A quantitative measure of polar vortex strength using the fu

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TitleA quantitative measure of polar vortex strength using the function MAbstractChanges in the dynamics of the stratospheric polar vortices can significantly affect the composition of air in the polar stratosphere, with the dynamics of the vortex barrier being particularly important. The FÌunction M Ìis a recently proposed measure for quantifying transport in dynamical systems. We show that it can be used not only to visualize the structure of the stratospheric polar region in detail but also to provide a basis for quantitative measures capturing important aspects of vortex dynamics. Two such measures have been calculated daily for August-October 2009 and 2010 in the Southern Hemisphere for potential temperatures of 600, 700, and 900 K, as well as for three different Northern Hemisphere winter periods for 900 K. We discuss a measure of vortex barrier strength and permeability based on the average value of the function M near the vortex edge. The second measure, associated with vortex barrier area, is obtained by calculating the area associated with values of M above a threshold. Both measures are found to be potentially useful, with the area-based measure providing the most convincing results. The measures are based on a Lagrangian framework and follow the vortex edge, allowing periods when the vortex retains its dynamical integrity to be identified even when the vortex is greatly distorted. We also discuss a strong linear correlation near the vortex edge between values of the function M calculated over different time periods, suggesting that the structure of the polar vortex is coherent over periods of at least 30 days. Key Points The function M dynamical measure is useful both qualitatively and quantitatively Quantitative measures of vortex dynamics based on the function M are tested The stratospheric polar vortex is usually coherent over a 30 day period Copyright2014. American Geophysical Union. All Rights Reserved.AcknowledgementsMERRA data were disseminated by the Global Modeling and Assimilation Office (GMAO) and the 571 GES DISC. A.J.M. would like to thank the EOS MLS team at the Jet Propulsion Laboratory/NASA for the provision of the EOS MLS data via their web site. This work was supported by the Royal Society of New Zealand Marsden Fund project Ã‰valuating the Impact of Excess Ionization on the Atmosphere.Ì

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1st AuthorSmith, M.AuthorSmith, M.McDonald, A.Year2014JournalJournal of Geophysical Research AtmospheresVolume119Number10Pages5966-5985DOI10.1002/2013JD020572URLhttps://www.scopus.com/inward/recor.....35ecd7b7b9c10fde9a200686eKeywordsDynamical systemsDynamicsLagrange multipliersUpper atmosphere, barrierDynamical integritiesLagrangianLagrangian frameworksPolar vortex strengthquantitativeQuantitative measuresStratospheric polar vortex, Vortex flow, Lagrangian analysisNorthern Hemispherepolar vortexpotential temperaturequantitative analysisstratospherevisualization, rank3Author KeywordsbarrierdynamicsLagrangianquantitativestratospherevortex

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TypeArticleCitationSmith, M. and McDonald, A. (2014) A quantitative measure of polar vortex strength using the function M. Journal of Geophysical Research Atmospheres, 119(10): 5966-5985 doi:10.1002/2013JD020572