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An investigation of the processes involved in tracer transport and exchanges within and between the different layers in the atmosphere
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- Author / Creator
- D'Amours, Réal
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This thesis investigates the transport and dispersion of substances injected in the different layers of the atmosphere, and the mechanisms by which these substances may be transferred from one layer to another. These investigations are based on results of simulations using Lagrangian dispersion models that were ``driven'' by large scale wind fields provided by the numerical weather analysis and prediction sytems in operation at the Canadian Meteorological Centre. The main substance of the thesis consists in three papers published during the course of my doctoral studies. Although each one of the papers constitutes a distinct scientific study, as a group, they are unified by their collective focus on transport within and exchange between the atmospheric layers. After a brief overview of the three main layers that account for most of the atmosphere's mass, and of their interfaces, the fundamental aspects of Lagrangian modelling, specially those concerning stochastic processes, are reviewed and discussed. Special attention is given to the relationship between the particles' trajectories in phase-space produced using a stochastic differential equation and the Fokker-Planck equation describing the time evolution of the probability density distribution of those particles in phase-space. The Lagrangian transport models developed and used operationally at the Canadian Meteorological Centre (CMC) of Environment Canada are presented, and the various simulated physical processes are also discussed. The models are applied to real cases of atmospheric transport and dispersion in the boundary layer, and are compared to available observations. Transport and dispersion of aerosols injected deeply into the stratosphere during the eruptions of the Alaskan volcanoes Okmok and Kasatochi in the summer of 2008 is investigated. The sulfate aerosol plumes resulting from these eruptions can be followed for many days after their injection into the stratosphere, illustrating clearly that the air circulates in rather well maintained streams with little vertical mixing in these layers. Investigations for the possible source regions of the 7Be observed near the surface at Harlech in the Alberta foothills, show that transfers between the lower stratosphere and the upper troposphere do occur regularly, but are generally confined to regions close to the tropopause. It is also seen that tropopause folds associated with well developed cyclonic systems induce strong and deep subsidence frequently enough to feed well maintained streams of stratospheric air into the mid and low troposphere, which later can be entrained into the boundary layer. The mechanisms governing exchange between the free troposphere and the planetary boundary layer are examined in detail with the aid of a simple diagnostic model developed to estimate the turbulent kinetic energy and the turbulent velocity variances. This model produces plausible profiles of the vertical velocity variance σw2, and of the vertical distribution of buoyancy production/destruction of this variance. The diagnosed entrainment zone (EZ) proves just as credible as that resulting from more complex models. It is found that the diagnosed σw2 profiles are smoothly attenuating in the entrainment zone, which is a few hundreds of meters deep, justifying a simplification in the calculation of Lagrangian trajectories across this zone.
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- Graduation date
- Fall 2015
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.