WhatIs: The run.def input file

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The run.def input file and its format

The run.def file is a text file that is read at run time by LMDZ (and must thus be present in the same directory as the executable). It contains the values of various parameters that the user can specify (as "key = value", where "key" is a predefined keyword and "value" may be a real, an integer, a string or a logical) and modify depending on the specific simulation that is intended, e.g. the line:

nday = 30

means that when the GCM will run, it will set parameter nday (the number of days to run) to 30.

Any line starting with # is a comment, e.g.

# nday : length of the simulation (in days)

The order in which parameters are given in the run.def file is not important, except if a parameter value is given more than once (not recommended!), then it is the last occurrence that prevails.

*.def files included in run.def

The run.def file can include other files (based on the same format, lines containing "key = value" or comments) using the INCLUDEDEF keyword, e.g.:


In practice, because there are many parameters that one can set/change, it is good practice to separate related sets of parameters in separate files, e.g.:



  • parameters put in run.def are related to the simulations setup (number of days to run, if coupled to an ocean -NEMO- or surface model -ORCHIDEE-, etc.)
  • physiq.def contains flags related to the physical package parametrizations
  • gcm.def contains parameters related to the dynamics, horizontal grid and time stepping schemes
  • vert.def contains parameters related to the vertical grid
  • config.def contains parameters related to the physical package configuration (outputs specifications, orbital /ozone/ aerosol setup, etc.)
  • guide.def contains parameters related to nudging
  • orchidee.def/inca.def/reprobus.def contain parameters related to these models (if they are used)

Reference def files

Reference *.def files are provided in the LMDZ/DefLists directory