Quantifying the effects of mixing and residual circulation on trends of stratospheric mean age of air

Ploeger, Felix; Ábalos, Marta; Birner, Thomas; Konopka, Paul; Legras, Bernard; Müller, Rolf; Riese, Martin

doi:10.1002/2014gl062927

Cited by 87 publications

(161 citation statements)

References 45 publications

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“…Crossisentropic vertical velocity has been deduced from the reanalysis forecast total diabatic heating rate (see Pommrich et al, 2014). We carried out a high-resolution reference simulations (CLaMS-ERAI), with the critical Lyapunov exponent chosen as λ c = 1.5 day −1 , resulting in good agreement with observed trace gas distributions as shown in several recent publications (e.g., Pommrich et al, 2014;Ploeger et al, 2015a). Furthermore, for the investigation of model diffusion effects we carried out two low-resolution sensitivity simulations, both driven by ERA-Interim meteorology but with varying the strength of parametrized small-scale mixing (either λ = 1.5 day −1 or λ = 1.0 day −1 ).…”

Section: Model Simulations With Emac and Clamsmentioning

confidence: 83%

“…Recently, Ploeger et al (2015b) calculated aging by mixing explicitly on resolved scales (in the following termed as "resolved aging by mixing") using the zonal mean isentropic tracer continuity equation (e.g., Andrews et al, 1987), which can be reformulated for AoA (e.g., Plumb, 2002). The formulation for the zonal mean continuity equation for AoA in isentropic coordinates is explained in detail by Ploeger et al (2015b) and by Ploeger et al (2015a). For the CLaMS simulation, where the potential temperature is the vertical coordinate, this analysis is used to calculate the local mixing tendency (M).…”

Section: Calculation Of Aging By Mixing On Resolved and Unresolved Scmentioning

confidence: 99%

“…However, trends in resolved aging by mixing result not only from trends in local mixing tendencies but also from changes in the residual circulation, as changes in RCTT change the time exposed to mixing (see Garny et al, 2014;Ploeger et al, 2015a). Those effects can be separated by calculating resolved aging by mixing with fixed local mixing tendencies (see Ploeger et al, 2015a ure 8 summarizes the zonal annual-mean-resolved aging by mixing trend due to circulation change for the simulations EMAC-RC1 (left column), EMAC-RC1SD (middle column) and CLaMS-ERAI (right column). All simulations agree that the resolved aging by mixing trend due to residual circulation change alone can explain the resolved aging by mixing trends above about 30 hPa (Fig.…”

Section: Mixing Efficiency Derived From the Tropical Leaky Pipe Modelmentioning

confidence: 99%

“…Moreover, observations with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument exist for the years 2002-2012 (Stiller et al, 2012), which show mainly a decrease in AoA in the Southern Hemisphere and an increase in the Northern Hemisphere. Chemical transport models (CTMs), if driven by certain reanalysis data, are able to qualitatively reproduce the observationally based AoA trends of Engel et al (2009) and Stiller et al (2012), as shown by Monge-Sanz et al (2013), Ploeger et al (2015a) and Diallo et al (2012).…”

Section: Introductionmentioning

confidence: 99%

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Effects of mixing on resolved and unresolved scales on stratospheric age of air

et al. 2017

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Abstract. Mean age of air (AoA) is a widely used metric to describe the transport along the Brewer-Dobson circulation. We seek to untangle the effects of different processes on the simulation of AoA, using the chemistry-climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) and the Chemical Lagrangian Model of the Stratosphere (CLaMS). Here, the effects of residual transport and two-way mixing on AoA are calculated. To do so, we calculate the residual circulation transit time (RCTT). The difference of AoA and RCTT is defined as aging by mixing. However, as diffusion is also included in this difference, we further use a method to directly calculate aging by mixing on resolved scales. Comparing these two methods of calculating aging by mixing allows for separating the effect of unresolved aging by mixing (which we term "aging by diffusion" in the following) in EMAC and CLaMS. We find that diffusion impacts AoA by making air older, but its contribution plays a minor role (order of 10 %) in all simulations. However, due to the different advection schemes of the two models, aging by diffusion has a larger effect on AoA and mixing efficiency in EMAC, compared to CLaMS. Regarding the trends in AoA, in CLaMS the AoA trend is negative throughout the stratosphere except in the Northern Hemisphere middle stratosphere, consistent with observations. This slight positive trend is neither reproduced in a free-running nor in a nudged simulation with EMAC -in both simulations the AoA trend is negative throughout the stratosphere. Trends in AoA are mainly driven by the contributions of RCTT and aging by mixing, whereas the contribution of aging by diffusion plays a minor role.

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Section: Model Simulations With Emac and Clamsmentioning

confidence: 83%

Section: Calculation Of Aging By Mixing On Resolved and Unresolved Scmentioning

confidence: 99%

Section: Mixing Efficiency Derived From the Tropical Leaky Pipe Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of mixing on resolved and unresolved scales on stratospheric age of air

et al. 2017

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“…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. Overall, it has become clear that the interpretation of changes in mean age as changes in residual circulation is inadequate, and that it rather represents a combination of changes in mixing and in residual transport.…”

Section: Introductionmentioning

confidence: 99%

Mean age of stratospheric air derived from AirCore observations

et al. 2017

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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.

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The need for accurate long‐term measurements of water vapor in the upper troposphere and lower stratosphere with global coverage

et al. 2016

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Water vapor is the most important greenhouse gas in the atmosphere although changes in carbon dioxide constitute the “control knob” for surface temperatures. While the latter fact is well recognized, resulting in extensive space-borne and ground-based measurement programs for carbon dioxide as detailed in the studies by Keeling et al. (1996), Kuze et al. (2009), and Liu et al. (2014), the need for an accurate characterization of the long-term changes in upper tropospheric and lower stratospheric (UTLS) water vapor has not yet resulted in sufficiently extensive long-term international measurement programs (although first steps have been taken). Here, we argue for the implementation of a long-term balloon-borne measurement program for UTLS water vapor covering the entire globe that will likely have to be sustained for hundreds of years.

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Quantifying the effects of mixing and residual circulation on trends of stratospheric mean age of air

Cited by 87 publications

References 45 publications

Effects of mixing on resolved and unresolved scales on stratospheric age of air

Effects of mixing on resolved and unresolved scales on stratospheric age of air

Mean age of stratospheric air derived from AirCore observations

The need for accurate long‐term measurements of water vapor in the upper troposphere and lower stratosphere with global coverage

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