Laminar Analogues of Atmospheric Phenomena
Creators: name: Atkinson, Jack William
Publisher: name: Apollo - University of Cambridge Repository
Year: 2020
Subjects: subject: Geophysical Fluid Dynamics
subject: Fluid Dynamics
subject: Fluid Mechanics
subject: Atmosphere
subject: Vortices
subject: Thermals
subject: Buoyancy
subject: Simulation
subject: Experiment
subject: Vortex Dynamics
subject: Meteorology
subject: Convection
subject: Geophysics
subject: FOS: Earth and related environmental sciences
subject: Rotating Flows
subject: Vortex Rings

description: This thesis comprises a series of investigations into isolated vortices that exist within the atmosphere. It consists of numerical and experimental investigations backed up by mathematical analysis. The main thrust of the work is in using laminar analogues of complex phenomena to aid the understanding of the key physical processes involved. The first portion of the research concerns the dynamics of eyes (regions of reversed flow) at the centres of vortices. We expand upon previous work investigating the process of eye formation in shallow rotating convection. Through a series of numerical simulations we observe that, as thermal forcing is increased, the system undergoes a Hopf bifurcation from a steady state to one in which the eye oscillates. Examining the nature of the oscillations we propose that this behaviour results from a trapped inertial wave, providing a range of evidence to support this theory. Following on from this we present a series of laboratory investigations designed to replicate our numerical studies. In addition to examining large scale circulations we also include some observations of rotating cellular convection. Though unsuccessful in generating a steady eye, our discussions of experiment design and implementation provide a number of insights, and we hope that future experimental work will build upon this preliminary study. The latter portion of the thesis is given over to the study of thermals. We consider the life cycle of an axisymmetric laminar thermal as it transitions through a number of distinct stages undergoing several morphological changes. A significant achievement of the study is to establish a mathematical framework that can be used throughout the life cycle, allowing us to shed light on the transitions between stages and address some previously unresolved questions. Our numerical results show the early stages of development to be key in determining the final properties of the buoyant vortex ring that is produced, with thermals displaying an independence above a critical Reynolds number. Another notable observation is that the wake left behind by the first vortex ring can itself roll up to form a second ring that follows after the first. It is hoped that this framework and our observations of laminar thermals might perhaps be useful in providing new approaches for studying atmospheric convection.
description: Funded primarily through a doctoral training award provided through the Engineering Department by the Engineering and Physical Sciences Research Council. Additional financial support from the UK Fluids Network, Peterhouse, and the Cambridge Philosophical Society.