GRIB "slabs"

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: GRIB "slabs"
• From: Jonathan Gregory <jonathan.gregory@xxxxxxxxxxxxx>
• Date: Fri, 04 Oct 2002 08:45:13 +0100

Dear Tim and others

> Then there is the issue of data on "slab" levels (eg average temperature
> between 1000 and 850 hPa etc). This can be dealt with using more than one
> co-ordinate variable for the vertical dimension, or a two dimensional
> coordinate variable.

The CF method for describing this is to provide the pressure boundaries of
the slab as boundary coordinate variables. The choice of level coordinate
values is arbitrary, but it is helpful to provide coordinates which would be
suitable for plotting, such as the midpoints of the layers.

dimensions:
  lon=96;
  lat=72;
  pressure=3;
variables:
  float temperature(pressure,lat,lon);
  float pressure(pressure);
    pressure:bounds="pressure_bnds";
    pressure:units="hPa";
  float pressure_bnds(pressure,2);
data:
  pressure=925, 725, 500;
  pressure_bnds=1000,850, 850,600, 600,400;

for layers 1000-850, 850-600 and 600-400 hPa.

Cheers

Jonathan Gregory  jonathan.gregory@xxxxxxxxxxxxx
phone +44 1344 854542  fax +44 1344 854898
Hadley Centre, Met Office, London Road, Bracknell, Berks., UK. RG12 2SY