[CF-metadata] Need for a new vertical coordinate definition:"Ocean generalized sigma coordinate"

From: Brian Eaton <eaton>
Date: Wed, 22 Dec 2004 15:05:56 -0700

On Wed, Dec 22, 2004 at 02:28:16PM -0500, Rich Signell wrote:
> >
> This seems to be agreeing with Brian's earlier statement that saving 4D
> fields of Z are allowed already, enabled by the "coordinates"
> attribute. Can one of you guys give an example of how this would be
> done? I have only seen the "coordinates" attribute used to specify
> two-dimensional longitude and latitude fields.

In general, the "coordinates" attribute is used to point to variables that
contain coordinate information that can't be represented by a coordinate
variable (note that the conventions always use the term coordinate variable
to mean a 1D variable whose name matches the name of its dimension). The
only restriction on an auxiliary coordinate variable are that its
dimensions are a subset (not necesarily proper) of the variable to which it
is attached (and of course there's an exceptional case for dealing with
label coordinates). So a simple example using a 4D z coordinate might look
like this:


dimensions:
  xc = 128 ;
  yc = 64 ;
  lev = 18 ;
  tim = 10 ;
variables:
  float T(tim,lev,yc,xc) ;
    T:long_name = "temperature" ;
    T:units = "K" ;
    T:coordinates = "z lon lat" ;
  float z(tim,lev,yc,xc)
    z:long_name = "height relative to ocean datum" ;
    z:units = "m" ;
    z:positive = "up" ;
  float xc(xc) ;
    xc:long_name = "x-coordinate in Cartesian system" ;
    xc:units = "m" ;
  float yc(yc) ;
    yc:long_name = "y-coordinate in Cartesian system" ;
    yc:units = "m" ;
  float lon(yc,xc) ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(yc,xc) ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
  float tim(tim) ;
    tim:long_name = "time" ;
    tim:units = "days since 1900-01-01" ;

An application knows that z is the vertical coordinate because it has the
"positive" attribute. It's not necessary for "lev" to have an associated
coordinate variable.

Brian
Received on Wed Dec 22 2004 - 15:05:56 GMT