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

Hardiman, Steven C.; Butchart, Neal; O’Connor, Fiona M.; Rumbold, Steven T.

doi:10.5194/gmd-10-1209-2017

Cited by 41 publications

(50 citation statements)

References 63 publications

(68 reference statements)

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“…2a and b). This effect is consistent with previous work that has shown that transport controls lower stratospheric ozone concentrations Hartmann, 1981;Rood and Douglass, 1985;Hartmann and Garcia, 1979;Silverman et al, 2018). The CCMI ensemble-mean (i.e., the mean of all 42 submodels) correlation between March ASO and March geopotential height and temperature is shown in Fig.…”

Section: Effect Of Arctic Stratospheric Ozone (Aso) On Polar Surface supporting

confidence: 92%

response to reviewer 2

Harari¹

2019

Preprint

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The Northern Hemisphere and tropical circulation response to interannual variability in Arctic stratospheric ozone is analyzed in a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models simulate a connection between ozone variability and temperature/geopotential height in the lower stratosphere similar to that observed. A connection between Arctic ozone variability and polar cap surface air pressure is also found, but additional statistical analysis suggests that it is mediated by the dynamical variability that typically drives the anomalous ozone concentrations. While the CCMI models also show a connection between Arctic stratospheric ozone and the El Niño-Southern Oscillation (ENSO), with Arctic stratospheric ozone variability leading to ENSO variability 1 to 2 years later, this relationship in the models is much weaker than observed and is likely related to ENSO autocorrelation rather than any forced response to ozone. Overall, Arctic stratospheric ozone is related to lower stratospheric variability. Arctic stratospheric ozone may also influence the surface in both polar and tropical latitudes, though ozone is likely not the proximate cause of these impacts and these impacts can be masked by internal variability if data are only available for ∼ 40 years.Published by Copernicus Publications on behalf of the European Geosciences Union.

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Section: Effect Of Arctic Stratospheric Ozone (Aso) On Polar Surface supporting

confidence: 92%

response to reviewer 2

Harari¹

2019

Preprint

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“…observations at a specific location, we expect that chemical transport models (CTMs) or CCMs with specified dynamics (CCM-SD) would be more accurate in capturing the O 3 variability and other dynamical variables than free-running CCMs; this has been demonstrated in previous studies (e.g. Hardiman et al, 2017). This could have implications for projecting long-term future O 3 trends using free-running CCMs.…”

Section: Ozone Trendsmentioning

confidence: 78%

“…Therefore, careful evaluations of free-running CCMs are needed. However, Hardiman et al (2017) also find that tropical upwelling and the stratospheric meridional circulation are difficult to constrain and are worse in the nudged simulations than in the free-running simulations. Here, we aim to attribute observed O 3 trends to various chemical and dynamical processes, and we consider that free-running CCMs are the more suitable models to be used in such study.…”

Section: Ozone Trendsmentioning

confidence: 88%

Attribution of recent ozone changes in the Southern Hemisphere mid-latitudes using statistical analysis and chemistry–climate model simulations

et al. 2017

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Abstract. Ozone (O 3 ) trends and variability from a 28-year (1987-2014) ozonesonde record at Lauder, New Zealand, have been analysed and interpreted using a statistical model and a global chemistry-climate model (CCM). Lauder is a clean rural measurement site often representative of the Southern Hemisphere (SH) mid-latitude background atmosphere. O 3 trends over this period at this location are characterised by a significant positive trend below 6 km, a significant negative trend in the tropopause region and the lower stratosphere between 9 and 15 km, and no significant trend in the free troposphere (6-9 km) and the stratosphere above 15 km. We find that significant positive trends in lower tropospheric ozone are correlated with increasing temperature and decreasing relative humidity at the surface over this period, whereas significant negative trends in the upper troposphere and the lower stratosphere appear to be strongly linked to an upward trend of the tropopause height. Relative humidity and the tropopause height also dominate O 3 variability at Lauder in the lower troposphere and the tropopause region, respectively. We perform an attribution of these trends to anthropogenic forcings including O 3 precursors, greenhouse gases (GHGs), and O 3 -depleting substances (ODSs), using CCM simulations. Results indicate that changes in anthropogenic O 3 precursors contribute significantly to stratospheric O 3 reduction, changes in ODSs contribute significantly to tropospheric O 3 reduction, and increased GHGs contribute significantly to stratospheric O 3 increases at Lauder. Methane (CH 4 ) likely contributes positively to O 3 trends in both the troposphere and the stratosphere, but the contribution is not significant at the 95 % confidence level over this period. An extended analysis of CCM results covering 1960-2010 (i.e. starting well before the observations) reveals significant contributions from all forcings to O 3 trends at Lauder -i.e. increases in GHGs and the increase in CH 4 alone all contribute significantly to O 3 increases, net increases in ODSs lead to O 3 reduction, and increases in non-methane O 3 precursors cause O 3 increases in the troposphere and reductions in the stratosphere. This study suggests that a long-term ozonesonde record obtained at a SH mid-latitude background site (corroborated by a surface O 3 record at a nearby SH midlatitude site, Baring Head, which also shows a significant positive trend) is a useful indicator for detecting atmospheric composition and climate change associated with human activities.

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“…As such, they are valuable tools for studying climate change on decadal to centennial timescales (e.g. Collins et al 2011;Gent et al 2011;Martin et al 2011;Hazeleger et al 2012;Flato et al 2013;Hurrell et al 2013;Hardiman et al 2017). However, these models are extremely computationally expensive.…”

Section: Introductionmentioning

confidence: 99%

Ocean circulation drifts in multi-millennial climate simulations: the role of salinity corrections and climate feedbacks

et al. 2018

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Low-resolution, complex general circulation models (GCMs) are valuable tools for studying the Earth system on multimillennial timescales. However, slowly evolving salinity drifts can cause large shifts in climatic and oceanic regimes over thousands of years. We test two different schemes for neutralising unforced salinity drifts in the FAMOUS GCM: surface flux correction and volumetric flux correction. Although both methods successfully maintain a steady global mean salinity, local drifts and subsequent feedbacks promote cooling (≈ 4 °C over 6000 years) and freshening (≈ 2 psu over 6000 years) in the North Atlantic Ocean, and gradual warming (≈ 0.2 °C per millennium) and salinification (≈ 0.15 psu per millennium) in the North Pacific Ocean. Changes in the surface density in these regions affect the meridional overturning circulation (MOC), such that, after several millennia, the Atlantic MOC (AMOC) is in a collapsed state, and there is a strong, deep Pacific MOC (PMOC). Furthermore, the AMOC exhibits a period of metastability, which is only identifiable with run lengths in excess of 1500 years. We also compare simulations with two different land surface schemes, demonstrating that small biases in the surface climate may cause regional salinity drifts and significant shifts in the MOC (weakening of the AMOC and the initiation then invigoration of PMOC), even when the global hydrological cycle has been forcibly closed. Although there is no specific precursor to the simulated AMOC collapse, the northwest North Pacific and northeast North Atlantic are important areas that should be closely monitored for trends arising from such biases.

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

Cited by 41 publications

References 63 publications

response to reviewer 2

response to reviewer 2

Attribution of recent ozone changes in the Southern Hemisphere mid-latitudes using statistical analysis and chemistry–climate model simulations

Ocean circulation drifts in multi-millennial climate simulations: the role of salinity corrections and climate feedbacks

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