Experimental Observations of Internal Vortex Structures in Steady Baroclinic Waves

Abstract

The basic structures of steady baroclinic waves observed in a differentially heated rotating-fluid annulus are well known to be composed of high and low pressure vortices, upper (eastward) and lower (westward) jet streams meandering through the vortices, and boundary layers. In order to find the structure of the vortices, the authors have conducted a series of experiments on a rotating-fluid annulus by injecting a few drops of red ink (and/or uranine solution) into a vortex or a jet and observing the results in the corotating reference frame of the wave that drifted eastward (counterclockwise) relative to the rotating annulus. The observed 3D ink patterns appearing in the fluid revealed the inner regions of the vortices. Their structures are composed of a core and a transition zone (separatrix layer). The core is a rather well-isolated region around the axis of the vortex and is split into separate upper and lower layers. The transition zone is a thin layer next to the core and the fluid is frequently transported to and from its outside, but rarely to the core. Then a weak upwelling caused by the Ekman pumping was observed in the lower layer of the core in the low pressure vortex and similarly a weak downwelling in the upper layer of the core in the high pressure vortex. In addition, the present experiments were found to yield some results that are similar to those determined in the numerical simulations of Sugata and Yoden which followed the Lagrangian motion of a fluid particle in the annulus.