  The Lamb dipole is a traveling wave solution to the two-dimensional Euler
equations introduced by S. A. Chaplygin (1903) and H. Lamb (1906) at the early
20th century. We prove orbital stability of this solution based on a vorticity
method initiated by V. I. Arnold. Our method is a minimization of a penalized
energy with multiple constraints that deduces existence and orbital stability
for a family of traveling waves. As a typical case, orbital stability of the
Lamb dipole is deduced by characterizing a set of minimizers as an orbit of the
dipole by a uniqueness theorem in the variational setting.
