Initial state and surface conditions

Usually, we want to set up an initial state of the atmopshere from data which is not on the grid we want to use for the gcm. Also, the surface conditions we want to impose are usually not on the grid of the gcm and the time sampling may not be what we need for the gcm. So we have a separate program, called ce0l (ce0l stands for "création état 0 limites"), which does customized space and time interpolation, producing an initial state and surface conditions ready to be ingested by the gcm. ce0l assumes that the initial atmospheric state you provide is on pressure levels and that the surface conditions are montly mean values, for one full calendar year. Note that, vertically, ce0l regrids from pressure levels to model (hybrid sigma-pressure) levels.

Beside regridding, ce0l has the task of setting up initial values for internal state variables of physical parameterisations. Finally, the parameterisation of the effect of sub-grid scale orography on atmospheric flow has parameters which are computed by the program ce0l from high-resolution (higher than the resolution of the gcm) data.

The source code for program ce0l is part of LMDZ. Compile the program ce0l with the same tools you use to compile the gcm. So, for example:

makelmdz_fcm -d 144x142x79 ... ce0l

instead of:

makelmdz_fcm -d 144x142x79 ... gcm

Run ce0l with the same getin files than those you want for gcm.

ce0l creates two files for initial state: start.nc for the dynamics part of gcm, startphy.nc for the physics part of gcm. ce0l creates one file for one year of boundary conditions: limit.nc.

The content of limit.nc and startphy.nc is not convenient for visualization because the geographical positions are not on a longitude-latitude grid. You can use our scripts to see the content of limit.nc or startphy.nc.

Here is a diagram showing the input and output files of program ce0l:

Note that it is possible to create a file limit.nc using SST, sea-ice fraction and land-sea mask from a coupled ocean-atmosphere, that is NEMO-LMDZ, run. See documentation IGCMG.