Maarten,
I believe that what your colleague should do is add a bounds variable
for the pressure and reduce the number of elements in the hPa coordinate
variable by one. The bounds variable provides a lower and upper bound
for each layer, so it captures the value currently being stored in the
extra element of the hPa coordinate variable. The values stored in the
hPa coordinate variable can be the lower bound pressures, the upper
bound pressures, or any value in between the two (layer center
pressures, for example).
Grace and peace,
Jim
On 2/19/15 10:56 AM, Maarten Sneep wrote:
> Hi,
>
> A colleague has a question that left me without an answer. He writes:
>
> I have a 3D ozone field with n_lon elements in longitude direction,
> n_lat elements in latitude direction and n_layer elements in the
> vertical direction. The corresponding pressure grid has the same number
> of elements in longitude and latitude directions, but since the pressure
> is given on the layer interfaces, the number of elements in the vertical
> direction is one more than for my ozone field. The dimensions of both
> fields are therefore:
>
> O3 = [ n_lon, n_lat, n_layer ]
> hPa = [ n_lon, n_lat, n_layer+1 ]
>
> I have looked at the CF-conventions 1.6 document, but
>
> * it's not clear to me if I could use a "boundary variable" (section 7).
> * the pressure field is irregular, so a hybrid solution
> (P = hyb_a + hyb_b*P_surf) is not an option (appendix D).
>
> The question is how to write these fields as two datasets to a netCDF
> file in a CF-compliant way, so that it is clear that the pressure field
> gives the vertical extent of the layers of the ozone field. I have
> thought of the following options:
>
> * use 4 dimensions (lon, lat, layers, layers+1), but in that case, the
> ozone and pressure datasets have a different third coordinate, while
> they are obviously linked.
> * separate the pressure field into a surface pressure field and all
> higher levels, but then you have two dataset for the air pressure.
>
> What is the preferred way of storing data with a vertical coordinate
> that is specified on the interfaces rather than on the layers
> themselves, ans where a coordinate variable doesn't provide the detail
> we need?
>
> Kind regards,
>
> Maarten Sneep
--
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Received on Thu Feb 19 2015 - 10:22:16 GMT
