eprintid: 18711
rev_number: 18
eprint_status: archive
userid: 602
dir: disk0/00/01/87/11
datestamp: 2009-12-22 16:16:02
lastmod: 2015-07-23 09:38:17
status_changed: 2009-12-22 16:16:02
type: thesis
metadata_visibility: show
item_issues_count: 0
creators_name: Matthewman, N.J.
creators_id: NJMAT10
title: A vortex dynamics perspective on stratospheric sudden warmings
ispublished: unpub
subjects: 10700
divisions: F59
abstract: A vortex dynamics approach is used to study the underlying mechanisms leading
to polar vortex breakdown during stratospheric sudden warmings (SSWs). Observational
data are used in chapter 2 to construct climatologies of the Arctic polar vortex
structure during vortex-splitting and vortex-displacement SSWs occurring between
1958 and 2002. During vortex-splitting SSWs, polar vortex breakdown is shown to
be typically independent of height (barotropic), whereas breakdown during vortex-displacement
SSWs is shown to be strongly height dependent (baroclinic).
In the remainder of the thesis (chapters 3-7), a hierarchy of models approach is
used to investigate a possible resonant excitation mechanism which is responsible for
the vortex breakdown seen in our observational study. A single layer topographically
forced vortex model is shown to exhibit vortex-splitting behaviour similar to that
observed during SSWs. Two analytical reductions, the first a fully nonlinear analytical
model of an elliptical vortex in strain and rotation velocity fields, the second a weakly
nonlinear asymptotic theory applied to a topographically forced vortex, show that
vortex-splitting in the model occurs due to a self-tuning resonance of the vortex with
the underlying topography.
Resonant excitation of an idealized polar vortex by topographic forcing is then investigated in a three-dimensional quasi-geostrophic model, with emphasis on the
vertical structure of the vortex during breakdown. It is shown that vortex breakdown
similar to that observed during displacement SSWs occurs due to a linear resonance
of a baroclinic mode of the vortex, whereas breakdown similar to that observed during
splitting SSWs occurs due to a resonance of the barotropic mode. The role of
self-tuning in these resonant behaviours is then discussed in relation to the analytic
reductions of the single layer model.
date: 2009-10
vfaculties: VMPS
oa_status: green
thesis_class: doctoral_open
language: eng
thesis_view: UCL_Thesis
dart: DART-Europe
primo: open
primo_central: open_green
lyricists_name: Matthewman, N
lyricists_id: NJMAT10
full_text_status: public
pages: 326
institution: UCL (University College London)
department: Department of Mathematics
thesis_type: Doctoral
citation:        Matthewman, N.J.;      (2009)    A vortex dynamics perspective on stratospheric sudden warmings.                   Doctoral thesis , UCL (University College London).     Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/18711/1/18711.pdf