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Intermittent assimilation with NEMO model

  • Compile the codes with the same cpp_key as for IAU. Also, you can modify the code (asminc.F90) to simplify your processing.
  • Edit namelist (the same field as for IAU), here is an example :
ln_trainc = .true.    !  Logical switch for applying tracer increments 
ln_dyninc = .true.    !  Logical switch for applying velocity increments 
ln_sshinc = .true.    !  Logical switch for applying SSH increments 
ln_asmdin = .true.    !  Logical switch for Direct Initialization (DI)

where 3 types of increment are applied. You should set the correction instance,

nitbkg    = 0          !  Timestep of background in [0,nitend-nit000-1] 
nitdin    = 0          !  Timestep of background for DI in [0,nitend-nit000-1] 

Set 0, if you want to correct the state before the model run for the current assimilation window ; otherwise, set another number.

  • Edit the increment file and backgroud file:

The increment file is the same as for IAU. The background file is as follows :

netcdf assim_background_state_DI {

       x = 121 ; 
       y = 81 ; 
       z = 11 ; 
       double un(t, z, y, x) ; 
       double vn(t, z, y, x) ; 
       double tn(t, z, y, x) ; 
       double sn(t, z, y, x) ; 
       double sshn(t, y, x) ; 

To generate this background file, copy directly these 5 variables in the restart file generated at the end of the assimilation window. Note that if you set

 n_bkgwri = .true.    !  Logical switch for writing out background state

A background file will be created by the model, but the 5 variables correspond to the variables at the beginning of the assimilation window (not at the end).

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