IAU NEMO

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Incremental Analysis Update (IAU) with NEMO model

  • Compile the model sources with cpp key key_asminc in the file cpp_SQB.fcm
  • Edit the namelist file

Edit the field &nam_asminc  ! assimilation increments ('key_asminc') usually situated at the end of the namelist file. If no increment is applied, set .false. to these four fields.

ln_trainc = .false.    !  Logical switch for applying tracer increments 
ln_dyninc = .false.    !  Logical switch for applying velocity increments 
ln_sshinc = .false.    !  Logical switch for applying SSH increments 
ln_asmiau = .false.    !  Logical switch for Incremental Analysis Updating (IAU)

Otherwise, depending on the increment parameter, set .true.

Moreover, set the increment applicaiton time window according to the IAU scheme used :

nitiaustr = 1         !  Timestep of start of IAU interval in [0,nitend-nit000-1] 
nitiaufin = 192        !  Timestep of end of IAU interval in [0,nitend-nit000-1] 

check the increment application in the file ocean.output. I think the interval should be[1, nitend-nit000+1]. the weighting function type : 0 : constant 1 : linear hat like (see doc. NEMO)

niaufn    = 0          !  Type of IAU weighting function
  • Edit the increment file

necessary elements : increment of tracer variables and/or dynamics variables and/or SSH if you have already eliminated the time interval tests in the code while compilation.

For example :

netcdf assim_background_increments {

 dimensions: 
       x = 121 ; 
       y = 81 ; 
       z = 11 ; 
variables: 
       double bckinu(z, y, x) ; 
       double bckinv(z, y, x) ; 
       double bckint(z, y, x) ; 
       double bckins(z, y, x) ; 
       double bckineta(y, x) ;

Otherwise, you have to add time, z_inc_dateb, z_inc_datef in the increment file (see, doc NEMO).

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