Radiation balance

[MartinDix]

Latest CM3 runs (e.g. cm3-run-16-09-2024) have a net TOA energy flux around 2.7 W/m^2 initially.

Met Office GC5 AMIP runs were tuned to give the desired radiation balance at N216, not N96. The tuning is described at https://code.metoffice.gov.uk/trac/gmed/wiki/ticket/573/TicketDetails describes the radiation tuning of the N216 version.

This is an extract of the table near the end of https://code.metoffice.gov.uk/trac/gmed/wiki/ticket/577/TicketSensitivityTests

	rsut	rlut	net
Obs CERES EBAF 4.1	99.0	240.3	+1.0
N96 RC3	98.56	239.53	+2.31
N216 RC3	99.07	240.59	+0.74

RC3 is almost the same as the final version, except for an update to the boundary layer buoyancy https://code.metoffice.gov.uk/trac/jules/ticket/1242.

Alejandro Bodas's presentation at the 2023 Momentum Workshop says they retuned the GC5-N96ORCA1 PI control aiming at rsut=99, rlut=240.5, close to CERES EBAF4 values (because UKESM suggested PI and current were pretty close). Used two_d_fsd_factor = 1.70, cape_timescale =2700 s in place of standard two_d_fsd_factor=1.65 cape_timescale=1800.0, though not clear if this is the final value.