This volume deals with various nonlinear phenomena in geophysical flows. Processes studied are, among others, the stability of currents and vortices, internal wave generation and propagation, and atmosphere-ocean interaction. The geographic extent of the processes discussed range from the local (the Gulf of California and other marginal seas) to the global (the general oceanic circulation). The studies contained in this volume are based on observations (in situ as well as satellite measurements), theoretical analysis (Hamiltonian fluid dynamics and stability theory), numerical simulations and laboratory experiments. This collection of excellent papers by international experts in geophysical fluid dynamics is based upon presentations at a colloquium held in memory of Professor Pedro Ripa on the first anniversary of his untimely death. The legacy of Professor Ripa is highly regarded in the field of geophysical fluid dynamics. Early in his scientific career he made two landmark contributions to the field by showing, in 1981, that potential vorticity conservation is a consequence, via Noether's Theorem, of the Lagrangian particle re-labelling symmetry. Two years later, he established the necessary conditions for instability in the shallow water equations, nowadays known as "Ripa's Theorem". Audience: A constant in Professor Ripa's work was the search for simplified or approximate models that contained the essential physics of the problem under study. This volume, composed to honour him, constitutes valuable reading for both researchers and graduate students interested in fluid mechanics and particularly in geophysical fluid dynamics.