64
3 Basics of Nonhydrostatic Modelling
In comparison, the CFL stability criteria (Eqs. 3.35 and 3.43) are often (but not
always!) associated with relatively shorter time steps.
3.15.5 Results
Surface cooling creates unstable density stratification in vicinity of the sea surface
(Fig. 3.33). The degree of unstable stratification increases over time to a point when
the critical Rayleigh number is exceeded and convection follows. This onset of
convection takes place in this experiment after approximately 40 min of simulation. Convection cells appear near the surface on a fairly small spatial scale set by
the grid spacing prescribed. Convection cells comprise individual sinking plumes
and compensating upward flows. Individual plumes attain vertical speeds of up to
12 cm/s.
Fig. 3.33 Exercise 8. Distributions of relative density (ρ − ρ s ) (color shading and contours) at
selected times of the simulation. Shown are values of relative density in a range between 0 and
0.02 kg/m
3
3 Basics of Nonhydrostatic Modelling
In comparison, the CFL stability criteria (Eqs. 3.35 and 3.43) are often (but not
always!) associated with relatively shorter time steps.
3.15.5 Results
Surface cooling creates unstable density stratification in vicinity of the sea surface
(Fig. 3.33). The degree of unstable stratification increases over time to a point when
the critical Rayleigh number is exceeded and convection follows. This onset of
convection takes place in this experiment after approximately 40 min of simulation. Convection cells appear near the surface on a fairly small spatial scale set by
the grid spacing prescribed. Convection cells comprise individual sinking plumes
and compensating upward flows. Individual plumes attain vertical speeds of up to
12 cm/s.
Fig. 3.33 Exercise 8. Distributions of relative density (ρ − ρ s ) (color shading and contours) at
selected times of the simulation. Shown are values of relative density in a range between 0 and
0.02 kg/m
3