A technique to identify vortex air using carbon monoxide observations

McDonald, A. J.; Smith, Madeleine Lindsay

doi:10.1002/2012jd019257

Cited by 13 publications

(25 citation statements)

References 55 publications

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“…In order to only capture peaks at times and locations where the vortex is well developed enough to analyse, we introduce a minimum zonal wind speed of +15.2 m s −1 (Nash et al, 1996) and a requirement for the PV gradient to be significantly above average (c.f. Manney and Lawrence, 2016), for both primary peak and secondary peaks.…”

Section: Detection Of Bifurcated Pv Gradientmentioning

confidence: 99%

“…Nash et al, 1996), or (ii) the EL of the maximum of the PV gradient times the average wind speed (e.g. Bodeker et al, 2002;Manney et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

“…Because there is a one-to-one correspondence between PV values and EL (see Fig. 1a of Nash et al, 1996), the PV values corresponding to the vortex boundary region can be used to map the size and location of the vortex in latitudelongitude coordinates. Methods to map the vortex in two dimensions often use climatological PV values corresponding to the vortex boundary (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Paparella et al, 1997), concentrations of long-lived trace gases (e.g. McDonald and Smith, 2013), Lagrangian metrics such as Lyapunov exponents or function M (e.g. Garny et al, 2007;Smith and McDonald, 2014;Serra et al, 2017), the complexity of tracer gradients through effective diffusivity (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…The increased resolution of recent reanalyses (Fujiwara et al, 2017) now allows us to resolve the structure of PV gradients in EL coordinates around the polar vortex in much finer detail than was available when the Nash et al (1996) definition was proposed. This paper investigates PV gradients during late winter and spring over the altitude range where the highest rates of Southern Hemisphere ozone depletion occur (mid-stratosphere).…”

Section: Introductionmentioning

confidence: 99%

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Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex

2018

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Abstract. The wintertime stratospheric westerly winds circling the Antarctic continent, also known as the Southern Hemisphere polar vortex, create a barrier to mixing of air between middle and high latitudes. This dynamical isolation has important consequences for export of ozone-depleted air from the Antarctic stratosphere to lower latitudes. The prevailing view of this dynamical barrier has been an annulus compromising steep gradients of potential vorticity (PV) that create a single semi-permeable barrier to mixing. Analyses presented here show that this barrier often displays a bifurcated structure where a double-walled barrier exists. The bifurcated structure manifests as enhanced gradients of PV at two distinct latitudes -usually on the inside and outside flanks of the region of highest wind speed. Metrics that quantify the bifurcated nature of the vortex have been developed and their variation in space and time has been analysed. At most isentropic levels between 395 and 850 K, bifurcation is strongest in mid-winter and decreases dramatically during spring. From August onwards a distinct structure emerges, where elevated bifurcation remains between 475 and 600 K, and a mostly single-walled barrier occurs at other levels. While bifurcation at a given level evolves from month to month, and does not always persist through a season, interannual variations in the strength of bifurcation display coherence across multiple levels in any given month. Accounting for bifurcation allows the region of reduced mixing to be better characterised. These results suggest that improved understanding of cross-vortex mixing requires consideration of the polar vortex not as a single mixing barrier but as a barrier with internal structure that is likely to manifest as more complex gradients in trace gas concentrations across the vortex barrier region.

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Section: Detection Of Bifurcated Pv Gradientmentioning

confidence: 99%

“…Nash et al, 1996), or (ii) the EL of the maximum of the PV gradient times the average wind speed (e.g. Bodeker et al, 2002;Manney et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex

2018

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A quantitative measure of polar vortex strength using the function M

Smith

McDonald

2014

JGR Atmospheres

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Changes 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 "Function M" is 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.

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Chemical definition of the mesospheric polar vortex

2015

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We present a simple chemical definition to demark the edge of the mesospheric polar vortices. Because this vortex definition does not rely on the wind field, it is useful in the mesosphere where wind observations are sparse and reanalysis winds are unreliable. The chemical definition is also insensitive to double jets that complicate vortex identification in the mesosphere. The algorithm is based on horizontal gradients of carbon monoxide (CO) and mirrors the widely used vortex edge definition in the stratosphere based on potential vorticity (PV) gradients. Here the approach is used to identify the Arctic vortex in the mesosphere during a 10 year (2004–2014) record of Microwave Limb Sounder data. Vortex size and shape comparisons are made where the CO and PV methods overlap in the upper stratosphere. A case study is presented during the NH 2008–2009 winter that demonstrates the fidelity of the CO gradient method on individual days and emphasizes the impact of double jets on methods to identify the polar vortex. We recommend transitioning from a PV or stream function‐based vortex definition in the stratosphere to using a CO gradient definition above 0.1 hPa (~60 km). The CO gradient method identifies a coherent region of high CO at 80 km that is confined to mid‐to‐high latitudes 99.8% of the time during Arctic winter. Taking advantage of the CO gradient method to identify the polar vortex adds ~20 km of reliable vortex information (from 60 to 80 km) in a region of the atmosphere where reanalyses are most suspect.

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A technique to identify vortex air using carbon monoxide observations

Cited by 13 publications

References 55 publications

Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex

Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex

A quantitative measure of polar vortex strength using the function M

Chemical definition of the mesospheric polar vortex

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