Thick clouds and aerosol differences in a recent cesm tag (alpha08a + updated cam tag) #271
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Thanks Adam - I've now made output from my CMAT analyses available to the group at https://webext.cgd.ucar.edu/Multi-Case/CMAT/CMATv1_CESM3dev/ I'm happy to walk everyone through it to show how it can be used. The first thing I look at is the table - to gauge the overall score of a run and its breakdowns into components. Then I'll look at the flags (in the archive table below). Most of our recent runs have global and NH albedos/SWCF that are too high. The runs are also drifting cold. Evaporation over ocean versus land is also too high. You can click on the flag links to see a plot that's the basis for the flag. I think you and I are looking at the same issue, per your analysis above. The NH ice issue seems to be a reasonable cause. Please let me know when your clone of 280 is ready to be run through the package and I'll see if score improve. Thanks! |
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can you point us to the atm/hist output of these cases? |
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Are there results yet about whether or not this looks like related to the
hygrosopicity bug fix?
…On Thu, Jan 22, 2026 at 2:29 PM Adam Herrington ***@***.***> wrote:
sure:
/glade/derecho/scratch/hannay/archive/b.e30_alpha07g.B1850C_LTso.ne30_t232_wgx3.271/
/glade/derecho/scratch/hannay/archive/b.e30_alpha08a.B1850C_LTso.ne30_t232_wgx3.280/
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Budget tables for these cases are located here: https://acomstaff.acom.ucar.edu/shawnh/ADF/b.e30_alpha07g.B1850C_LTso.ne30_t232_wgx3.271_60_70_vs_b.e30_alpha08a.B1850C_LTso.ne30_t232_wgx3.280_60_70/website/index.html. |
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Thanks a lot. Here are some comments: |
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… -Shawn
On Fri, Jan 23, 2026 at 9:01 AM tilmes ***@***.***> wrote:
@shawnusaf <https://github.com/shawnusaf> Could you run the diagnostics
table for the total column, not just below 500hPa, also could you run the
ADF, including zonal means for the aerosols (all modes)?
Thanks Simone
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Coupled simulations using a newer cesm tag (alpha08a) with an updated cam tag (cam6_4_142) has thicker clouds compared to the previous tag we were using, alpha07g. Run 280 is a B1850C_LTso run with this newer cesm tag, and run 271 uses the older alpha07g tag. The atmosphere parameter tunings are identical in these two runs, other than the increase of
seasalt_emis_scale= 1.25->1.5 to compensate for lower sea salt burdens in the new cam tag, owing to a bug fix to the aerosol hygroscopicity (ESCOMP/CAM#1462).As shown below, the cloud radiative forcings are larger in 280, w/ more negative SWCF and more positive LWCF:
The aerosol burdens are also different, with SOA being larger and sea salt being less:
While SO4 (sulfate) has the same burden, its vertical distribution in 280 is very different from 271, especially near the tropopause:
Back to the clouds, 280 has larger cloud numbers and mass, in both low altitudes (liquid clouds) and high altitudes (ice clouds), although ice cloud increases are primarily in the NH.
Map plots of LWP and IWP differences show the geographical distribution of the cloud changes:
I suspect that the aerosol changes are causing the cloud changes, since the cloud parameters are identical in 280 and 271. My first guess is that the hygroscopicity bug fix is leading to the aerosol changes, and so I currently have a clone of 280 running, but reverting the hygroscopicity bug fix, in order to see whether the aerosols and clouds looks more like 271. I'll update this thread as those results come in.
@cecilehannay @dlawrenncar @JulioTBacmeister @islasimpson @tilmes @jfasullo
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