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CO2 concentrations for RCP using RRTMG Scheme

T

Tanmoy

New member
I am currently running WRF (v4.5.2) simulations using bias-corrected CMIP5 data for RCP 4.5, 6.0 and 8.5. For the LW and SW scheme, I'm using the RRTMG scheme. From the user guide for WRF v4.5 (Welcome to WRF User’s Guide! — WRF Users Guide documentation), it is described that the CO2 concentration (in ppm) for the RRTMG scheme is given by the equation 280 + 90*exp(0.02*(year - 2000). However, will it not be the same for all RCP scenarios?? Also, within the namelist variable, we also have the option to use CAMtr_volume_mixing_ratio files, by using ghg_input = 1, but it s written that "default is SSP 2 with RCP 4.5 -> SSP245". So, is it going to be the same for all RCPs, if this option is turned on??

I'm also attaching an image with the difference within the values of CAMtr_volume_mixing_ratio.SSP245 (CAM-SSP245) and CAMtr_volume_mixing_ratio.SSP585 (CAM-SSP585) with respect to default formula from RRTMG scheme for CO2 concentrations.
1752651722440.png
 
Hello everyone,

Regarding the post above I have did some research and found that I was wrong in many instances. The methodology that I was following all along were not correct. So, I'm sharing the correct methodology to run climate simulations, for anyone who would face the same confusion and issue as me (This steps would be helpful if CAM LW and SW, RRTM, RRTMG LW and SW, RRTMG_fast LW and SW are being used):

1) Pre-process the climate data accordingly and create the metgrid output (met_em.d0*) files. (I'm not explaining it in details as technical documents and literature are available for this).

2) Link the met_em.d0* files from WPS directory to the WRF/run directory.

Code: 
ln -sf .../WPS/met_em.d0*  .../WRF/run/.

3) Edit the namelist.input file with the parameters. Also enable ghg_input within the &physics section as this will specify WRF model to use CAMtr_volume_mixing_ratio table to lookup for the values of CO2, N20, CH4, CFC-11 and CFC-12.

Code: 
&physics
 ghg_input = 1

4) Before running the real.exe program. Check if the correct CAMtr_volume_mixing_ratio table is being used for the simulation. Use the following command to check

Code: 
ls -ls CAMtr_volume_mixing_ratio

5) If the correct tables are not link, then,

For RCP scenarios (CMIP5 data):

Code: 
ln -sf CAMtr_volume_mixing_ratio.RCPx CAMtr_volume_mixing_ratio

For SSP scenarios (CMIP6 data):

Code: 
ln -sf CAMtr_volume_mixing_ratio.SSPx CAMtr_volume_mixing_ratio

Here, x represents the respective pathways.

6) After linking the tables, follow the steps required for normal WRF simulations.


Regarding the equation followed by RRTMG for CO2 (in ppm) = 280 + 90*exp(0.02*(year - 2000), it is to calculate the current year data when not enabling the ghg_input within &physics section. It is used in normal WRF simulations.


Note: All the above mentioned process and explaination are as per my findings and it could be wrong. So, if there is any mistake, please let me know.


Best Wishes,
Tanmoy Sen
 
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