Default specification of "User Defined" rates for WACCM-D

[cjeffery]

Apologies in advance to seasoned WACCM-D users... I assume that this is going to be a trivial question with an embarrassingly obvious solution.

I can't seem to figure out why cam/src/chemistry/pp_waccm_mad_mam4/chem_mech.in for the "User Defined" rates does not seem to agree with the rates stated in Verronen et al, "WACCM-D", 2016.

As a simple example, for the reaction
pir7 (273) Hp_4H2O + M -> H2O + M + Hp_3H2O rate = ** User defined ** (372)

Verronen (2016) states the rate is 0.015 * (300/T)**8.5 * exp(-9000/T)

I was expecting to find this rate in the chem_mech.in file or maybe another file like what mozart does with mo_setrxt.F90

But, unfortunately, despite my searching, I can't see to find where this rate is given in the code.

If someone could please point me to the correct chem_mech.in file, or the correct .F90 file, that would be greatly appreciated.

Apologies for a trivial question,
Chris Jeffery,
Los Alamos National Laboratory

 

[mmills]

There is a section for WACCM-D chemistry in components/cam/src/chemistry/mozart/mo_usrrxt.F90:

tp(:)             = 300._r8 * tinv(:)

...

if ( has_d_chem ) then

...

        call comp_exp( exp_fac, -9000._r8 * tinv, ncol )
        rxt(:,k,pir_ndx(7))  = (1.5e-1_r8 * tp(:)**9.1_r8) * exp_fac(:)

...

     endif

The index, pir_ndx=7, comes from the pir7 label in the chem_mech.in for this reaction. The rate in mo_usrrxt.F90 is therefore different from what you have written from Verronen (2016) in that the exponent is 9.1 instead of 8.5, and the pre-exponent is 1.5e-1 instead of 1.5e-2. It is possible that the factor of 10 in the pre-exponent is due to the units.