The effects of mixing on age of air

Garny, Hella; Birner, Thomas; Bönisch, Harald; Bunzel, Felix

doi:10.1002/2013jd021417

Cited by 121 publications

(264 citation statements)

References 41 publications

Supporting

Mentioning

245

Contrasting

Order By: Relevance

“…However, as recently pointed out by Abalos et al [2013a] this local Eulerian view does not allow the air parcel history to be analyzed. Consequently, the AoA variability may be locally dominated by the residual circulation effect, while mixing has affected the air parcel earlier on its pathway and, indeed, is important for its composition [see, e.g., Garny et al, 2014]. On the other hand, the clear advantage of the local (Eulerian) view is that it provides information about the local processes of residual circulation and mixing, which will be exploited in the following.…”

Section: Local Circulation and Mixing Effects And Relation To Circulamentioning

confidence: 99%

“…It has been shown that stronger mixing increases recirculation into the tropics and increases AoA [e.g., Neu and Plumb, 1999;Strahan et al, 2009;SPARC-CCMVal, 2010]. Recently, Garny et al [2014] pointed out that mixing between tropics and extratropics in the lowest part of the stratosphere crucially affects AoA at all levels above the mixing level, causing an additional aging. They diagnosed the effect of mixing as the difference between simulated AoA and the transit time along the residual circulation and denoted this difference as "aging by mixing. "…”

Section: Nonlocal (Integrated) Mixing Effect: "Aging By Mixing"mentioning

confidence: 99%

See 1 more Smart Citation

Variability of stratospheric mean age of air and of the local effects of residual circulation and eddy mixing

et al. 2015

View full text Add to dashboard Cite

We analyze the variability of mean age of air (AoA) and of the local effects of the stratospheric residual circulation and eddy mixing on AoA within the framework of the isentropic zonal mean continuity equation. AoA for the period 1988–2013 has been simulated with the Lagrangian chemistry transport model CLaMS driven by ERA‐Interim winds and diabatic heating rates. Model simulated AoA in the lower stratosphere shows good agreement with both in situ observations and satellite observations from Michelson Interferometer for Passive Atmospheric Sounding, even regarding interannual variability and changes during the last decade. The interannual variability throughout the lower stratosphere is largely affected by the quasi‐biennial‐oscillation‐induced circulation and mixing anomalies, with year‐to‐year AoA changes of about 0.5 years. The decadal 2002–2012 change shows decreasing AoA in the lowest stratosphere, below about 450 K. Above, AoA increases in the Northern Hemisphere and decreases in the Southern Hemisphere. Mixing appears to be crucial for understanding AoA variability, with local AoA changes resulting from a close balance between residual circulation and mixing effects. Locally, mixing increases AoA at low latitudes (40°S–40°N) and decreases AoA at higher latitudes. Strongest mixing occurs below about 500 K, consistent with the separation between shallow and deep circulation branches. The effect of mixing integrated along the air parcel path, however, significantly increases AoA globally, except in the polar lower stratosphere. Changes of local effects of residual circulation and mixing during the last decade are supportive of a strengthening shallow circulation branch in the lowest stratosphere and a southward shifting circulation pattern above.

show abstract

Section: Local Circulation and Mixing Effects And Relation To Circulamentioning

confidence: 99%

Section: Nonlocal (Integrated) Mixing Effect: "Aging By Mixing"mentioning

confidence: 99%

Variability of stratospheric mean age of air and of the local effects of residual circulation and eddy mixing

et al. 2015

View full text Add to dashboard Cite

show abstract

“…They show an uneven distribution of trends with positive trends in the middle stratosphere of the Northern Hemisphere but negative trends in the Southern Hemisphere. Modelling work by Garny et al (2014) showed that mixing has a strong influence on mean age and that enhanced mixing leads to higher mean ages in large parts of the stratosphere (aging by mixing). Ploeger et al (2015) then showed that trends in mean age are to a large degree also influenced by trends in mixing and not only in residual transport.…”

Section: Introductionmentioning

confidence: 99%

Mean age of stratospheric air derived from AirCore observations

et al. 2017

View full text Add to dashboard Cite

Abstract. Mean age of stratospheric air can be derived from observations of sufficiently long-lived trace gases with approximately linear trends in the troposphere. Mean age can serve as a tracer to investigate stratospheric transport and long-term changes in the strength of the overturning BrewerDobson circulation of the stratosphere. For this purpose, a low-cost method is required in order to allow for regular observations up to altitudes of about 30 km. Despite the desired low costs, high precision and accuracy are required in order to determine mean age. We present balloonborne AirCore observations from two midlatitude sites: Timmins in Ontario/Canada and Lindenberg in Germany. During the Timmins campaign, five AirCores sampled air in parallel with a large stratospheric balloon and were analysed for CO 2 , CH 4 and partly CO. We show that there is good agreement between the different AirCores (better than 0.1 %), especially when vertical gradients are small. The measurements from Lindenberg were performed using small low-cost balloons and yielded very comparable results. We have used the observations to extend our long-term data set of mean age observations at Northern Hemisphere midlatitudes. The time series now covers more than 40 years and shows a small, statistically non-significant positive trend of 0.15 ± 0.18 years decade −1 . This trend is slightly smaller than the previous estimate of 0.24 ± 0.22 years decade −1 which was based on observations up to the year 2006. These observations are still in contrast to strong negative trends of mean age as derived from some model calculations.

show abstract

“…Mixing levels are defined in the TLP by the ratio of horizontal mixing mass flux to horizontal mean mass flux scaled by the width of the tropical pipe region (Garny et al, 2014). Ray et al (2016) found that the CMAM30HR simulations best match the ACE-FTS measurements when the w * is between 0.27 mm/s and 0.32 mm/s (a reduction from the fitting estimate of 0.4 mm/s) and ranges from 0.7 to 1.…”

Section: Using a Tropical Leaky Pipe Model To Interpret Cmam30hrmentioning

confidence: 99%

“…Garny et al (2014) found that, in the subtropical 30 lower stratosphere, younger air is the result of a combination of a speeding up of the overturning circulation and weaker mixing or recirculation of the stratospheric air between the tropics and midlatitudes. This may be evidence for insufficient mixing in the specified dynamics simulations being the cause of a too-rapid BDC.…”

mentioning

confidence: 99%

Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements

Kolonjari¹,

Plummer²,

Walker³

et al. 2017

Preprint

View full text Add to dashboard Cite

Abstract.Stratospheric transport in global circulation models and chemistry-climate models is an important component in simulating the recovery of the ozone layer as well as changes in the climate system. The Brewer-Dobson circulation is not well constrained by observations and further investigation is required to resolve uncertainties related to the mechanisms driving the circulation. This study has assessed the specified dynamics mode of the Canadian Middle Atmosphere Model (CMAM30) by compar-5 ing to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) profile measurements of CFC-11 (CCl 3 F), CFC-12 (CCl 2 F 2 ), and N 2 O. In the CMAM30 specified dynamics simulation, the meteorological fields are nudged using the ERA-Interim Reanalysis and a specified tracer was used for each species, with hemispherically-defined surface measurements used as the boundary condition. A comprehensive sampling technique along the line-of-sight of the ACE-FTS measurements has been employed to allow for direct comparisons between the simulated and measured tracer concentrations. 10The model consistently overpredicts tracer concentrations in the lower stratosphere, particularly in the Northern Hemisphere winter and spring seasons. The three mixing barriers investigated, including the polar vortex, the extratropical tropopause, and the tropical pipe, show that there are significant inconsistencies between the measurements and the simulations. In particular, the CMAM30 simulation exhibits too little isentropic mixing in the June-July-August season.

show abstract

The effects of mixing on age of air

Cited by 121 publications

References 41 publications

Variability of stratospheric mean age of air and of the local effects of residual circulation and eddy mixing

Variability of stratospheric mean age of air and of the local effects of residual circulation and eddy mixing

Mean age of stratospheric air derived from AirCore observations

Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements

Contact Info

Product

Resources

About