[gradsusr] Reading CMAQ netcdf files in GrADS

[Yaqiang Wang]

This is a guess solution.

In global attributes:
GDTYP = 2  means it is a lambert conformal projection;
P_GAM is standard longitude;   -97
P_ALP is south true latitude;  33
P_BET is north true latitude;  45
NCOLS is the size of the native grid in the x direction;  112
NROWS is the size of the native grid in the y direction;  79
XCELL is grid X increment in meters; 12000
YCELL is grid Y increment in meters; 12000

You can set YCENT(40) and  XCENT(-97) as reference latitude and
longitude respectively. The corresponding i and j of reference point
are 40 and 56.5.

So the PDEF line is: PDEF 112 79 LCCR 40 -97 40 56.6 33 45 -97 12000 12000

On Fri, Dec 16, 2011 at 4:40 AM, Huddleston, John
<Huddleston at cira.colostate.edu> wrote:
> Yes, I do. I am busy right now. I will get back to you. John
>
> ________________________________
> From: arlindo.dasilva at gmail.com [arlindo.dasilva at gmail.com] On Behalf Of
> Arlindo da Silva [dasilva at alum.mit.edu]
> Sent: Thursday, December 15, 2011 12:54 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
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>



-- 
*************************************************
Dr. Yaqiang Wang
Chinese Academy of Meteorological Sciences (CAMS)
46, Zhong-Guan-Cun South Avenue
Beijing, 100081
China

yaqiang.wang at gmail.com

http://www.meteothinker.com
**************************************************