Fix velocity exchanges across tripolar seam

src/BoundaryConditions/fill_halo_regions_zipper.jl

@@ -77,7 +77,7 @@ end
 
     # We substitute the redundant part of the last row to ensure consistency
     @inbounds u[i, Ny, k] = ifelse(i > Nx ÷ 2, sign * u[i′, Ny, k], u[i, Ny, k])
-    
+
     return nothing
 end
 
@@ -93,6 +93,8 @@ end
         end
     end
 
+    @inbounds v[i, Ny, k] = ifelse(i > Nx ÷ 2, sign * v[i′, Ny + 1, k], v[i, Ny, k])
+
     return nothing
 end
 

test/test_zstar_coordinate.jl

@@ -67,7 +67,7 @@ const C = Center
 const F = Face
 
 @testset "ZStar coordinate scaling tests" begin
-    @info "testing the ZStar coordinate scalings"
+    @info "Testing ZStar coordinate scalings..."
 
     z = MutableVerticalDiscretization((-20, 0))
 
@@ -103,7 +103,7 @@ const F = Face
 end
 
 @testset "MutableVerticalDiscretization tests" begin
-    @info "testing the MutableVerticalDiscretization in ZCoordinate mode"
+    @info "Testing the MutableVerticalDiscretization in ZCoordinate mode..."
 
     z = MutableVerticalDiscretization((-20, 0))
 
@@ -195,7 +195,7 @@ end
 
                     info_msg = info_message(grid, free_surface)
                     @testset "$info_msg" begin
-                        @info "  Testing a $info_msg"
+                        @info "  Testing a $info_msg..."
                         model = HydrostaticFreeSurfaceModel(; grid,
                                                             free_surface,
                                                             tracers = (:b, :c),
@@ -213,7 +213,7 @@ end
             end
         end
 
-        @info "  Testing a ZStar and Runge Kutta 3rd order time stepping"
+        @info "  Testing a ZStar and Runge Kutta 3rd order time stepping..."
 
         topology = topologies[2]
         rtg  = RectilinearGrid(arch; size=(10, 10, 20), x=(0, 100kilometers), y=(-10kilometers, 10kilometers), topology, z=z_stretched)
@@ -277,8 +277,12 @@ end
 
             # Instead of initializing with random velocities, infer them from a random initial streamfunction
             # to ensure the velocity field is divergence-free at initialization.
-            ψ = Field{Center, Center, Center}(grid)
-            set!(ψ, rand(size(ψ)...))
+            ψ = Field{Face, Face, Center}(grid)
+	    # Set streamfunction amplitude ~10⁶ to yield non-negligible initial velocities.
+	    # Grid spacing in the test grid ranges from 10⁵ to 10⁶ meters,
+            # so taking spatial derivatives (∂ψ/∂x or ∂ψ/∂y) divides by grid spacing,
+            # resulting in velocity magnitudes on the order of O(1) m/s.
+            set!(ψ, 10^6 * rand(size(ψ)...))
             uᵢ = ∂y(ψ)
             vᵢ = -∂x(ψ)