Lfairhead le 23 janvier 2021 à 18:10

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Lfairhead : Page créée avec « == What one needs to know to be able to run at a different model resolution == This page contains some information and tips to help you setup a successful run at a differ... »

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== What one needs to know to be able to run at a different model resolution ==

This page contains some information and tips to help you setup a successful run at a different (horizontal) resolution

# You will need input and forcing files at the sought resolution
# You will need to adapt the (dynamics) time step As explained in the LMDZ Tutorial courses "dynamics: ..." (e.g. here) there is a simple rule of thumb to know to what extent you need to change the "day_step" (number of dynamical steps per day): day_step(max(iim,jjm)=N) ~ day_step(max(iim,jjm)=M) * N/M Check what the reference values (in the gcm.def.* files in the LMDZ/Deflist directory) are for a given N are to evaluate what is needed for M Example: currently, in gcm.def_144x142 i.e. for iim=144,jjm=142 , day_step=672 so to run at twice that resolution you should halve the time steps and thus use day_step=1944 (and adapt iphysiq accordingly, i.e. double it here)
#You might need to change the dissipation constants This is more tricky and less linear than for the time steps; in practice some trial and error will be needed but overall you will need to increase dissipation (i.e. lower le teta* constants)
# At present, physics need to be run at a timestep of 15 minutes so you need to adjust iphysiq according to the formula iphysiq = 900 * day_step / 86400

As guidelines, and starting values, you could use or extrapolate from those given in the table below:

{|class="wikitable"
! Resolution
! day_step
! tetagdiv
! tetagrot
! tetatemp
! iphysiq
|-
|96 x 95 (CMIP5) || 480 ( = 180 s) || 5400. || 5400. || 5400. || 5 ( = 15 min)
|-
|144 x 142 (CMIP6) || 672 ( ~ 128 s) || 3600. || 21600. || 10800. || 7 ( = 15 min)
|-
|256 x 256 (QUEST) || 1344 (~ 64 s) || 1200. || 7800. || 3800. || 14 ( = 15 min)
|}

If you have values for other resolutions that work well for you, don't hesitate to contact us so that we can include them in the table

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HowTo: Run at different horizontal resolutions - Historique des versions

Lfairhead le 23 janvier 2021 à 18:10

Lfairhead : Page créée avec « == What one needs to know to be able to run at a different model resolution == This page contains some information and tips to help you setup a successful run at a differ... »