Context

iom_getatt is a generic routine that currently (in dev_merge_2016 branch) accepts integer and real arguments. The interface for this is done correctly in iom.F90 but at the next level (iom_nf90.F90) one routine satisfies both uses with optional arguments and complicated logic. This is not easily extended for the additional case of character attributes.

Changes

The best solution is to introduce a proper generic routine into iom_nf90.F90. At the same time the option to read either file or variable attributes can be added for all types (currently it is only available for real attributes). The user will see only one routine: iom_getatt( fid, attr_name, retvar, var_name) where varname is optional (if omitted a file attribute is looked for), and retvar can be either integer, real or a character string. Inside iom.F90, iom_getatt is an interface to three routines: iom_g0d_iatt, iom_g0d_ratt and iom_g0d_catt. Each of these calls a generic routine: iom_nf90_getatt which is, in turn, an interface to three routines: iom_nf90_iatt, iom_nf90_ratt and iom_nf90_catt which are defined in iom_nf90.F90.

Context

Attempts to derive a SETTE test for SAS configurations by comparing restarts in restart ability tests has revealed a minor issue with sbc_tsc_b values differing between continuous runs and restarted runs covering the same period. Differences are found in halo regions which have no impact on results but invalidate the proposed new test.

Analysis

The cause has been traced to the initialisation carried out in trasbc.F90. Currently the code is (in shorter, pre-OMP form):

      IF( kt == nit000 ) THEN             !* 1st time-step
         IF( ln_rstart .AND.    &               ! Restart: read in restart file
              & iom_varid( numror, 'sbc_hc_b', ldstop = .FALSE. ) > 0 ) THEN
            IF(lwp) WRITE(numout,*) '          nit000-1 sbc tracer content field read in the restart file'
            zfact = 0.5_wp
            CALL iom_get( numror, jpdom_autoglo, 'sbc_hc_b', sbc_tsc_b(:,:,jp_tem) )   ! before heat content sbc trend
            CALL iom_get( numror, jpdom_autoglo, 'sbc_sc_b', sbc_tsc_b(:,:,jp_sal) )   ! before salt content sbc trend
         ELSE                                   ! No restart or restart not found: Euler forward time stepping
            zfact = 1._wp
            sbc_tsc(:,:,:) = 0._wp
            sbc_tsc_b(:,:,:) = 0._wp
         ENDIF
      ELSE                                !* other time-steps: swap of forcing fields
         zfact = 0.5_wp
         sbc_tsc_b(:,:,:) = sbc_tsc(:,:,:)
      ENDIF
      !                             !==  Now sbc tracer content fields  ==!
      DO jj = 2, jpj
         DO ji = fs_2, fs_jpim1   ! vector opt.
            sbc_tsc(ji,jj,jp_tem) = r1_rau0_rcp * qns(ji,jj)   ! non solar heat flux
            sbc_tsc(ji,jj,jp_sal) = r1_rau0     * sfx(ji,jj)   ! salt flux due to freezing/melting
         END DO
      END DO

Note that on a restart, sbc_tsc is not initialised and only inner points are subsequently set before the:

         sbc_tsc_b(:,:,:) = sbc_tsc(:,:,:)

instruction on the next time step. Thus the unused haloes can (and do) contain arbitrary values unless unset values are automatically set to zero by the compiler.

Recommendation

The simplest solution is to introduce a:

            sbc_tsc(:,:,:) = 0._wp

immediately before the first call to iom_get.

Of course for OMP operability what actually needs to be inserted is:

            DO jn = 1, jpts
!$OMP PARALLEL DO schedule(static) private(jj, ji)
               DO jj = 1, jpj
                  DO ji = 1, jpi
                     sbc_tsc(ji,jj,jn) = 0._wp  ! needed just to ensure haloes are consistent across restarts
                  END DO
               END DO
            END DO

Context

With the move to full dynamic allocation there is no need to retain a uniform jpi and jpj across all processing regions. Allowing these to vary will permit simplification by removing the possibility of 'ghost' rows or columns and therefore remove the need for the confusing number of start and end markers such as nldi and nlci. This work will also simplify the introduction of wider haloes and will be used as an opportunity to reduce the size of the lib_mpp.F90 code base by introducing generic functions in .h90 files that can be included multiple times with different preprocessor settings. This work builds on the developments completed in branches/2017/dev_r7832_HPC08_lbclnk_3rd_dim and #1880

Implementation

See https://forge.ipsl.jussieu.fr/nemo/wiki/2017WP/ROBUST-08_AndrewC-MPP_no_ghost for details and associated development branch: branches/2017/dev_r8126_ROBUST08_no_ghost