Convective Circulations in an Idealized Fluid System

by Vinogradova, Nadia.

Abstract (Summary)
We investigate the role of boundary layer forcing and surface heterogeneities on the intensity and spectral distribution of the convective circulations of an idealized convective system. Our ultimate goal is to further the understanding of atmospheric convection. However, we depart from realistic atmospheric convection and study an idealized convective system known as the Rayleigh-Bénard model in two dimensions. We extended the classical Rayleigh-Bénard model to include the effects of boundary heterogeneities. These effects are included, in particular through a sinusoidally variable surface temperature. In this idealized model, the Rayleigh number plays the role of convective available potential energy (CAPE) in atmospheric convection, while the boundary heterogeneities in the temperature play the role of boundary layer forcing. In particular, we study the effects of boundary forcing on the intensity and spectral distribution of convective circulations in great detail. We consider the problem in the linear and weakly nonlinear regimes. In the linear regime, we find an analytical solution for Rayleigh-Bénard convection with boundary forcing. We show that the inclusion of periodic boundary forcing causes discontinuities in the linear solution when critical conditions are approached. In the nonlinear regime, we find the solution by direct numerical simulation. The nonlinearities not only remove the discontinuities, but also lead to the appearance of non-trivial modes in the solution. The classical modes appear when the Rayleigh number is supercritical and the amplitude of the boundary forcing is small. Modes governed by boundary forcing dominate when its amplitude is large. Non-trivial modes with wavenumbers different from either the classical or the boundary modes appear only for intermediate values of the boundary forcing. The transitions between regions dominated by the classical Rayleigh forcing, mixed forcing, and boundary forcing depend on the Rayleigh 12 number and the wavenumber of the boundary forcing. We conclude that boundary forcing has non-trivial effects on convective circulations. This result might have important implications for atmospheric convection. Indeed, it suggests that atmospheric convection over the relatively homogeneous oceans would have different spectral distribution compared to that over heterogeneous land surfaces. This result is consistent with observations. 13
Bibliographical Information:


School:The University of Arizona

School Location:USA - Arizona

Source Type:Master's Thesis



Date of Publication:

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