To investigate experimentally 3D chaotic Lagrangian motion in steady baroclinic waves, long-term particle tracking was conducted on the wavenumber-3, 4 and 5 flows in a differentially-heated rotating annulus fluid. With the use of fluorescent solution microcapsules as tracer particles and an automated tracking system, the trajectories were observed in each wavenumber for more than 10 hours. Tracer particles in all the observed trajectories preferred to track the same cyclic route of the flow

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... ions for about half of the total time and were chaotically trapped in the vortices where they resided for an indefinite time. The preference of this cyclic route has been expected from the numerical investigation of the Lagrangian motion made by Sugata and Yoden (1994) and supports their Lagrangian view of the heat transport. Furthermore, a few interesting results were obtained for the wavenumber dependence of the Lagrangian motion: a transition rate, which is the number of the region transitions per time, grows slightly as the wavenumber increases; on the Lagrangian view, the total inward heat flux of wavenumber-5 is considered distinctively larger than those of wavenumber-3 and 4.