[ncl-talk] SSP interpolation

[Buzan, Jonathan]

Hi Dennis,

Ah that’s great. I’ll test those out.
I also have found out that cdo has a command that will calculate the area of grid cells.
cdo gridarea infile outfile

Cheers,
-Jonathan





On Apr 21, 2021, at 10:34 PM, Dennis Shea <shea at ucar.edu<mailto:shea at ucar.edu>> wrote:

Hi Jonathan,

It was called to my attention that there are some undocumented 'area_' functions in shea_util.ncl.
I am not sure if any of these would be what you want.

%> less "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"

Search for:
area_global_rectilinear_grid
area_polar_region
area_earth_region

I guess I was too lazy to document them!
The shea_util.ncl library is automatically loaded.






On Wed, Apr 21, 2021 at 9:49 AM Buzan, Jonathan <jbuzan at purdue.edu<mailto:jbuzan at purdue.edu>> wrote:
Thanks Dennis, I’ll work this out.

Cheers,
-Jonathan



On Apr 21, 2021, at 5:21 PM, Dennis Shea <shea at ucar.edu<mailto:shea at ucar.edu>> wrote:

I don't think there is a function but for rectilinear grids (ie: lat[*],  lon[*] )

cell_area= (pi/180)*R^2* ((sind(lat(i)*rad) - sind(lat(j)*rad))*dlon);  dlon in radians

R:  radius of earth: rearth = 6371.220      ; default; kilometers; ECMWF uses this value

see: get_d2r<http://www.ncl.ucar.edu/Document/Functions/Contributed/get_d2r.shtml>, get_pi<http://www.ncl.ucar.edu/Document/Functions/Contributed/get_pi.shtml>

EG:

rad = 0.0174532925199433 (double)
rad = 0.01745329  (float)


For 2D lat/lon, it would be a bit more tedious





On Wed, Apr 21, 2021 at 8:27 AM Buzan, Jonathan via ncl-talk <ncl-talk at mailman.ucar.edu<mailto:ncl-talk at mailman.ucar.edu>> wrote:
Hi NCL-Talk,

I am working with SSP files. They are incomplete 1km x 1km lat-lon grids (aka the omit high latitudes), with missing/fill values over oceans. The population data is absolutes, not density per area. All of this makes it hard to interpolate to a low resolution grid approximate to CMIP data (aka 100 km x 100 km).

I was thinking that I would divide each grid cell by the area to get a density value, then interpolate that to 1°x1° grid. But, I am having trouble finding a NCL function that will calculate the area of a grid cell.

Is there one?

Cheers,
-Jonathan


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