[Mitgcm-support] Momentum timestep

[mitgcm-support at dev.mitgcm.org]

Hi,

I'am going to check-in some changes in the momentum timestepping,
1) store u*,v* in gU,V instead of in gu,vNm1 (tracers timestepping is 
   already done in the same way). This affects several S/R
   but has no impact on output.
2) move the forcing and the CD scheme from mom_fluxform & mom_vecinv 
   to timestep.F 

The motivations for (2) are:
 a) to allow to put the momForcing out of the Adams-Bashforth.
  (since it seems logical to keep the AB in timestep.F, then the forcing
   has to follows).
 b) CD scheme needs to be called after the forcing, so it has to move also.
   Anyway, uVelD & vVelD are step-forward in mom_cdscheme, and seems logical 
   to have also this call in timestep.F.
   Doing like this allows to use the CD scheme with mom_vecinv.
 c) this open the way for doing the AB on u,v instead of gU,gV.
  [this improve the energy conservation and was actually used for the 
   NLFS-conservation paper]

(2) affects the outputs (at the truncation level) since the sequence 
  of addition to gU,gV (+Forcing , +Coriolis, + MetricTerm ... ) is modified.
  (will need to update the output.txt of the high sensitive test exp,
   glob-ocean-pressure, lab_sea and nat_box)

Also I propose to add a running flag parameter for the CD-scheme,
 (useCDscheme) default value =FALSE 
 This means that when using the CD scheme, "useCDscheme=.TRUE." will have 
 to be added to the "data" file.
 (I plan to add "WARNING" when useCDscheme=.TRUE. is missing)

Any comments ?

See you,

Jean-Michel