[Click on picture to see
lobe area calculations.]

Lobe dynamics provides a general theoretical framework, based on invariant manifold ideas from dynamical systems theory, for discussing, describing and quantifying organized structures in a fluid flow and determining their influence on transport. In particular, using lobe dynamics we can discover, describe, and quantify

• flow barriers,
• transport "alleyways",
• water mass exchanges,
• relations between flow structures and statistical quantities of transport.

In other words, lobe dynamics tells us the most important fluid particle trajectories. Consequently, it should prove useful for both interpreting and designing Lagrangian drifter experiments.

Lobe dynamics can be used in the setting of an analytically defined velocity field (dynamical system) or in the case where the dynamical system is given in the form of a "data file", such as the output of a numerical simulation or a remote-sensing experiment.

Techniques from dynamical systems theory, particularly invariant manifolds and lobe dynamics, allow us to describe the flow structures associated with intergyre transport as well as precisely calculate intergyre flux.

Dynamical systems theory provides a rigorous definition of the boundary between the southern and northern gyres. By "rigorous" we mean that at a given time, all fluid particles in the so-constructed southern gyre either make a clockwise revolution around the southern gyre, or earlier have made such a revolution to arrive at their location at the given time. Likewise, all fluid particles in the northern gyre move in the counter-clockwise direction.

The boundary is constructed from pieces of two special curves: an unstable manifold emanating from the western boundary, and a stable manifold emanating from the eastern boundary. These curves intersect to form regions called lobes, and it is only fluid inside the lobes that can participate in intergyre transport. Hence, the areas of the lobes can be directly related to the intergyre transport.

Since these lobes are the sole mechanism for intergyre transport, their movement and geometrical shape give a complete description of the intergyre transport process. [Click on the picture at top left to see lobe area calculations.]