[ncl-talk] unrotate grib2 data projected into polar stereographic projection

[Juliette Lapeyre]

Hi,


I am using grib2 data from the RDPA CaPA project (https://weather.gc.ca/grib/grib2_RDPA_ps10km_e.html) and I would like to change the polar stereographic projection to NAD 83/UTM zone 14.


I can that there are three variables that I should  use (gridrot_0, gridlat_0, gridlon_0) but I don't understand how to apply the formulas indicated in gridrot_0 (see below). What are exactly Vearth, Vgrid, Uearth and Ugrid ? I guess "rot" is the value of grid_rot for each coordinate ?


Thanks,


Juliette


    gridrot_0
           Size:       493x399
           Dimensions: xgrid_0,ygrid_0
           Datatype:   single
           Attributes:
                       note2     = 'apply formulas to derive u and v components relative to earth'
                       note1     = 'u and v components of vector quantities are resolved relative to grid'
                       formula_v = 'Vearth = cos(rot)*Vgrid - sin(rot)*Ugrid'
                       formula_u = 'Uearth = sin(rot)*Vgrid + cos(rot)*Ugrid'
                       units     = 'radians'
                       GridType  = 'Polar Sterographic Projection (North or South)'
                       long_name = 'vector rotation angle'
    gridlat_0
           Size:       493x399
           Dimensions: xgrid_0,ygrid_0
           Datatype:   single
           Attributes:
                       La1       = 32.5
                       Lo1       = 225
                       Lov       = 249
                       Dx        = 15
                       Dy        = 15
                       units     = 'degrees_north'
                       grid_type = 'Polar Sterographic Projection (North or South)'
                       long_name = 'latitude'
                       corners   = [3.25e+01 2.45e+01 4.63e+01 6.52e+01]
    gridlon_0
           Size:       493x399
           Dimensions: xgrid_0,ygrid_0
           Datatype:   single
           Attributes:
                       La1       = 32.5
                       Lo1       = 225
                       Lov       = 249
                       Dx        = 15
                       Dy        = 15
                       units     = 'degrees_east'
                       grid_type = 'Polar Sterographic Projection (North or South)'
                       long_name = 'longitude'
                       corners   = [-1.35e+02 -7.24e+01 -2.10e+01  1.59e+02]



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