Gray atmosphere run

[ReiChemke]

Hello,

I want to run CESM1 in its fully coupled configuration, but I want to have the absorption coefficient of CO2 independent of wavenumber. Is that even possible?

Thanks!

Rei

 

[islas]

Hi Rei,

I'm not sure how this would be done. The gray radiation scheme is currently a stand-alone simpler physics package at ./components/cam/src/physics/simple/frierson* in tags cesm2_3_alpha16a and later. Using that is probably not what you would want if you want to have a fully coupled configuration with realistic land since it would be a big undertaking to change that scheme to provide all the fields needed for the coupler. It's probably simpler to try to override what RRTMG does in term of wavenumber-dependent CO2 absorption. I think this would require advice from someone with more expertise in the radiation scheme (@brianpm ?). But my guess would be you'd want to modify something in radae.F90. Perhaps you'd want to modify the subroutine "trcab" within that which is where it looks like the trace gas absorptivities are set. Maybe somehow you can change the CO2 ones to be wavenumber independent in there.

Isla

 

[brianpm]

Oof. I'm not sure what a good approach would be. I agree that modifying how RRTMG works is probably easier than trying to move the gray radiation scheme into the CAM physics. I wonder if you could intercept the optical properties in CAM/src/physics/rrtmg/aer_src/rrtmg_lw_rad.f90 ... I see this for example:

!  Calculate the gaseous optical depths and Planck fractions for
!  each longwave spectral band.

      call taumol(nlay, pavel, wx, coldry, &
                  laytrop, jp, jt, jt1, planklay, planklev, plankbnd, &
                  colh2o, colco2, colo3, coln2o, colco, colch4, colo2, &
                  colbrd, fac00, fac01, fac10, fac11, &
                  rat_h2oco2, rat_h2oco2_1, rat_h2oo3, rat_h2oo3_1, &
                  rat_h2on2o, rat_h2on2o_1, rat_h2och4, rat_h2och4_1, &
                  rat_n2oco2, rat_n2oco2_1, rat_o3co2, rat_o3co2_1, &
                  selffac, selffrac, indself, forfac, forfrac, indfor, &
                  minorfrac, scaleminor, scaleminorn2, indminor, &
                  fracs, taug)

Without diving in more, I'm not sure whether CO2 can be totally isolated from other gases because of the correlated-k approach in RRTMG. Getting some input from radiation experts would be a good idea on this one.

 

[ReiChemke]

Thanks, Isla and Brian, for the detailed and quick responses! I will take a look at the rrtmg_lw_rad.F90 and radae.F90 files, and will let you know if I find something useful. Brian, if you have a radiation expert in mind who could provide some input on this issue, please let me know.

Thanks again!