Diabatic Ekman Turbulence

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The circulation of the tropical atmosphere is, in part, organized by regions of strong rotation, or vortical turbulence. Some of these regions develop into tropical cyclones. A fundamental fluid dynamical model will be developed, which captures the essential processes that allow coherent vortical structures to emerge in the tropical atmosphere, the diabatic Ekman turbulence model. Unlike simpler models (shallow water or two-level quasigeostrophic) it can represent two processes that are necessary for the formation of tropical cyclones, Ekman pumping and wind-induced surface heat exchange (WISHE). Preliminary numerical experiments using this model demonstrate that diabatic Ekman turbulence can spontaneously self-organize into intense hurricane-like vortices. Two lines of research will be carried out. The first is to study the emergence of coherent structures, focusing on the predictability of the frictional radiative convective equilibrium that is achieved with a given parameter setting. Preliminary results indicate that the same parameter settings can result in discrete quasi-equilibrated states with different numbers and intensities of vortices. The dependence of the equilibrated states and their predictability on the initial conditions and the parameter settings will be explored. The second activity is a study of the dynamical mechanisms that operate in the diabatic Ekman turbulence model, including those that give rise to the intensification of individual cyclones, the processes that produce vortex mergers and vortex symmetrization, and the interactions between waves and vortices.Broader impacts of this work are in its relevance to the development and growth of tropical cyclones, with possible implications for their statistical prediction. The model will be developed as an educational tool. A student will be involved in the research through a collaboration with the University of Washington.