70
3 Basics of Nonhydrostatic Modelling
3.17.4 Results
The surface heat loss triggers convective mixing in the surface layer (Fig. 3.38).
Convective plumes extend to the sea floor in shallow regions and penetrate into the
pycnocline in deeper portions of the model domain. They create internal waves at
the pycnocline that operate to entrain pycnocline water into the surface mixed layer.
The aspect ratio of convection cells is of the order of 2. An exception are the
shallow regions where the aspect ratio approaches values of 4. This bias is presumably caused by the relatively coarse grid spacing chosen, which does not adequately
resolve the length scale of convection cells in this region.
Owing to limited penetration, the density gain in shallow water exceeds that
in deeper water, so that a density contrast between shallower and deeper regions
develops over time. With the vanishing surface heat flux, the dense water formed in
the shallow regions forms of a gravity current flowing downward on the slope. This
triggers a return flow in upper parts of the water column, which is a requirement of
volume conservation, driven by a lateral pressure gradient owing to an inclined sea
surface.
Fig. 3.38 Exercise 10. Snapshots of density distribution (shading and contours) at selected times
of the simulation
3 Basics of Nonhydrostatic Modelling
3.17.4 Results
The surface heat loss triggers convective mixing in the surface layer (Fig. 3.38).
Convective plumes extend to the sea floor in shallow regions and penetrate into the
pycnocline in deeper portions of the model domain. They create internal waves at
the pycnocline that operate to entrain pycnocline water into the surface mixed layer.
The aspect ratio of convection cells is of the order of 2. An exception are the
shallow regions where the aspect ratio approaches values of 4. This bias is presumably caused by the relatively coarse grid spacing chosen, which does not adequately
resolve the length scale of convection cells in this region.
Owing to limited penetration, the density gain in shallow water exceeds that
in deeper water, so that a density contrast between shallower and deeper regions
develops over time. With the vanishing surface heat flux, the dense water formed in
the shallow regions forms of a gravity current flowing downward on the slope. This
triggers a return flow in upper parts of the water column, which is a requirement of
volume conservation, driven by a lateral pressure gradient owing to an inclined sea
surface.
Fig. 3.38 Exercise 10. Snapshots of density distribution (shading and contours) at selected times
of the simulation