Is the Brewer‐Dobson circulation increasing or moving upward?

Oberländer‐Hayn, Sophie; Gerber, Edwin P.; Abalichin, Janna; Akiyoshi, Hideharu; Kerschbaumer, Andreas; Kubin, Anne; Kunze, Markus; Langematz, Ulrike; Meul, Stefanie; Michou, Martine; Morgenstern, Olaf; Oman, Luke D.

doi:10.1002/2015gl067545

Cited by 72 publications

(85 citation statements)

References 38 publications

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“…The negative trend could indicate either an acceleration of the BDC (accompanied by related changes of isentropic mixing; see e.g. Ploeger et al, 2015a) or an additional upward shift of the circulation pattern as suggested by Oberländer-Hayn et al (2016). In any case, the strongest negative trend of about −0.25 yr decade −1 occurs in the northern tropics and is consistent with trends derived from model calculations (e.g.…”

Section: Discussionsupporting

confidence: 72%

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

Stiller

Fierli

Ploeger³

et al. 2017

Atmos. Chem. Phys.

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Abstract. In response to global warming, the BrewerDobson circulation in the stratosphere is expected to accelerate and the mean transport time of air along this circulation to decrease. This would imply a negative stratospheric age of air trend, i.e. an air parcel would need less time to travel from the tropopause to any point in the stratosphere. Age of air as inferred from tracer observations, however, shows zero to positive trends in the northern mid-latitude stratosphere and zonally asymmetric patterns. Using satellite observations and model calculations we show that the observed latitudinal and vertical patterns of the decadal changes of age of air in the lower to middle stratosphere during the period 2002-2012 are predominantly caused by a southward shift of the circulation pattern by about 5 • . After correction for this shift, the observations reveal a hemispherically almost symmetric decrease of age of air in the lower to middle stratosphere up to 800 K of up to −0.25 years over the 2002-2012 period with strongest decrease in the northern tropics. This net change is consistent with long-term trends from model predictions.

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Section: Discussionsupporting

confidence: 72%

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

Stiller

Fierli

Ploeger³

et al. 2017

Atmos. Chem. Phys.

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“…This is in accordance with results from ECMWF reanalysis data for the past 2 decades (Wilcox et al, 2012). As indicated by Oberländer-Hayn et al (2016) regarding the BDC, the upward shift of the tropopause affects the interpretation of vertical profile differences between future and past. An air parcel which would have already entered the stratosphere under present-day conditions may be still considered tropospheric in the future.…”

Section: Implications Of a Rising Tropopause On Vsls Mixing Ratio Prosupporting

confidence: 78%

“…Chemical reactions are not computed interactively, e.g., via the EMAC submodel mecca (Sander et al, 2011a). The VSLS lifetime due to reaction with OH has been fixed to monthly mean values from the National Centre for Meteorological Research (CNRM) (Michou et al, 2011;Morgenstern et al, 2016) model calculations, while photolysis rates are computed within the EMAC submodel jval (Sander et al, 2014). Only in these simulations with simplified chemistry, OH concentrations have been set to zero in the lower troposphere (700-1000 hPa) to reduce the variability of ground level volume mixing ratio (VMR) of VSLS.…”

Section: Model and Experimentsmentioning

confidence: 99%

Brominated VSLS and their influence on ozone under a changing climate

et al. 2017

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Abstract. Very short-lived substances (VSLS) contribute as source gases significantly to the tropospheric and stratospheric bromine loading. At present, an estimated 25 % of stratospheric bromine is of oceanic origin. In this study, we investigate how climate change may impact the oceanatmosphere flux of brominated VSLS, their atmospheric transport, and chemical transformations and evaluate how these changes will affect stratospheric ozone over the 21st century.Under the assumption of fixed ocean water concentrations and RCP6.0 scenario, we find an increase of the oceanatmosphere flux of brominated VSLS of about 8-10 % by the end of the 21st century compared to present day. A decrease in the tropospheric mixing ratios of VSLS and an increase in the lower stratosphere are attributed to changes in atmospheric chemistry and transport. Our model simulations reveal that this increase is counteracted by a corresponding reduction of inorganic bromine. Therefore the total amount of bromine from VSLS in the stratosphere will not be changed by an increase in upwelling. Part of the increase of VSLS in the tropical lower stratosphere results from an increase in the corresponding tropopause height. As the depletion of stratospheric ozone due to bromine depends also on the availability of chlorine, we find the impact of bromine on stratospheric ozone at the end of the 21st century reduced compared to present day. Thus, these studies highlight the different factors influencing the role of brominated VSLS in a future climate.

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“…We evaluate the trends in the diabatic circulation from these three reanalysis data products and demonstrate that although there are trends in upwelling through pressure surfaces, the diabatic overturning through isentropes does not have the same clear trends. This result implies that much of the trend in the BDC might be attributable to changes in the thermal structure, supporting the conclusions of Oberländer-Hayn et al (2016). Finally, in this section we examine the upper and lower branches of the circulation in the diabatic circulation.…”

Section: Introductionsupporting

confidence: 49%

“…The mechanism for this increase in models involves the warming of the troposphere and cooling of the stratosphere strengthening the upper flank of the subtropical jets, causing the critical layers and Rossby wave drag to move upwards, allowing more Rossby wave activity in the lower stratosphere (Shepherd and McLandress, 2011; , 2011). It has also been suggested that this represents more of a "lifting" of the circulation as the height of the tropopause increases and that the mass circulation is largely unchanged (Oberländer-Hayn et al, 2016). Because the strength of the circulation is typically evaluated at a fixed pressure level, the rising tropopause height and associated rising circulation patterns would appear as an acceleration even if the total mass transport through the stratosphere were to remain unchanged.…”

Section: The Brewer-dobson Circulation Trends and Stratospheric Impmentioning

confidence: 99%

Age of air and the circulation of the stratosphere

Linz¹

2017

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The circulation of air in the stratosphere is important for the distribution of radiativelyimportant trace gases, such as ozone and water vapor, and other chemical species, including ozone-depleting chlorofluorocarbons. Age of air in the stratosphere is an idealized tracer with unique mathematical properties, which we exploit to derive a theory for the relationship of tracer observations to the stratospheric circulation. We show that the meridional age gradient is a measure of the global diabatic circulation, the total overturning strength through an isentropic surface, and test this time-dependent theory in a simple atmospheric general circulation model. We apply the theory to satellite data of sulfur hexafluoride (SF 6 ) and nitrous oxide to derive the first observationally-based estimates of the global meridional overturning circulation strength at all levels in the stratosphere. These two independent global satellite data products agree to within 5% on the strength of the diabatic circulation in the lower stratosphere. We compare to reanalyses and find broad agreement in the lower stratosphere and disagreement (∼ 100%) in the upper stratosphere. To understand the relationship between the diabatic circulation and other metrics of the circulation, we calculate it in a state-of-the-science atmospheric model and in three different reanalysis data products. The variability of the global diabatic circulation is very similar to one typical circulation metric, and it is correlated with total column ozone in the tropics and in Southern hemisphere midlatitudes in both a model and in reanalysis-data comparisons. Furthermore, we develop a metric for the mean adiabatic mixing, showing that it is related to the meridional age difference and the vertical gradient of age. We calculate this metric for a range of simple model runs to determine its utility as a measure of mixing. We find very little mixing of air into the tropics in the mid-stratosphere, and the vertical structure of mixing in the lower stratosphere and upper stratosphere varies among model runs and between hemispheres. A picture of global average stratospheric circulation could thus be obtained using age of air data, given reliable long-term records.

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Is the Brewer‐Dobson circulation increasing or moving upward?

Cited by 72 publications

References 38 publications

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

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

Brominated VSLS and their influence on ozone under a changing climate

Age of air and the circulation of the stratosphere

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