[gradsusr] Fwd: Wind speed & dir at a 4D point

[Carolyn Sorensen]

Hello Grads users,

I am a complete GRIB novice and I hope someone can help.

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".)

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.

Oh and unfortunately I have to run on Windows, I'll be using C++.

My ctl file looks like this:
dset ^als.grib2
index ^als.grib2.idx
undef 9.999E+20
title als.grib2
* produced by g2ctl v0.0.7
* command line options: -0 als.grib2
* 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
dtype grib2
pdef 151 113 lccr 16.281000 -126.138 1 1 25.000000 25.000000 -95 
40635.000000 40635.000000
xdef 214 linear -139.856122 0.384841900824187
ydef 114 linear 16.281000 0.369409090909091
tdef 1 linear 16Z24sep2008 1mo
* PROFILE hPa
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
options pascals
vars 97 *[I've deleted most of the variables from the list below.]*
UGRDprs    37,100  0,2,2 ** (1000 975 950 925 900.. 200 175 150 125 100) 
U-Component of Wind [m/s]
UGRD10m   0,103,10   0,2,2 ** 10 m above ground U-Component of Wind [m/s]
UGRD90_60mb  0,108,9000,6000   0,2,2 ** 90-60 mb above ground 
U-Component of Wind [m/s]
UGRD150_120mb  0,108,15000,12000   0,2,2 ** 150-120 mb above ground 
U-Component of Wind [m/s]
UGRD30_0mb  0,108,3000,0   0,2,2 ** 30-0 mb above ground U-Component of 
Wind [m/s]
UGRD180_150mb  0,108,18000,15000   0,2,2 ** 180-150 mb above ground 
U-Component of Wind [m/s]
UGRD120_90mb  0,108,12000,9000   0,2,2 ** 120-90 mb above ground 
U-Component of Wind [m/s]
UGRD60_30mb  0,108,6000,3000   0,2,2 ** 60-30 mb above ground 
U-Component of Wind [m/s]
UGRDmwl   0,6,0   0,2,2 ** max wind U-Component of Wind [m/s]
UGRDtrop   0,7,0   0,2,2 ** tropopause U-Component of Wind [m/s]
USTMsfc   0,1,0   0,2,194 ** surface U-Component Storm Motion [m/s]
VGRDprs    37,100  0,2,3 ** (1000 975 950 925 900.. 200 175 150 125 100) 
V-Component of Wind [m/s]
VGRD10m   0,103,10   0,2,3 ** 10 m above ground V-Component of Wind [m/s]
VGRD90_60mb  0,108,9000,6000   0,2,3 ** 90-60 mb above ground 
V-Component of Wind [m/s]
VGRD150_120mb  0,108,15000,12000   0,2,3 ** 150-120 mb above ground 
V-Component of Wind [m/s]
VGRD30_0mb  0,108,3000,0   0,2,3 ** 30-0 mb above ground V-Component of 
Wind [m/s]
VGRD180_150mb  0,108,18000,15000   0,2,3 ** 180-150 mb above ground 
V-Component of Wind [m/s]
VGRD120_90mb  0,108,12000,9000   0,2,3 ** 120-90 mb above ground 
V-Component of Wind [m/s]
VGRD60_30mb  0,108,6000,3000   0,2,3 ** 60-30 mb above ground 
V-Component of Wind [m/s]
VGRDmwl   0,6,0   0,2,3 ** max wind V-Component of Wind [m/s]
VGRDtrop   0,7,0   0,2,3 ** tropopause V-Component of Wind [m/s]
VVELprs    37,100  0,2,8 ** (1000 975 950 925 900.. 200 175 150 125 100) 
Vertical Velocity (Pressure) [Pa/s]
VVEL150_120mb  0,108,15000,12000   0,2,8 ** 150-120 mb above ground 
Vertical Velocity (Pressure) [Pa/s]
VVEL90_60mb  0,108,9000,6000   0,2,8 ** 90-60 mb above ground Vertical 
Velocity (Pressure) [Pa/s]
VVEL60_30mb  0,108,6000,3000   0,2,8 ** 60-30 mb above ground Vertical 
Velocity (Pressure) [Pa/s]
VVEL120_90mb  0,108,12000,9000   0,2,8 ** 120-90 mb above ground 
Vertical Velocity (Pressure) [Pa/s]
VVEL30_0mb  0,108,3000,0   0,2,8 ** 30-0 mb above ground Vertical 
Velocity (Pressure) [Pa/s]
VVEL180_150mb  0,108,18000,15000   0,2,8 ** 180-150 mb above ground 
Vertical Velocity (Pressure) [Pa/s]
ENDVARS

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.

Thanks much!
Carolyn

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