[gradsusr] Reading CMAQ netcdf files in GrADS

[Huddleston, John]

Arlindo

I am attaching a utility I wrote that will create a gridded polygon shapefile. I ran it with the commands:

grid2shp -1 984000 -2 '-384000' -x 112 -y 79 -s 12000 -o cmaqgrid

It created a shapefile called cmaqgrid which I then projected to WGS84 and then determined the extent of the grid in WGS84 space. The image is attached.

It is for North America Lambert Conformal Conic; so, users in other parts of the world should remove the PRJ file and copy in the appropriate projection file.

My first  guess would be

dset ^file.ncf
dtype netcdf
title Vertically integrated atmos chem/aerosol vbles
pdef 112  79 lcc 32.95 -75.4 1 1 33 45 -97.00 12000 12000
undef -9999
xdef 112 linear -84.49    0.168
ydef  79 linear  32.95    0.15
zdef 1 linear 1 1
tdef 48 linear 00:00Z01jul2011 1dy
vars 1
AOD=>aod  1 t,z,y,x Aerosol Optical Depth
endvars

However, once I see the image in GrADS, I would tweak the numbers. The utility was statically built with MinGW. The source and Makefile is included for Linux users.

John Huddleston



From: arlindo.dasilva at gmail.com [mailto:arlindo.dasilva at gmail.com] On Behalf Of Arlindo da Silva
Sent: Thursday, December 15, 2011 12:55 PM
To: Huddleston, John
Cc: GrADS Users Forum
Subject: Reading CMAQ netcdf files in GrADS

Hi John,

    Something tells me that you might know this. I have these CMAQ netcdf files from the DISCOVER-AQ campaign (see ncdump below). Do you happen to know the PDEF line that goes with these? I have the grid metrics in a separate file, I could always write some code to remap these, but if grads can do it on the fly it would be good enough for the exploratory data analysis that I need to perform.

   Thanks,

       Arlindo

-----

netcdf UMA_AOD {
dimensions:
            TSTEP = UNLIMITED ; // (48 currently)
            DATE-TIME = 2 ;
            LAY = 1 ;
            VAR = 1 ;
            ROW = 79 ;
            COL = 112 ;
variables:
            int TFLAG(TSTEP, VAR, DATE-TIME) ;
                        TFLAG:units = "<YYYYDDD,HHMMSS>" ;
                        TFLAG:long_name = "TFLAG           " ;
                        TFLAG:var_desc = "Timestep-valid flags:  (1) YYYYDDD or (2) HHMMSS                                " ;
            float AOD(TSTEP, LAY, ROW, COL) ;
                        AOD:long_name = "AOD             " ;
                        AOD:units = "unitless        " ;
                        AOD:var_desc = "AOD by Mie in VIS file                                                          " ;

// global attributes:
                        :IOAPI_VERSION = "$Id: @(#) ioapi library version 3.0 $                                           " ;
                        :EXEC_ID = "????????????????                                                                " ;
                        :FTYPE = 1 ;
                        :CDATE = 2011182 ;
                        :CTIME = 164809 ;
                        :WDATE = 2011182 ;
                        :WTIME = 164809 ;
                        :SDATE = 2011182 ;
                        :STIME = 130000 ;
                        :TSTEP = 10000 ;
                        :NTHIK = 1 ;
                        :NCOLS = 112 ;
                        :NROWS = 79 ;
                        :NLAYS = 1 ;
                        :NVARS = 1 ;
                        :GDTYP = 2 ;
                        :P_ALP = 33. ;
                        :P_BET = 45. ;
                        :P_GAM = -97. ;
                        :XCENT = -97. ;
                        :YCENT = 40. ;
                        :XORIG = 984000. ;
                        :YORIG = -384000. ;
                        :XCELL = 12000. ;
                        :YCELL = 12000. ;
                        :VGTYP = 1 ;
                        :VGTOP = 200.f ;
                        :VGLVLS = 1.f, 0.9959855f ;
                        :GDNAM = "AQF_CONUS_5x    " ;
                        :UPNAM = "setup           " ;
                        :VAR-LIST = "AOD             " ;
                        :FILEDESC = "hourly 1-layer cross-point Visibility Information

--
Arlindo da Silva
dasilva at alum.mit.edu<mailto:dasilva at alum.mit.edu>
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