A note on forced versus internal variability of the stratosphere

Hardiman, Steven C.; Butchart, Neal; Haynes, P. H.; Hare, Sylvia H. E.

doi:10.1029/2007gl029726

Cited by 22 publications

(28 citation statements)

References 22 publications

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“…3). The positive correlation between ENSO and tropical upwelling is in agreement with the studies by García-Herrera et al (2006) and Hardiman et al (2007), that state stronger wave activity and subsequent forcing of the BDC in positive phases of the ENSO.…”

Section: Influence Of Enso On Tropical Upwellingsupporting

confidence: 93%

“…1), and even up to 3 K at about 50 • N. The difference pattern in temperature is in close agreement with results from earlier studies on SST forcing of temperature (see e.g. Kodama et al, 2007;Hardiman et al, 2007).…”

Section: Temperature and Ozonesupporting

confidence: 92%

“…Unlike for the extratropics, the effects of tropical SST anomalies and namely the ENSO on extratropical waves (Ineson and Scaife, 2009), and subsequently modulation of the PW flux into the stratosphere and the BDC (Hardiman et al, 2007;García-Herrera et al, 2006) are well studied. It is shown that this relationship also holds for the REF1 simulation used here, with positive correlations of tropical upwelling with the ENSO index in the northern winter season.…”

Section: Discussionmentioning

confidence: 99%

“…The results generally suggest that the ENSO signal is communicated to the stratosphere by planetary wave modulation and subsequent changes in the mean meridional circulation. For example García-Herrera et al (2006) and Hardiman et al (2007) show positive correlations between ENSO indices and tropical upwelling, indicating stronger planetary wave fluxes and therefore a stronger meridional circulation in ENSO warm phases and vice versa in ENSO cold phases.…”

Section: Introductionmentioning

confidence: 99%

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Impact of prescribed SSTs on climatologies and long-term trends in CCM simulations

2009

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Abstract. Chemistry-Climate Model (CCM) simulations are commonly used to project the past and future development of the dynamics and chemistry of the stratosphere, and in particular the ozone layer. So far, CCMs are usually not interactively coupled to an ocean model, so that sea surface temperatures (SSTs) and sea ice coverage are prescribed in the simulations. While for future integrations SSTs have to be taken from precalculated climate model projections, for CCM experiments resembling the past either modelled or observed SSTs can be used. This study addresses the question to which extent atmospheric climatologies and long-term trends for the recent past simulated in the CCM E39C-A differ when choosing either observed or modelled SSTs. Furthermore, the processes of how the SST signal is communicated to the atmosphere, and in particular to the stratosphere are examined. Two simulations that differ only with respect to the prescribed SSTs and that span years 1960 to 1999 are used.Significant differences in temperature and ozone climatologies between the model simulations are found. The differences in ozone are attributed to differences in the meridional circulation, which are in turn driven by weaker wave forcing in the simulation with generally lower SSTs. The long-term trends over 40 years in annual mean temperature and ozone differ only in the troposphere, where temperatures are directly influenced by the local SST trends. Differences in temperature and ozone trends are only found on shorter time scales. The trends in tropical upwelling, as a measure of the strength of the Brewer-Dobson circulation (BDC), differ strongly between the simulations. A reverse from negative to positive trends is found in the late 1970s in the simulation using observed SSTs while trends are positive throughout the Correspondence to: H. Garny (hella.garny@dlr.de) simulation when using modelled SSTs. The increase in the BDC is a robust feature of the simulations only after about 1980 and is evident mainly in the tropics in the lower stratosphere.

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Section: Influence Of Enso On Tropical Upwellingsupporting

confidence: 93%

Section: Temperature and Ozonesupporting

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impact of prescribed SSTs on climatologies and long-term trends in CCM simulations

2009

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“…7a) is localized to heights of around 150-50 hPa. Since this difference does not extend throughout the troposphere, it is thought unlikely to be due to differences in sea surface temperatures per se (Hardiman et al, 2007). The same difference as that seen in 100 hPa temperature is also seen in 70 hPa water vapour concentrations (Fig.…”

Section: Tropicsmentioning

confidence: 67%

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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Influence of ENSO on the QBO: Results from an ensemble of idealized simulations

Schirber

2015

JGR Atmospheres

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The El Niño-Southern Oscillation (ENSO) changes convection in the tropics and therefore the excitation of equatorial waves. Equatorial waves propagate from the troposphere upward where they drive the quasi-biennial oscillation (QBO) in the stratosphere. In this work, we analyze the effect of ENSO on the QBO utilizing an atmospheric general circulation model in a comprehensive experimental setup. We construct two ensembles of different QBO initial conditions, with the onset of a westerly (QBOW) and easterly (QBOE) jet at 10 hPa. In the course of an 18 months simulation period, the two sets of initial conditions experience each El Niño (EL) and La Niña (LA) boundary conditions. Due to the increased tropospheric temperatures during EL conditions compared to LA conditions, the experiments show an increase in tropospheric wave activity which increases QBO forcing in the stratosphere in EL. The underlying easterly jet in QBOW is weaker during EL compared to LA, while the underlying westerly jet in QBOE is stronger during EL compared to LA. On one hand, the weaker underlying jet in QBOW and the increase in QBO forcing due to waves cause a faster downward propagation for the westerly jet in QBOW during EL. On the other hand, the stronger underlying jet in QBOE opposes the increased QBO forcing due to waves for QBOE during EL. Therefore, the downward propagation speed of the easterly jet in QBOE is similar during EL and LA conditions. Changes in stratospheric tropical upwelling associated with EL and LA do not affect QBO properties in the simulation.

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A note on forced versus internal variability of the stratosphere

Cited by 22 publications

References 22 publications

Impact of prescribed SSTs on climatologies and long-term trends in CCM simulations

Impact of prescribed SSTs on climatologies and long-term trends in CCM simulations

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

Influence of ENSO on the QBO: Results from an ensemble of idealized simulations

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