[ncl-talk] regridding WRF to coarser grid using "conserve" method

[Juris Almonte]

Dear NCL help,

I am having trouble regridding my WRF precipitation data (4 km) to a coarser grid (10 km grid with a polar stereographic projection) using the “conserve” method. I should note that it works for the “bilinear method”. I get the following error when using the “conserve” method. I am using NCL V6.3.

20170621 172919.788 INFO             PET0 Running with ESMF Version 6.3.0rp1
20170621 172940.034 ERROR            PET0 ~~~~~~~~~~~~~~~~~~~~ Concave Element Detected ~~~~~~~~~~~~~~~~~~~~
20170621 172940.034 ERROR            PET0   concave elem. id=683007
20170621 172940.034 ERROR            PET0
20170621 172940.034 ERROR            PET0   concave elem. coords (lon [-180 to 180], lat [-90 to 90]) (x,y,z)
20170621 172940.034 ERROR            PET0   -----------------------------------------------------------------
20170621 172940.034 ERROR            PET0     0  (-100.720581,  89.804306)  (-0.000635, -0.003356, 0.999994)
20170621 172940.034 ERROR            PET0     1  (-76.010437,  89.767494)  (0.000981, -0.003938, 0.999992)
20170621 172940.034 ERROR            PET0     2  (-133.219574,  89.857407)  (-0.001704, -0.001814, 0.999997)
20170621 172940.034 ERROR            PET0     3  (130.780121,  89.925125)  (-0.000854, 0.000990, 0.999999)
20170621 172940.034 ERROR            PET0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
20170621 172940.035 ERROR            PET0 ESMCI_Regrid_F.C:178 c_esmc_regrid_create() Invalid argument - Dst contains a concave cell
20170621 172940.035 ERROR            PET0 ESMCI_Regrid_F.C:434 c_esmc_regrid_create() Invalid argument Internal subroutine call returned Error
20170621 172940.035 ERROR            PET0 ESMF_Regrid.F90:321 ESMF_RegridStore Invalid argument - Internal subroutine call returned Error
20170621 172940.035 ERROR            PET0 ESMF_FieldRegrid.F90:1008 ESMF_FieldRegridStoreNX Invalid argument - Internal subroutine call returned Error
20170621 172940.035 ERROR            PET0 ESMF_RegridWeightGen.F90:1152 ESMF_RegridWeightGenFile Invalid argument - Internal subroutine call returned Error


 I have searched the archives regarding this error and have changed the longitudes of both the source and destination grids so that it goes from 0-360 instead of -180 to 180 as suggested,  but I still get the same error.  I have FTP’d the files in the following script.

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/esmf/ESMF_regridding.ncl"

begin
;---Data file containing source grid
    src_file = "/home/umalmonj/Jan_Apr_monthly_total_2d.nc"                    ;;---Change (likely)
    src_constants = "/global/scratch/umalmonj/WRF/juris/CTRL/2D/wrfout_conus_constants.nc"
    sfile    = addfile(src_file,"r")
    constants = addfile(src_constants,"r")

;---Get variable to regrid
prec_acc_nc = sfile->PREC_ACC_NC
var = dim_sum_n_Wrap(prec_acc_nc,0) ; this sums the variable for the 4 months
    src_lat  = constants->XLAT(0,:,:)                   ;;---Change (maybe)
    src_lon  = constants->XLONG(0,:,:)                 ;;---Change (maybe)
    var at lat2d = src_lat            ;;---Change (likely)
    src_lon = where(src_lon.lt.0,src_lon+360,src_lon)
    var at lon2d=src_lon

;---Data file containing destination grid
    dst_file = "/global/scratch/umalmonj/WRF/juris/CaPA/AccumulatedtotalPrecipitation.nc"                    ;;---Change (likely)
    dfile    = addfile(dst_file,"r")
    dst_lat  = dfile->gridlat_0                   ;;---Change (likely)
    dst_long  = dfile->gridlon_0                  ;;---Change (likely)
    dst_lon = where(dst_long.lt.0,dst_long+360,dst_long)

;---Set up regridding options
    Opt                   = True

;---"bilinear" is the default. "patch" and "conserve" are other options.
    Opt at InterpMethod      = "conserve"       ; might want to use conservative for precip

    Opt at WgtFileName       = "curv_to_curv.nc"  ; optional

    Opt at SrcGridLat        = src_lat           ; source grid
    Opt at SrcGridLon        = src_lon
    Opt at SrcRegional       = True              ;;--Change (maybe)
    Opt at SrcFileName  = src_file          ; optional, but good idea
    Opt at SrcGridMask         = where(.not.ismissing(var),1,0) ; Necessary if has
                                                           ; missing values.


    Opt at DstGridLat        = dst_lat             ; destination grid
    Opt at DstGridLon        = dst_lon
    Opt at DstRegional       = True              ;;--Change (maybe)
    Opt at DstGridMask = where(.not.ismissing(dst_lat).and.\
                          .not.ismissing(dst_lon),1,0) ; Necessary if lat/lon
                                                      ; has missing values.
; there is an attribute in the dest. file called "corners", but there are four
; diff. numbers for both the lon and lat variables
; just let NCL figure out the corners...
;    Opt at DstLLCorner = (/12.21208,217.1075/)
;    Opt at DstURCorner = (/79.82558,147.6248/)
    Opt at ForceOverwrite    = True
    Opt at PrintTimings      = True
    Opt at Debug             = True

    var_regrid = ESMF_regrid(var,Opt)     ; Do the regridding

    printVarSummary(var_regrid)


Any help would be greatly appreciated,

Juris


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