[Met_help] Input data for point-stat tool

[John Halley Gotway]

Valerio,

I do think that it would be reasonable to massage your NetCDF files into a format that METv1.1 would read.  However, METv1.1 is only compatible with a rather rigid format of NetCDF at this point.  For
the next release of MET, version 2.0, we're planning to support a more general format of NetCDF.

Currently, MET expects gridded NetCDF data to abide by the following conventions:

(1) dimensions named "lat" and "lon" define the dimension of the data.
(2) variables have only two dimensions, "lat" and "lon".
(3) variables are named using the GRIB code abbreviation for the GRIB field they represent and are in the units prescribed by that GRIB code.  For example, a variable containing accumulated
precipitation would be named "APCP" (GRIB code abbreviation) and its units would be millimeters.
(4) several variable attributes are required to define the initialization, valid, and accumulation (if applicable) times.
(5) global attributes defining the grid on which the data resides must be defined.

The definition of the grid in (5) is necessary to perform conversions between lat/lon and grid x/y.

I've attached a sample output file from PCP-Combine.  This example contains data on a lat/lon grid - which I'm guessing is the projection your data is on.  The attached file that ends in ".dump" is
just a dump of the NetCDF header.  In that file, please note the following:

(1) The "lat" and "lon" dimensions are defined.
(2) The variable named APCP contains accumulated precipitation in mm.  The GRIB codes and corresponding abbreviations are defined here: http://www.nco.ncep.noaa.gov/pmb/docs/on388/table2.html
(3) The APCP variable contains the several attributes, but only the following are actually read by the code: level, init_time_ut, valid_time_ut, and accum_time (if not applicable, just set to 0).
The "_ut" is for unixtime, or seconds since January 1, 1970.
(4) Global attributes defining the projectsion:
:Projection = "LatLon" ;
:lat_ll_deg = "25.063000 degrees_north" ;
:lon_ll_deg = "-124.938000 degrees_east" ;
:delta_lat_deg = "0.125000 degrees" ;
:delta_lon_deg = "0.125000 degrees" ;
:Nlat = "224 grid_points" ;
:Nlon = "464 grid_points" ;
Here you'll just insert your grid definition info.

Hope that helps, and feel free to write with more questions about this.

John Halley-Gotway
johnhg at ucar.edu


capecchi wrote:
> Dear met_help,
> I'm currently involved in WRF verification issues for a biometeorological
> service in Italy.
> I'm interested in point-stat tools but I have, as input forecast data,
> NetCDF files derived and post-elaborated from WRF GRIB1 output.
> I read from MET User Guide that I'm supposed to provide as input data only
> GRIB1 files or NetCDF format
> that is output from the Pcp-Combine tool; I'm wondering if my NetCDF file
> format are like the Pcp-Combine tool's format
> (I'm attaching one as sample) or if you can suggest me some NetCDF to GRIB1
> converter tools (like cdo, nco, or...)
> Thanks in advance for any help you can give me, regards, Valerio Capecchi
> 
> **************************************************************************
> 
> Valerio Capecchi
> 
> --------------------------------------------------------------------------
> Interdepartemental Centre of Bioclimatology - University of Florence
> Piazzale delle Cascine 18
> 50144 Firenze. Italia
> Tel: +39 0553288257
> Fax: +39 055332472
> 
> WEB http://www.unifi.it/cib
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> EDIFICIO D
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> fax  +39 055  444083
> 
> http://www.lamma.rete.toscana.it/bioclima
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netcdf nam.20070330.ncep110 {
dimensions:
	lat = 224 ;
	lon = 464 ;
variables:
	float lat(lat, lon) ;
		lat:units = "degrees_north" ;
		lat:long_name = "Latitude" ;
		lat:_FillValue = -9999.f ;
	float lon(lat, lon) ;
		lon:units = "degrees_east" ;
		lon:long_name = "Longitude" ;
		lon:_FillValue = -9999.f ;
	float APCP(lat, lon) ;
		APCP:grib_code = 61 ;
		APCP:units = "kg/m^2" ;
		APCP:long_name = "Total precipitation" ;
		APCP:level = "SFC" ;
		APCP:_FillValue = -9999.f ;
		APCP:init_time = "20070330_000000" ;
		APCP:init_time_ut = 1175212800 ;
		APCP:valid_time = "20070331_120000" ;
		APCP:valid_time_ut = 1175342400 ;
		APCP:accum_time = "6 hours" ;

// global attributes:
		:FileOrigins = "File /home/johnhg/nam.20070330.ncep110.nc generated 20080923_163157 UTC on host billiken by the PCP-Combine tool" ;
		:RunCommand = "Addition: /home/johnhg/nam.20070330.ncep110.grb with accumulation of 3 hours plus /home/johnhg/nam.20070330.ncep110.grb with accumulation of 3 hours." ;
		:Projection = "LatLon" ;
		:lat_ll_deg = "25.063000 degrees_north" ;
		:lon_ll_deg = "-124.938000 degrees_east" ;
		:delta_lat_deg = "0.125000 degrees" ;
		:delta_lon_deg = "0.125000 degrees" ;
		:Nlat = "224 grid_points" ;
		:Nlon = "464 grid_points" ;
}