Tiled Fix files for MERRA2 ingestion in UFS

[DeniseWorthen]

During a recent code manager tag-up, the possibility of using the MERRA2 data on the tiled grids was raised.

Tiled MERRA2 files can be created off-line using the following procedure:

• Create a SCRIP file which describes the MERRA2 grid using netCDF operators (NCO) function ncremap

ncremap -g MERRA2_SCRIP.nc -G latlon=361,576#lat_typ=cap

• Create the bilinear regrid weights between between the MERRA2 grid and the C96 tiles (MERRA2.to.C96.nc). The following code snip shows the fortran code required:

      method=ESMF_REGRIDMETHOD_BILINEAR
      fsrc = 'MERRA2_SCRIP.nc'
      fdst = 'C96_mosaic.nc'
      fwgt = 'MERRA2.to.C96.nc'
      fpath = '/scratch1/NCEPDEV/global/glopara/fix/fix_fv3_gmted2010/C96'
    
      call ESMF_RegridWeightGen(srcFile=trim(fsrc),dstFile=trim(fdst), &
                           weightFile=trim(fwgt), regridmethod=method, &
                           unmappedaction=ESMF_UNMAPPEDACTION_IGNORE, &
                           ignoreDegenerate=.true., &
                           tileFilePath=trim(fpath), rc=rc)

• Interpolate the MERRA2 data to the tiles as shown in the code snip, where mdat is the MERRA2 data for each tracer and each month and the arrays row, col and S are obtained from the weights file generated above and dst3d is the mapped MERRA2 data on each tile.

     src_field(:,1:nlev) = reshape(mdat(1:nlons,1:nlats,1:nlev), (/nlons*nlats,nlev/))

      dst_field = 0.0
      do i = 1,n_s
        ii = row(i); jj = col(i)
        dst_field(ii,:) = dst_field(ii,:) + S(i)*src_field(jj,:)
      enddo

    do i = 0,ntile-1
       istr = i*npx*npx+1
       iend = istr+npx*npx-1
      
       dst3d(:,:,1:nlev) = reshape(dst_field(istr:iend,1:nlev), (/npx,npx,nlev/))

• Write the array dst3d into a tiled file for each tracer, writing all months into the same tiled file.

For C96, the above procedure results in 6 files which are approximately 560MB each. For C384, the 6 files are each about 4.8 GB. The current MERRA2 input data is contained in 12 files of approximate 1GB each.