Model Physics

The physics in the IFS model is approximated to an idealized relaxation towards a radiative-convective equilibrium profile.

Radiation and Convection are parameterized as :

where Q is the heating/cooling and k is the relaxation coefficient towards Radiative-Convective equilibrium (Held and Suarez, 1994; Wedi and Smolarkiewicz, 2009).

Configuration

The changes to the OpenIFS scripts and source code to run the model are as follows:

Changes to the Namelist variables:

It is important to correctly set the NAMELIST to configure the Held-Suarez testcase. The variables shown below need to be changed from normal forecast settings.

&NAEPHY
   LEPHYS=false,           ! turns off all physics
   LERADI=false,           ! ..and radiation

&NAMPHY
   LREASUR=false,          !  This may be needed to avoid reading surface fields.

&NAMFPC
   NFPPHY=0,   ! No surface fields in post-processing
               ! remove 133 from MFP3DF and MFP3DFP
   NFP3DFT=0,
   NFP3DFV=0,

Activate Held-Suarez testcase

To activate, change these variables in the model dynamical core and control setup namelists:

&NAMDYNCORE
   LDYNCORE=true,       ! the initial prognostic fields are set up in suspecg2
   LHELDSUAREZ=true,    ! the idealized simplified HS physics will be called under ec_phys_drv
   NTESTCASE=15,        ! or anything large enough in order to go to the "else" case in 
                        ! suspecg2: flat orog, uniform surface pressure and no wind
   RU00_DYN=0.,         ! no wind
   RT00_DYN=315., 
   RP00_DYN=100000.,    ! uniform pressure
   NOISEVOR=1,          ! some noise to break the symmetry

&NAMCT0
   N3DINI=7,          ! thermal profile to start HS case in suspecg2
   NFRPOS = 1,        ! post-processing output frequency; set to every timestep
   NPOSTS(0)=1,       ! number of outputs
   NPOSTS(1)= xxx,    ! the first output (array index '1') will be at time step xxx,
                      ! to test you can try xxx= last time step of your run (NSTOP)).

&NAMMCC
   LMCCEC = false,       ! turn off updating of the boundary conditions,
   LMCCIEC = false,      ! .. and their interpolation in time from the climatology files

For more details about the action of these namelist variables, please see the namelist file in 'ifs/namelist' and it's corresponding module in 'ifs/module' (e.g. ifs/namelist/namct0.nam.h and ifs/module/yomct0.F90).

Fields and Files needed

You can use any initial files as initial conditions. The prognostic variables will be overwritten. The orography is flat. There is no initial mean wind, only perturbation in the vorticity to break the symmetry.

Changes to code :

Edit suphy.F90

Change line containing

USE YOMDYNCORE, ONLY: LAQUA, LDYNCORE

to

USE YOMDYNCORE, ONLY: LAQUA, LDYNCORE, LHELDSUAREZ

and line containing

Edit code in suspecg2.F90 (under K3DINI=7 in suspecg2) 

LLDYN=LDYNCORE.AND.NOT.(LAQUA.OR.LHELDSUAREZ)

to
LLDYN=LDYNCORE.AND.NOT.LAQUA

ZPRESHX(0)=VAH(0)+VBH(0)*ZVP00
DO JLEV=NFLEVG,1,-1
ZPRESHX(JLEV)=VAH(JLEV)+VBH(JLEV)*ZVP00
ENDDO

DO JLEV=1,NFLEVG
DO JWORD=1,NGPTOT
ZPRS=0.5_JPRB*(ZPRESHX(JLEV)+ZPRESHX(JLEV-1))
ZTLAT = 315._JPRB- RDELTA_T*SIN(GELAT(JWORD))**2
ZTALT = RDELTA_THETA * LOG(ZPRS/ZVP00)*COS(GELAT(JWORD))**2
ZT(JWORD,JLEV) = MAX ( 200._JPRB,&
& (ZTLAT -ZTALT)*(ZPRS/ZVP00)**(RD/RCPD) )
ENDDO
ENDDO

References

Held I, Suarez M. 1994. A proposal for the intercomparison of the dynamical cores of atmospheric general circulation models. Bull. Am. Meteorol. Soc. 73: 1825–1830.

Wedi, N. P. and Smolarkiewicz, P. K. (2009), A framework for testing global non-hydrostatic models. Q.J.R. Meteorol. Soc., 135: 469–484. doi:10.1002/qj.377

Model fields from experiment

Fig. 1 : Zonal mean wind field from a 1500 day long model run for the Held-Suarez testcase. The model fields are averaged for the last 1000 days.

Fig. 2 : Zonal mean temperature field from a 1500 day long model run for the Held-Suarez testcase. The model fields are averaged for the last 1000 days.