mass and heat budgets in NEMO

[clem]

Context

Mass and heat fluxes in NEMO are a bit messy and should be cleaned at some point. Therefore this ticket is a reminder for what should be done (or discussed) for the next NEMO release

As far as I understand, the mass budget of the ocean+ice/snow is written:

$Doce + Dice + Dsnow = - emp_oce - emp_ice + rnf - fwfisf$

• emp_ice is E-P over sea ice
• emp_oce includes calving ("calving_cea") in addition to E-P over ocean
• runoffs include icerbergs ("iceberg_cea") in addition to river runoff
• fwfisf is the ice-shelf melting (<0 = melting)

This interleaving of variables makes things complicated when it comes to define a heat budget.

• calving => we suppose Tcal = 0degC (i.e. no sensible flux) and latent heat is removed from qns to take into account the ocean heat uptake to melt the ice (in sbccpl.F90)
• river runoff => we suppose Trnf = SST (in sbcrnf.F90)
• iceberg => latent heat is removed from qns (in sbccpl.F90) but since we treat iceberg as a runoff, its temperature is also at the SST (in sbcrnf.F90)
• ice-shelf => latent heat is removed from the ocean directly as a temperature change and the sensible flux is taken into account with a melting temperature fixed at -1.9 degC (in sbcisf.F90)

Note that in coupled mode you generally have:

• iceberg = half of the Antarctic fresh water flux is distributed in the ocean according to a climatology of icebergs distribution
• iceshelf = half of the Antarctic fresh water flux is distributed along the coast where there is iceshelf
• calving = Greenland fresh water is uniformly distributed

Fix

• separate calving from emp_oce?
• separate river runoff from icerbegs?
• change temperature of the ice-shelf when melting?
• change temperature for calving?
• fwfisf does not follow the convention for runoff (>0 = input for the ocean)
• other things?