Physical Simulation of Baroclinic Waves and Vortices in The Atmosphere

Atmospheric flows are often associated with long waves which, in the presencet of fronts (regions with large spatial gradients of temperature or density) can produce vortices as a result of instability. Vortex motion also can lead to front formation. These processes are often associated with potential vorticity advection, which is nonlinear and, hence, not easily computable. Laboratory experiments (physical simulation) can help us to understand such complex processes in atmosphere and ocean. We present some laboratory experiments in a rotating fluid in which temperature (or density) gradients are imposed producing wavy circulations that can, under certain conditions, become unstable and result in vortices. One of the experiments involves rotating annulus in which a circular layer of uniform depth is subjected to a radial temperature gradient. Thermal Rossby and Taylor number values similar to those in large scale atmospheric flows are chosen for these experiments. The results show that baroclinic instability can produce wavy motion, which grows and produces flow pattern as well as vortices which are comparable to the atmospheric flow pattern. In another experiment, a baroclinic vortex is produced by injecting a buoyant fluid on the free surface of a denser layer of fluid (usually satlier water) in solid-body rotation. Flow visualization and measurement show that for a relatively small source Froude number when the size of the vortex is about four times the internal Rossby radius of deformation of the environment, the vortex goes unstable and usually turns in two vortices (with circumferential wave number 2) and some of the potential energy of the flow is released into the kinetic energy of the flow. Such behavior is also observed in the polar stratospheric vortex, which has implications for the formation of ozone hole in polar atmosphere.