# tendency in physical process

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#### cibaouc

##### New member
Dear WRF community,

Thanks for your attention, I am not familiar with WRF dynamics codes, so please pardon me if these questions are quite basic. I want to add a macrophysics scheme to my model. The macrophysics scheme would modify the T (temperature), qv (mixing ratio), ql (cloud water mixing ratio) and qi (cloud ice mixing ratio). The macrophysics scheme is called by module_first_rk_step_part1, just like other physical schemes (radiation, surface, PBL, cumulus). But I am confused about T, qv, ql and qi modifies in physical processes.
I guess there is a part of codes calculated the sum of T, qv, ql and qi modifies in physical processes in one time step. Just like “tend = RTHRATEN+RTHBLTEN+RTHCUTEN+RTHSHTEN” ? And where are the codes? I am not sure if this guess is correct.
Or the T, qv, ql and qi modify are calculated in every physical process, that is, for example the “t_phy” is modified in radiation_driver, but the “t_phy” is just “intend(in)” in code, and if so, what is the role of RTHRATEN? Just for diagnosis?

I appreciate any help. Thank you very much!

Hi,

This question involves in how the WRF handles the physical tendency terms.
(1) Note that in various physics schemes, only the tendency of the physical variable is calculated, while the physical variable itself is not updated.
(2) All the physical tendencies from various schemes are added in phys/module_physics_addtenc.F, and the sum of all the tendencies later are used to update the physical variable.
Please look how RTHRATHEN is treated in the WRF system, which can serve as a good example how to manage your macrophysics scheme and related tendencies.