Wave (a) has a density profile
where 
kgm 
, 
and
l, the interface thickness, is 0.0192m. Away from the interface
the asymptotical densities are 
= 998 kgm and
= 1090 kgm . The potential density can be considered
as being the same as the fluid density here.
Wave (b) has 
which gives an
interface width of 
10lu. In the upper fluid the density is
proportional to 
and in the lower fluid it is proportional to
. In the interface region we expect the density to vary
in a smooth manner, similar to that shown in figure
4-6 for the order parameter.
Away from
the interface the ratio of the potential densities is 
.