The stability of one-layer vortices with inhomogeneous horizontal density distributions
is examined both analytically and numerically. Attention is focused on elliptical
vortices for which the formal stability theorem proved by Ochoa, Sheinbaum & Pavía
(1988) does not apply. Our method closely follows that of Ripa (1987) developed for
the homogeneous case; and indeed they yield the same results when inhomogenities
vanish. It is shown that a criterion from the formal analysis – the necessity of a radial
increase in density for instability – does not extend to elliptical vortices. In addition, a
detailed examination of the evolution of the inhomogeneous density fields, provided
by numerical simulations, shows that homogenization, axisymmetrization and loss of
mass to the surroundings are the main effects of instability.