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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
creating 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, and NCONF=202 is the vorticity equation model.

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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2

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).

The model will require requires the vorticity, divergence, ln(Ps) (contains the geopotential of the free surface) and orography when starting from real fields.

The Euler advection scheme can only be run on a regular Gaussian grid however (see below for example) .whereas the semi-Lagrangian advection is normally run on the reduced Gaussian grid.

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title	T255 shallow-water test case

A test for the shallow-water model at spectral horizontal resolution T255 is available from the OpenIFS ftp site to try. Note: Only licensed institutes are provided with the userid/password to access the OpenIFS ftp site.

Code Block
ftp ftp.ecmwf.int cd case_studies/shallow_water get t255_swtest.tar.gz

This example comes with initial files, namelist and job script. The namelist is configured to run the semi-Lagrangian advection. A few lines in the job script may need altering for your local setup.

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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.

grib_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 Note that the initial fields themselves are not used with the idealized configurations. The initial files are there to correctly set the grid, hence stl1 is used in this example to get for the initial gridpoint file because its values will be overwritten and not used to initialize the model fields.

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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The following MARS request will retrieve ERA-Interim (T255) vorticity, divergence and geopotential fields together with a gridpoint field that can be used to create the initial ICMSH and ICMGG files in a similar way to the above method.

Change the model level if required.

Code Block

title	Retrieve spectral fields from MARS for shallow-water model
collapse	true

retrieve,
  class="ei",
  type=an,
  stream=oper,
  date=20100212,
  time=12,
  step=0,
  expver=1,
  param=VOR/D/Z,
  levelist=1,
  levtype=ml,
  target="sh_ml"

Code Block

title	Retrieve gridpoint field from MARS for shallow-water model
collapse	true

 retrieve,
  class="ei",
  type=an,
  stream=oper,
  date=20091227,
  time=12,
  step=0,
  expver=1,
  param=139,
  levelist=off,
  levtype=sfc,
  target="sfc_gg"

and then set the appropriate ICMSH and ICMGG file names and experiment number as shown in the previous example.

Namelists

It is extremely important to correctly set the NAMELIST to configure the shallow-water model correctly.

Two examples are given here, one for semi-Lagrangian advection, the other for Euler advection. Euler advection must use a regular gaussian grid. It will not work with a reduced grid. The users user is free to alter some parameters such as the timestep, filtering etc.

The examples below show the variables to change from normal forecast settings.

Warning

If using the Euler method, make sure a smaller suitable choice of timestep compared to the semi-Lagrangian setup is used. Also, ensure the Asselin time-filter is on.

Code Block

title	semi-Lagrangian advection namelist
collapse	true

code

Code Block

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

!
!  Shallow-water model with Euler steppingsemi-Lagrangian advection.
!
&NAMDYN
 TSTEP=300.0, The variables below must be set in order to      correctly configure
! reduce timestepthe for Euler stepping
 REPS1=0.01,                ! turn on Asselin time-filtering coefficient
 REPS2=0.01,
 LHDIFFM=.false.,   shallow-water model.
!  Other variables (if present) can be left as-is.

For namelist : NAMDYN
 HDIRVOR=1.e15,        !  horizontal diffusion on / offparameters
 LSETTLSHDIRDIV=1.false.e15,        ! see code !for extrapolations in SL schemefurther description
 LSETTLSTHDIRSP=.false., 1.e15,
 LHDIFFM=true,
 NDIFFACT=6,
 LSETTLS=true,         ! ditto
/
&NAMCT0
 NCONF=201 ensure SL scheme is enabled
 LSETTLST=true,
 SITR=350.,            ! reference temperature
 REFGEO=78452.0,  ! model configuration: 201 =  ! reference geopotential for shallow-water (see yomct0.F90)
 LSLAG=.false. model

For namelist: NAMCT0
 NFPOS=0,              ! turndisable offfullpos semipost-lagrangian schemeprocessing
 LTWOTLN2DINI=.false.1,             ! disable two-time-level SL scheme.
 LRFRIC=.false.2D initialisation switch
 LTWOTL=true,          ! enable !two-time turnlevel offSL Rayleigh frictionscheme
 LSLPHY=.false.,            ! turn off splitSl time-stepphysics physicsoption
 LVERTFELSPRT=.false.,           ! turn off 'virtual verticaltemperature' finiteas elementspectral schemevariable
 N2DININFRHIS=110,            ! frequency of results output
 NUNDEFLD=0, ! initialise  1 = Haurwitz wave, 2 = real fields
 LSPRT=.false.,             ! if T temperature is 'virtual temperature'
 LFPOS=false ! make sure uninitialised variables are all set to zero

For namelist: NAMARG
 NCONF=201,            ! select shallow-water ! turn off fullpos diagnostics, does not work with SW
 N3DINI=0,      configuration
 LSLAG=true,           ! enable SL scheme
 UTSTEP=1800.0,         ! model timestep ! no 3D initialisation
 NSTOP=600(resolution dependent)

For namelist: NAMPAR0
 NPROC=1,              ! only use !1 no.MPI of steps to run
/
&process in 2-D.
 NPRGPEW=1,            ! required for 2-D configurations

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
/
&NAMDIM
  NUNDEFLDLRFRIC=0false,         ! turn off Rayleigh friction

Code Block

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

! make sure uninitialised variables are all set to zero
/

Gotchas

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 does not go through the usual code path (if NCONF=1) and uses a older code to output.

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).

Info

title	Make sure FULLPOS is off

Related to the above, the shallow-water model does not use the FULLPOS part of the model for output (namelist NAMFPC) normally used when NCONF=1 (3D primitive equation model).

Make sure FULLPOS is off by setting:

Code Block
&NAMCT0 LFPOS=false,

in the fort.4 namelist file.

Info

title	Undefined fields initialized to zero

Make sure that all variables in the model are initialized to zero. The SW model can output fields that are not used.

To do this set the namelist variable:

Code Block
&NAMDIM NUNDEFLD=0,

Plotting

data is spectral

Code notes

Other switches are used internally:

! LR2D : 2D shallow water or vorticity model

  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 SW model

For namelist: NAMCT0
 LRFRIC=false,         ! 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
 LSLAG=true,           ! enable SL scheme
 LSLPHY=false,         ! turn off Sl physics option
 LSPRT=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

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. Users will usually see a failure from the grib_api library (typically grib_set_real8_array).

Info

title	Make sure FULLPOS is off

Related to the above, the shallow-water model does not use the FULLPOS part of the model for output (namelist NAMFPC) normally used when NCONF=1 (3D primitive equation model).

Make sure FULLPOS is off by setting:

Code Block
&NAMCT0 LFPOS=false,

in the fort.4 namelist file.

Info

title	Undefined fields initialized to zero

Make sure that all variables in the model are initialized to zero. The SW model can output fields that are not used.

To do this set the namelist variable:

Code Block
&NAMDIM NUNDEFLD=0,

Plotting

The shallow-water model outputs fields only in spectral space, only ICMSH output files are generated. To plot the fields they will first need converting to gridpoint form.

The figure at the top of this page was generated using 'Metview'. The 'GRIB Filter' icon was used:

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.

Anchor
codechanges
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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.
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

Code notes

Other switches related to the shallow-water model setup are used internally: LR2D & LRSHW.! LRSHW : 2D shallow water model

The IFS starts with a huge amount of setup. The setup setups are mainly done under the routines called su0yoma and su0yomb (all setup routines starts by start with 'su'). They are themselves called by the first layer of the model cnt0. Then, the following layers cnt1, cnt2, cnt3 are called (forget about them for now) and finally, we reach cnt4 which contains the time loop. The routine which does one time step is called stepo (there are many different way of calling it as you could see in the "jungle" routine cnt4).

A time step starts in spectral space (all prognostic fields are in spectral space).

A standard time step (corresponding to time t) goes like thisas: the spectral fields (which are at time t) are transformed to GP space (Legendre invinverse transform. followed by Fourier invinverse transform.). Then the grid point computations start. At the end of the GP computation, the prognostic fields for next time step t+dt contain the explicit guess + half of the semi-implicit (SI) correction. This guess is transformed back to spectral space where we solve the SI problem to compute the other half of the SI correction. End of time step ....is reached. At the beginning of next time step, the new spectral fields will then be the new fields for the new time t...

In the current routine suspecb, you can chose choose between idealized cases or read one level of a grib flie 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 spc2 spc with the 2D configurations calling spc2.

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

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