Re: [ferret_users] vertical coordinates

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Patrick
Yes, you can have vertical axes with different senses, positive upwards 
or or downwards.

If you are creating the netcdf file, then adding this attribute to the 
axis will ensure that it is treated as a depth axis.

               sigma:positive = "down" ;

Or if defining an axis in Ferret, just add the qualifier /DEPTH to the 
definition of the axis when it is to be positive in the downward direction.

Ansley

Brockmann Patrick wrote:
> Hi all,
>
> How to store two vertical coordinates in different order in a netCDF 
> file ?
>
> I have a 3D variable XYZ where Z is a sigma vertical coordinate
> (from 1 at ground to 0 at the top of the atmosphere).
> The netcdf variable is stored with k=1 ground, k=11 top of the atm
>
> Now, if I define sigma as
> sigma = 0.989417, 0.9596861, 0.9065547, 0.8214576, 0.7043947, 0.5639313,
>    0.4149028, 0.2744395, 0.1573766, 0.07227948, 0.01914804 ;
> So with a decreasing order
> when I open the file with ferret, the axis is reordered and variable 
> is then available with
> an increase axis.
> Thus I get
> yes? shade var[k=1] representing top of the atmosphere. It should be 
> ground.
>
> The problem could be a simple convention to accept but it is more 
> complicated to explain
> if you have 2 vertical axis such as an altitude (with an increasing 
> order) and a sigma (with a descreasing order).
> In first case k=1 will represent ground, k=11 in the second case.
> k=1 should reprensent the ground in both case.
>
> So is there a way to store in a netcdf file, one vertical axis in a 
> descreasing order and one in
> an increasing order ?
>
> Patrick