Stratosphere-Mesosphere exchange: Long term changes and drivers

2021 ◽  
Author(s):  
Radek Zajíček ◽  
Petr Pišoft ◽  
Roland Eichinger ◽  
Petr Šácha
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Residual Circulation ◽  
Research Attention ◽  
Mass Fluxes ◽  
Main Driver ◽  
Climate Model Simulations ◽  
Conceptual Study ◽  
Mass Circulation ◽  
Mean Circulation

<p>The meridional overturning mass circulation in the middle atmosphere, i.e. the Brewer-Dobson circulation (BDC), was first discovered before decades based on the distribution of trace gases and a basic analytical concept of BDC has been derived using the transformed Eulerian mean equations. Since then, BDC is usually defined as consisting of a diffusive part, and an advective, residual mean circulation. In the vertical, BDC is separated into two branches – a shallow branch in the lower stratosphere and a deep branch higher in the middle atmosphere.<br />Climate model simulations robustly show that the advective BDC part accelerates in connection to the greenhouse gas-induced climate change and this acceleration dominates the middle atmospheric changes in climate model projections. A prominent quantity that is being studied as a proxy for advective BDC changes is the net tropical upwelling across the tropopause, which measures the amount of mass advected by residual circulation from the troposphere to the stratosphere per unit of time. The upper BDC branch received considerably less research attention than its shallow part, but features some striking phenomenon in the terrestrial atmosphere. It couples the stratosphere and mesosphere and is also responsible for a large portion of interhemispheric transport and coupling in the middle atmosphere.<br />In our research, for the first time, we produce a conceptual study of the advective stratosphere-mesosphere exchange. The analysis of advective exchange of mass between the stratosphere and mesosphere, i.e. the advective mass transport across the stratopause represents another step towards a better understanding of the structure of the upper BDC part and at the same time provides valuable insights into the relatively little-explored stratopause region. We investigate the variability and trends in mass fluxes from the stratosphere to the mesosphere and vice versa based on data from the EMAC-L90 model CCMI-1 simulation for the period 1960-2100. We develop an analytical method that allows us to attribute the changes of transport to causative factors such as acceleration of residual circulation, variable height of the stratopause, change of a geometric shape of the stratopause and changes in width of the upwelling and downwelling regions. The main driver of the increasing mass exchange between the stratosphere and the mesosphere is the faster circulation, however, the other terms are not negligible. The derived methodology offers the possibility of using an analogous procedure also for the tropopause in the future.</p>

scholarly journals Technical Note: A simple procedure for removing temporal discontinuities in ERA-Interim upper stratospheric temperatures for use in nudged chemistry-climate model simulations

2014 ◽  
Vol 14 (3) ◽  
pp. 1547-1555 ◽  
Author(s):  
C. McLandress ◽  
D. A. Plummer ◽  
T. G. Shepherd
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Simple Procedure ◽  
Stratospheric Ozone ◽  
Technical Note ◽  
Strong Temperature Dependence ◽  
Transient Effects ◽  
Climate Model Simulations ◽  
The Times

Abstract. This note describes a simple procedure for removing unphysical temporal discontinuities in ERA-Interim upper stratospheric global mean temperatures in March 1985 and August 1998 that have arisen due to changes in satellite radiance data used in the assimilation. The derived temperature adjustments (offsets) are suitable for use in stratosphere-resolving chemistry-climate models that are nudged (relaxed) to ERA-Interim winds and temperatures. Simulations using a nudged version of the Canadian Middle Atmosphere Model (CMAM) show that the inclusion of the temperature adjustments produces temperature time series that are devoid of the large jumps in 1985 and 1998. Due to its strong temperature dependence, the simulated upper stratospheric ozone is also shown to vary smoothly in time, unlike in a nudged simulation without the adjustments where abrupt changes in ozone occur at the times of the temperature jumps. While the adjustments to the ERA-Interim temperatures remove significant artefacts in the nudged CMAM simulation, spurious transient effects that arise due to water vapour and persist for about 5 yr after the 1979 switch to ERA-Interim data are identified, underlining the need for caution when analysing trends in runs nudged to reanalyses.

scholarly journals Extratropical age of air trends and causative factors in climate projection simulations

2019 ◽  
Vol 19 (11) ◽  
pp. 7627-7647 ◽  
Author(s):  
Petr Šácha ◽  
Roland Eichinger ◽  
Hella Garny ◽  
Petr Pišoft ◽  
Simone Dietmüller ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Model ◽  
Climate Projection ◽  
Residual Circulation ◽  
Wave Forcing ◽  
Open Questions ◽  
Transit Times ◽  
Causative Factors ◽  
Climate Model Simulations ◽  
Changes Over Time

Abstract. Climate model simulations show an acceleration of the Brewer–Dobson circulation (BDC) in response to climate change. While the general mechanisms for the BDC strengthening are widely understood, there are still open questions concerning the influence of the details of the wave driving. Mean age of stratospheric air (AoA) is a useful transport diagnostic for assessing changes in the BDC. Analyzing AoA from a subset of Chemistry–Climate Model Initiative part 1 climate projection simulations, we find a remarkable agreement between most of the models in simulating the largest negative AoA trends in the extratropical lower to middle stratosphere of both hemispheres (approximately between 20 and 25 geopotential kilometers (gpkm) and 20–50∘ N and S). We show that the occurrence of AoA trend minima in those regions is directly related to the climatological AoA distribution, which is sensitive to an upward shift of the circulation in response to climate change. Also other factors like a reduction of aging by mixing (AbM) and residual circulation transit times (RCTTs) contribute to the AoA distribution changes by widening the AoA isolines. Furthermore, we analyze the time evolution of AbM and RCTT trends in the extratropics and examine the connection to possible drivers focusing on local residual circulation strength, net tropical upwelling and wave driving. However, after the correction for a vertical shift of pressure levels, we find only seasonally significant trends of residual circulation strength and zonal mean wave forcing (resolved and unresolved) without a clear relation between the trends of the analyzed quantities. This indicates that additional causative factors may influence the AoA, RCTT and AbM trends. In this study, we postulate that the shrinkage of the stratosphere has the potential to influence the RCTT and AbM trends and thereby cause additional AoA changes over time.

scholarly journals Extratropical Age of Air trends and causative factors in climate projection simulations

2019 ◽  
Author(s):  
Petr Šácha ◽  
Roland Eichinger ◽  
Hella Garny ◽  
Petr Pišoft ◽  
Simone Dietmüller ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Model ◽  
Climate Projection ◽  
Residual Circulation ◽  
Wave Forcing ◽  
Open Questions ◽  
Transit Times ◽  
Causative Factors ◽  
Climate Model Simulations ◽  
Changes Over Time

Abstract. Climate model simulations show a Brewer-Dobson circulation (BDC) acceleration in the course of climate change. While the mechanisms for the BDC strengthening are well understood, there are still open questions concerning its dynamical driving. Mean age of stratospheric air (AoA) is a useful transport diagnostic for accessing changes of the BDC. Analysing AoA from a subset of Chemistry Climate Model Initiative part 1 climate projection simulations, we find a remarkable agreement between most of the models in simulating the largest negative AoA trends in the extratropical lower to middle stratosphere of both hemispheres (approximately between 20 gpkm and 25 gpkm and 20°–50°N/S). We show that the occurrence of AoA trend minima in those regions is directly related to the climatological AoA distribution being sensitive to an upward shift of the circulation in response to a climate change. But also other factors like a reduction of aging by mixing (AbM) and residual circulation transit times (RCTTs) contribute to the AoA distribution changes by widening the AoA isolines. Furthermore we analyze the time evolution of AbM and RCTT trends in the extratropics and examine the connection to possible drivers like local residual circulation strength, net tropical upwelling and wave driving. However, after the correction for a vertical shift of pressure levels, we find only seasonally significant trends of residual circulation strength and zonal mean wave forcing (resolved and unresolved) without a clear relation between the trends of the analyzed quantities. This indicates that additional causative factors may influence the AoA, RCTT and AbM trends. Namely, we postulate a possible influence of stratospheric shrinkage on RCTT, AbM and therefore also on AoA trends. In this study, we postulate that the shrinkage of the stratosphere has the potential to influence the RCTT and AbM trends and thereby cause additional AoA changes over time.

scholarly journals Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years 

2021 ◽  
Author(s):  
Aleix Cortina-Guerra ◽  
Juan José Gomez-Navarro ◽  
Belen Martrat ◽  
Juan Pedro Montávez ◽  
Alessandro Incarbona ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
Sea Surface ◽  
The West ◽  
The Past ◽  
Main Driver ◽  
Climate Model Simulations ◽  
Past 1000 Years

Abstract. High resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lions was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mb in the Northern Hemisphere (200 N-900 N and 1000 W-800 E). Correlations revealed a pattern similar to the Eastern Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 yr of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone Sea Surface Temperature (SST) reconstructions that documented an increase in the west-east basin gradients during EMT-type events.

scholarly journals Will climate change increase ozone depletion from low-energy-electron precipitation?

2010 ◽  
Vol 10 (19) ◽  
pp. 9647-9656 ◽  
Author(s):  
A. J. G. Baumgaertner ◽  
P. Jöckel ◽  
M. Dameris ◽  
P. J. Crutzen
Keyword(s):  
Climate Change ◽  
Geomagnetic Activity ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Energetic Electron ◽  
Electron Precipitation ◽  
Change Scenario ◽  
Residual Circulation ◽  
Ozone Loss ◽  
Winter Time

Abstract. We investigate the effects of a strengthened stratospheric/mesospheric residual circulation on the transport of nitric oxide (NO) produced by energetic particle precipitation. During periods of high geomagnetic activity, energetic electron precipitation (EEP) is responsible for winter time ozone loss in the polar middle atmosphere between 1 and 6 hPa. However, as climate change is expected to increase the strength of the Brewer-Dobson circulation including extratropical downwelling, the enhancements of EEP NOx concentrations are expected to be transported to lower altitudes in extratropical regions, becoming more significant in the ozone budget. Changes in the mesospheric residual circulation are also considered. We use simulations with the chemistry climate model system EMAC to compare present day effects of EEP NOx with expected effects in a climate change scenario for the year 2100. In years of strong geomagnetic activity, similar to that observed in 2003, an additional polar ozone loss of up to 0.4 μmol/mol at 5 hPa is found in the Southern Hemisphere. However, this would be approximately compensated by an ozone enhancement originating from a stronger poleward transport of ozone from lower latitudes caused by a strengthened Brewer-Dobson circulation, as well as by slower photochemical ozone loss reactions in a stratosphere cooled by risen greenhouse gas concentrations. In the Northern Hemisphere the EEP NOx effect appears to lose importance due to the different nature of the climate-change induced circulation changes.

scholarly journals Odd hydrogen response thresholds for indication of solar proton and electron impact in the mesosphere and stratosphere

2020 ◽  
Author(s):  
Tuomas Häkkilä ◽  
Pekka T. Verronen ◽  
Luis Millán ◽  
Monika E. Szela̧g ◽  
Niilo Kalakoski ◽  
...  
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Solar Proton ◽  
Polar Regions ◽  
Impact Detection ◽  
Climate Simulations ◽  
Flux Measurements ◽  
Hydrogen Response ◽  
Response Thresholds ◽  
Climate Model Simulations

Abstract. Understanding the atmospheric forcing from energetic particle precipitation (EPP) is important for climate simulations on decadal time scales. However, presently there are large uncertainties in energy-flux measurements of electron precipitation. One approach to narrow these uncertainties is by analyses of EPP direct atmospheric impacts and their relation to measured EPP fluxes. Here we use odd hydrogen observations from the Microwave Limb Sounder and Whole Atmosphere Community Climate Model simulations, together with EPP fluxes from the GOES and POES satellites, to determine the response thresholds to solar proton events (SPEs) and radiation belt electron (RBE) precipitation. We consider a range of altitudes in the middle atmosphere, and all magnetic latitudes from pole to pole. We find that the lower flux limits for day-to-day EPP impact detection using OH and HO2 are of the order of 102 protons/cm2/s/sr (E > 10 MeV) and 104 electrons/cm2/s/sr (E = 100–300 keV). Based on the simulations, nighttime OH and HO2 are good EPP indicators in the polar regions, and provide best coverage in altitude and latitude. Due to larger background concentrations, daytime detection requires larger EPP fluxes and is possible in the mesosphere only. SPE detection is easier than RBE detection because a wider range of polar latitudes is affected. We also find that MLS OH observations indicate a clear nighttime response to SPE and RBE in the mesosphere, similar to the simulations, while HO2 data are overall too noisy for confident EPP detection.

scholarly journals Hemispheric asymmetries in recent changes of the stratospheric circulation

2022 ◽  
Author(s):  
Felix Ploeger ◽  
Hella Garny
Keyword(s):  
Hemispheric Asymmetry ◽  
Climate Models ◽  
Climate Model ◽  
Transport Model ◽  
Internal Variability ◽  
Residual Circulation ◽  
Hemispheric Asymmetries ◽  
Model Simulations ◽  
Transit Times ◽  
Climate Model Simulations

Abstract. Despite the expected opposite effects of ozone recovery, the stratospheric Brewer-Dobson circulation (BDC) has been found to weaken in the Northern hemisphere (NH) relative to the Southern hemisphere (SH) in recent decades, inducing substantial effects on chemical composition. We investigate hemispheric asymmetries in BDC changes since about 2000 in simulations with the transport model CLaMS driven with different reanalyses (ERA5, ERA-Interim, JRA-55, MERRA-2) and contrast those to a suite of free-running climate model simulations. We find that age of air increases robustly in the NH stratosphere relative to the SH in all reanalyses considered. Related nitrous oxide changes agree well between reanalysis-driven simulations and satellite measurements, providing observational evidence for the hemispheric asymmetry in BDC changes. Residual circulation metrics further show that the composition changes are caused by structural BDC changes related to an upward shift and strengthening of the deep BDC branch, resulting in longer transit times, and a downward shift and weakening shallow branch in the NH relative to the SH. All reanalyses agree on this mechanism. Although climate model simulations show that ozone recovery will lead to overall reduced circulation and age of air trends, the hemispherically asymmetric signal in circulation trends is small compared to internal variability. Therefore, the observed circulation trends over the recent past are not in contradiction to expectations from climate models. Furthermore, the hemispheric asymmetry in BDC trends imprints on the composition of the lower stratosphere and the signal might propagate into the troposphere, potentially affecting composition down to the surface.

scholarly journals Technical Note: A simple procedure for removing temporal discontinuities in ERA-Interim upper stratospheric temperatures for use in nudged chemistry-climate model simulations

2013 ◽  
Vol 13 (10) ◽  
pp. 25801-25825 ◽  
Author(s):  
C. McLandress ◽  
D. A. Plummer ◽  
T. G. Shepherd
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Simple Procedure ◽  
Stratospheric Ozone ◽  
Technical Note ◽  
Strong Temperature Dependence ◽  
Transient Effects ◽  
Climate Model Simulations ◽  
The Times

Abstract. This note describes a simple procedure for removing unphysical temporal discontinuities in ERA-Interim upper stratospheric temperatures in March 1985 and August 1998 that have arisen due to changes in satellite radiance data used in the assimilation. The derived adjustments (offsets) to the global mean temperatures are suitable for use in chemistry-climate models that are nudged to ERA-Interim winds and temperatures. Simulations using a nudged version of the Canadian Middle Atmosphere Model (CMAM) show that the inclusion of the temperature adjustments produces temperature time series that are devoid of the large jumps in 1985 and 1998. Due to its strong temperature dependence, the simulated upper stratospheric ozone is also shown to vary smoothly in time, unlike in a nudged simulation without the adjustments where abrupt changes in ozone occur at the times of the temperature jumps. While the adjustments to the ERA-Interim temperatures remove significant artefacts in the nudged CMAM simulation, spurious transient effects that arise due to water vapour and persist for about five years after the 1979 switch to ERA-Interim data are identified, underlining the need for caution when analysing trends in runs nudged to reanalyses.

scholarly journals Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years

2021 ◽  
Vol 17 (4) ◽  
pp. 1523-1532
Author(s):  
Aleix Cortina-Guerra ◽  
Juan José Gomez-Navarro ◽  
Belen Martrat ◽  
Juan Pedro Montávez ◽  
Alessandro Incarbona ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
East Atlantic ◽  
The Past ◽  
Gulf Of Lion ◽  
Main Driver ◽  
Climate Model Simulations ◽  
Past 1000 Years

Abstract. High-resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lion was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mbar in the Northern Hemisphere (20–90∘ N and 100∘ W–80∘ E). Correlations revealed a pattern similar to the East Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 years of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone sea surface temperature (SST) reconstructions that documented an increase in the west–east basin gradients during EMT-type events.

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