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Section

The source code changes to run OpenIFS 43r3 in nudged configuration are under version control in the OpenIFS Git repository in branch feature/nudging.

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In order to control the model's nudgint nudging configuration the following source code files are relevant:

  • namrlx.nam.h  –  the namelist block which appears in the fort.4 file. These variables allow to customise the model's nudging behaviour without recompiling the model source code.
  • yomrlx.F90  – definition of in this module the  variables in the namelist block are defined.
  • surlx.F90  – this is the setup routine for the namelist variables, including initialisation of the variableswhich includes their initialisation with default values and consistency checks.
  • updrlxref.F90  – this subroutine updates the reference fields for the relaxation.

The code in the nudging branch of OpenIFS 43r3 nudging branch differs from that in IFS insofar that the variables CLPSHRLX and CLPGGRLX have been added to the namelist. These two variables allow to specify the location of the directory with the forcing files on the file system.  If these are not set then the model will expect to find the forcing files in the experiment directory.

To enable nudging the namelist NAMRLX will need to be included in the namelist file fort.4. The values below show one possible configuration reflecting standard settings. As described previously, the question of which variables should be relaxed to the external analysis, the model grid domain where relaxation is applied, and the tightness of the nudging, controlled by the relaxation coefficient, are very much dependent on the objective of the model experiment.

Code Block
titleDefault settings in the NAMRLX namelist
    &NAMRLX
      LRLXG=true,    ! Master switch to enable nudging
      LRLXVO=true,   ! vorticity
      LRLXDI=true,   ! divergence
      LRLXTE=true,   ! temperature
      LRLXQ=true,    ! specific humidity
      LRLXQL=true,   ! liquid water
      LRLXQI=true,   ! ice water
      LRLXQC=true,   ! cloud fraction
      LRLXLP=true,   ! log surf pressure
      LRLXO3=true,   ! ozone
      XRLXVO=0.5,    ! relaxation coefficient
      XRLXDI=0.5,
      XRLXTE=0.5,
      XRLXQ=0.5,
      XRLXO3=0.5,
      XRLXLP=0.5,
      ALATRLX1=90,   ! latitude domain for nudging
      ALATRLX2=-90,
      ALONRLX1=0,    ! longitude domain for nudging
      ALONRLX2=360,
      AXRLX=-0.5,    ! smoothing parameter for lon, lat and in the vertical
      AYRLX=-0.5,
      AZRLX=1.0,
      NRLXLMIN=1,    ! top model level for nudging
      NRLXLMAX=60,   ! bottom model level for nudging
      CLPSHRLX='../rlxml/sh/',  ! relative path to spectral forcing files
      CLPGGRLX='../rlxml/gg/',  ! relative path to gridpoint forcing files
    /

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