Seasonal Variability of the Polar Stratospheric Vortex in an Idealized AGCM with Varying Tropospheric Wave Forcing

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

doi:10.1175/jas-d-14-0191.1

Cited by 36 publications

(58 citation statements)

References 45 publications

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“…We use 40 hybrid vertical levels that are terrain following near the surface and transition to pressure levels by 115 hPa. Unlike previous studies using similar idealized models (e.g., Polvani and Kushner 2002;Kushner and Polvani 2006;Gerber and Polvani 2009;Gerber 2012;Sheshadri et al 2015), the model solver is not pseudospectral. It is the finite-volume dynamical core used in the GFDL Atmospheric Model, version 3, (AM3; Donner et al 2011), the atmospheric component of GFDL's CMIP5 coupled climate model.…”

Section: Verification In a Simple Atmospheric Gcm A Model Setupmentioning

confidence: 99%

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

Linz

Plumb

Gerber

et al. 2016

Journal of the Atmospheric Sciences

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The strength of the Brewer-Dobson circulation is difficult to estimate using observations. Trends in the age of stratospheric air, deduced from observations of transient tracers, have been used to identify trends in the circulation, but there are ambiguities in the relationship between age and the strength of the circulation. This paper presents a steady-state theory and a time-dependent extension to relate age of air directly to the diabatic circulation of the stratosphere. In steady state, it is the difference between the age of upwelling and downwelling air through an isentrope and not the absolute value of age that is a measure of the strength of the diabatic circulation through that isentrope. For the time-varying case, expressions for other terms that contribute to the age budget are derived. An idealized atmospheric general circulation model with and without a seasonal cycle is used to test the time-dependent theory and to find that these additional terms are small upon annual averaging. The steady-state theory holds as well for annual averages of a seasonally varying model as for a perpetual-solstice model. These results are a step toward using data to quantify the strength of the diabatic circulation.

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Section: Verification In a Simple Atmospheric Gcm A Model Setupmentioning

confidence: 99%

“…With a lower stratosphere-troposphere transition, this topographic forcing and lapse rate were found by Sheshadri et al (2015) to create the most realistic Northern and Southern Hemisphere-like seasonal behavior. The model is run until the age has equilibrated (27 yr) and then for another 50 yr, which provide the statistics for these results.…”

mentioning

confidence: 93%

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

Linz

Plumb

Gerber

et al. 2016

Journal of the Atmospheric Sciences

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“…Observational (e.g., Baldwin & Dunkerton, 1999, 2001 and modeling studies Kushner & Polvani, 2004;Polvani & Kushner, 2002;Sheshadri et al, 2015) have established that variability in the polar vortex can influence the troposphere, all the way to the Earth's surface, on time scales relevant to both weather and climate. In thermal wind balance with this temperature gradient exists a strong westerly jet, the stratospheric polar vortex.…”

Section: Introductionmentioning

confidence: 99%

Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains

White

Battisti

Sheshadri

2018

Geophysical Research Letters

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The impact of mountains on stratospheric circulation is explored using the Whole Atmosphere Community Climate Model. The “Mongolian mountains” decrease the boreal winter stratospheric jet strength by ∼1/3 and increase the frequency of major sudden stratospheric warmings from 0.08 year−1 to the observed 0.60 year−1. These changes are twice the magnitude of the impacts of the Tibetan plateau and Himalayas. Consistent with the decrease in the zonal jet, there is enhanced Eliassen‐Palm flux convergence; this is predominantly from changes in wave propagation pathways through changes to the upper troposphere circulation, not from an increased amplitude of planetary waves reaching the stratosphere. The Mongolian mountains have the greater impact on upper tropospheric circulation due to their meridional location. The Rocky Mountains have no significant impact on the stratospheric jet. Changes in wave propagation in response to the Mongolian mountains are similar to those associated with major sudden stratospheric warming events in observations.

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“…The lapse rate is = 4 K/km, and the topography is 4 km high. With a lower stratospheretroposphere transition, this topographic forcing and lapse rate were found by Sheshadri et al (2015) to create the most realistic Northern and Southern Hemisphere-like seasonal behavior. The model is run until the age has equilibrated (27 years) and then for another 50 years, which provide the statistics for these results.…”

Section: Model Setupmentioning

confidence: 93%

“…Unlike previous studies using similar idealized models (e.g. Polvani and Kushner 2002, Kushner and Polvani 2006, Gerber and Polvani 2009, Gerber 2012, Sheshadri et al 2015, the model solver is not pseudospectral. It is the finite-volume dynamical core used in the GFDL Atmospheric Model Version 3 (AM3; Donner et al 2011), the atmospheric component of GFDL's CMIP5 coupled climate model.…”

Section: Model Setupmentioning

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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Seasonal Variability of the Polar Stratospheric Vortex in an Idealized AGCM with Varying Tropospheric Wave Forcing

Cited by 36 publications

References 45 publications

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

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

Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains

Age of air and the circulation of the stratosphere

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