Opened 2 months ago

#2585 new help

vn10.9 vm. Nudging to model analysis output

Reported by: admg26 Owned by: um_support
Priority: normal Component: UKCA
Keywords: ukca, nudging Cc:
Platform: Monsoon2 UM Version: 10.9



Monsoon 2

All changes have been committed and the suite is not running

Model: UKCA vn10.9 /branches/dev/alisonming/vn10.9_nudging
(note that fcm_make_um > Sources > um_sources currently uses the version in my home directory)

Suite: u-ba153

I have been trying to get nudging to model output working (even though it is not officially supported). Here is what I have done.

1) I ran ~3 years of a clean UM/UKCA vn10.9 stable release (u-ax344) to generate the u, v and theta fields needed. I've used netcdf output every 6 hours on the model grid. This seems to work quite well.

2) I renamed all the netcdf files according to the format expected by the nudging code. The files can be found in


3) In /branches/dev/alisonming/vn10.9_nudging/src/atmosphere/nudging/, I have made a few code changes.

  • The grid resolution is changed in nudging_control.F90
  • The variables u, v and Theta are labelled as follows in the netcdf files.
u: STASH_m01s00i002
v: STASH_m01s00i003
Theta: STASH_m01s00i004

Variables names are redefined in the nudging code as needed.

  • In nudging_varloader_pressure_lev.F90, line 398 onwards, (Case(2)), the code converts the input temperature to theta. Since I am already reading in theta, I commented out the code that converts T to Theta.

3) In the suite u-ba153, um > UM Science Settings > Section 39 - Nudging, ndg_relax_uvalue and ndg_relax_value are set to 2.0e-5 (which is about half that recommended for 6 hourly data). The relaxation parameter for T is 0.

This version runs okay.

Problem 1: The output of u and v (archived on crum) don't look very close to what I am nudging to.

Problem 2: If I turn on the nudging to T with the same factor, the model blows up.

Any insight on this would be really appreciated.

Thank you!


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