minor bug in code to do Euler timestep in dyn_nxt

[davestorkey]

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Context

If we use an Euler forward timestep at the beginning of the integration then we don't need to time-filter the fields and so we just swap them in the following lines in dyn_nxt:

! Time filter and swap of dynamics arrays
! ------------------------------------------
IF( neuler == 0 .AND. kt == nit000 ) THEN !* Euler at first time-step: only swap

DO jk = 1, jpkm1

un(:,:,jk) = ua(:,:,jk) ! un <-- ua
vn(:,:,jk) = va(:,:,jk)

END DO

For the velocity fields we just swap "after" to "now", not "now" to "before" because the "now" and "before" fields are initialised to be the same in istate_init. But with the time-split solution for the free surface the "now" field does in fact get updated in dyn_spg_ts to be consistent with the barotropic solution:

! Correct velocities so that the barotropic velocity equals (un_adv, vn_adv) (in all cases)
DO jk = 1, jpkm1

un(:,:,jk) = ( un(:,:,jk) + un_adv(:,:)*r1_hu_n(:,:) - un_b(:,:) ) * umask(:,:,jk)
vn(:,:,jk) = ( vn(:,:,jk) + vn_adv(:,:)*r1_hv_n(:,:) - vn_b(:,:) ) * vmask(:,:,jk)

END DO

So in fact the "now" velocity is different to the "before" velocity on an Euler timestep and we should swap "now" to "before" velocities in dyn_nxt.

(This is a very minor bug but it prevents me from obtaining bit comparison with the new version of the code with a time-dimension in the prognostic fields).

Analysis

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Fix

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[jchanut]

Removing the conditional statement at line 128 of dynnxt.F90 should work:

 IF( .NOT.ln_bt_fw ) THEN
	            ! Remove advective velocity from "now velocities"
	            ! prior to asselin filtering

Generally speaking: I think that barotropic fluxes correction should be implemented in the code as for ztilde diffusive fluxes (un_td, vn_td): Baroclinic velocities should remain unchanged during the time stepping, fluxes should be updated only when doing tracer advection and in the continuity equation.

[davestorkey]

In 11480:

Error: Failed to load processor CommitTicketReference

No macro or processor named 'CommitTicketReference' found

[davestorkey]

In 12026:

Error: Failed to load processor CommitTicketReference

No macro or processor named 'CommitTicketReference' found

[davestorkey]

Fixed in trunk @ 12026.