Infrastructure for PMSL calculation

CONTRIBUTORS.md

@@ -22,4 +22,5 @@
 | MetBenjaminWent  | Benjamin Went          | Met Office  | 2026-01-30 |
 | jcsmeto          | James Cunningham-Smith | Met Office  | 2026-02-06 |
 | thomasmelvin     | Thomas Melvin          | Met Office  | 2026-01-15 |
-| ericaneininger   | Erica Neininger        | Met Office  | 2026-03-02 |
+| ericaneininger   | Erica Neininger        | Met Office  | 2026-03-02 |
+| iboutle          | Ian Boutle             | Met Office  | 2026-03-06 |

components/science/source/algorithm/sci_geometric_constants_mod.x90

@@ -785,6 +785,7 @@ contains
     type(field_type),             pointer :: dA_at_w2
     type(function_space_type),    pointer :: w2_fs
     integer(tik)                          :: id
+    integer(kind=i_def)                   :: depth
 
     ! Initialise inventory if it hasn't been done so already
     if (.not. dx_at_w2_inventory%is_initialised()) then
@@ -802,7 +803,8 @@ contains
 
       if ( LPROF ) call start_timing( id, 'runtime_constants.geometric' )
 
-      call dx_at_w2_inventory%add_field(dx_at_w2, w2_fs, mesh)
+      depth = mesh%get_halo_depth()
+      call dx_at_w2_inventory%add_field(dx_at_w2, w2_fs, mesh, halo_depth=depth)
       call invoke( X_divideby_Y(dx_at_w2, detj_at_w2, dA_at_w2) )
 
       if ( LPROF ) call stop_timing( id, 'runtime_constants.geometric' )
@@ -1272,6 +1274,7 @@ contains
     type(field_type),             pointer :: height
     character(len=str_def)                :: inventory_name
     integer(tik)                          :: id
+    integer(kind=i_def)                   :: depth
 
     ! Determine inventory based on space
     select case (space_id)
@@ -1312,8 +1315,9 @@ contains
 
       if ( LPROF ) call start_timing( id, 'runtime_constants.geometric' )
 
+      depth = mesh%get_halo_depth()
       space => function_space_collection%get_fs(mesh, 0, 0, space_id)
-      call inventory%add_field(height, space, mesh)
+      call inventory%add_field(height, space, mesh, halo_depth=depth)
 
       call invoke( get_height_kernel_type(height, chi, scaled_radius) )
 

components/science/source/kernel/algebra/copy_field_halo_kernel_mod.F90

@@ -0,0 +1,72 @@
+!-------------------------------------------------------------------------------
+! (c) Crown copyright 2026 Met Office. All rights reserved.
+! The file LICENCE, distributed with this code, contains details of the terms
+! under which the code may be used.
+!-------------------------------------------------------------------------------
+!> @brief Copy a field to specified halo depth
+
+module copy_field_halo_kernel_mod
+
+  use argument_mod,         only: arg_type,                  &
+                                  GH_FIELD, GH_REAL,         &
+                                  GH_READ, GH_WRITE,         &
+                                  OWNED_AND_HALO_CELL_COLUMN,&
+                                  ANY_DISCONTINUOUS_SPACE_1
+  use constants_mod,        only: r_def, i_def
+  use kernel_mod,           only: kernel_type
+
+  implicit none
+
+  private
+
+  !> Kernel metadata for Psyclone
+  type, public, extends(kernel_type) :: copy_field_halo_kernel_type
+    private
+    type(arg_type) :: meta_args(2) = (/                                    &
+         arg_type(GH_FIELD, GH_REAL, GH_WRITE, ANY_DISCONTINUOUS_SPACE_1), &
+         arg_type(GH_FIELD, GH_REAL, GH_READ,  ANY_DISCONTINUOUS_SPACE_1)  &
+         /)
+    integer :: operates_on = OWNED_AND_HALO_CELL_COLUMN
+  contains
+    procedure, nopass :: copy_field_halo_code
+  end type copy_field_halo_kernel_type
+
+  public :: copy_field_halo_code
+
+contains
+
+  !> @brief Copy field to specified halo depth
+  !> @param[in]     nlayers       The number of layers
+  !> @param[in,out] field_out     Output field
+  !> @param[in]     field_in      Input field
+  !> @param[in]     ndf           Number of degrees of freedom per cell
+  !> @param[in]     undf          Number of total degrees of freedom
+  !> @param[in]     map           Dofmap for the cell at the base of the column
+  subroutine copy_field_halo_code(nlayers,          &
+                                  field_out,        &
+                                  field_in,         &
+                                  ndf, undf, map)
+
+    implicit none
+
+    ! Arguments added automatically in call to kernel
+    integer(kind=i_def), intent(in) :: nlayers
+    integer(kind=i_def), intent(in) :: ndf, undf
+    integer(kind=i_def), intent(in), dimension(ndf) :: map
+
+    ! Arguments passed explicitly from algorithm
+    real(kind=r_def), intent(in), dimension(undf) :: field_in
+    real(kind=r_def), intent(inout), dimension(undf) :: field_out
+
+    ! Local arguments
+    integer(kind=i_def) :: k, dof
+
+    do dof = 1, ndf
+      do k = 0, nlayers-1
+        field_out(map(dof)+k) = field_in(map(dof)+k)
+      end do
+    end do
+
+  end subroutine copy_field_halo_code
+
+end module copy_field_halo_kernel_mod

components/science/unit-test/kernel/algebra/copy_field_halo_kernel_mod_test.pf

@@ -0,0 +1,36 @@
+!-----------------------------------------------------------------------------
+! (C) Crown copyright 2026 Met Office. All rights reserved.
+! For further details please refer to the file LICENCE which you should have
+! received as part of this distribution.
+!-----------------------------------------------------------------------------
+!
+!-------------------------------------------------------------------------------
+module copy_field_halo_kernel_mod_test
+
+  use constants_mod, only : r_def, i_def
+  use funit
+
+  implicit none
+
+contains
+
+  @test
+  subroutine test_of_copy_field_halo()
+
+    use copy_field_halo_kernel_mod, only : copy_field_halo_code
+
+    implicit none
+
+    real(kind=r_def)            :: field_out(3), field_in(3)
+    real(kind=r_def), parameter :: tol = 1.0e-14_r_def
+    integer(kind=i_def)         :: map(1)
+
+    field_in(:) = [ -10.0_r_def, 0.0_r_def, 10.0_r_def ]
+    map(:) = [1]
+
+    call copy_field_halo_code(3, field_out, field_in, 1, 3, map)
+    @assertEqual( field_out, field_in, tol )
+
+  end subroutine test_of_copy_field_halo
+
+end module copy_field_halo_kernel_mod_test