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Much of my previous research has been performed in the field of geophysical fluid dynamics. Specifically, my research has focussed on the role played by quasi-two-dimensional (Q2D) vortex structures in the earth's atmosphere and oceans. Two-dimensional motions occur in situations where some physical mechanism acts to suppress the motion of the fluid so that the flow is restricted in one direction. In the case of the earth's atmosphere and oceans, differences in salinity and temperature and/or the rotation of the Earth cause geophysical flows to behave as quasi, or almost, two-dimensional. Vortex structures arise due to a local forcing on the fluid and are set apart from the background fluid by their physical properties [1]. One of the primary vortex structures is the vortex dipole which consists of a strong jet of fluid with a system of two vortices of opposite rotational sense at its front (Fig. 1). The vortex structures that occur in nature tend to be long-lived and can travel great distances before they dissipate. This implies that they greatly affect our weather and climate since they contribute to the transport of dust, heat, salt and chemical substances [2]. These vortices interact with one another to form a turbulent flow. Laboratory experiments can be used as an effective tool for studying these Q2D flows. |
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| One of my research projects focussed on the role played by the interaction between vortices and rigid boundaries in the general dynamics of a Q2D flow. The effects of boundaries on the evolution of these flows have been observed to occur naturally in closed or semi-enclosed elongated basins in which the wind-driven circulation leads to the formation of regular arrays of vortices. These flow patterns play an important role in the dynamics of these regions because they may lead to efficient transport and mixing of passive substances such as salt or nutrients. As such, the study of the effect of rigid boundaries on the flow evolution of Q2D turbulence is of importance. I preformed an experimental investigation of the variations of the net angular momentum that arise in Q2D turbulence. These variations were then shown to be a result of the | |
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emergence of vortex dipoles in the flow and the subsequent interaction of these dipoles with the walls of the tank (Fig 2). Also, the extent to which the dipole-wall interactions influence the global characteristics of the turbulent flow, in particular the net angular momentum was investigated. The results were then presented at the Canadian Undergraduate Physics Conference 2003 as well as in a paper that was published in Geophysical and Astrophysical Fluid Dynamics [3]. |
This investigation was then expanded to include the influence of the rotation of the Earth on these flows. On a rotating planet the effect of the Coriolis parameter will change according to the latitudinal position on the earth's surface (Beta-effect). The large-scale structures that are present in the atmosphere and oceans can span several degrees of latitude and as such they are influenced by the changing Coriolis parameter. In direct opposition to 3D turbulent flows, 2D turbulence consists of many small vortices that combine over time to form a small number of large vortex structures. The inverse energy cascade is a characteristic feature of 2D |
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| turbulence through which the energy that was contained in the many smaller vortices cascades up to larger length scale of the resulting vortices. When the 2D turbulent flows occur on the beta-plane however, the inverse cascade of energy is found to be halted by the formation of zonal jets. These jets have been observed in many geophysical systems and are a common feature in the atmospheres of Jupiter, Saturn and the Earth. The emergence of these zonal jets from Q2D turbulent flows on the beta-plane was investigated as well as the role played by vortex structures in the formation and maintenance of these jets. The results of this study were then presented in a paper that is accepted for publication in Geophysical and Astrophysical Fluid Dynamics [4] |  |
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References 1. Voropayev, S. I. and Afanasyev, Y. D. Vortex Structures in a Stratified Fluid. Chapman and Hall, London (1994). 2. Maassen, S. R. "Self-organization of confined two-dimensional flows." PhD thesis, Eindhoven University of Technology, The Netherlands (2000). 3. Wells, J. and Afanasyev, Ya. (2003) "Decaying quasi-two-dimensional turbulence in a rectangular container: laboratory experiments" Geophys. Astrophys. Fluid Dynamics, 98 (1), 1-20 (2004). 4. Afanasyev, Y. D. and Wells, J., "Quasi-two-dimensional turbulence on the polar beta-plane: laboratory experiments" Geophys. Astrophys. Fluid Dynamics, 99 (1), 1-17 (2005). | |