How to change the climate forcing with libIGCM

Author: S. Luyssaert
Last revision: 2020/28/02, A. Ducharne

This page is only relevant for ORCHIDEE offline runs.

The list of available climate forcing datasets is provided on ​https://forge.ipsl.fr/orchidee/wiki/Documentation/Forcings. This page also gives information on two drivers which are are available to run ORCHIDEE offline, and the required structure of the forcing files for each driver.

1. If you use the "standard" driver (orchidee_ol)

This driver can make use of all the shared atmospheric forcing datasets. The standard libIGCM configurations already offer the choice between two forcings:

• CRU-NCEP at 2° with ​OOL_SEC_STO_FG2
• WFDEI_GPCC/v1 at 0.5° with ​OOL_SEC_STO_FG3

If you want to change the default forcing of the above configurations, you must change the following line in COMP/orchidee_ol.card, like below to change CRU-NCEP with PGF

[BoundaryFiles]
#List=  (${R_IN}/SRF/METEO/CRU-NCEP/v5.3.2/twodeg/cruncep_twodeg_${year}.nc, forcing_file.nc)
List=  (${R_IN}/SRF/METEO/Princeton_GPCC/v1/1deg_3h/PGF_GPCC_1deg_3h__${year}.nc, forcing_file.nc)
ListNonDel= ()

A special case is if you want loop over certain years, usually for spin-up. To do so, you need to change "${year}" in the above line by "${CyclicYear}", and to define the nb of years that you "recycle" by adding the following lines in your config.card:

# Forcing data between 1901 and 1920
CyclicBegin=1901
CyclicEnd=1910

This example is taken from the standard configuration ​OOL_SEC_STO_FG1trans, designed to make a spin-up over 140 years by recycling A 10-yr period (but with time varying CO2 and vegetation maps). See How to loop over years with libIGCM for more information on how to cycle over forcing years.

2. If you use the "new" driver (orchideedriver)

An example with libIGCM is provided in the standard ORCHIDEE_OL configurations under the name OOL_SEC_STO_FG3nd, designed to use WFDEI_GPCC/v2, see ​https://forge.ipsl.fr/orchidee/browser/trunk/ORCHIDEE_OL/OOL_SEC_STO_FG3nd

The atmospheric forcing dataset is defined in ochidedriver.card, where you must insert a line for the simulated year, and two other lines for the previous and following years:

[BoundaryFiles]
List=  (${R_IN}/SRF/METEO/WFDEI_GPCC/v2/leap/WFDEI_GPCC_${year_m1}.nc, forcing_yearm1.nc),\
       (${R_IN}/SRF/METEO/WFDEI_GPCC/v2/leap/WFDEI_GPCC_${year}.nc, forcing_year.nc),\
       (${R_IN}/SRF/METEO/WFDEI_GPCC/v2/leap/WFDEI_GPCC_${year_p1}.nc, forcing_yearp1.nc)