Abstract
The Lagrangian flow around a Kida vortex [J. Phys. Soc. Jpn. 50, 3517 (1981)], an elliptical two-dimensional vortex patch embedded in a uniform and constant background shear, is described by a nonintegrable two-degree-of-freedom Hamiltonian. For small values of shear, there exist large chaotic zones surrounding the vortex, often much larger than the vortex itself and extremely close to its boundary. Motion within the vortex is integrable. Implications for two-dimensional turbulence are discussed.