•For dispersive waves, the shape of a wave group will not
remain constant as the group
propagates.
•Furthermore, the group generally broadens in the course
of time, that is, the energy is dispersed.
•When waves are dispersive, the speed of the wave group
is generally different from
the average phase speed of the individual Fourier components.
•In synoptic-scale atmospheric disturbances, however, the
group velocity exceeds the
phase velocity.