The parameters of
atmospheric waves[?] such as
group velocity or vertical
wavenumber depend on
mean flow direction and strength. Thus, for instance westerlies might be a good
waveguide for eastward-traveling waves, but might strongly
dissipate westward-traveling waves because the vertical wavenumber decreases or increases, respectively. Modification of the waves'
group velocity will chage their speed of
meridional propagation, directing them more polewards or more equatorwards.