Hello Nemo community,
I am starting to run 2-way nested simulations with Nemo4.2.1-Agrif, I’ve started with a simple test in my regional configuration of a nest with no temporal nor spatial refinement. Child is initialized from parent who in turn is initialized from a TS field only, so initial velocity in the domain is 0.
However comparing this run with a no nest one, even though I set rn_sponge_tra , rn_sponge_dyn , rn_trelax_tra , rn_trelax_dyn all to 0, I see a difference in the signal of velocity and sea level at the boundaries in the first few timesteps.
I dugged a bit in the code and eventually found that while the nest correctly starts with initial velocities at 0, velocities appear during the first barotropic timestep :
-In dynspg_ts.F90 line 364 , the subroutine Agrif_dta_ts is called just before the loop for barotropic time integration, in that subroutine (in agrif_oce_interp.F90) the variables ubdy and vbdy are modified by taking velocity from the parent (call routine Agrif_Bc_variable), however when I do a sum of one of this variable in the code, it is nonzero at the first call (ie, start of first baroclinic timestep).
-This leads to nonzero values during the first barotropic timestep for zhU,zhV (after the call to subroutine agrif_dyn_ts_flux , line 514 of dynspg_ts.F90). For the parent, those variables are correctly 0 during the first barotropic timestep.
So my question is, when Agrif_dta_ts is called by the child in dynspg_ts.F90, has the parent already started its barotropic integration ? Otherwise I don’t understand where it gets nonzero values to fill ubdy…
Some more info
Here is the code I use to sum ubdy :
$diff agrif_oce_interp.F90 ../../../src/NST/agrif_oce_interp.F90
61,62d60
< # include "do_loop_substitute.h90"
< !^TST
682,683d679
< REAL(wp) :: tvel ! TST
< INTEGER :: ji, jj!TST
[...]
736,744d714
< IF(lwp) WRITE(numout,*) '-----TSTagrdtats2----ts=',kt
< tvel=0._wp
< DO_2D( nn_hls-1, nn_hls-1, nn_hls-1, nn_hls-1 )
< tvel=tvel+ ubdy(ji,jj)
< END_2D
< CALL mpp_sum( 'trdglo', tvel)
< IF(lwp) WRITE(numout,*) 'sum DO(ubdy) = ',tvel
< IF(lwp) WRITE(numout,*) '-----------------'
Since the nemo agrif testcase (ORCA2 with 3 nests) also has a nest without refinement (1st one), I looked there too and get the same behaviour. From 1_ocean.output:
dyn:hpg_sco : hydrostatic pressure gradient trend
~~~~~~~~~~~ s-coordinate case, OCE original scheme used
dyn_spg_ts : surface pressure gradient trend
~~~~~~~~~~ free surface with time splitting
-----TSTagrdtats2----ts= 1
sum DO(ubdy) = -484270105.158229
-----------------
Thanks,
Margaux