The Relationship between Age of Air and the Diabatic Circulation of the Stratosphere

Linz, Marianna; Plumb, R. Alan; Gerber, Edwin P.; Sheshadri, Aditi

doi:10.1175/jas-d-16-0125.1

Cited by 36 publications

(94 citation statements)

References 36 publications

(49 reference statements)

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“…At higher altitudes (above about 10 km above the tropical tropopause, i.e., about 26 km or 30 hPa) the age difference is a better mea- sure of tropical residual circulation velocities. This result is in agreement with Linz et al (2016). (2) The mixing efficiencies derived for the models will bear non-negligible information of vertical dispersion and are not necessarily good measures of the relative strength of horizontal mixing.…”

Section: Impact Of Vertical Dispersion On Aoa Profilessupporting

confidence: 87%

“…Nevertheless, diffusion due to unresolved processes and numerical diffusion (see also next section) contribute to varying degrees of vertical dispersion. Linz et al (2016) estimate a lower stratospheric diffusivity of K = 0.1 m 2 s −1 based on isentropic coordinate diagnostics. This value is consistent with earlier estimates (e.g., Sparling et al, 1997).…”

Section: Impact Of Vertical Dispersion On Aoa Profilesmentioning

confidence: 99%

“…As discussed in Neu and Plumb (1999) and in Linz et al (2016) (for isentropic coordinates). In the following, the TLP model is modified by including vertical diffusion (calculated as a Lagrangian random walk model, see Sect.…”

Section: Impact Of Vertical Dispersion On Aoa Profilesmentioning

confidence: 99%

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Quantifying the effect of mixing on the mean age of air in CCMVal-2 and CCMI-1 models

et al. 2018

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Abstract. The stratospheric age of air (AoA) is a useful measure of the overall capabilities of a general circulation model (GCM) to simulate stratospheric transport. Previous studies have reported a large spread in the simulation of AoA by GCMs and coupled chemistry-climate models (CCMs). Compared to observational estimates, simulated AoA is mostly too low. Here we attempt to untangle the processes that lead to the AoA differences between the models and between models and observations. AoA is influenced by both mean transport by the residual circulation and two-way mixing; we quantify the effects of these processes using data from the CCM inter-comparison projects CCMVal-2 (Chemistry-Climate Model Validation Activity 2) and CCMI-1 (Chemistry-Climate Model Initiative, phase 1). Transport along the residual circulation is measured by the residual circulation transit time (RCTT). We interpret the difference between AoA and RCTT as additional aging by mixing. Aging by mixing thus includes mixing on both the resolved and subgrid scale. We find that the spread in AoA between the models is primarily caused by differences in the effects of mixing and only to some extent by differences in residual circulation strength. These effects Published by Copernicus Publications on behalf of the European Geosciences Union. are quantified by the mixing efficiency, a measure of the relative increase in AoA by mixing. The mixing efficiency varies strongly between the models from 0.24 to 1.02. We show that the mixing efficiency is not only controlled by horizontal mixing, but by vertical mixing and vertical diffusion as well. Possible causes for the differences in the models' mixing efficiencies are discussed. Differences in subgrid-scale mixing (including differences in advection schemes and model resolutions) likely contribute to the differences in mixing efficiency. However, differences in the relative contribution of resolved versus parameterized wave forcing do not appear to be related to differences in mixing efficiency or AoA.

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Section: Impact Of Vertical Dispersion On Aoa Profilessupporting

confidence: 87%

Section: Impact Of Vertical Dispersion On Aoa Profilesmentioning

confidence: 99%

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Quantifying the effect of mixing on the mean age of air in CCMVal-2 and CCMI-1 models

et al. 2018

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“…11). Furthermore, Linz et al (2016) argue that it is the latitudinal gradient in age of air, and not age itself, that best diagnoses the strength of the meridional mass circulation and that this gradient, at any height, is independent of the circulation above. This latitudinal gradient is much improved in the HadGEM3-ES model as compared to UMUKCA-METO.…”

Section: Tropicsmentioning

confidence: 99%

The Met Office HadGEM3-ES chemistry–climate model: evaluation of stratospheric dynamics and its impact on ozone

et al. 2017

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Abstract. Free-running and nudged versions of a Met Office chemistry-climate model are evaluated and used to investigate the impact of dynamics versus transport and chemistry within the model on the simulated evolution of stratospheric ozone. Metrics of the dynamical processes relevant for simulating stratospheric ozone are calculated, and the free-running model is found to outperform the previous model version in 10 of the 14 metrics. In particular, large biases in stratospheric transport and tropical tropopause temperature, which existed in the previous model version, are substantially reduced, making the current model more suitable for the simulation of stratospheric ozone. The spatial structure of the ozone hole, the area of polar stratospheric clouds, and the increased ozone concentrations in the Northern Hemisphere winter stratosphere following sudden stratospheric warmings, were all found to be sensitive to the accuracy of the dynamics and were better simulated in the nudged model than in the free-running model. Whilst nudging can, in general, provide a useful tool for removing the influence of dynamical biases from the evolution of chemical fields, this study shows that issues can remain in the climatology of nudged models. Significant biases in stratospheric vertical velocities, age of air, water vapour, and total column ozone still exist in the Met Office nudged model. Further, these can lead to biases in the downward flux of ozone into the troposphere.

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“…The relationship between age of air and the diabatic circulation of the stratosphere This chapter was published as Marianna Linz, R. Alan Plumb, Edwin P. Gerber, Aditi Sheshadri, 2016: The Relationship between Age of Air and the Diabatic Circulation of the Stratosphere. J. Atmos.…”

Section: Tracer Observationsmentioning

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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The Relationship between Age of Air and the Diabatic Circulation of the Stratosphere

Cited by 36 publications

References 36 publications

Quantifying the effect of mixing on the mean age of air in CCMVal-2 and CCMI-1 models

Quantifying the effect of mixing on the mean age of air in CCMVal-2 and CCMI-1 models

The Met Office HadGEM3-ES chemistry–climate model: evaluation of stratospheric dynamics and its impact on ozone

Age of air and the circulation of the stratosphere

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