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Double CO2 experiment?

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I would like to run a double-CO2 simulation in WRF version 4.0.2. From what I gathered, the CO2 amount is set as a constant in the LW radiation module ( i am using ra_lw_physics = 4 and ra_sw_physics = 4). Am I correct that in order to double the CO2 amount, all I need to do is to change the CO2 constant (default is 379 ppmv) in module_ra_rrtmg_lw.F to the value I want? Are there other modules that I should tinker with?

Thanks very much for advising!
To run the double CO2 experiment, you need to modify both the module_ra_rrtmg_sw.F and module_ra_rrtmg_lw.F. In these two codes, you will find the line below :

data co2 / 379.e-6 /

(line 10215 in module_ra_rrtmg_sw.F and line 11716 in module_ra_rrtmg_lw.F).

I am also experimenting with CO2 changes. Chapter 5, Section 2.1 of the User's Guide states:

RRTMG scheme (4): A newer version of RRTM. It includes the MCICA method of random cloud overlap. For major trace gases, CO2=379e-6 (valid for 2005), N2O=319e-9, CH4=1774e-9. See section 2.3 for the time-varying option. Since V4.2, the CO2 value is replaced by a function of the year: CO2(ppm) = 280 + 90 exp(0.02*(year-2000)), which has about 4% of error for 1920s and 1960s, and about 1 % after year 2000 when compared to observed values.

Am I right in thinking that this is the line that needs to be changed in module_ra_rrtmg_sw.F (line 10329) and module_ra_rrtmg_lw.F (line 11893) in the most recent version of the code?

! Annual function for co2 in WRF v4.2
co2 = (280. + 90.*exp(0.02*(yr-2000)))*1.e-6

Hi rddixon,

You are right about the CO2 changes. Such changes should be made if you run WRFV4.2 and newer version.

The changes I suggested in the previous posts are for older version of WRF (WRFV4.1 and older versions).