Impact of the tau's code on the hydrological cycle

[adamrher]

The latest version of CESM3 produces an overly active hydrological cycle, with greater LHFLX and global mean precipitation rates than observations & CESM2. NorESM is trying to address the same issue in their code base. This discussion is aimed at testing whether CLUBB's tau's code, set by clubb_l_diag_Lscale_from_tau=.true. reduces the intensity of our hydrological cycle.

Some F-case experiments indicate that tau's is reducing our global mean PRECT & LHFLX values. Interestingly, combining expldiff=F with tau's doesn't reduce the global mean PRECT & LHFLX as much as expldiff=F w/ the default Lscale based algorithm. The latter combination unfortunately leads to excessive tropical SST amplitudes in full-coupled CESM3, hence the interest in the tau's solution.

LWCF is way too weak in the tau's code and needs to be tuned up, which seems to be causing too negative RESTOM. The ADF diags for the FLTa experiments are here:

https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_rg_1979_1980_vs_Obs/
https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_rg_1979_1980_vs_cam123_dflt_rg_1979_1980/
https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_expldiffF_1979_1980_vs_cam123_dflt_rg_1979_1980/

@vlarson @bstephens82 @adagj @gold2718

See also our prior discussion on the tau's code from 2 years ago #262

[bstephens82]

I ran some additional taus tests with the tuning

micro_mg_dcs=600e-6
hetfrz_dust_scalfac = 0.1
microp_aero_wsubi_scale = 1.5

with both clubb_l_do_expldiff_rtm_thlm=T and F. Here are the ADF diags for those taus experiments. They don't look much better in terms of RESTOM or LWCF: low values of LWCF even with the tunings, 20 W/m2 or so.

expldiff=T
https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_dust_rg_1979_1980_vs_cam123_dflt_rg_1979_1980/

expldiff=F
https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_edF_dust_1979_1980_vs_cam123_dflt_rg_1979_1980/

[bstephens82]

Some additional experiments boosting hetfrz_dust_scalfac 0.1-->0.25 seem strikingly persistent in their behavior. Still negative RESTOM, still low LWCF means:

expldiff=T:
https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_dust2_rg_1979_1980_vs_cam123_dflt_rg_1979_1980/

expldiff=F:
https://webext.cgd.ucar.edu/FLTHIST/pmf/atm/cam123_taus_edF_dust2_1979_1980_vs_cam123_dflt_rg_1979_1980/