Implementing CoupledDA

[ateruzzi]

The coupled DA aims at use the physical DA (PHY DA) results to updated nutrients in biogeochemistry.
3DVar with coupled DA will:

• read the density increments provided by PHY DA
• read the pre-computed correlations between density and nutrients
• calculate the nutrient increments (nitrate and phosphate)
• update the restarts accordingly

[ateruzzi]

The name of the main subroutine has been updated from oceanvar to biovar (not necessary for coupled DA, just a matter of formality).

Starting to intorduce the reading of PHY DA increments.

[ateruzzi]

The code compiles correctly BUT it is only for testing density-nutrient DA in a simplified framework:

• The update is done on nitrate outside to the DA iteration

  3dVarBio/cnv_inn.f90

  Lines 65 to 68 in fc4b5dc

  	if (drv%densnut .eq. 1) then
  	grd%n3n(:,:,:) = 0.0
  	call ver_hor_densnut(grd%n3n)
  	endif

• Single profiles of density increments are read

  3dVarBio/get_densincr_arg.f90

  Line 1 in fc4b5dc

  subroutine get_densincr_arg

• Nitrate increments are calculated on the model grid levels

  3dVarBio/get_densincr_arg.f90

  Line 1 in fc4b5dc

  subroutine get_densincr_arg

• The horizontal operator is applied

  3dVarBio/ver_hor_densnut.f90

  Line 71 in fc4b5dc

  !********** APPLY RECURSIVE FILTERS ********** !

• Phosphate is updated accordingly and RSTafter files are written

  3dVarBio/biovar.f90

  Lines 140 to 142 in fc4b5dc

  	if (drv%dnc .eq. 1) then
  	call wrt_nut_stat
  	endif

NOTE1 that this version is for testing density-nutrent DA alone (nitrate profiles assimilation is overwritten).
NOTE2 To test the code an assimilation has to be performed (NOT nitrate)

[ateruzzi]

Compiled and tested for:

• assimilation of some O2 profiles
• apply increments on n3n and n1p based on a single density increment profile

NB: it does work only if drv%nut = 1

• density increments should be relatively dense on the vertical, as it is not interpolated by EOFs
• correlation radius quite small at the moment