nucleate_ice_cam sets ice cloud frac to combined ice+liquid cloud frac

[adamrher]

What happened?

Bug in the following block of nucleate_ice_cam.F90

   call pbuf_get_field(pbuf, ast_idx, ast, start=(/1,1,itim_old/), kount=(/pcols,pver,1/))

   icecldf(:ncol,:pver) = ast(:ncol,:pver)

ast is not ice cloud frac, but combined ice+liquid cloud frac. Changing the pbuf_get_field to aist_idx results in a slight reduction in CLDICE and NUMICE (compare FLTHIST to FLTHIST bugfix; note these are only 2 year runs):

@fvitt @tilmes

What are the steps to reproduce the bug?

Run the FLTHIST compset.

What CAM tag were you using?

cam6_4_047

What machine were you running CAM on?

CISL machine (e.g. cheyenne)

What compiler were you using?

Intel

Path to a case directory, if applicable

No response

Will you be addressing this bug yourself?

Yes

Extra info

copy this to SourceMods to run w/ bug fix:

/glade/derecho/scratch/aherring/cam7_nochem_FLTHIST_ne30pg3_ne30pg3_mg17_3968pes_241222_aist-bug_Nx2yrs/SourceMods/src.cam/nucleate_ice_cam.F90