Edge issue in Regridding Daymet Joined Tiles with ESMF_Regridding on NCL 6.1.0

Dear NCL,

I was using the following script to regridding the joined Daymet grid (1
KM) to 3 acrmin, in which the projection was translated from LLC to lonlat
and the resolution from 1 KM to 3 arcmin. However, after I tried to
comparing different interpolation method based on the 3 arcmin data (I used
a conserve method for the ESMF regridding), I found the this 3 arcmin data
has problem in the edge/boundary.

I am including a graphs here to show the problem:
[image: Inline image 1]
The edge(coast and land) place especially in Maine (also massachusetts)
looks weird after the regridding, a mixture of no data value and real
values, and when I do a statistical of year sum, I got very small
values(below 10 mm) for one year.

The script I was using is:

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl"
    vname ="pr"
    srcFileName = vname + ".NE." + year +".nc"
    ;srcFileName = "NE_all_1980_correct_prcp.nc"
    srcPathName = srcDirName+srcFileName
    sfile = addfile(srcPathName,"r")

;---Set the destination file name
    dstDirName = "/data/ecr/yangping/DAYMET/Grid/Intermediate/"
    system("/bin/mkdir -p "+ dstDirName)
    dstFileName = str_upper(vname)+"."+year+"_1KM.esmf.nc"
    dstPathName = dstDirName+dstFileName

    setfileoption("nc","Format","LargeFile")

    ;out=addfile("/data/ecr/yangping/DAYMET/Grid/3MIN/" + vname +
 "_3MIN_lonlat_" + year+".nc","c")
    outDirName = "/data/ecr/yangping/DAYMET/Grid/3MIN/"
    outFileName = vname + ".3MIN.lonlat." + year+".nc"
    outPathName = outDirName + outFileName
    system("/bin/rm -f "+outPathName) ; delete any pre-existing file
    out=addfile(outPathName,"c")

;--- ESMF regrid method: "conserve", "bilinear", "patch"
     method = "conserve"
; method = "patch"

;===================================================

;---Options
    Opt = True
    Opt@SrcTitle = "Daymet Joined Grid "+year+" to rectlinear" ;
optional
    Opt@WgtFileName = dstDirName + "Daymet_to_Rect.Wgt.nc"

    Opt@ForceOverwrite = True
  ;;Opt@PrintTimings = True

;---Get the source file Daymet lat/lon grid
    lat2d = sfile->lat
    lon2d = sfile->lon

    dim2d = dimsizes(lat2d)
    nlat = dim2d(0)
    nlon = dim2d(1)

    print(nlat)
    print(nlon)

;---Get the Daymet source variable
    var = sfile->$vname$ ; (time, y, x)=>(365,232,221)

   ;Opt@SrcGridType = "curvilinear"
    Opt@SrcGridLat = lat2d
    Opt@SrcGridLon = lon2d

;---Create the destination lat/lon grid
    dll=0.05 ;3MIN
    latrange=abs(max(lat2d)-min(lat2d))
    lonrange=abs(max(lon2d)-min(lon2d))
    kpts_lat= toint(latrange/dll)+1
    kpts_lon= toint(lonrange/dll)+1
    lat = fspan( min(lat2d),max(lat2d), kpts_lat )
    lon = fspan( min(lon2d),max(lon2d), kpts_lon )

    newlon = fspan(-84.025,-64.875,384)
    newlat = fspan(34.875,50.125,306)

    Opt@DstGridType = "rectilinear"
    ;Opt@DstGridLat = lat
    Opt@DstGridLat = newlat
    ;Opt@DstGridLon = lon
    Opt@DstGridLon = newlon

    Opt@CopyVarCoords= True ; default for 6.1.0

    Opt@InterpMethod = method
    Opt@SrcRegional = True
    Opt@DstRegional = True

    var_regrid = ESMF_regrid(var,Opt) ; Do the regridding for 'var'
    printVarSummary(var_regrid)
    var_regrid@grid_mapping = "lonlat" ;
    out->$vname$=var_regrid ;output the regridding result

Can some here where is the problem and how to fix it?

Look forward to hearing from you.

Regards,

Ping

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