Opened 6 months ago

Closed 3 months ago

#2585 closed help (fixed)

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!


Change History (4)

comment:1 Changed 3 months ago by willie

Hi Alison,

Sorry about the very late response. Nudging is discussed in the UM document 083 "Nudging the Unified Model" by Mohit Dalvi at the Met Office. I think your questions would be more ably answered by Mohit.


comment:2 Changed 3 months ago by admg26


No worries. You can close this ticket. Given all the other things I am doing, I think I am going to give up on the nudging.


comment:3 Changed 3 months ago by admg26

Last edited 3 months ago by admg26 (previous) (diff)

comment:4 Changed 3 months ago by willie

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