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Home >  Publications >  Manuals > Grib API>   
   




 
 

Sub-area of a quasi-regular gaussian grid (ECMWF convention)
Element Contents GRIB API keys
1 Data representation type, = 4 gridType
2 Not specified for quasi-regular (reduced) grids.
3 Number of points along a meridian (Nj). Nj
Ny
4 Latitude of the first grid point, La1. latitudeOfFirstGridPointInDegrees*1000
5 Longitude of the first grid point, Lo1. longitudeOfFirstGridPointInDegrees*1000
6 Resolution flag, = 0 (direction increments not given) ijDirectionIncrementGiven*128
7 Latitude of the last grid point, La2. latitudeOfLastGridPointInDegrees*1000
8 Longitude of the last grid point, Lo2. longitudeOfLastGridPointInDegrees*1000
9 i direction increment. Cannot be used for quasi-regular (reduced) grids. iDirectionIncrementInDegrees*1000
10 Number of parallels between a pole and the Equator,ie the gaussian grid number. numberOfParallelsBetweenAPoleAndTheEquator
11 Scanning mode flags (see WMO code table 8)

iScansNegatively

jScansNegatively

jPointsAreConsecutive

12 Number of vertical coordinate parameters. NV
13 Latitude of the southern pole of rotation. latitudeOfSouthernPoleInDegrees*1000
14 Longitude of the southern pole of rotation. longitudeOfSouthernPoleInDegrees*1000
15 Latitude of the pole of stretching. latitudeOfPoleOfStretchingInDegrees *1000
16 Longitude of the pole of stretching. longitudeOfPoleOfStretchingInDegrees *1000
17 1 = quasi-regular (reduced) grid. gridType
18
Earth flag:
0 Earth assumed spherical with radius 6367.47 km.
64 Earth assumed oblate spheroidal with size as determined by IAU in 1965:
6378.160km, 6356.775km, f=1/297.0
earthIsOblate
19
Components flag.
0 Resolved u and v components of vector quantities relative to easterly
and northerly directions; or not used.
8 Resolved u and v components of vector quantities relative to the
defined grid in the direction of increasing x and y (or i and j)
coordinates respectively.
uvRelativeToGrid
20-22 Reserved. Set to 0.
23-nn NN, the number of points along a full parallel (360 degrees) is defined for each latitude row in the sub-area. The number of parallels is given by Nj above. See the algorithm below for calculating the actual number of points along each sub-area latitude row (ECMWF convention). pl

The number of points Np within a subarea along a parallel of a reduced grid can be obtained as:

   Np = [(Loe-Low)/Res] + 1

where:

Loe = Lo2
Res = 360000/NN
If Mod(Lo1/Res,1.0) = 0,
Incr = 0
otherwise
Incr = 1
Ninter = [Lo1/Res] + Incr
Low = Ninter*Res ; Low -> (Low - 360000) if Lo2 is less then Lo1.


 

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