Fix ice thickness and pressure where above flotation

We don't want ice thickness and pressure to exceed their flotation
values.  Previously, we were only making sure that ice draft did
not exceed its flotation value (i.e. the draft was above the bed).

compass/ocean/mesh/remap_topography.py

@@ -158,16 +158,17 @@ def run(self):
             ds_out[var] = xr.where(valid, ds_out[var] / norm, 0.)
 
         thickness = ds_out.landIceThkObserved
+        bed = ds_out.bed_elevation
+        flotation_thickness = - (ocean_density / ice_density) * bed
+        # not allowed to be thicker than the flotation thickness
+        thickness = np.minimum(thickness, flotation_thickness)
+
         ds_out['landIcePressureObserved'] = ice_density * g * thickness
 
         # compute the ice draft to be consistent with the land ice pressure
         # and using E3SM's density of seawater
-        draft = - (ice_density / ocean_density) * thickness
-        bed = ds_out.bed_elevation
-
-        # can't be deeper than the bed
-        draft = xr.where(draft >= bed, draft, bed)
 
-        ds_out['landIceDraftObserved'] = draft
+        ds_out['landIceDraftObserved'] = \
+            - (ice_density / ocean_density) * thickness
 
         write_netcdf(ds_out, 'topography_remapped.nc')