[ncl-talk] unrotate grib2 data projected into polar stereographic projection
Juliette Lapeyre
Juliette.Lapeyre at USherbrooke.ca
Thu Jan 11 11:22:02 MST 2018
Thank you Denis,
I understand better now!
Juliette
________________________________
De : Dennis Shea <shea at ucar.edu>
Envoyé : lundi 8 janvier 2018 18:46:15
À : Juliette Lapeyre
Cc : ncl-talk at ucar.edu
Objet : Re: [ncl-talk] unrotate grib2 data projected into polar stereographic projection
The:
formula_u : Uearth = sin(rot)*Vgrid + cos(rot)*Ugrid
formula_v : Vearth = cos(rot)*Vgrid - sin(rot)*Ugrid
Are for 'directional' quantities (eg: vectors): the {U/V}grid are the wind components on the rotated grid. *IF* you had vector quantities these equations must be used to transform to winds relative to the earth's poles.
===
Your file(s) contain scalar quantities. Hence, no rotation need be performed.
Use gridlat_0 and gridlon_0 for plotting
f = addfile("CMC_RDPA_APCP...grib2", "r")
; APCP_P8_L1_GST0_acc6h attributes include
: type_of_statistical_processing : Accumulation
; statistical_process_duration : 6 hours (ending at forecast time)
p6 = f->APCP_P8_L1_GST0_acc6h ; ( ygrid_0, xgrid_0 )
printVarSummary(p6)
print(MinMax(p6, 0)
; plot
p6 at lat2d = f->gridlat_0 ; for plotting only
p6 at lon2d = f->gridlon_0
====
Also, just for fun try
%> ncl_filedump CMC_RDPA_APCP...grib2 -itime | less
The -itime will add a time (record) dimension
APCP_P8_L1_GST0_acc6h ( initial_time0_hours, ygrid_0, xgrid_0 )
It will also add time information.
Good luck
On Mon, Jan 8, 2018 at 9:01 AM, Juliette Lapeyre via ncl-talk <ncl-talk at ucar.edu<mailto:ncl-talk at ucar.edu>> wrote:
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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