ocean_vmix_init Subroutine

   subroutine ocean_vmix_init(this, grid, nz_ml)
      !! Allocate the kv / kt / ks diffusivity fields at layer
      !! interfaces.  Default values: kv = kv_bg (= pp81_nu_bg),
      !! kt = ks = kt_bg (= pp81_kappa_bg) at interior interfaces;
      !! boundary interfaces k=1 and k=nz+1 are zeroed (closed BC).
      !! BL fields (`bl_depth`, `gamma_*`) seed at zero.  `ks` is
      !! allocated so the assembly stage (`vmix_assemble`) can
      !! floor/clip it; `vmix_split_kd_heat_salt` derives its live
      !! value from `kt` every stage, and `vdiff_apply_tracers`
      !! consumes it for salinity + every passive tracer.
      !!
      !! `smooth_scratch` is NOT allocated here — it is allocated lazily
      !! in `configure_ocean_vmix` only when `kd_smooth_iterations > 0`
      !! (before `ocean_state_enter_data`).  The `enter_data` path
      !! already guards on `allocated(smooth_scratch)`.
      class(ocean_vmix_t), intent(inout) :: this
      type(hgrid_t), intent(in) :: grid
      integer, intent(in), optional :: nz_ml
      integer :: nx, ny, nz

      nx = grid%nx_total
      ny = grid%ny_total
      nz = 1
      if (present(nz_ml)) nz = nz_ml

      allocate (this%kv(nx, ny, nz + 1))
      allocate (this%kt(nx, ny, nz + 1))
      allocate (this%ks(nx, ny, nz + 1))
      allocate (this%kd_bg(nx, ny, nz + 1))
      ! kv_bg/kt_bg/ks_bg + kv/kt/ks/kd_bg all seed from pp81_* here
      ! (structural invariant, see `vmix_seed_backgrounds`).  The SAME
      ! call re-derives them after `&ocean_vmix_nml pp81_*` reaches the
      ! slot at configure — see `rdb_ocean_setup.F90:configure_ocean_lateral`.
      call this%seed_backgrounds()
      allocate (this%bl_depth(nx, ny), source=0.0_wp)
      allocate (this%b0(nx, ny), source=0.0_wp)
      allocate (this%gamma_t(nx, ny, nz + 1), source=0.0_wp)
      allocate (this%gamma_s(nx, ny, nz + 1), source=0.0_wp)

      this%is_init = .true.
   end subroutine ocean_vmix_init