Voir la source de HowTo: Run at different horizontal resolutions

== 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 <br />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):<br />day_step(max(iim,jjm)=N) ~ day_step(max(iim,jjm)=M) * N/M<br />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<br />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<br />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<br />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