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OpenIFS includes a number of idealised configurations. In this article we explain how to:

setup and run a shallow-water model
set idealized (e.g. Rossby-Haurwitz wave) or real single level field.
enable semi-Lagrangian or Euler timestepping
create the initial fields

Configuration

The shallow-water (SW) configuration is one of several that exist in OpenIFS (and IFS). The configuration is set by the variable NCONF in namelist NAMCT0 (see yomct0.F90). The normal 3D primitive equation configuration uses NCONF=1.

For the 2D SW configuration, NCONF=201.

The 2D SW model can be initialised in various idealized states or from a single level real field. This initialisation is controlled by another variable, N2DINI in the namelist NAMCT0.

As these idealized configurations are primarily research tools, they may vary from one major model release to another and not all options found in the code are guaranteed to work.

N2DINI = 1 in NAMCT0 will initialise the Rossby-Haurwitz wave case (Williamson et al, J. Comput. Phys., 1992).
N2DINI = 3 in NAMCT0 will initialise the SW model with real fields read from GRIB.

The reader is invited to look in suspecb.F90 to see what other initialisation options as possible (N2DINI=42 does not work).

Although there is mention of NCONF=202 (the Vorticity Equation configuration) in the code, this does not work.

Warning

title	Warning: code changes required for OpenIFS 38r1

OpenIFS 38r1 (all versions) require code changes in order to be able to run with N2DINI=3 (initialized with real fields). Please see Code Changes below.

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Getting data

The SW model still needs the ICMSH (spectral fields) and ICMGG (gridpoint) files to correctly start. In the idealized case, these are read solely to set the model's spectral and gridpoint resolution and the model will overwrite the initial state read from file (see the code in suspecb.F90).

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title	Creating initial fields from existing GRIB files

The GRIB files from an existing experiment can also be used to create initial files for the shallow-water model. In the following example, the initial files from the T21 test case distributed with the OpenIFS tarfile are used.

Code Block

title	Extract starting files from existing experiment
collapse	true

#  Extract a single level (level 1) for the shallow water model
#  and change the experiment id in the file.

expid="epc8"
newid="sw01"

grib_copy -w level=1,shortName=vo ICMSHepc8INITICMSH${expid}INIT tmp
grib_set -s experimentVersionNumber=epc9"$newid" -w experimentVersionNumber=epc8"$expid" tmp vo.grb

grib_copy -w level=1,shortName=d  ICMSHepc8INITICMSH${expid}INIT tmp
grib_set -s experimentVersionNumber=epc9"$newid" -w experimentVersionNumber=epc8"$expid" tmp d.grb

grib_copy -w shortName=z          ICMSHepc8INIT ICMSH${expid}INIT z.grb

#  Combine the 3 files to form the spectral initial file
cat vo.grb d.grb z.grb  > ICMSHepc9INIT

#  ICMSH${newid}INIT

#  Create gridpoint file (stl1 is used in this example)
grib_copy -w shortName=stl1 ICMGGepc8INITICMGG${expid}INIT gg.grb
grib_set -s experimentVersionNumber=epc9${newid} -w experimentVersionNumber=epc8${expid} gg.grb ICMGGepc9INITICMGG${newid}INIT

For idealized configurations the field in the initial data file is used correctly set the grid. The actual values are overwritten by the model code to set the idealized start. Hence stl1 is used in this example to for the initial gridpoint file because its values will be overwritten and not used to initialize the model fields.

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If you have access to the MARS archive at ECMWF then an example of how to retrieve single level fields for use with the SW model is:

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Code Block

title	semi-Lagrangian advection namelist (43r3)
collapse	true

!  Shallow-water model with semi-Lagrangian advection.
!  The variables below must be set in order to correctly configure
!  the shallow-water model.
!  Other variables (if present) can be left as-is.

For namelist : NAMDYN
 HDIRVOR=1.e15,        ! horizontal diffusion parameters
 HDIRDIV=1.e15,        ! see code for further description
 HDIRSP=1.e15,
 LHDIFFM=true,
 NDIFFACT=6,
 TSTEP=1800.0,         ! model timestep (resolution dependent)
 LSETTLS=true,         ! ensure SL scheme is enabled
 LSETTLST=true,
 SITR=350.,            ! reference temperature
 REFGEO=78452.0,       ! reference geopotential for SWshallow-water model

For namelist: NAMCT0
 LRFRICNFPOS=false0,         ! turn of Rayleigh friction
 LFPOS=false,          ! disable fullpos post-processing
 N2DINI=1,             ! 2D initialisation switch
 NCONF=201,            ! select shallow-water configuration
 LTWOTL=true,          ! enable two-time level SL scheme
 LSLAGLSLPHY=truefalse,         ! turn !off enableSl SLphysics schemeoption
 LSLPHYLSPRT=false,          ! turn off Sl physics option
 LSPRT=false, 'virtual temperature' as spectral variable
 NFRHIS=10,         ! turn off 'virtual! temperature'frequency asof spectralresults variableoutput
 LFRHISNUNDEFLD=100,            ! frequency of results outputmake sure uninitialised variables are all set to zero

For namelist: NAEPHYNAMARG
 LEPHYSNCONF=false201,            ! turnselect off ECMWF Physics package (master switch)
 LERADI=falseshallow-water configuration
 LSLAG=true,           ! turnenable offSL radiation scheme

For namelist: NAMDYNA
 LGRADSP=.false., UTSTEP=1800.0,         ! disablemodel de-aliasing the pressure gradient termtimestep (resolution dependent)

For namelist: NAMDIMNAMPAR0
  NUNDEFLDNPROC=01,              ! makeonly sureuse uninitialised1 variablesMPI areprocess all set to zero

Code Block

title	Euler advection namelist
collapse	true

!  Shallow-water model with Euler advection.
!  The variables below must be set in order to correctly configure
!  the shallow-water model.
!  Other variables (if present) can be left as-is.

For namelist: NAMDYN
 TSTEP=300.0in 2-D.
 NPRGPEW=1,            ! required for 2-D configurations

For namelist: NAEPHY
 LEPHYS=false,           ! turn off ECMWF !Physics reducepackage timestep for Euler stepping(master switch)
 REPS1LERADI=0.01false,                ! turn onoff Asselin time-filtering coefficient
 REPS2=0.01,
 LHDIFFMradiation scheme

For namelist: NAMDYNA
 LGRADSP=.false.,           ! disable horizontalde-aliasing diffusionthe onpressure /gradient offterm
 LSETTLSLRFRIC=.false.,           ! extrapolationsturn inoff SLRayleigh friction

Code Block

title	semi-Lagrangian advection namelist (40r1)
collapse	true

!  Shallow-water model with semi-Lagrangian advection.
!  The variables below must be set in order to correctly configure
!  the shallow-water model.
!  Other variables (if present) can be left as-is.

For namelist : NAMDYN
 HDIRVOR=1.e15,scheme
 LSETTLST=.false.,          ! ditto

For namelist: NAMCT0
 NCONF=201,                 ! model configuration: 201 = shallow-water (see yomct0.F90)
 LSLAG=.false.,             ! turnhorizontal off semi-lagrangian schemediffusion parameters
 LTWOTLHDIRDIV=1.false.e15,        ! see code for !further disable two-time-level SL scheme.
 LRFRIC=.false.description
 HDIRSP=1.e15,
 LHDIFFM=true,
 NDIFFACT=6,
 TSTEP=1800.0,            ! turnmodel offtimestep Rayleigh(resolution frictiondependent)
 LSLPHYLSETTLS=.false.true,         ! ensure SL !scheme turnis off split time-step physics
 LVERTFE=.falseenabled
 LSETTLST=true,
 SITR=350.,            ! turn off vertical finite element schemereference temperature
 N2DINIREFGEO=178452.0,       ! reference geopotential for SW model

For namelist: NAMCT0
 LRFRIC=false,   ! initialise  1 = Haurwitz wave,! 2turn =of realRayleigh fieldsfriction
 LSPRTLFPOS=.false.,             ! ifdisable T temperature is 'virtual temperature'
 LFPOS=falsefullpos post-processing
 N2DINI=1,             ! 2D !initialisation turn off fullpos diagnostics, does not work with SW
 N3DINI=0,switch
 NCONF=201,            ! select shallow-water configuration
 LTWOTL=true,          ! no 3D initialisation
 NSTOP=600 enable two-time level SL scheme
 LSLAG=true,           ! enable SL scheme
 LSLPHY=false,         ! no.turn ofoff stepsSl tophysics runoption
 NFRHISLSPRT=10,false,          ! turn off 'virtual temperature' as spectral variable
 NFRHIS=10,            ! frequency of results output

For namelist: NAEPHY
 LEPHYS=false,           ! turn off ECMWF Physics package (master switch)
 LERADI=false,           ! turn off radiation scheme

For namelist: NAMDYNA
 LGRADSP=.false.,        ! disable de-aliasing the pressure gradient term

For namelist: NAMDIM
  NUNDEFLD=0,            ! make sure uninitialised variables are all set to zero

Also, add a blank namelist to fort.4 for the idealized cases. Some configurations selected using N2DINI will expect to find a namelist NAMSWE.

Code Block
&NAMSWE /

Gotchas

There are a number of issues that can cause the model to fail. Please make sure:

Code Block

title	Euler advection namelist
collapse	true

!  Shallow-water model with Euler advection.
!  The variables below must be set in order to correctly configure
!  the shallow-water model.
!  Other variables (if present) can be left as-is.

For namelist: NAMDYN
 TSTEP=300.0,               ! reduce timestep for Euler stepping
 REPS1=0.01,                ! turn on Asselin time-filtering coefficient
 REPS2=0.01,
 LHDIFFM=.false.,           !  horizontal diffusion on / off
 LSETTLS=.false.,           ! extrapolations in SL scheme
 LSETTLST=.false.,          ! ditto

For namelist: NAMCT0
 NCONF=201,                 ! model configuration: 201 = shallow-water (see yomct0.F90)
 LSLAG=.false.,             ! turn off semi-lagrangian scheme
 LTWOTL=.false.,            ! disable two-time-level SL scheme.
 LRFRIC=.false.,            ! turn off Rayleigh friction
 LSLPHY=.false.,            ! turn off split time-step physics
 LVERTFE=.false.,           ! turn off vertical finite element scheme
 N2DINI=1,                  ! initialise  1 = Haurwitz wave, 2 = real fields
 LSPRT=.false.,             ! if T temperature is 'virtual temperature'
 LFPOS=false,               ! turn off fullpos diagnostics, does not work with SW
 N3DINI=0,                  ! no 3D initialisation
 NSTOP=600,                 ! no. of steps to run
 NFRHIS=10,                 ! frequency of results output

For namelist: NAEPHY
 LEPHYS=false,           ! turn off ECMWF Physics package (master switch)
 LERADI=false,           ! turn off radiation scheme

For namelist: NAMDYNA
 LGRADSP=.false.,        ! disable de-aliasing the pressure gradient term

For namelist: NAMDIM
  NUNDEFLD=0,            ! make sure uninitialised variables are all set to zero

Also, add a blank namelist to fort.4 for the idealized cases. Some configurations selected using N2DINI will expect to find a namelist NAMSWE.

Code Block
&NAMSWE /

Gotchas

There are a number of issues that can cause the model to fail. Please make sure:

Info

title	GRIB_GRIBEX_MODE_ON

The model will fail unless the environment variable:

export GRIB_GRIBEX_MODE_ON=1

is set in the job script. This is because the shallow-water code uses a different set of subroutines for output and does not go through the usual code path for 3D forecasts (if NCONF=1).

Otherwise the model will crash at the first output attempt.

Info

title	GRIB_GRIBEX_MODE_ON

The model will fail unless the environment variable:

export GRIB_GRIBEX_MODE_ON=1

is set in the job script. This is because the shallow-water code uses a different set of subroutines for output and does not go through the usual code path for 3D forecasts (if NCONF=1).

Otherwise the model will crash at the first output attempt. Users will usually see a failure from the grib_api library (typically grib_set_real8_array).

...

Code Block

title	Metview GRIB filter icon example for plotting spectral data

READ,
    DATA       = 'ICMSHepc9+000594',
    INTERPOLATION = LINEAR FIT,
    GRID       = 5/5,
    GAUSSIAN   = REGULAR

For more information about Metview please see Using Metview with OpenIFS or contact openifs-support@ecmwf.int.

Code changes

Warning

if running OpenIFS 38r1 (all versions), code changes are required before using the shallow water option initialized with real fields (N2DINI=3 & NCONF=201).

Changes are required because the shallow-water code uses older code for reading GRIB data that was omitted from OpenIFS before the shallow-water option was made available.

Required steps to enable shallow-water code option

REGULAR

For more information about Metview please see Using Metview with OpenIFS or contact openifs-support@ecmwf.int.

Anchor
codechanges
codechanges
Code changes

Warning

if running OpenIFS 38r1 (all versions), code changes are required before using the shallow water option initialized with real fields (N2DINI=3 & NCONF=201).

Changes are required because the shallow-water code uses older code for reading GRIB data that was omitted from OpenIFS before the shallow-water option was made available.

Required steps to enable shallow-water code option

Download the OpenIFS 38r1 shallow-water replacement source tarball: openifs38r1_sw_newsrc.tgz
(this file is also available on the OpenIFS ftp site)
Make a backup copy of the OpenIFS source code in the directory where the OpenIFS model files were unpacked:
Code Block
cp -r src src.orig

Delete some files that will be replaced:

Code Block
rm src/openifs/dummy/decops2.f90 rm src/openifs/dummy/gribex.f90 rm src/openifs/emos/pbio/emosnum.F rm src/openifs/emos/pbio/fortint.h rm -r src/openifs/emos/gribex # delete entire 'gribex' director

Unpack the tarfile downloaded above. This will create a new directory 'src/openifs/emos/gribex'.
Make sure the tarfile is in the top level directory that contains 'src':
Code Block
# Make sure openifs38r1_sw_newsrc.tgz is in the directory that contains 'src. tar xzvf openifs38r1_sw_newsrc.tgz
Verify that 'src/openifs/emos/gribex' exists and contains source code.
Download the OpenIFS 38r1 shallow-water replacement source tarball: openifs38r1_sw_newsrc.tgz
(this file is also available on the OpenIFS ftp site)
Make a backup copy of the OpenIFS source code in the directory where the OpenIFS model files were unpacked:
Code Block
cp -r src src.orig
Delete some files that will be replaced:
Code Blockrm src/openifs/dummy/decops2.f90 rm src/openifs/dummy/gribex.f90 rm src/openifs/emos/pbio/emosnum.F rm src/openifs/emos/pbio/fortint.h rm -r src/openifs/emos/gribex # delete entire 'gribex' director
To compile the code if using GNU/gfortran, it may be necessary to enable the use of cray pointers.
Edit 'make/oifs.cfg' and change:
Code Block
oifs.prop{fc} = $OIFS_FC
to:
Code Block
oifs.prop{fc} = $OIFS_FC -fcray-pointer

...

In the routine suspecb, you can choose between idealized cases or read one level of a grib file (N2DINI is the key for this choice). suspecb is called at cnt3 level - the first part of the GP computations are done from a routine called CPG2 which is a very simplified version of the 3D GP computation, the other (lagged, mostly SL computation) are done in CPG2_LAG Both cpg2 and cpg2_lag are called by the driver routine gp_model which is also the driver routine of the 3D GP computation. - the spectral computation are done under spc with the 2D configurations calling spc2.

Info
with thanks to Nils Wedi and Sylvie Malardel, ECMWF.

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