Making NEMO_book.pdf showed undefined references. The file attached resolves them.

Salut, hello, bonjour, privet, etc...

Origin: In the ORCA2 configuration and using the CLIO forcing, sometimes, for an unknown reason, the latent and sensible heat fluxes blow up in the equator region near the east coast of continents (e.g., east of South America near the Amazone region). I could not figure out why, but I guess the new surface module is more explicit than it used to be and hence, more unstable. The present bugfix is a dirty plaster to prevent that. But I argue that a dirty plaster on a dirty formulation of the forcing is not a problem.

Proposed solution: The heat transfer coefficient zchcm blows up. Let's limit its value!

Code processing: in sbcblk_clio.F90
replace this line :

zchcm = zcmcmn / ( 1. - zchn * zpsih / ( vkarmn * zcmn ) )

by those lines (much more beautiful, no ?) :

! sometimes the ratio zchn * zpsih / ( vkarmn * zcmn ) is too close to 1
! and zchcm becomes very very big
zcmax = 0.1 ! choice for maximum value of the heat transfer coefficient, guided by my intuition
zrmax = 1 - 3.e-4 / zcmax ! maximum value of the ratio
zchcm = zcmcmn / ( 1. - MIN ( zchn * zpsih / ( vkarmn * zcmn ) , zrmax ) )

Effect:
Very small on the results. But you need this to run more than 5 years with CLIO on the NEC.

A bientot, Martin!

What is this about???
Dear reader,
This is an important enhancement of LIM3 to improve its stability in ORCA2 configuration at least. By default, the horizontal gradient of sea surface height is not activated. It should.

How to activate that???

1. Uncomment the two lines starting with zdsshx and zdsshy in limrhg.F90.
   
2. Define ssh_m in sbc_oce.F90:
   

REAL(wp), PUBLIC, DIMENSION(jpi,jpj) :: ssh_m !: mean (nn_fsbc time-step) sea surface height [m]

3. Compute ssh_m in sbc_ssm.F90 (see attached file)

Bur is there any effect ???
Of course, yes!!! It definitely stabilizes the sea ice near the Canadian Archipelago and reduces the chances of model crash.

Merci pour votre collaboration!
Salutations distinguées,
Martin!