Re: Help using function of "ESMF_Regrid" to regrid global emission data

Re: the script and data you sent offline:

The following are both *rectilinear* grids:
   GEOS5.1_19x2_20050101.nc
   IPCC_emissions_RCP45_SO2_anthropogenic_2005_0.5x0.5_v1_21_12_2009.nc

---
netcdf GEOS5.1_19x2_20050101 {
dimensions:
         lat = 96 ;
         lon = 144 ;
         lev = 72 ;
         time = UNLIMITED ; // (4 currently)
         ilev = 73 ;
variables:
         float lat(lat) ;
                 lat:units = "degrees_north" ;
                 lat:long_name = "latitude" ;
         float lon(lon) ;
                 lon:units = "degrees_east" ;
                 lon:long_name = "longitude" ;
[SNIP]
---
netcdf IPCC_emissions_RCP45_SO2_anthropogenic_2005_0.5x0.5_v1_21_12_2009 {
dimensions:
         lat = 360 ;
         lon = 720 ;
         time = UNLIMITED ; // (12 currently)
variables:
         float lat(lat) ;
                 lat:long_name = "Latitude" ;
                 lat:units = "degrees_north " ;
                 lat:comment = "center of cell" ;
         float lon(lon) ;
                 lon:long_name = "Longitude" ;
                 lon:units = "degrees_east" ;
                 lon:comment = "center of cell" ;
[SNIP]
----
Not a big deal but having the WRF letters implies the WRF model
   Opt@WgtFileName       = "rec_to_WRF.nc"
Since you want rectilinear to rectilinear, I'd suggest
  Opt@WgtFileName       = "rec360x720_to_rec96x144.nc"
--
Neither grid is a
   "Regional CONUS Lambert Confrontal Projection" (36kmx36km)"
or, more likely,
   "Regional CONUS Lambert Conformal Projection" (36kmx36km)"
Why is map projection mentioned in the email?
====
As to your original question
"..it turns out the regridding data are still not consistent
with the original ones. There will be 5%-15% less
compared with original dataset, depending on the species."
The code you sent uses 'bilinear' not 'conserve' regrid
Bilinear performs a weighted average of the four closest points.
Hence the interpolated values are lower than the original grid
(0)	========
(0)	AreaAvg_var       =1.69607e-12 kg m-2 s-1
(0)	AreaAvg_var_regrid=1.48177e-12 kg m-2 s-1
(0)	========
(0)	ratio: bilinear : (AreaAvg_var_regrid/AreaAvg_var)=0.873647
0)	========
(0)	AreaAvg_var       =1.69607e-12 kg m-2 s-1
(0)	AreaAvg_var_regrid=1.69259e-12 kg m-2 s-1
(0)	========
(0)	ratio: conserve : (AreaAvg_var_regrid/AreaAvg_var)=0.997951
Attached code
On 6/17/13 12:42 PM, Yuqiang Zhang wrote:
> Hi Everyone
>
>
>
> I am intending to use the "ESMF_regrid" function to regrid my "Global
> Lon-Lat projection" of emission data (unit in kg/s or kg/m2/s) in 0.5x0.5
> degree to a "Regional CONUS Lambert Confrontal Projection" (36kmx36km).
> After I read the sample scripts on the NCL website and I thought I could do
> that. However, after regridding, my total emissions in the region are not
> consistent with my original data at the same region. First I thought this
> may be because the two regions are not exactly overlapped as one is in
> lon-lat projection and another one is in LLC. Then I tried to use the
> function to regrid this global emission to another coarse resolution global
> (2x.2.5 degree) as I did before using function "
> <http://www.ncl.ucar.edu/Document/Functions/Contributed/area_conserve_remap_
> Wrap.shtml> area_conserve_remap_Wrap ", it turns out the regridding data are
> still not consistent with the original ones. There will be 5%-15% less
> compared with original dataset, depending on the species.
>
>
>
> Can anyone tell me whether or not I can use this function to do that. If
> possible, should I keep the unit of "kg/m2/s" or convert to "kg/s"?
>
>
>
> Regards,
>
>
>
>
>
> -----------------------------------------------------------------
>
> -----------------------------------------------------------------
>
> Yuqiang Zhang
>
> PhD student
>
> Environmental Science and Engineering Department
>
> Univerisyt of North Carolina at Chapel Hill
>
>
>
>
>
>
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