[ncl-talk] regridding EASE snow data

[Michael Notaro]

Does anyone have a suggestions for quickly regridding

EASE snow cover data, with the following characteristics,


latitude(720 rows, 720 columns)

longitude(720 rows, 720 columns)

cover(720 rows, 720 columns)


to a new 0.2 degree x 0.2 degree grid, with the following

characteristics?


lat=fspan(0.,90.,451)

lon=fspan(0.,180.,901)

grid(451,901)


It needs to be regridded, not interpolated, as

the values are 10 for snow covered land and

20 for non-snow covered land.


I've tried using getind_latlon2d within dual

do loops, but it was extremely slow.


My latest attempt is below, using mask

to reduce data to only nearby locations.

In this case, I am trying to regrid 14 years

worth of daily snow cover.


Thanks, Michael




load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"

begin


cvr=new((/14,12,31,720,720/),float)

cvr at _FillValue=1e+35

cvr=1e+35


a=addfile("1999/nhtsd25e2_19990101_v01r01.nc","r")

latitude=a->latitude ; (rows,cols)

longitude=a->longitude


do iyr=0,13

  do imn=0,11

    do id=0,30

      years=iyr+1999

      if (imn.le.8) then

        months="0"+(imn+1)

      else

        months=""+(imn+1)

      end if

      if (id.le.8) then

        days="0"+(id+1)

      else

        days=""+(id+1)

      end if

      filen=""+years+"/nhtsd25e2_"+years+""+months+""+days+"_v01r01.nc"

      if (isfilepresent(filen)) then

        a=addfile(filen,"r")

        cvr(iyr,imn,id,:,:)=byte2flt(a->ims_snow_cover_extent(0,:,:)) ; byte (time, 720 rows, 720 cols) 10=snow covered land; 20=snow free land

      end if

    end do

  end do

end do


lat=fspan(0.,90.,451)

lat!0="lat"

lat at units="degrees_north"

lat&lat=lat


lon=fspan(0.,180.,901)

lon!0="lon"

lon at units="degrees_east"

lon at lon=lon


grid=new((/14,12,31,451,901/),float)

grid at _FillValue=1e+35

grid=1e+35


do i=0,450

  do j=0,900


    cover=mask(cvr,latitude.ge.lat(i)+0.5,False)

    cover=mask(cover,latitude.le.lat(i)-0.5,False)

    cover=mask(cover,longitude.ge.lon(j)+0.5,False)

    cover=mask(cover,longitude.le.lon(j)-0.5,False)


    do iyr=0,13

      do imn=0,11

        do id=0,30


          snow=num(cover(iyr,imn,id,:,:).eq.10)

          nosnow=num(cover(iyr,imn,id,:,:).eq.20)

          combined=snow+nosnow


          if (combined.gt.0) then

            if (snow.ge.nosnow) then

              grid(iyr,imn,id,i,j)=100.

            else

              grid(iyr,imn,id,i,j)=0.

            end if

          end if


        end do

      end do

    end do


  end do

end do

year=ispan(1999,2012,1)

year!0="year"

year&year=year

month=ispan(1,12,1)

month!0="month"

month&month=month

day=ispan(1,31,1)

day!0="day"

day&day=day


grid!0="year"

grid!1="month"

grid!2="day"

grid!3="lat"

grid!4="lon"

grid&year=year

grid&month=month

grid&day=day

grid&lat=lat

grid&lon=lon


system("rm climo_snowcover_asia.nc")

out=addfile("climo_snowcover_asia.nc","c")

out->grid=grid




Michael Notaro
Associate Director
Nelson Institute Center for Climatic Research
University of Wisconsin-Madison
Phone: (608) 261-1503
Email: mnotaro at wisc.edu
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