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OpenIFS includes a number of idealised configurations. In this article we explain how to configure the model for an 'aqua-planet' simulation. An aqua-planet is one that includes no topography and no land. It's a highly simplified representation of Earth but useful for a number of studies.

Further information

See for example, the PCMDI Aqua-Planet website or the University of Reading Aqua-Planet experiment website.

Step-by-step guide

Configuring OpenIFS for an aqua-planet simulation only requires appropriate changes to the model namelist. No changes to the model code are required.

  1. Changes to the NAMDYNCORE namelist. This controls the configuration for the model's dynamical core.
    Edit the fort.4 file (containing the input model namelist) and make sure the settings are as below. You may find this namelist is blank in your file as this namelist does not need altering for normal forecasts, in which case add the following:

    Namelist settings for dynamical core : NAMDYNCORE
    &NAMDYNCORE
LDYNCORE=true,       ! switches on idealized planet configurations.
LAQUA=true,          ! switches on idealized aqua planet.
MSSTSCHEME=4,        ! controls SST choice for aquaplanet (see ifs/module/yomdyncore.F90 for more details).
RPLRADI=1,           ! Earth radius factor; 1 for normal earth
RCORIOI=1,           ! Coriolis acceleration factor; 1 for normal Earth
NOISEVOR=1,          ! if 1 add initial noise in vorticity
/



  2. Ensure that the mass conservation correction is enabled to prevent mass drifting in long integrations.
    Edit namelist NAMDYN in the fort.4 file and add (or change) this variable:

    Ensure mass conservation : NAMDYN
    &NAMDYN
LMASCOR=true,        ! if true, apply mass correction.
/

    Edit namelist NAMCT0 in fort.4 to set the mass correction frequency:

    Ensure mass conservation: NAMCT0
    &NAMCT0
NFRMASSCON=24,      ! frequency of mass conversation fixups (time-steps)



  3. There are normally no changes required to the NAEPHY namelist. This controls the behaviour of the model physics and is included here for completeness.
    If necessary edit the fort.4 file (containing the input model namelist) and make sure the settings are as below.

    Namelist settings for model physics: NAEPHY
    &NAEPHY
LEPHYS=true,     ! switch the full ECMWF physics package on/off.
LEVDIF=true,     ! turn on/off the vertical diffusion scheme.
LESURF=true,     ! turn on/off the interface surface processes.
LECOND=true,     ! turn on/off the large-scale condensation processes.
LECUMF=true,     ! turn on/off the mass-flux cumulus convection.
LEPCLD=true,     ! turn on/off the prognostic cloud scheme.
LEEVAP=true,     ! turn on/off the evaporation of precipitation
LEVGEN=true,     ! turn on/off Van Genuchten hydrology (with soil type field)
LESSRO=true,     ! turn on/off orographic (VIC-type) runoff
LECURR=false,    ! if true, ocean current boundary condition is used.
LEGWDG=true,     ! turn on/off gravity wave drag.
LEGWWMS=true,    ! turn on/off the Warner-McIntyre-Scinocca non-orographic gravity wave drag scheme.
LEOZOC=true,     ! turn on/off the climatological ozone.
LEQNGT=true,     ! turn on/off the negative humidity fixer.
LERADI=true,     ! turn on/off the radiation scheme.
LERADS=true,     ! turn on/off the interactive surface radiative properties.
LESICE=true,     ! turn on/off the interactive sea-ice processes.
LEO3CH=false,    ! turn on/off the ozone chemistry (for prognostic ozone).
LEDCLD=true,     ! turn on/off the diagnostic cloud scheme.
LDUCTDIA=false,  ! turn on/off computation and archiving of ducting diagnostics.
LWCOU=false,     ! turn on/off coupled wave model (n.b. always off for OpenIFS model).
LWCOU2W=false,   ! turn on/off two-way interaction with the wave model (n.b. always off for OpenIFS model).
/

    Note in this example, the model physics is turned on (enabled). By setting LEPHYS=false, the model would run an aqua-planet with the physics switched off.
    For more information on these switches see the relevant modules in the model code: yoephy.F90 and yoewcou.F90.

  4. Other settings of interest.
    The above is all that's necessary to enable aqua-planet in the model. However, you may want to experiment with other model options.

    Initialisation
    &NAMCT0
N3DINI=0,  ! normally 0 to initialise the model from a real atmosphere, but see ifs/module/yomdyncore.F90 for other possibilities.

Please note that aqua-planet and other idealized configurations are a research tool and therefore may change between model versions.

For further assistance with idealised configurations of OpenIFS, please contact: openifs-support@ecmwf.int.

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