Add diags for east, north velocity components.

- This is required for our BOEM-funded Arctic project. It needs
  something similar for SIS2 as well.

src/diagnostics/MOM_diagnostics.F90

@@ -136,6 +136,7 @@ module MOM_diagnostics
   integer :: id_sst  = -1, id_sst_sq = -1, id_sstcon = -1
   integer :: id_sss  = -1, id_sss_sq = -1, id_sssabs = -1
   integer :: id_ssu  = -1, id_ssv    = -1
+  integer :: id_ssu_east = -1, id_ssv_north = -1
 
   ! Diagnostic IDs for  heat and salt flux fields
   integer :: id_fraz         = -1
@@ -1283,6 +1284,8 @@ subroutine post_surface_dyn_diags(IDs, G, diag, sfc_state, ssh)
 
   ! Local variables
   real, dimension(SZI_(G),SZJ_(G)) :: speed  ! The surface speed [L T-1 ~> m s-1]
+  real :: ssu_east(SZI_(G),SZJ_(G))        ! Surface velocity due east component [L T-1 ~> m s-1]
+  real :: ssv_north(SZI_(G),SZJ_(G))       ! Surface velocity due north component [L T-1 ~> m s-1]
   integer :: i, j, is, ie, js, je
 
   is = G%isc ; ie = G%iec ; js = G%jsc ; je = G%jec
@@ -1304,6 +1307,17 @@ subroutine post_surface_dyn_diags(IDs, G, diag, sfc_state, ssh)
     call post_data(IDs%id_speed, speed, diag, mask=G%mask2dT)
   endif
 
+  if (IDs%id_ssu_east > 0 .or. IDs%id_ssv_north > 0) then
+    do j=js,je ; do i=is,ie
+      ssu_east(i,j) = ((0.5*(sfc_state%u(I-1,j) + sfc_state%u(I,j))) * G%cos_rot(i,j)) + &
+                      ((0.5*(sfc_state%v(i,J-1) + sfc_state%v(i,J))) * G%sin_rot(i,j))
+      ssv_north(i,j) = ((0.5*(sfc_state%v(i,J-1) + sfc_state%v(i,J))) * G%cos_rot(i,j)) - &
+                       ((0.5*(sfc_state%u(I-1,j) + sfc_state%u(I,j))) * G%sin_rot(i,j))
+    enddo ; enddo
+    if (IDs%id_ssu_east > 0 ) call post_data(IDs%id_ssu_east, ssu_east, diag, mask=G%mask2dT)
+    if (IDs%id_ssv_north > 0 ) call post_data(IDs%id_ssv_north, ssv_north, diag, mask=G%mask2dT)
+  endif
+
 end subroutine post_surface_dyn_diags
 
 
@@ -1912,6 +1926,10 @@ subroutine register_surface_diags(Time, G, US, IDs, diag, tv)
       'Sea Surface Meridional Velocity', 'm s-1', conversion=US%L_T_to_m_s)
   IDs%id_speed = register_diag_field('ocean_model', 'speed', diag%axesT1, Time, &
       'Sea Surface Speed', 'm s-1', conversion=US%L_T_to_m_s)
+  IDs%id_ssu_east = register_diag_field('ocean_model', 'ssu_east', diag%axesT1, Time, &
+      'Eastward velocity', 'm s-1', conversion=US%L_T_to_m_s)
+  IDs%id_ssv_north = register_diag_field('ocean_model', 'ssv_north', diag%axesT1, Time, &
+      'Northward velocity', 'm s-1', conversion=US%L_T_to_m_s)
 
   if (associated(tv%T)) then
     IDs%id_sst = register_diag_field('ocean_model', 'SST', diag%axesT1, Time, &