Satellite observations and modelling of transport in the upper troposphere through the lower mesosphere during the 2006 major stratospheric sudden arming

Abstract. An unusually strong and prolonged stratospheric sudden warming (SSW) in January 2006 was the first major SSW for which globally distributed long-lived trace gas data are available covering the upper troposphere through the lower mesosphere. We use Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) data, the SLIMCAT Chemistry Transport Model (CTM), and assimilated meteorological analyses to provide a comprehensive picture of transport during this event. The upper tropospheric ridge that triggered the SSW was associated with an elevated tropopause and layering in trace gas profiles in conjunction with stratospheric and tropospheric intrusions. Anomalous poleward transport (with corresponding quasi-isentropic troposphere-to-stratosphere exchange at the lowest levels studied) in the region over the ridge extended well into the lower stratosphere. In the middle and upper stratosphere, the breakdown of the polar vortex transport barrier was seen in a signature of rapid, widespread mixing in trace gases, including CO, H2O, CH4 and N2O. The vortex broke down slightly later and more slowly in the lower than in the middle stratosphere. In the middle and lower stratosphere, small remnants with trace gas values characteristic of the pre-SSW vortex lingered through the weak and slow recovery of the vortex. The upper stratospheric vortex quickly reformed, and, as enhanced diabatic descent set in, CO descended into this strong vortex, echoing the fall vortex development. Trace gas evolution in the SLIMCAT CTM agrees well with that in the satellite trace gas data from the upper troposphere through the middle stratosphere. In the upper stratosphere and lower mesosphere, the SLIMCAT simulation does not capture the strong descent of mesospheric CO and H2O values into the reformed vortex; poor CTM performance in the upper stratosphere and lower mesosphere results primarily from biases in the diabatic descent in assimilated analyses.

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Satellite observations and modeling of transport in the upper troposphere through the lower mesosphere during the 2006 major stratospheric sudden warming

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-4775-2009 ◽

2009 ◽

Vol 9 (14) ◽

pp. 4775-4795 ◽

Cited By ~ 58

Author(s):

G. L. Manney ◽

R. S. Harwood ◽

I. A. MacKenzie ◽

K. Minschwaner ◽

D. R. Allen ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Lower Stratosphere ◽

Transport Model ◽

Polar Vortex ◽

Trace Gas ◽

Transport Barrier ◽

Stratospheric Sudden Warming ◽

Upper Troposphere ◽

Comprehensive Picture ◽

Middle Stratosphere

Abstract. An unusually strong and prolonged stratospheric sudden warming (SSW) in January 2006 was the first major SSW for which globally distributed long-lived trace gas data are available covering the upper troposphere through the lower mesosphere. We use Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) data, the SLIMCAT Chemistry Transport Model (CTM), and assimilated meteorological analyses to provide a comprehensive picture of transport during this event. The upper tropospheric ridge that triggered the SSW was associated with an elevated tropopause and layering in trace gas profiles in conjunction with stratospheric and tropospheric intrusions. Anomalous poleward transport (with corresponding quasi-isentropic troposphere-to-stratosphere exchange at the lowest levels studied) in the region over the ridge extended well into the lower stratosphere. In the middle and upper stratosphere, the breakdown of the polar vortex transport barrier was seen in a signature of rapid, widespread mixing in trace gases, including CO, H2O, CH4 and N2O. The vortex broke down slightly later and more slowly in the lower than in the middle stratosphere. In the middle and lower stratosphere, small remnants with trace gas values characteristic of the pre-SSW vortex lingered through the weak and slow recovery of the vortex. The upper stratospheric vortex quickly reformed, and, as enhanced diabatic descent set in, CO descended into this strong vortex, echoing the fall vortex development. Trace gas evolution in the SLIMCAT CTM agrees well with that in the satellite trace gas data from the upper troposphere through the middle stratosphere. In the upper stratosphere and lower mesosphere, the SLIMCAT simulation does not capture the strong descent of mesospheric CO and H2O values into the reformed vortex; this poor CTM performance in the upper stratosphere and lower mesosphere results primarily from biases in the diabatic descent in assimilated analyses.

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Intercomparison and evaluation of satellite peroxyacetyl nitrate observations in the upper troposphere – lower stratosphere

10.5194/acp-2016-386 ◽

2016 ◽

Author(s):

R. J. Pope ◽

N. A. D. Richards ◽

M. P. Chipperfield ◽

D. P. Moore ◽

S. A. Monks ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Lower Stratosphere ◽

Transport Model ◽

Regional Distribution ◽

Michelson Interferometer ◽

Lower Atmosphere ◽

Chemical Transport Model ◽

Peroxyacetyl Nitrate ◽

Subsequent Formation ◽

Upper Troposphere

Abstract. Peroxyacetyl nitrate (PAN) is an important chemical species in the troposphere as it aids the long-range transport of NOx and subsequent formation of O3 in relatively clean remote regions. Over the past few decades observations from aircraft campaigns and surface sites have been used to better understand the regional distribution of PAN. However, recent measurements made by satellites allow for a global assessment of PAN in the upper troposphere – lower stratosphere (UTLS). In this study, we investigate global PAN distributions from two independent retrieval methodologies, based on measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, on board ENVISAT from the Institute of Meteorology and Climate Research (IMK), Karlsruhe Institute of Technology and the Department of Physics and Astronomy, University of Leicester (UoL). Retrieving PAN from MIPAS is challenging due to the weak signal in the measurements and contamination from other species. Therefore, we compare the two MIPAS datasets with observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), insitu aircraft data and the TOMCAT 3-D chemical transport model. MIPAS shows peak UTLS PAN concentrations over the biomass burning regions (e.g. ranging from 150 to > 200 pptv at 150 hPa) and during the summertime Asian monsoon as enhanced convection aids the vertical transport of PAN from the lower atmosphere. At 150 hPa, we find significant differences between the two MIPAS datasets in the tropics, where IMK PAN concentrations are larger by 50–100 pptv. Comparisons between MIPAS and ACE-FTS show better agreement with the UoL MIPAS PAN concentrations at 200 hPa, but with mixed results above this altitude. TOMCAT generally captures the magnitude and structure of climatological aircraft PAN profiles within the observational variability allowing it to be used to investigate the MIPAS PAN differences. TOMCAT-MIPAS comparisons show that the model is both positively (UoL) and negatively (IMK) biased against the satellite products. These results show that satellite PAN observations are able to detect realistic spatial variations in PAN in the UTLS, but further work is needed to resolve differences in existing retrievals to allow quantitative use of the products.

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Technical note: Reanalysis of Aura MLS chemical observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-13647-2019 ◽

2019 ◽

Vol 19 (21) ◽

pp. 13647-13679 ◽

Cited By ~ 5

Author(s):

Quentin Errera ◽

Simon Chabrillat ◽

Yves Christophe ◽

Jonas Debosscher ◽

Daan Hubert ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Transport Model ◽

Michelson Interferometer ◽

Polar Vortex ◽

Methyl Chloride ◽

Technical Note ◽

Chemical Transport Model ◽

Stratospheric Polar Vortex ◽

Upper Troposphere ◽

Independent Observations

Abstract. This paper presents a reanalysis of the atmospheric chemical composition from the upper troposphere to the lower mesosphere from August 2004 to December 2017. This reanalysis is produced by the Belgian Assimilation System for Chemical ObsErvations (BASCOE) constrained by the chemical observations from the Microwave Limb Sounder (MLS) on board the Aura satellite. BASCOE is based on the ensemble Kalman filter (EnKF) method and includes a chemical transport model driven by the winds and temperature from the ERA-Interim meteorological reanalysis. The model resolution is 3.75∘ in longitude, 2.5∘ in latitude and 37 vertical levels from the surface to 0.1 hPa with 25 levels above 100 hPa. The outputs are provided every 6 h. This reanalysis is called BRAM2 for BASCOE Reanalysis of Aura MLS, version 2. Vertical profiles of eight species from MLS version 4 are assimilated and are evaluated in this paper: ozone (O3), water vapour (H2O), nitrous oxide (N2O), nitric acid (HNO3), hydrogen chloride (HCl), chlorine oxide (ClO), methyl chloride (CH3Cl) and carbon monoxide (CO). They are evaluated using independent observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and N2O observations from a different MLS radiometer than the one used to deliver the standard product and ozonesondes. The evaluation is carried out in four regions of interest where only selected species are evaluated. These regions are (1) the lower-stratospheric polar vortex where O3, H2O, N2O, HNO3, HCl and ClO are evaluated; (2) the upper-stratospheric–lower-mesospheric polar vortex where H2O, N2O, HNO3 and CO are evaluated; (3) the upper troposphere–lower stratosphere (UTLS) where O3, H2O, CO and CH3Cl are evaluated; and (4) the middle stratosphere where O3, H2O, N2O, HNO3, HCl, ClO and CH3Cl are evaluated. In general BRAM2 reproduces MLS observations within their uncertainties and agrees well with independent observations, with several limitations discussed in this paper (see the summary in Sect. 5.5). In particular, ozone is not assimilated at altitudes above (i.e. pressures lower than) 4 hPa due to a model bias that cannot be corrected by the assimilation. MLS ozone profiles display unphysical oscillations in the tropical UTLS, which are corrected by the assimilation, allowing a good agreement with ozonesondes. Moreover, in the upper troposphere, comparison of BRAM2 with MLS and independent observations suggests a positive bias in MLS O3 and a negative bias in MLS H2O. The reanalysis also reveals a drift in MLS N2O against independent observations, which highlights the potential use of BRAM2 to estimate biases between instruments. BRAM2 is publicly available and will be extended to assimilate MLS observations after 2017.

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Direct inversion of circulation from tracer measurements – Part 2: Sensitivity studies and model recovery tests

10.5194/acp-2020-72 ◽

2020 ◽

Author(s):

Thomas von Clarmann ◽

Udo Grabowski

Keyword(s):

Lower Stratosphere ◽

Velocity Fields ◽

Trace Gas ◽

Meridional Transport ◽

Upper Troposphere ◽

Direct Inversion ◽

Circulation Patterns ◽

Sensitivity Studies ◽

Reference Fields ◽

Middle Stratosphere

Abstract. The direct inversion of the 2D continuity equation allows to infer the effective meridional transport of trace gases in the middle stratosphere. This methods exploits the information both given by the displacement of patterns in measured trace gas distributions and by the approximate balance between sinks and horizontal as well as vertical advection. Model recovery tests have shown that with the current setup of the algorithm, this method reliably reproduces the circulation patterns in the entire analysis domain from 6 to 66 km altitude. Due to the regularization of the inversion, velocities above about 30 km are more likely under- than overestimated. This is explained by the fact that the measured trace gas distributions at higher altitudes generally contain less information and that the regularization of the inversion pushes results towards zero. Weaker regularization would in some cases allow a more accurate recovery of the velocity fields. However, there is a price to pay in that the risk of convergence failure increases. No instance was found where the algorithm generated artificial patterns not present in the reference fields. Most information on effective velocities above 50 km is included in measurements of CH4, CO, H2O, and N2O, while CFC-11, HCFC-22, and CFC-12 constrain the inversion most efficiently in the middle stratosphere. H2O is a particularly important tracer in the upper troposphere/lower stratosphere. SF6 and CCl4 contain generally less information but still contribute to the reduction of the estimated uncertainties.

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Direct inversion of circulation from tracer measurements – Part 2: Sensitivity studies and model recovery tests

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-2509-2021 ◽

2021 ◽

Vol 21 (4) ◽

pp. 2509-2526

Author(s):

Thomas von Clarmann ◽

Udo Grabowski

Keyword(s):

Lower Stratosphere ◽

Velocity Fields ◽

Trace Gas ◽

Meridional Transport ◽

Upper Troposphere ◽

Direct Inversion ◽

Circulation Patterns ◽

Sensitivity Studies ◽

Reference Fields ◽

Middle Stratosphere

Abstract. The direct inversion of the 2D continuity equation allows for the inference of the effective meridional transport of trace gases in the middle stratosphere. This method exploits the information given by both the displacement of patterns in measured trace gas distributions and the approximate balance between sinks and horizontal as well as vertical advection. Model recovery tests show that with the current setup of the algorithm, this method reliably reproduces the circulation patterns in the entire analysis domain from 6 to 66 km altitude. Due to the regularization of the inversion, velocities above about 30 km are more likely under- than overestimated. This is explained by the fact that the measured trace gas distributions at higher altitudes generally contain less information and that the regularization of the inversion pushes results towards 0. Weaker regularization would in some cases allow a more accurate recovery of the velocity fields, but there is a price to pay in that the risk of convergence failure increases. No instance was found where the algorithm generated artificial patterns not present in the reference fields. Most information on effective velocities above 50 km is included in measurements of CH4, CO, H2O, and N2O, while CFC-11, HCFC-22, and CFC-12 constrain the inversion most efficiently in the middle stratosphere. H2O is a particularly important tracer in the upper troposphere or lower stratosphere. SF6 and CCl4 generally contain less information but still contribute to the reduction in the estimated uncertainties. With these tests, the reliability of the method has been established.

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Intercomparison and evaluation of satellite peroxyacetyl nitrate observations in the upper troposphere–lower stratosphere

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-13541-2016 ◽

2016 ◽

Vol 16 (21) ◽

pp. 13541-13559 ◽

Cited By ~ 9

Author(s):

Richard J. Pope ◽

Nigel A. D. Richards ◽

Martyn P. Chipperfield ◽

David P. Moore ◽

Sarah A. Monks ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Lower Stratosphere ◽

Transport Model ◽

Regional Distribution ◽

Michelson Interferometer ◽

Lower Atmosphere ◽

Chemical Transport Model ◽

Peroxyacetyl Nitrate ◽

Subsequent Formation ◽

Upper Troposphere

Abstract. Peroxyacetyl nitrate (PAN) is an important chemical species in the troposphere as it aids the long-range transport of NOx and subsequent formation of O3 in relatively clean remote regions. Over the past few decades observations from aircraft campaigns and surface sites have been used to better understand the regional distribution of PAN. However, recent measurements made by satellites allow for a global assessment of PAN in the upper troposphere–lower stratosphere (UTLS). In this study, we investigate global PAN distributions from two independent retrieval methodologies, based on measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, on board Envisat from the Institute of Meteorology and Climate Research (IMK), Karlsruhe Institute of Technology, and the Department of Physics and Astronomy, University of Leicester (UoL). Retrieving PAN from MIPAS is challenging due to the weak signal in the measurements and contamination from other species. Therefore, we compare the two MIPAS datasets with observations from the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS), in situ aircraft data and the 3-D chemical transport model TOMCAT. MIPAS shows peak UTLS PAN concentrations over the biomass burning regions (e.g. ranging from 150 to >  200 pptv at 150 hPa) and during the summertime Asian monsoon as enhanced convection aids the vertical transport of PAN from the lower atmosphere. At 150 hPa, we find significant differences between the two MIPAS datasets in the tropics, where IMK PAN concentrations are larger by 50–100 pptv. Comparisons between MIPAS and ACE-FTS show better agreement with the UoL MIPAS PAN concentrations at 200 hPa, but with mixed results above this altitude. TOMCAT generally captures the magnitude and structure of climatological aircraft PAN profiles within the observational variability allowing it to be used to investigate the MIPAS PAN differences. TOMCAT–MIPAS comparisons show that the model is both positively (UoL) and negatively (IMK) biased against the satellite products. These results indicate that satellite PAN observations are able to detect realistic spatial variations in PAN in the UTLS, but further work is needed to resolve differences in existing retrievals to allow quantitative use of the products.

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What drives the observed variability of HCN in the troposphere and lower stratosphere?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-10883-2009 ◽

2009 ◽

Vol 9 (3) ◽

pp. 10883-10912 ◽

Cited By ~ 1

Author(s):

Q. Li ◽

P. I. Palmer ◽

H. C. Pumphrey ◽

P. Bernath ◽

E. Mahieu

Keyword(s):

Atmospheric Chemistry ◽

Lower Stratosphere ◽

Transport Model ◽

Atmospheric Transport ◽

Chemistry Transport Model ◽

Upper Troposphere ◽

Annual Variations ◽

Surface Emission ◽

Chemistry Experiment ◽

Temporal Overlap

Abstract. We use the GEOS-Chem global 3-D chemistry transport model to investigate the relative importance of chemical and physical processes that determine observed variability of hydrogen cyanide (HCN) in the troposphere and lower stratosphere. Consequently, we reconcile ground-based FTIR column measurements of HCN, which show annual and semi-annual variations, with recent space-borne measurements of HCN mixing ratio in the tropical lower stratosphere, which show a large two-year variation. We find that the observed column variability over the ground-based stations is determined by a superposition of HCN from several regional burning sources, with GEOS-Chem reproducing these column data with a positive bias of 5%. GEOS-Chem reproduces the observed tropical HCN variability from the Microwave Limb Sounder and the Atmospheric Chemistry Experiment satellite instruments with a negative bias of 7%. We show the tropical biomass burning emissions explain mostly the observed HCN variations in the upper troposphere and lower stratosphere (UTLS), with the remainder due to atmospheric transport and HCN chemistry. In the mid and upper stratosphere, atmospheric dynamics progressively exerts more influences on HCN variations. The extent of temporal overlap between African and other continental burning seasons is key in establishing the apparent bienniel cycle in the UTLS. Similar analysis of other, shorter-lived trace gases have not observed the transition between annual and bienniel cycles in the UTLS probably because the signal of inter-annual variations from surface emission has vanished before arriving at the lower stratosphere (LS), due to shorter atmospheric lifetimes.

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Technical note: Reanalysis of Aura MLS Chemical Observations

10.5194/acp-2019-530 ◽

2019 ◽

Cited By ~ 1

Author(s):

Quentin Errera ◽

Simon Chabrillat ◽

Yves Christophe ◽

Jonas Debosscher ◽

Daan Hubert ◽

...

Keyword(s):

Atmospheric Chemistry ◽

Transport Model ◽

Michelson Interferometer ◽

Polar Vortex ◽

Methyl Chloride ◽

Technical Note ◽

Chemical Transport Model ◽

Stratospheric Polar Vortex ◽

Upper Troposphere ◽

Independent Observations

Abstract. This paper presents a reanalysis of the atmospheric chemical composition from the upper troposphere to the lower mesosphere from August 2004 to December 2017. This reanalysis is produced by the Belgian Assimilation System for Chemical ObsErvations (BASCOE) constrained by the chemical observations from the Microwave Limb Sounder (MLS) onboard the Aura satellite. BASCOE is based on the Ensemble Kalman Filter (EnKF) method and includes a chemical transport model driven by the winds and temperature from the ERA-Interim meteorological reanalysis. The model resolution is 3.75° in longitude, 2.5° in latitude and 37 vertical levels from the surface to 0.1 hPa with 25 levels above 100 hPa. The outputs are provided every 6 hours. This reanalysis is called BRAM2 for BASCOE Reanalysis of Aura MLS, version 2. Vertical profiles of eight species from MLS version 4 are assimilated and are evaluated in this paper: ozone (O3), water vapour (H2O), nitrous oxide (N2O), nitric acid (HNO3), hydrogen chloride (HCl), chlorine oxide (ClO), methyl chloride (CH3Cl) and carbon monoxide (CO). They are evaluated using independent observations from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACEFTS), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES), N2O observations from another MLS radiometer than the one used to deliver the standard product and ozonesondes. The evaluation is done in four regions of interest where only selected species are evaluated. These regions are (1) the lower stratospheric polar vortex where O3, H2O, N2O, HNO3, HCl and ClO are evaluated, (2) the upper stratospheric lower mesospheric polar vortex where H2O, N2O, HNO3 and CO are evaluated, (3) the tropical tropopause layer (TTL) where O3, H2O, CO and CH3Cl are evaluated and (4) the middle stratosphere where O3, H2O, N2O, HNO3, HCl, ClO and CH3Cl are evaluated. In general BRAM2 reproduces MLS observations within their uncertainties and agrees well with independent observations, with several limitations discussed in this paper (see the summary in Sect. 5.5). In particular, ozone is not assimilated at altitudes above (i.e. pressures lower than) 4 hPa due to a model bias that cannot be corrected by the assimilation. MLS ozone profiles display unphysical oscillations in the TTL which are corrected by the assimilation, allowing a good agreement with ozonesondes. Moreover, in the upper troposphere, comparison of BRAM2 with MLS and independent observations suggests a positive bias in MLS O3 and a negative bias in MLS H2O. The reanalysis also reveals a drift in MLS N2O against independent observations which highlights the potential use of BRAM2 to estimate biases between instruments. BRAM2 is publicly available and will be extended to assimilate MLS observations post 2017.

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A PV-based determination of the transport barrier in the Asian summer monsoon anticyclone

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-10593-2015 ◽

2015 ◽

Vol 15 (7) ◽

pp. 10593-10628 ◽

Cited By ~ 3

Author(s):

F. Ploeger ◽

C. Gottschling ◽

S. Griessbach ◽

J.-U. Grooß ◽

G. Günther ◽

...

Keyword(s):

Summer Monsoon ◽

Large Scale ◽

Lower Stratosphere ◽

Transport Model ◽

Asian Summer Monsoon ◽

Deep Convection ◽

Polar Vortex ◽

Time Averaging ◽

Transport Barrier ◽

Asian Summer

Abstract. The Asian summer monsoon provides an important pathway of tropospheric source gases and pollution into the lower stratosphere. This transport is characterized by deep convection and steady upwelling, combined with confinement inside a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS). In this paper, we show that a barrier to horizontal transport along the 380 K isentrope in the monsoon anticyclone can be determined from the potential vorticity (PV) field, following the polar vortex criterion by Nash et al. (1996). Due to large dynamic variability of the anticyclone, the corresponding maximum in the PV gradient is weak and additional constraints are needed (e.g., time averaging). Notwithstanding, PV contours in the monsoon anticyclone agree well with contours of trace gas mixing ratios (CO, O3) and mean age from model simulations with a Lagrangian chemistry transport model (CLaMS) and MLS satellite observations. Hence, the PV-based transport barrier reflects the separation between air inside the anticyclone core and the background atmosphere well. For the summer season 2011 we find an average PV value of 3.6 PVU for the transport barrier in the anticyclone on the 380 K isentrope.

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Structural changes in the shallow and transition branch of the Brewer–Dobson circulation induced by El Niño

10.5194/acp-2018-688 ◽

2018 ◽

Author(s):

Mohamadou Diallo ◽

Paul Konopka ◽

Michelle L. Santee ◽

Rolf Müller ◽

Mengchu Tao ◽

...

Keyword(s):

El Niño ◽

Structural Changes ◽

Lower Stratosphere ◽

Transport Model ◽

El Nino ◽

Southern Oscillation ◽

Satellite Observations ◽

Trace Gas ◽

Residual Circulation ◽

Mixing Ratios

Abstract. The stratospheric Brewer–Dobson circulation (BD-circulation) determines the transport and lifetime of key radiatively active trace gases and further impacts surface climate through downward coupling. Here, we quantify the variability in the lower stratospheric BD-circulation induced by the El Nino Southern Oscillation (ENSO), using satellite trace gas measurements and simulations with the Lagrangian chemistry transport model, CLaMS, driven by ERA-Interim and JRA-55 reanalyses. We show that despite discrepancies in the deseasonalised ozone (O3) mixing ratios between CLaMS simulations and satellite observations, the patterns of changes in the lower stratospheric O3 anomalies induced by ENSO agree remarkably well over the 2005–2016 period. Particularly during the most recent El Niño in 2015–2016, both satellite observations and CLaMS simulations show the largest negative tropical O3 anomaly in the record. Regression analysis of different metrics of the BD-circulation strength, including mean age of air, vertical velocity, residual circulation and age spectrum, shows clear evidence for structural changes of the BD-circulation in the lower stratosphere induced by El Niño, consistent with observed O3 anomalies. These structural changes during El Niño include a weakening of the transition branch of the BD-circulation between about 370–420 K (∼ 100–70 hPa) and equatorward of about 60° and, a strengthening of the shallow branch at the same latitudes and between about 420–500 K (∼ 70–30 hPa). The strengthening of the shallow branch induces negative tropical O3 anomalies due to enhanced tropical upwelling, while the weakening of the transition branch combined with enhanced downwelling due to the strengthening shallow branch leads to positive O3 anomalies in the extratropical upper troposphere-lower stratosphere (UTLS). Our results suggest that a shift of the ENSO basic state toward more frequent El Niño-like conditions in a warming future climate will substantially alter UTLS trace gas distributions due to these changes in the vertical structure of the stratospheric circulation.

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