Implementing Marine Organic Aerosols to CESM2 #531

[XiZhao1013]

We expand the Modal Aerosol Module (MAM) in CESM2-CAM6 to consider the emission of marine organic aerosol (MOA) as well as its impacts by acting as cloud condensation nuclei (CCN) and ice nucleation particles (INPs).

MOA is an important source for CCN and INPs over the Southern Ocean and has shown important climate implications over the remote oceans, which are detailed in this recent paper (Zhao and Liu et al, ACP, 2021).

There is a general interest in MOA in the community. We would like to share our MOA code in CAM6 with the community, which can be found here.

Summary of our code developments:

• added emission of MOA
• added CCN and INPs effects of MOA
• Code development is currently based on the cesm2.0.1-rc.01

Thank you in advance to @lkemmons for helping with reviewing our changes.

[nusbaume]

I was told by @cmcclus that she will be opening the PR for this, so am assigning this issue to her.

[adamrher]

Is MOA going to be a brand new tracer in the model? Or is it just a biogenic property added to an existing aerosol tracer?

[XiZhao1013]

Is MOA going to be a brand new tracer in the model? Or is it just a biogenic property added to an existing aerosol tracer?

MOA is going to be a new tracer. Since it has different aerosol properties(density, hygroscopicity, nucleation ability) compared with existing aerosol species.

[cmcclus]

will be two new aerosol tracers - Aitken and Accumulation modes

[XiZhao1013]

will be two new aerosol tracers - Aitken and Accumulation modes

Thanks, Christina. One comment here, MOA is emitted to Aitken and Accumulation modes with the assumption of internally mixed with sea salt (more information cloud be found in Zhao et al., ACP, 2021; Burrows et al., 2018).

[adamrher]

Still a little confused. Mind you I am just starting to get my head around all the tracers in the model. There are currently three sea-salt tracers: ncl_a1, ncl_a2, ncl_a3. Are we adding more? Or just enhancing these three existing ones?

[XiZhao1013]

Still a little confused. Mind you I am just starting to get my head around all the tracers in the model. There are currently three sea-salt tracers: ncl_a1, ncl_a2, ncl_a3. Are we adding more? Or just enhancing these three existing ones?

We are adding more, we will add mom_a1, mom_a2, and mom_a4.

[XiZhao1013]

I have implemented the MOA into the development branch. But each time when I output MOA (mom_a1, TMmom_a1...), the writing process takes more than 1 hour (the MOA can be output, but very slow). I will be very appreciative if anyone could give any suggestion on this. @cmcclus @nusbaume

[gold2718]

@XiZhao1013, can you include a CAM fork + branch here? I might be able to spot something that is increasing the history output time.
Alternatively (or in addition), please post a case directory on an accessible machine (e.g., Cheyenne).

[XiZhao1013]

Thanks for your suggestion, it is very instructive for a new user of GitHub @gold2718.

the branch name: MAM4_MOA
CAM fork: XiZhao1013 / CAM (not sure if I provide the right information)

Case directory on Cheyenne: /gpfs/fs1/work/xizhao/cesm2_develop_branch_new/cases/cesm2_mom_new_4
Model output: /gpfs/fs1/scratch/xizhao/test_case/cesm2_mom_new_4/run

[gold2718]

You are writing to /gpfs, can you try writing to /glade/scratch instead? That is much faster in most cases (especially from the compute nodes).
Also, you are using a very old format for user_nl_cam, is there a need for that?