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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
 
Sequence of images of smoke within a stratospheric vortex observed by CALIOP satellite instrument, over period 7 January to 9 February 2020, during which the centre of the smoke rises from 17.5km to 25km. (From Khaykin et al 2020.)
Brief summary: 
The formation and maintenance of long-lived smoke-filled vortices, observed in the stratosphere following intense wildfires in Canada in 2017 and in Australia in 2019-20, will be studied using dynamical theory and numerical simulations.
Importance of the area of research concerned: 
Smoke from strong wildfires regularly penetrates the stratosphere and is subsequently transported and dispersed on hemispheric scales, providing a substantial perturbation to the stratospheric aerosol layer. Smoke is a very effective absorber of solar radiation and in some recent cases it has been observed that the resulting heating has caused the formation of long-lived coherent vortices which inhibit the dispersion [1]. These vortices and the smoke within them may ascend several km, overcoming the extratropical descent expected in the large-scale circulation [2]. A complete description of these vortices must include the radiative properties of smoke, the effect of heating on atmospheric vortices (e.g. [3]) and the transport of smoke, which will be affected by interaction between the vortex and the large-scale flow. Vortex formation and accompanying organisation of transport may be relevant to other perturbations of the stratosphere, such as injection of volcanic aerosol, and its implications for future climate and chemical change need to be assessed.
Project summary : 
The project will study the combination of physical and fluid-dynamical processes acting in the formation, maintenance and vertical displacement of smoke-filled vortices. The focus will be on the vortex scale, typically a few 100km in the horizontal and a few km in the vertical. A set of models will be constructed, starting with axisymmetric models where the relative motion of the smoke and the vortex is imposed according to simple rules and then moving on to full numerical simulation in 3-D models which represent the transport of the smoke in more detail. Specific questions to be addressed will include the requirements, e.g. on the initial density of the smoke, for the formation of coherent vortices, the rate of loss of smoke from the vortex as it moves in the vertical, and the role of processes such as convective or inertial instability in determining the structure of strong vortices.
What will the student do?: 
The student will gain experience in theoretical and computational fluid dynamics, defining and studying mathematical models, using a variety of methods including numerical simulation of 3-D time dependent flows. The student will, with the supervisors, consider how best to design models to capture and isolate the key physical processes active in the formation of smoke-driven vortices. The aim will be to reduce the complex details of real atmospheric flows to simplified models that, whilst retaining the essential physics, can be thoroughly studied to address well-posed scientific questions and to establish basic scientific principles. Numerical simulations will be carried out an existing and well-tested numerical model (DIABLO). Local supercomputing facilities will be used, with parallel computation available when needed. Diagnostic tools available will include passive tracers and Lagrangian particles, which will provide extra information on transport and mixing. Offline calculations using a radiation code will be used to as a basis for model design and for scientific interpretation of results of simulations.
References - references should provide further reading about the project: 
Allen, D. R., Fromm, M. D., Kablick III, G. P., and Nedoluha, G. E. 2020. Smoke with Induced Rotation and Lofting (SWIRL) in the Stratosphere, J. Atmos. Sci., 77, 4297–4316, https://doi.org/10.1175/JAS-D-20-0131.1.
Lestrelin, H., Legras, B., Podglajen, A., and Salihoglu, M. 2021. Smoke-charged vortices in the stratosphere generated by wildfires and their behaviour in both hemispheres: comparing Australia 2020 to Canada 2017, Atmos. Chem. Phys., 21, 7113–7134, https://doi.org/10.5194/acp-21-7113-2021.
Haynes, P. H., Ward, W. E., 1993: The effect of realistic radiative transfer on potential vorticity structures, including the influence of background shear and strain. J. Atmos. Sci., 50, 3431—3453. https://doi.org./10.1175/1520-0469(1993)050%3C3431:TEORRT%3E2.0.CO;2
Applying
You can find out about applying for this project on the Department of Applied Mathematics and Theoretical Physics (DAMTP) page.
Department of Applied Mathematics and Theoretical Physics PhD Admissions
Dr John Taylor
Professor Peter Haynes