Using a barotropic model in spherical geometry, we construct new
steadily travelling vortex pairs and study their stability properties.
We consider pairs
composed of both point and finite-area vortices, and we represent the rotating
with a set of zonal strips of uniform vorticity. After constructing the
for a single point-vortex pair, we embed it in a rotating background, and
the equilibrium configurations that travel at constant speed without changing
For equilibrium solutions, we find that the stability depends on the relative
(which may be positive or negative) of the vortex pair to the rotating
eastward-travelling pairs are always stable, while westward-travelling
pairs are unstable
when their speeds approach that of the linear Rossby–Haurwitz waves.
finding also applies (with minor differences) to the case when the vortices
are of finite
area; in that case we find that, in addition to the point-vortex-like instabilities,
rotating background excites some finite-area instabilities for vortex pairs
otherwise be stable. As for practical applications to blocking events,
for which the
slow westward pairs are relevant, our results indicate that free barotropic
are highly unstable, and thus suggest that forcing mechanisms must play
role in maintaining atmospheric blocking events.