WACCMX NO chemistry

[fvitt]

Issue Type

Other (please describe below)

Issue Description

After the JPL19 chemistry updates in tag cam6_3_095 it was noted that the thermosphere was much warmer. The change in thermosphere temperature had been traced to the change in rate parameters for reaction

   N + O2  -> NO + O

From Hanli's notes:

NO chemistry: Had a discussion (Doug K., Dan, Nick, Hanli) on August 16 2024. I didn’t hear any objections to adopting Fernandez et al (1998) for N(4S)+O2, and Duff et al (2003) for N(2D)+O2. In addition, we have added the following to WACCM-X (Roble, 1995, included in TIEGCM):

   N2D + NO -> N2  + O
   N2D  -> N4S+hv
   N2D + e  -> N4S + e + 2.38 eV

They slightly reduce NO, but also slightly cool the thermosphere (10 K in the upper thermosphere), probably due to decrease of N2D and thus exothermic heating.

Will this change answers?

Yes

Will you be implementing this yourself?

Yes, but I will need some help

[fvitt]

Hanli's source mods are here:

/glade/u/home/liuh/cesm/waccmx_N_O2rate03_Duff_plus

where he has updates to these reactions (in chem_mech.in):

[agn2d]                N2D -> N                                                 ; 1.06e-5
[usr_N2D_O2,cph=177.51] N2D + O2  -> NO + O1D
[N2D_NO,cph=543.13]    N2D + NO  -> N2 + O                                      ; 7e-11
[usr_N2D_e,cph=229.61] N2D + e  -> N + e
[usr_N_O2,cph=133.75]  N + O2  -> NO + O                                        

And new code for user defined reaction rates (in mo_usrrxt.F90):

 !-----------------------------------------------------------------
 !       ... N + O2 -> NO + O  Abel Fernandez, A. Goumri, and Arthur Fontijn; 1998
 !-----------------------------------------------------------------
        if( usr_N_O2_ndx > 0 ) then
           call comp_exp( exp_fac, -2557._r8*tinv, ncol )
           rxt(:,k,usr_N_O2_ndx) = 2.0e-18_r8 * temp(:ncol,k)**2.15_r8 * exp_fac(:)
        end if
 
 !-----------------------------------------------------------------
 !       ... N2D + O2 -> NO + O  Duff, J.W., H. Dothe, and R. D. Sharma, 2003
 !-----------------------------------------------------------------
        if( usr_N2D_O2_ndx > 0 ) then
           rxt(:,k,usr_N2D_O2_ndx) = 6.2e-12_r8 * temp(:ncol,k)/300.0_r8
        end if       
 
 !-----------------------------------------------------------------
 !       ... N2D + e -> N + e  Roble, 1995
 !-----------------------------------------------------------------
        if( usr_N2D_e_ndx > 0 ) then
           rxt(:,k,usr_N2D_e_ndx) = 3.6e-10_r8 * sqrt(tempe(:ncol,k)/300.0_r8)
       end if

[fvitt]

@dkinnison @hanli-liu @dan800 @lkemmons @mijeong135

Hanli has indicated that these changes should be applied to WACCM as well as WACCMX. Are we okay with that? @lkemmons may need to provide new waccm mechanism files produced by the chemistry Cafe.

@hanli-liu, It looks like the N2D + e -> N + e reaction rate is dependent on electron temperature which is only available in WACCMX. Should we use neutral temperature for this reaction rate in WACCM?

[hanli-liu]

In the lower thermosphere it is ok to assume electron temperature and ion temperature are equal to neutral temperature. So I think in WACCM it's ok to set the temperature to neutral temperature.

[dan800]

@fvitt I expect these changes to not impact WACCM and agree with @hanli-liu that keeping WACCM and WACCM-X chemistry aligned is a good thing to do. Can a short term SD run be completed to make sure there are no adverse impacts in WACCM?

[fvitt]

I believe Jun is doing some testing for these changes in waccm. @jzhan166 or @dkinnison can comment on the testing.