guidance for cdo ap2hl
Added by Sylvia Sullivan over 3 years ago
I am wondering how to use the ap2hl operator most accurately. I have output on 120 model levels where I increased resolution in the upper atmosphere relative using the sleve_nml. Then I used cdo ap2hl to remap this output onto 100 equally-spaced heights between 14 and 22 km but I do not have a sense of the accuracy of this vertical remapping. When I compare vertical profiles of simulated temperature to observations, the agreement is poor (differences ~ 10K), and I suspect the vertical regridding is the problem. So is there guidance for best using cdo ap2hl? more specifically..
(1) Do the heights given to ap2hl need to span the full range that approximately corresponds to the model levels (e.g. 0-30 km rather than 14-22 km)?
(2) Is there some way to use the vertical grid file, particularly variable z_ifc, to more accurately specify the heights given to ap2hl?
(3) Is it more accurate to directly output on height levels than to use cdo ap2hl on model-level output?
Many thanks,
Sylvia
Replies (2)
RE: guidance for cdo ap2hl - Added by Uwe Schulzweida over 3 years ago
Hello Sylvia,
The operator ap2hl calculates the height levels from the 3D air pressure. The height is converted to pressure using the following formula:
plevel = 101325*exp(hlevel/-7000)So this is only an approximation to calculate the height levels. It is more accurate to output the height levels directly, if this is possible.
In the next CDO version there will be the function gh2hl. It calculates the height levels from the geometric height (3D variable: geometric_height_at_full_level_center). It works similar to ap2hl, but it's not documented, yet.
You can find a preliminary version in the download area or under mistral:/home/mpim/m214003/local/bin/cdo.
Cheers,
Uwe
RE: guidance for cdo ap2hl - Added by Sylvia Sullivan over 3 years ago
Belated thanks for the reply, Uwe.