Shift of subtropical transport barriers explains observed hemispheric asymmetry of decadal trends of age of air

Stiller, G. P.; Fierli, F.; Ploeger, Felix; Cagnazzo, Chiara; Funke, B.; Haenel, Florian; Reddmann, Thomas; Riese, Martin; Clarmann, T. von

doi:10.5194/acp-17-11177-2017

Cited by 45 publications

(49 citation statements)

References 43 publications

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“…Recently, Stiller et al (2017) found the same meridional pattern in N 2 O from the CLaMS CTM model, driven by the ERA-Interim reanalysis, and explored the hemispheric symmetry in the AoA, confirming a southward displacement of the stratospheric circulation pattern between the potential temperature levels of 500 and 800 K. Additionally, Garfinkel et al (2017), using the GEOSCCM model, also found an increase in the Northern Hemisphere AoA for the period after 1992 when including the stratospheric aerosols and ODS evolution in the simulation. The positive trend peaks between 20 and 30 • N and extends from 20 to 40 km.…”

Section: Discussion Of the Hemispheric Asymmetrymentioning

confidence: 99%

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

et al. 2017

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Abstract. Over 20 years of stratospheric NO 2 vertical column density (VCD) data from ground-based zenith DOAS spectrometers were used for trend analysis, specifically, via multiple linear regression. Spectrometers from the Network for the Detection of Atmospheric Composition Change (NDACC) cover the subtropical latitudes in the Northern Hemisphere (Izaña, 28 • N), the southern Subantarctic (Ushuaia, 55 • S) and Antarctica (Marambio, 64 • S, and Belgrano, 78 • S). The results show that for the period 1993-2014, a mean positive decadal trend of +8.7 % was found in the subtropical Northern Hemisphere stations, and negative decadal trends of −8.7 and −13.8 % were found in the Southern Hemisphere at Ushuaia and Marambio, respectively; all trends are statistically significant at 95 %. Belgrano only shows a significant decadal trend of −11.3 % in the summer/autumn period. Most of the trends result from variations after 2005. The trend in the diurnal build-up per hour (DBU) was used to estimate the change in the rate of N 2 O 5 conversion to NO 2 during the day. With minor differences, the results reproduce those obtained for NO 2 . The trends computed for individual months show large monthto-month variability. At Izaña, the maximum occurs in December (+13.1 %), dropping abruptly to lower values in the first part of the year. In the Southern Hemisphere, the polar vortex dominates the monthly distributions of the trends. At Marambio, the maximum occurs in mid-winter (−21 %), whereas at the same time, the Ushuaia trend is close to its annual minimum (−7 %). The large difference in the trends at these two relatively close stations suggests a vortex shift towards the Atlantic/South American area over the past few years. Finally, the hemispheric asymmetry obtained in this work is discussed in the framework of the results obtained by previous works that considered tracer analysis and BrewerDobson circulation. The results obtained here provide evidence that the NO 2 produced by N 2 O decomposition is not the only cause of the observed trend in the stratosphere and support recent publications pointing to a dynamical redistribution starting in the past decade.

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Section: Discussion Of the Hemispheric Asymmetrymentioning

confidence: 99%

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

et al. 2017

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“…In particular, Ray et al (2014) and Ploeger et al (2015) find that changes in isentropic mixing have contributed to recent observed mean age trends in the LS. Most recently, Stiller et al (2017) suggest that these changes are connected to a southward shift of the Brewer-Dobson circulation. As such a shift may also imply changes in lower stratospheric mixing, however, this finding is not necessarily inconsistent with the ones discussed in the earlier studies.…”

Section: Geophysical Research Lettersmentioning

confidence: 99%

Recent Decline in Extratropical Lower Stratospheric Ozone Attributed to Circulation Changes

Wargan

Orbe

Pawson

et al. 2018

Geophysical Research Letters

100

115

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The 1998–2016 ozone trends in the lower stratosphere are examined using the Modern‐Era Retrospective Analysis for Research and Applications Version 2 (MERRA‐2) and related National Aeronautics and Space Administration products. After removing biases resulting from step changes in the MERRA‐2 ozone observations, a discernible negative trend of −1.67 ± 0.54 Dobson units per decade (DU/decade) is found in the 10‐km layer above the tropopause between 20°N and 60°N. A weaker but statistically significant trend of −1.17 ± 0.33 DU/decade exists between 50°S and 20°S. In the Tropics, a positive trend is seen in a 5‐km layer above the tropopause. Analysis of an idealized tracer in a model simulation constrained by MERRA‐2 meteorological fields provides strong evidence that these trends are driven by enhanced isentropic transport between the tropical (20°S–20°N) and extratropical lower stratosphere in the past two decades. This is the first time that a reanalysis data set has been used to detect and attribute trends in lower stratospheric ozone.

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“…Bönisch et al () highlighted the importance of structural changes in the residual circulation showing decoupled changes in the deep and shallow branches at the beginning of the 21st century. Moreover, the AoA estimates reveal a robust interhemispheric asymmetry in the trends over 2002–2012 (Haenel et al, ; Khaykin et al, ; Mahieu et al, ; Stiller et al, , ). It remains unclear what has led to these changes in the trends before and after 2000.…”

Section: Introductionmentioning

confidence: 99%

New Insights on the Impact of Ozone‐Depleting Substances on the Brewer‐Dobson Circulation

et al. 2019

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It has recently been recognized that, in addition to greenhouse gases, anthropogenic emissions of ozone‐depleting substances (ODS) can induce long‐term trends in the Brewer‐Dobson circulation (BDC). Several studies have shown that a substantial fraction of the residual circulation acceleration over the last decades of the twentieth century can be attributed to increasing ODS. Here the mechanisms of this influence are examined, comparing model runs to reanalysis data and evaluating separately the residual circulation and mixing contributions to the mean age of air trends. The effects of ozone depletion in the Antarctic lower stratosphere are found to dominate the ODS impact on the BDC, while the direct radiative impact of these substances is negligible over the period of study. We find qualitative agreement in austral summer BDC trends between model and reanalysis data and show that ODS are the main driver of both residual circulation and isentropic mixing trends over the last decades of the twentieth century. Moreover, aging by isentropic mixing is shown to play a key role on ODS‐driven age of air trends.

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Shift of subtropical transport barriers explains observed hemispheric asymmetry of decadal trends of age of air

Cited by 45 publications

References 43 publications

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

Recent Decline in Extratropical Lower Stratospheric Ozone Attributed to Circulation Changes

New Insights on the Impact of Ozone‐Depleting Substances on the Brewer‐Dobson Circulation

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Shift of subtropical transport barriers explains observed hemispheric asymmetry of decadal trends of age of air

Cited by 45 publications

References 43 publications

Hemispheric asymmetry in stratospheric NO&lt;sub&gt;2&lt;/sub&gt; trends

Hemispheric asymmetry in stratospheric NO&lt;sub&gt;2&lt;/sub&gt; trends

Recent Decline in Extratropical Lower Stratospheric Ozone Attributed to Circulation Changes

New Insights on the Impact of Ozone‐Depleting Substances on the Brewer‐Dobson Circulation

Contact Info

Product

Resources

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Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends