999E+20<br>
title als.grib2<br>
* produced by g2ctl v0.0.7<br>
* command line options: -0 als.grib2<br>
* griddef=1:0:(151 x 113):grid_template=30: Lambert Conformal:
(151 x 113) input WE:SN output WE:SN res 8 Lat1 16.281000 Lon1
233.862000 LoV 265.000000 LatD 25.000000 Latin1 25.000000 Latin2
25.000000 LatSP 0.000000 LonSP 0.000000 North Pole (151 x 1<br>
dtype grib2<br>
pdef 151 113 lccr 16.281000 -126.138 1 1 25.000000 25.000000 -95
40635.000000 40635.000000<br>
xdef 214 linear -139.856122 0.384841900824187<br>
ydef 114 linear 16.281000 0.369409090909091<br>
tdef 1 linear 16Z24sep2008 1mo<br>
* PROFILE hPa<br>
zdef 37 levels 100000 97500 95000 92500 90000 87500 85000 82500
80000 77500 75000 72500 70000 67500 65000 62500 60000 57500
55000 52500 50000 47500 45000 42500 40000 37500 35000 32500
30000 27500 25000 22500 20000 17500 15000 12500 10000<br>
options pascals<br>
vars 97 <b>[I've deleted most of the variables from the list
below.]</b><br>
UGRDprs 37,100 0,2,2 ** (1000 975 950 925 900.. 200 175 150
125 100) U-Component of Wind [m/s]<br>
UGRD10m 0,103,10 0,2,2 ** 10 m above ground U-Component of
Wind [m/s]<br>
UGRD90_60mb 0,108,9000,6000 0,2,2 ** 90-60 mb above ground
U-Component of Wind [m/s]<br>
UGRD150_120mb 0,108,15000,12000 0,2,2 ** 150-120 mb above
ground U-Component of Wind [m/s]<br>
UGRD30_0mb 0,108,3000,0 0,2,2 ** 30-0 mb above ground
U-Component of Wind [m/s]<br>
UGRD180_150mb 0,108,18000,15000 0,2,2 ** 180-150 mb above
ground U-Component of Wind [m/s]<br>
UGRD120_90mb 0,108,12000,9000 0,2,2 ** 120-90 mb above ground
U-Component of Wind [m/s]<br>
UGRD60_30mb 0,108,6000,3000 0,2,2 ** 60-30 mb above ground
U-Component of Wind [m/s]<br>
UGRDmwl 0,6,0 0,2,2 ** max wind U-Component of Wind [m/s]<br>
UGRDtrop 0,7,0 0,2,2 ** tropopause U-Component of Wind [m/s]<br>
USTMsfc 0,1,0 0,2,194 ** surface U-Component Storm Motion
[m/s]<br>
VGRDprs 37,100 0,2,3 ** (1000 975 950 925 900.. 200 175 150
125 100) V-Component of Wind [m/s]<br>
VGRD10m 0,103,10 0,2,3 ** 10 m above ground V-Component of
Wind [m/s]<br>
VGRD90_60mb 0,108,9000,6000 0,2,3 ** 90-60 mb above ground
V-Component of Wind [m/s]<br>
VGRD150_120mb 0,108,15000,12000 0,2,3 ** 150-120 mb above
ground V-Component of Wind [m/s]<br>
VGRD30_0mb 0,108,3000,0 0,2,3 ** 30-0 mb above ground
V-Component of Wind [m/s]<br>
VGRD180_150mb 0,108,18000,15000 0,2,3 ** 180-150 mb above
ground V-Component of Wind [m/s]<br>
VGRD120_90mb 0,108,12000,9000 0,2,3 ** 120-90 mb above ground
V-Component of Wind [m/s]<br>
VGRD60_30mb 0,108,6000,3000 0,2,3 ** 60-30 mb above ground
V-Component of Wind [m/s]<br>
VGRDmwl 0,6,0 0,2,3 ** max wind V-Component of Wind [m/s]<br>
VGRDtrop 0,7,0 0,2,3 ** tropopause V-Component of Wind [m/s]<br>
VVELprs 37,100 0,2,8 ** (1000 975 950 925 900.. 200 175 150
125 100) Vertical Velocity (Pressure) [Pa/s]<br>
VVEL150_120mb 0,108,15000,12000 0,2,8 ** 150-120 mb above
ground Vertical Velocity (Pressure) [Pa/s]<br>
VVEL90_60mb 0,108,9000,6000 0,2,8 ** 90-60 mb above ground
Vertical Velocity (Pressure) [Pa/s]<br>
VVEL60_30mb 0,108,6000,3000 0,2,8 ** 60-30 mb above ground
Vertical Velocity (Pressure) [Pa/s]<br>
VVEL120_90mb 0,108,12000,9000 0,2,8 ** 120-90 mb above ground
Vertical Velocity (Pressure) [Pa/s]<br>
VVEL30_0mb 0,108,3000,0 0,2,8 ** 30-0 mb above ground
Vertical Velocity (Pressure) [Pa/s]<br>
VVEL180_150mb 0,108,18000,15000 0,2,8 ** 180-150 mb above
ground Vertical Velocity (Pressure) [Pa/s]<br>
ENDVARS<br>
</font></small><br>
Any and all help, suggestions etc. would be very much appreciated.
This is way outside my area of expertise and it has me feeling like
a real GRIB and meteo DUMMY.<br>
<br>
Thanks much!<br>
Carolyn<br>
<br>
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