Replacing the Dust Aerosol Online Calculation with Emission Data Yielded Significantly Different Outcomes.

[CaliFornia]

I am running simulation with CESM2.1.4. The model uses MAM4 to calculate aerosol number concentration and mass concentration.

What I want to do:
Simulation 1: output the emission flux of dust (both number and mass flux)
Simulation 2: read in the (daily) output of dust number and mass flux from Simulation 1, instead of online calculation.

What I expect:
Similar results of number and mass concentrations of dust between the two simulations.

What I did:
Simulation 1: I modified the aero_model.F90 and run a 10-year simulation with F2010Climo composet, and output the mass and number emission flux for dust.
Simulation 2: Then I disabled the calculation of them (by commenting out 'call dust emis'), and in the user_namelist add the output from simulation 1 as emission files.

What I get:
Very different result between the two simulations, such as the dust concentration during the first 12 months:


Any ideas on why is that? I appreciate any comments.

 

[rrbuchholz]

Hi there!

Did you check that the CESM defined surface fluxes of dust matched your files you were saving by modifying aero_model_F90?
The variables for example to save would be: SFdst_a3

Also, what is the temporal resolution of your emission flux files - they may differ from the "online" time resolution.

Best,
Rebecca

 

[CaliFornia]

Hi there!

Did you check that the CESM defined surface fluxes of dust matched your files you were saving by modifying aero_model_F90?
The variables for example to save would be: SFdst_a3

Also, what is the temporal resolution of your emission flux files - they may differ from the "online" time resolution.

Best,
Rebecca

Hi Thank you so much for your response!

1. I did named the variable 'SFdst_a3' in the emission file before put it into the srf_emis_specifier section in the namelist.
2. I output this variable with avgflag_pertape = 'A'; mfilt = '1'; nhtfrq = '-24'.
So the time resolution of the file will be daily, with time_bnds set to 2010.
I am using F2010Climo, and the srf_emis_type = 'CYCLICAL', and I am not sure if I can use the daily emission. I think the emission file will be interpolated by the model right? And the emission data are flux in (molecules/cm2/s), time resolution should not be a problem I guess:


3. I am so confused why the mass concentration and number concentration can be so different (about ~100 times different) when surface flux are so close:

 

[Danny Leung]

Hi,
From your description for now I would just think of a few things to check upon:
1. It sounds like you outputted SFdst_a3 for your input in srf_emis_specifier. I assume you also did SFdst_a1 and SFdst_a2 as well? If not, you may be missing some dust emissions.
2. It you did, then maybe the difference just comes from the missing diurnal cycle, which is due to the fact that dust emission is modeled online every time step while you are feeding srf_emis_specifier once per day with a daily mean dust emission. I am not sure if missing the diurnal cycle causes a the issues you see though.
3. I would also double check that you did your unit conversion of SFdst_a3 from mass emission flux (kg/m2/s) to number emission flux (molec/m2/s) correctly.

And then I am not sure what you mean in your point number 3, when you mention number flux vs mass flux and number conc vs mass conc. SFdst_a3 is mass emission flux (kg/m2/s). To my understanding CAM does not by default output number emission flux of aerosol. CAM also does not by default output number concentration of dust. How did you output and compare your dust mass concentration and dust number concentration and see they differ by two orders of magnitude?

Best,
Danny