Opened 11 years ago

Closed 10 years ago

#338 closed help (fixed)

UM vn 4.5 hybrid sigma pressure coefficients ?

Reported by: alindfor Owned by: lois
Component: UM Model Keywords: hybrid sigma pressure, coefficients
Cc: mjm@… Platform:
UM Version: 4.5



I am running some experiments with HadAM3 (vn 4.5.1) and would need to translate the model vertical coordinate, given as hybrid sigma pressure, into normal pressure.

To do this, one would need the hybrid A and B coefficients as indicated by the equation beneath:

p = a(k)*p0 + b(k)*ps

p=normal pressure
a,b=hybrid coefficients
k=model level
ps=surface pressure
p0=reference pressure (usually 1013hPa)

I searched the NCAS web and helpdesk tickets but did not find information on where to find these hybrid coefficients. Do you know how to retrieve them?

Thankful for all help.


Change History (2)

comment:1 Changed 11 years ago by lois

  • Owner changed from um_support to lois
  • Status changed from new to assigned

Hello Anders,

These coefficients will be in the header of the UM output files. The full description of the UM file header is described in document F3 in
You could use a tool like uminfo (avaialbel on HECToR)
to look at what is in the UM header.

But if you want to convert UM model levels to pressure levels then there are already many ways to do this so my advice is to look at the options before you write your own routine! The first place I would look for vn4.5 is MDIAG, which is described and downloadable here
I also expect the UKMO library should be able to do this, Simon Tett is an author so he should know, otherwise the documentation is here

I hope that this is the what you need, ask agian if not


comment:2 Changed 10 years ago by lois

  • Resolution set to fixed
  • Status changed from assigned to closed
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