Extinction coefficient wavelength

[BEGUE Nelson]

Hi all,

I am using the CAM5-MAM7 model for my studies (FSTRATMAM7 compset) and now I have a doubt regarding the Extinction coefficient. Indeed, There is no information in the master list concerning the wavelength at which the Extinction coefficient is calculated. I would like to know the wavelength associated to the Extinction coefficient that the model gives from the output.

I really appreciate any help

Thanks
Nelson

 

[dbailey]

I am moving this to the CAM forum.

 

[brianpm]

It sounds like you are wondering about the aerosol extinction? There are several things that might be output as extinction, but I don't see any that appear as "extinction coefficient". For example, searching for outfld calls in the CAM src directory:

$grep -Iinr "outfld.*extinct" .
./physics/cam/modal_aer_opt.F90:1070:   call outfld('EXTINCTdn'//diag(list_idx),  extinct, pcols, lchnk)
./physics/cam/modal_aer_opt.F90:1086:   call outfld('EXTINCT'//diag(list_idx),  extinct, pcols, lchnk)
./physics/cam/modal_aer_opt.F90:1106:      call outfld('EXTINCTUVdn',     extinctuv,     pcols, lchnk)
./physics/cam/modal_aer_opt.F90:1107:      call outfld('EXTINCTNIRdn',    extinctnir,    pcols, lchnk)
./physics/cam/modal_aer_opt.F90:1161:      call outfld('EXTINCTUV',     extinctuv,     pcols, lchnk)
./physics/cam/modal_aer_opt.F90:1162:      call outfld('EXTINCTNIR',    extinctnir,    pcols, lchnk)

Assuming you're interested in aerosol extinction, I think the relevant code is in the file:
$CESM/components/cam/src/physics/cam/modal_aer_opt.F90

The variable tauxar is the layer extinction optical depth, and has dimensions of columns, levels, [shortwave, longwave] bands. For both shortwave and longwave, there's a loop where tauxar is computed like tauxar(i,k,ilw) = tauxar(i,k,ilw) + dopaer(i).

That dopaer is the "aerosol optical depth in layer". It is computed as dopaer(i) = pext(i)*mass(i,k) (shortwave) or dopaer(i) = pabs(i)*mass(i,k) (longwave).

Mass is just the layer mass.

pext is "parameterized specific extinction (m2/kg)" This is determined based on "cext" and some conditional logic that appears to depend on the aerosol size. "cext" appears to be derived from interpolation of the specific extinction... but I could be misinterpreting exactly what is going on there.

Please take a look at that code to see if it helps alleviate your doubt.

Maybe more useful is the reference at the top of that code:

Ghan, S. J., and Zaveri, R. A. (2007), Parameterization of optical properties for hydrated internally mixed aerosol, J. Geophys. Res., 112, D10201, doi:10.1029/2006JD007927.