[CF-metadata] WRF staggered grids and vertical coordinates

From: John Caron <caron>
Date: Tue, 27 Jan 2004 16:47:18 -0700

Jonathan Gregory wrote:

>Dear John
>
>If I have understood this correctly, a CF-compliant file would have to include
>the variables latForU and lonForU, because it is mandatory to supply 2D lat and
>lon variables if lat and lon are not axes. These variables should be listed in
>the coordinates attribute of U, so the data of U can be located in latitude
>and longitude. Isn't it OK to do it in this straightforward way?
>
>There would then be no relation shown in the file between the two grids. My
>point is that this relation (the staggering) can be deduced by inspecting the
>coordinates. Given that this is the case, I don't see the need to introduce any
>new convention to indicate it explicitly, because this would be redundant.
>
>Best wishes
>
>Jonathan
>
>
>
Yes, if you are willing to explicitly include latForU and lonForU, you
wouldnt need the staggering.

To be explicit, for WRF, you will need 4 extra 3D variables (in
principle you might need as many 8 3D variables).

  float lat2(t, y, x_stag);
  float lon2(t, y, x_stag);

  float lat3(t, y_stag, x);
  float lon3(t, y_stag, x);

and 6 new 4D vertical coordinates (possibly only 3 if they dont need to
keep P and PB seperate) (in principle you might need as many as 16 4D
variables).

  float P2(t, z, y, x_stag);
  float PB2(t, z, y, x_stag);

  float P3(t, z, y_stag, x);
  float PB3(t, z, y_stag, x);

  float P4(t, z_stag, y, x);
  float PB4(t, z_stag, y, x);

It seems to me like a lot of overhead. But the real problem I think is
that it obscures the relationship of the coordinate systems, making it
more difficult to combine the staggered U,V,W fields into a vector wind.
Its quite a simple and common relationship, deducing it is non trivial
and likely wont be done automatically.

Im willing to tell the WRF people they need to do that, but if they dont
want to i guess they will have to create their own Convention.
Received on Tue Jan 27 2004 - 16:47:18 GMT