B208 回転円筒水槽実験における定常傾圧波の渦の構造の観測

Abstract

The basic structure of steady baroclinic waves observed in a differentially-heated rotating-fluid annulus is 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, we 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 co-rotating reference frame of the wave which drifted eastward (counter-clockwise) relative to the rotating annulus. The observed 3-D ink patterns appearing in the fluid revealed the inner region 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 a 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 downwelling caused by the Ekman pumping was observed in the upper layer of the core in the high-pressure vortex and similarly a weak upwelling in the lower layer of the core in the low-pressure vortex. In addition, the present experiments were found to yield some results which are similar to those determined in the numerical simulations of Sugata and Yoden (1994) which followed the Lagrangian motion of a fluid particle in the annulus.