Laboratory Experiments of Lagrangian Motions in a Steady Baroclinic Wave

Internal Structures of Vortices

Abstract

The basic structure of steady baroclinic waves observed in a differentially-heated rotating-fluid annulus is found to be composed of high- and low-pressure vortices, upper-level (eastward) and lower-level (westward) jet-streams meandering through the vortices, and boundary layers. On the basis of this structure, recently, Sugata and Yoden (1994) numerically studied the Lagrangian motion of a fluid particle in the annulus. Stimulated by their results, we conducted experiments on a rotating-fluid annulus by injecting drops of red ink into a jet or a vortex and observing the results in the co-rotating frame of the drifting wave. The observed 3-D ink patterns appearing in the fluid revealed the inner region of the vortices. That is, their structures are composed of a core region, which is rather well isolated and split into separate upper and lower layers, and next to the core a transition zone where fluid particles are frequently transported to and from its outside, but rarely to the core region. Several interesting phenomena observed in the annulus are also presented, such as one suggestive of the Ekman pumping found in the low-pressure vortex.