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There is a small error in OpenIFS 38r1 in the code that sets the SST for the 3KW1 case of Neale & Hoskins. This code incorrectly sets the latitudinal width to 30o instead of 60o.
This error is corrected in later versions of OpenIFS.
The required code changes are small. In the file: src/ifs/phys_ec/gp_sstaqua.F90, find the lines 233:238:
The use of RPHID needs to be corrected to 60o:
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Configuring OpenIFS for an aqua-planet simulation requires appropriate changes to:
In the sections below, we walk through the namelist options explaining how to configure the aqua-planet.
The model namelist NAMDYNCORE
controls the configuration for idealized cases, including the aqua-planet.
To enable the aqua-planet 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 it does not need altering for normal forecasts, in which case add the following:
&NAMDYNCORE LDYNCORE=true, ! switches on idealized planet configurations. LAQUA=true, ! switches on idealized aqua planet. MSSTSCHEME=1, ! controls SST choice for aquaplanet following Neale & Hoskins (2000a) (see ifs/module/yomdyncore.F90 for more details). ! 1 = Control; 2 = Peaked; 3 = Flat; 4 = Qobs; 5 = Control5N; 6 = 1KEQ, chi=1.0; ! 7 = 3KEQ, chi=3.0, width=15 deg; 8 = 3KW1, chi=3.0, width=30 deg; 9 = const. SST / |
The SST modifications can be further changed using the variables defined in ifs/phys_ec/gp_sstaqua.F90
:
RLAMBDA0 : Longitude of maximum SST anomaly RLAMBDAD, RPHID: Half width in long/lat of SST anomaly RCHI : Maximum magnitude of SST anomaly |
For more details of the SST configuration, see: ifs/phys_ec/gp_sstaqua.F90
and refer to the Neale & Hoskins (2001) publication.
If idealized initial states are used (see below) rather than real initial fields, it can be useful to introduce some initial noise into the vorticity field. For starting from analysed fields this is not needed:
&NAMDYNCORE NOISEVOR=1, ! if 1 add initial noise in vorticity |
Enable mass conservation correction to prevent mass drifting in long integrations.
Edit namelist NAMDYN in the fort.4 file and add (or change) this variable:
&NAMDYN LMASCOR=true, ! if true, apply mass correction. |
Edit namelist NAMCT0 in fort.4 to set the mass correction frequency:
&NAMCT0 NFRMASSCON=24, ! frequency of mass conversation fixups (time-steps) |
Aqua-planet simulations normally use the full model physics. By setting LEPHYS=false
, the model would run an aqua-planet with all the physics switched off.
For aqua-planet simulations the prognostic ozone scheme and transport of ozone should be disabled using these logicals in their namelists:
&NAMGFL YO3_NL%LGP=false, ! turns off transport of prognostic ozone &NAEPHY LEO3CH=false, ! turns off prognostic ozone & uses climatological ozone instead |
The physics namelist NAEPHY
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.
Note in this example, the model physics is turned on (enabled).
For more information on these switches see the relevant modules in the model code: yoephy.F90
(and yoewcou.F90 for the coupling to the wave model)
.
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OpenIFS (and IFS) can be initialized either with real fields or idealized starting conditions.This is controlled both by the namelist switch N3DINI
and by the code in the model.
It is crucial that the orography, surface pressure and land-sea-mask are set correctly (see below).
&NAMCT0 N3DINI=0, ! normally 0 to initialise the model from a real atmosphere, but see ifs/module/yomdyncore.F90 for other possibilities. |
In order to correctly run the aqua-planet in OpenIFS (and IFS), it is important that the orography field in the model is set to zero to ensure a flat surface. The surface pressure must also be adjusted to be consistent with the flat orography and the land-sea-mask in the model set to zero to indicate all sea-points.
There are two ways in which this can be achieved; either take an existing set of model initial files (the ICM*INI* files) and interpolate pressure to the surface, or run the model and adjust the orography and pressure whilst the model is running to prevent a sudden 'shock'.
ECMWF took part in the 2012 Dynamical Core Model Intercomparison Project (DCMIP). More information can be found here: https://www.earthsystemcog.org/projects/dcmip-2012/
OpenIFS would like to thank Sylvie Malardel (ECMWF) and Peter Bechtold (ECMWF) for their assistance in preparing this material