Changing the initial concentration of cloud condensation nuclei (CCN) in WRF

[Rupa]

Hello WRF community.
1. Is there a way to change the concentration of CCN used in microphysics schemes ? Like by changing fortran modules in wrf/phys, or Registry, or even a simpler option like the namelist variable ccn_conc . I want to see how CCNs behave in the presence and absence of aerosols (to be supplied later in WRF chem) , how they affect precipitation even without chem turned on.

2. Doing a little literature review I have learned that in many microphysics schemes, CCN concentration is built in or prognostic (it doesn't really depend on aerosols). It can also be coupled with WRF chem results by using aerosol aware microphysics options. Is my understanding correct?

3. I also do not understand the exact purpose of ccn_conc = variable in the namelist. Does it change the default concentration of ccn in WDM schemes, hence reducing or decreasing precipitation, changing activation rates? Does it have any relation with aerosols?

I would be thankful if someone would clarify these confusions for me.

 

[Ming Chen]

Hi Rupa,
Please see my answers below:

Hello WRF community.
1. Is there a way to change the concentration of CCN used in microphysics schemes ? Like by changing fortran modules in wrf/phys, or Registry, or even a simpler option like the namelist variable ccn_conc . I want to see how CCNs behave in the presence and absence of aerosols (to be supplied later in WRF chem) , how they affect precipitation even without chem turned on.

ccn_conc is CCN concentration used by WDM schemes. nssl_cccn = 0.7e9 is CCN for NSSL scheme (mp_physics= 18). CCN can also be predicted in NSSL when nssl_ccn_on = 1. You are able to change nssl_cccn or ccn_conc for some sensitivity tests.
In other microphysics schemes, CCN is calculated in various ways. There is no option to simply change a single value in these schemes.

2. Doing a little literature review I have learned that in many microphysics schemes, CCN concentration is built in or prognostic (it doesn't really depend on aerosols). It can also be coupled with WRF chem results by using aerosol aware microphysics options. Is my understanding correct?

You are right that in many microphysics schemes, CCN concentration is built in or prognostic. I suppose it can be coupled with wrf-chem when running with aerosol aware microphysics options. But I am not sure how to do the coupling.

3. I also do not understand the exact purpose of ccn_conc = variable in the namelist. Does it change the default concentration of ccn in WDM schemes, hence reducing or decreasing precipitation, changing activation rates? Does it have any relation with aerosols?

ccn_conc is used by WDM schemes. It is passed onto the scheme and then used to calculate other CCN-related variables. More details can be found, for example, in module_mp_wdm5.F, module_mp_wdm7.F, etc.

I would be thankful if someone would clarify these confusions for me.

Hope I have answered some of your questions. I am not an expert in wrf-chem and hopefully someone in the community can give more information.

 

[Rupa]

Thank you so much!

Hi Rupa,
Please see my answers below:

ccn_conc is CCN concentration used by WDM schemes. nssl_cccn = 0.7e9 is CCN for NSSL scheme (mp_physics= 18). CCN can also be predicted in NSSL when nssl_ccn_on = 1. You are able to change nssl_cccn or ccn_conc for some sensitivity tests.
In other microphysics schemes, CCN is calculated in various ways. There is no option to simply change a single value in these schemes.


You are right that in many microphysics schemes, CCN concentration is built in or prognostic. I suppose it can be coupled with wrf-chem when running with aerosol aware microphysics options. But I am not sure how to do the coupling.

ccn_conc is used by WDM schemes. It is passed onto the scheme and then used to calculate other CCN-related variables. More details can be found, for example, in module_mp_wdm5.F, module_mp_wdm7.F, etc.

Hope I have answered some of your questions. I am not an expert in wrf-chem and hopefully someone in the community can give more information.