GAMMAS archived output

[HazelMooney]

Describe your problem or question:

Using CLM4.5.
gamma_sm = 1.0
In the version of CLM I am using, gamma_sm is coded to = 1.0, so drought stress response is turned off. Then I plot archived GAMMAS data, rather than 1 the data is constant at 0.89
Does this reflect the application of a normalisation coefficient in output history for GAMMA variables?
Would this be the canopy coefficient?

Thank you

 

[slevis]

I'm not familiar, so I looked directly in the code and found this variable list. I did not check whether this is different in clm4.5 versus clm5 versus post-clm5, but I hope it helps:

    real(r8) :: gamma                   ! activity factor (accounting for light, T, age, LAI conditions)
    real(r8) :: gamma_p                 ! activity factor for PPFD
    real(r8) :: gamma_l                 ! activity factor for PPFD & LAI
    real(r8) :: gamma_t                 ! activity factor for temperature
    real(r8) :: gamma_a                 ! activity factor for leaf age
    real(r8) :: gamma_sm                ! activity factor for soil moisture
    real(r8) :: gamma_c                 ! activity factor for CO2 (only isoprene)

You may also find useful documentation in the corresponding Technote section:

2.30. Biogenic Volatile Organic Compounds (BVOCs) — ctsm CTSM master documentation

 

[slevis]

Looking at the code some more I found:

          ! Impact of soil moisture on isoprene emission
          if (megan_use_gamma_sm) then
             gamma_sm = get_gamma_SM(btran(p))
          else
             gamma_sm = 1._r8
          end if

...so it seems gamma_sm is not necessarily always 1.

 

[slevis]

Though keep in mind that I'm looking at the latest development code, and your version may look a bit (or very) different.

 

[Matteo_Mastro]

Hi, I've been dealing with gamma_sm in CLM5, in our version is set to 1 as well as follows:

          ! Activity factor for soil moisture: all species (commented out for now)
          !          gamma_sm = get_gamma_SM(clayfrac(p), sandfrac(p), h2osoi_vol(c,:), h2osoi_ice(c,:), &
          !               col%dz(c,:), soilstate_inst%bsw_col(c,:), watsat(c,:), sucsat(c,:), root_depth(patch%itype(p)))
          gamma_sm = 1.0_r8

If values are <1, to my understanding, is because you should account for actual land_frac in some specific areas, like lakes.
Hope it helps.