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See detailStratospheric fluorine as a tracer of circulation changes: comparison between infrared remote-sensing observations and simulations with five modern reanalyses
Prignon, Maxime ULiege; Chabrillat, S.; Friedrich, M. et al

in Journal of Geophysical Research. Atmospheres (2021), 126(19),

Using multidecadal time-series of ground-based and satellite Fourier transform infrared measurements of inorganic fluorine (i.e., total fluorine resident in stratospheric fluorine reservoirs), we ... [more ▼]

Using multidecadal time-series of ground-based and satellite Fourier transform infrared measurements of inorganic fluorine (i.e., total fluorine resident in stratospheric fluorine reservoirs), we investigate stratospheric circulation changes over the past 20 years. The representation of these changes in five modern reanalyses are further analysed through chemical-transport model (CTM) simulations. From the observations but also from all reanalyses, we show that the inorganic fluorine is accumulating less rapidly in the Southern Hemisphere than in the Northern Hemisphere during the twenty-first century. Comparisons with a study evaluating the age-of-air of these reanalyses using the same CTM allow us to link this hemispheric asymmetry to changes in the Brewer-Dobson circulation (BDC), with the age-of-air of the Southern Hemisphere getting younger relative to that of the Northern Hemisphere. Large differences in simulated total columns and absolute trend values are, nevertheless, depicted between our simulations driven by the five reanalyses. Superimposed on this multidecadal change, we, furthermore, confirm a 5-to-7-year variability of the BDC that was first described in a recent study analysing long-term time series of hydrogen chloride (HCl) and nitric acid (HNO3). It is important to stress that our results, based on observations and meteorological reanalyses, are in contrast with the projections of chemistry-climate models in response to the coupled increase of greenhouse gases and decrease of ozone depleting substances, calling for further investigations and the continuation of long-term observations. [less ▲]

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See detailFirst retrievals of peroxyacetyl nitrate (PAN) from ground-based FTIR solar spectra recorded at remote sites, comparison with model and satellite data
Mahieu, Emmanuel ULiege; Fischer, Emily V.; Franco, Bruno et al

in Elementa: Science of the Anthropocene (2021), 9(1),

Peroxyacetyl nitrate (PAN) is the main tropospheric reservoir of NOx (NO + NO2). Its lifetime can reach several months in the upper cold troposphere. This enables the long-range transport of NOx radicals ... [more ▼]

Peroxyacetyl nitrate (PAN) is the main tropospheric reservoir of NOx (NO + NO2). Its lifetime can reach several months in the upper cold troposphere. This enables the long-range transport of NOx radicals, under the form of PAN, far from the regions of emission. The subsequent release of NOx through the PAN thermal decomposition leads to the efficient formation of tropospheric ozone (O3), with important consequences for tropospheric oxidative capacity and air quality. The chemical properties of PAN have stimulated the progressive development of remote-sensing products by the satellite community, and recent additions open the prospect for the production of decadal and near-global time series. These products will provide new constraints on the distribution and evolution of this key trace gas in the Earth’s atmosphere, but they will also require reliable measurements for validation and characterization of performance. We present an approach that has been developed to retrieve PAN total columns from ground-based high-resolution solar absorption Fourier transform infrared (FTIR) spectra. This strategy is applied to observations recorded at remote FTIR stations of the Network for the Detection of Atmospheric Composition Change (NDACC). The resulting data sets are compared with total column time series derived from IASI (Infrared Atmospheric Sounding Interferometer) satellite observations and to a global chemical transport model. The results are discussed in terms of their overall consistency, mutual agreement, and seasonal cycles. Noticeable is the fact that the FTIR data point to substantial deficiencies in the global model simulation over high latitudes, a poorly sampled region, with an underestimation of the PAN columns during spring, at the peak of the seasonal cycle. Finally, we suggest avenues for development that should make it possible to limit intra- or intersite biases and extend the retrieval of PAN to other NDACC stations that are more affected by water vapor interferences. [less ▲]

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See detailStratospheric circulation changes: investigations using multidecadal observations and simulations of inorganic fluorine
Prignon, Maxime ULiege

Doctoral thesis (2021)

The intense human activity of the past two hundred years has perturbed the subtle balance existing between the spheres of the Earth system. The atmospheric composition has been modified with massive ... [more ▼]

The intense human activity of the past two hundred years has perturbed the subtle balance existing between the spheres of the Earth system. The atmospheric composition has been modified with massive emissions of greenhouse gases and substances depleting the life-essential ozone layer (ODSs). The most known to the general public resulting changes are certainly the global warming of the troposphere and the dramatic formation of the Antarctic ozone hole. However, it is less generally known that the most robustly modelled response to the increase of greenhouse gases, and the resulting global warming, is a speeding-up of the transport circulation occurring in the stratosphere, the atmospheric layer that is situated well above our head, between 10 and 50 km. This transport circulation, referred to as the Brewer-Dobson circulation (BDC), controls the distribution of ozone and other long-lived gaseous constituents of the stratosphere. Therefore, it is crucial to characterize the BDC and its changes to assess precisely the healing of the ozone layer, expected to occur gradually in the twenty-first century as most of ODS emissions have been successfully phased out by the Montreal Protocol on Substances that Deplete the Ozone Layer, including its Amendments and Adjustments. In this work, we investigated BDC changes through their impact on multidecadal time-series of stratospheric fluorine. To this end, we include ground-based Fourier transform infrared time-series from Jungfraujoch (Switzerland, 46°N) and Lauder (New Zealand, 45°S), Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) satellite time-series and five simulations performed by the BASCOE chemical-transport model (CTM). These simulations are driven by the five modern meteorological reanalyses of the atmosphere. Thus, we assess the representation of the investigated BDC changes in state-of-the-art reanalyses which are designed to represent at best the atmospheric state over the past 30 years. We first improved the retrieval strategy of HCFC-22 (CHF2Cl), the most abundant hydrochlorofluorocarbon (HCFC) and the second source of fluorine in the stratosphere, using infrared solar spectra recorded at Jungfraujoch. We showed that HCFC-22 accumulation rates are progressively decreasing in the last decade, highlighting the success of the Montreal Protocol. Furthermore, this first step allowed us to demonstrate the validity of our BASCOE CTM set-up. Indeed, it is the first time that this model is used for such simulations, hence new features were implemented just before and during this thesis project and needed to be validated. The investigations on the impact of BDC changes on the time-series of stratospheric fluorine showed that, for the past twenty years, the BDC has been changing asymmetrically, with the Southern Hemisphere branch getting stronger relative to that of the Northern Hemisphere. Observational datasets and all of the five reanalyses are qualitatively in agreement with this change. However, this important finding is opposed to all model projections, notably used to project ozone recovery, modelling a weakening of the southern branch, in response to increases in greenhouse gases and to decreases in ODSs, calling for further investigations. Superimposed to this 20 year-trend, we have further confirmed a 5-to-7-year variability of the stratosphere, a feature which allows to put into perspective recent studies questioning specific stratospheric variabilities and associated hemispheric asymmetries. [less ▲]

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See detailPreliminary study of long-term trends of N2O as a proxy of the Brewer-Dobson Circulation
Minganti, Daniele ULiege; Chabrillat, Simon; Errera, Quentin et al

Scientific conference (2021, February 26)

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See detailClimatological impact of the Brewer–Dobson circulation on the N2O budget in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses
Minganti, Daniele ULiege; Chabrillat, Simon; Christophe, Yves et al

in Atmospheric Chemistry and Physics (2020), 20(21), 1260912631

The Brewer–Dobson circulation (BDC) is a stratospheric circulation characterized by upwelling of tropospheric air in the tropics, poleward flow in the stratosphere, and downwelling at mid and high ... [more ▼]

The Brewer–Dobson circulation (BDC) is a stratospheric circulation characterized by upwelling of tropospheric air in the tropics, poleward flow in the stratosphere, and downwelling at mid and high latitudes, with important implications for chemical tracer distributions, stratospheric heat and momentum budgets, and mass exchange with the troposphere. As the photochemical losses of nitrous oxide (N2O) are well known, model differences in its rate of change are due to transport processes that can be separated into the mean residual advection and the isentropic mixing terms in the transformed Eulerian mean (TEM) framework. Here, the climatological impact of the stratospheric BDC on the long-lived tracer N2O is evaluated through a comparison of its TEM budget in the Whole Atmosphere Community Climate Model (WACCM), in a chemical reanalysis of the Aura Microwave Limb Sounder version 2 (BRAM2) and in a chemistry transport model (CTM) driven by four modern reanalyses: the European Centre for Medium-Range Weather Forecasts Interim reanalysis (ERA-Interim; Dee et al., 2011), the Japanese 55-year Reanalysis (JRA-55; Kobayashi et al., 2015), and the Modern-Era Retrospective analysis for Research and Applications version 1 (MERRA; Rienecker et al., 2011) and version 2 (MERRA-2; Gelaro et al., 2017). The effects of stratospheric transport on the N2O rate of change, as depicted in this study, have not been compared before across this variety of datasets and have never been investigated in a modern chemical reanalysis. We focus on the seasonal means and climatological annual cycles of the two main contributions to the N2O TEM budget: the vertical residual advection and the horizontal mixing terms. The N2O mixing ratio in the CTM experiments has a spread of approximately ∼20 % in the middle stratosphere, reflecting the large diversity in the mean age of air obtained with the same CTM experiments in a previous study. In all datasets, the TEM budget is closed well; the agreement between the vertical advection terms is qualitatively very good in the Northern Hemisphere, and it is good in the Southern Hemisphere except above the Antarctic region. The datasets do not agree as well with respect to the horizontal mixing term, especially in the Northern Hemisphere where horizontal mixing has a smaller contribution in WACCM than in the reanalyses. WACCM is investigated through three model realizations and a sensitivity test using the previous version of the gravity wave parameterization. The internal variability of the horizontal mixing in WACCM is large in the polar regions and is comparable to the differences between the dynamical reanalyses. The sensitivity test has a relatively small impact on the horizontal mixing term, but it significantly changes the vertical advection term and produces a less realistic N2O annual cycle above the Antarctic. In this region, all reanalyses show a large wintertime N2O decrease, which is mainly due to horizontal mixing. This is not seen with WACCM, where the horizontal mixing term barely contributes to the TEM budget. While we must use caution in the interpretation of the differences in this region (where the reanalyses show large residuals of the TEM budget), they could be due to the fact that the polar jet is stronger and is not tilted equatorward in WACCM compared with the reanalyses. We also compare the interannual variability in the horizontal mixing and the vertical advection terms between the different datasets. As expected, the horizontal mixing term presents a large variability during austral fall and boreal winter in the polar regions. In the tropics, the interannual variability of the vertical advection term is much smaller in WACCM and JRA-55 than in the other experiments. The large residual in the reanalyses and the disagreement between WACCM and the reanalyses in the Antarctic region highlight the need for further investigations on the modeling of transport in this region of the stratosphere. [less ▲]

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See detailObserved and simulated atmospheric inorganic fluorine: short term and long term trends related to circulation changes
Prignon, Maxime ULiege; Bernath, P. F.; Chabrillat, S. et al

Conference (2020, October 15)

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See detailObserved Hemispheric Asymmetry in Stratospheric Transport Trends From 1994 to 2018
Strahan, Susan E.; Smale, Dan; Douglass, Anne R. et al

in Geophysical Research Letters (2020), 47(17), 2020088567

Abstract Total columns of the trace gases nitric acid (HNO3) and hydrogen chloride (HCl) are sensitive to variations in the lower stratospheric age of air, a quantity that describes transport time scales ... [more ▼]

Abstract Total columns of the trace gases nitric acid (HNO3) and hydrogen chloride (HCl) are sensitive to variations in the lower stratospheric age of air, a quantity that describes transport time scales in the stratosphere. Analyses of HNO3 and HCl columns from the Network for the Detection of Atmospheric Composition Change panning 77°S to 79°N have detected changes in the extratropical stratospheric transport circulation from 1994 to 2018. The HNO3 and HCl analyses combined with the age of air from a simulation using the MERRA2 reanalysis show that the Southern Hemisphere lower stratosphere has become 1 month/decade younger relative to the Northern Hemisphere, largely driven by the Southern Hemisphere transport circulation. The analyses reveal multiyear anomalies with a 5- to 7-year period driven by interactions between the circulation and the quasi-biennial oscillation in tropical winds. This hitherto unrecognized variability is large relative to hemispheric transport trends and may bias ozone trend regressions. [less ▲]

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See detailN2O-based climatology of the Brewer Dobson Circulation in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses
Minganti, Daniele ULiege; Chabrillat, Simon; Christophe, Yves et al

Conference (2020, May 05)

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See detailQuantification of Stratospheric Ozone Recovery Due to Anthropogenic Halogens
Salawitch, R. J.; Tribett, W.; Wales, P. et al

Conference (2020, January 14)

Human release of CFCs and other ozone depleting substances (ODS) has led to a slow, steady erosion of the thickness of the global ozone layer over the past several decades. The ozone layer has begun to ... [more ▼]

Human release of CFCs and other ozone depleting substances (ODS) has led to a slow, steady erosion of the thickness of the global ozone layer over the past several decades. The ozone layer has begun to recover due to actions taken under the Montreal Protocol, which has led to a decrease in the atmospheric abundance of ozone depleting substances. Yet, unreported emissions of CFC-11 have led to a slower than expected decline, and there has been a rise in the atmospheric abundance of chlorinated very short lived (VSL) compounds not regulated under the Montreal Protocol. In this presentation, we examine time series of ozone and halogens from a variety of observational platforms to quantify the attribution of the change in stratospheric ozone that is due to halogens. Our focus is on the extra-polar region: i.e., the state of the ozone layer between 55S and 55N where the vast majority of the world’s population resides. We will quantify the effect of continued release of CFC-11 and the presence of chlorinated VSL species on the recovery of the ozone layer. Additionally, we will use atmospheric observations to evaluate several proposed formulations for defining the quantity known as “Equivalent Effective Stratospheric Chlorine” (EESC) and assess the impact of these formulations on the projected recovery of the ozone layer. [less ▲]

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See detailN2O-based climatology of the Brewer-Dobson Circulation in WACCM, a chemical renalysis and a CTM driven by four dynamical reanalyses
Minganti, Daniele ULiege; Chabrillat, Simon; Christophe, Yves et al

Poster (2019, December 11)

The Brewer-Dobson Circulation (BDC) plays a major role in the stratospheric dynamics in terms of tracer transport through the mean residual meridional advection and the isentropic two-way mixing. The ... [more ▼]

The Brewer-Dobson Circulation (BDC) plays a major role in the stratospheric dynamics in terms of tracer transport through the mean residual meridional advection and the isentropic two-way mixing. The climatological BDC in the Whole Atmosphere Community Climate Model (WACCM) is separated in those components and evaluated through a comparison with a chemical reanalysis of Aura MLS (BRAM2) and with a chemistry-transport model driven by four modern reanalyses (ERA-Interim, JRA-55, MERRA and MERRA2), using the Transformed Eulerian Mean (TEM) analysis of the long-lived tracer N2O and focusing on the vertical residual advection and the horizontal two-way mixing terms. In the wintertime Southern polar region the horizontal mixing term in WACCM shows near-zero values, while all the reanalyses show strong negative contributions. This disagreement is likely due to the different representation of the polar transport barrier, that affects the mixing inside the polar vortex. In this region the reanalyses are characterized by large uncertainties of the TEM analysis, i.e. the residual term of the budget is quite large (the N2O TEM budget is not fully closed). In the wintertime Northern polar latitudes WACCM shows smaller values of the horizontal mixing term compared to the reanalyses, which show lower uncertainties of the TEM budget. The agreement is improved in the middle and low latitudes, especially in the Northern Hemisphere: the differences are smaller and the residual term is lower compared to the polar latitudes. The inter-annual variability of the horizontal mixing term is large in the Southern polar latitudes during austral fall and in the Northern polar latitudes during boreal winter. [less ▲]

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See detailSurveillance à long terme de l’atmosphère terrestre à la station du Jungfraujoch
Mahieu, Emmanuel ULiege; Flock, Olivier ULiege; Notholt, Justus et al

in Bulletin de la Société Royale des Sciences de Liège (2019, November), 88

It is in the early 1950s that researchers from the University of Liège have recorded the first atmospheric solar spectra at the Jungfraujoch scientific station, in the Swiss Alps, at a time when climate ... [more ▼]

It is in the early 1950s that researchers from the University of Liège have recorded the first atmospheric solar spectra at the Jungfraujoch scientific station, in the Swiss Alps, at a time when climate change was not a matter of worry. These pioneering observations have allowed to confirm that methane and carbon monoxide were ubiquitous constituents of the Earth’s atmosphere. The recording of atmospheric spectra resumed in the mid-1970s, stimulated by rising concerns related to possible stratospheric ozone depletion. Since then, this monitoring activity has been conducted at that site without interruption, allowing to gather high-quality data crucial for the characterization of the Earth’s atmosphere and of the changes affecting it, resulting from anthropogenic activities or natural causes. In this paper, we present some recent results relevant for the verification of international environmental treaties. [less ▲]

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See detailImproved FTIR retrieval strategy for HCFC-22 (CHClF2), comparisons with in situ and satellite datasets with the support of models, and determination of its long-term trend above Jungfraujoch
Prignon, Maxime ULiege; Chabrillat, Simon; Minganti, Daniele ULiege et al

in Atmospheric Chemistry and Physics (2019), 19(19), 1230912324

Hydrochlorofluorocarbons (HCFCs) are the first, but temporary, substitution products for the strong ozone-depleting chlorofluorocarbons (CFCs). In this work, we present and validate an improved method to ... [more ▼]

Hydrochlorofluorocarbons (HCFCs) are the first, but temporary, substitution products for the strong ozone-depleting chlorofluorocarbons (CFCs). In this work, we present and validate an improved method to retrieve the most abundant HCFC in the atmosphere, allowing its evolution to be monitored independently in the troposphere and stratosphere. These kinds of contributions are fundamental for scrutinizing the fulfilment of the Montreal Protocol on Substances that Deplete the Ozone Layer. [less ▲]

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See detailPost-peak trend of upper stratospheric hydrogen chloride derived from ground-based FTIR solar spectra and model simulations
Mahieu, Emmanuel ULiege; Prignon, Maxime ULiege; Servais, Christian ULiege et al

Conference (2019, May 23)

After several decades of sustained increase, hydrogen chloride (HCl, the main reservoir for stratospheric chlorine) showed a maximum abundance around 1997. Since then, its decrease has been documented ... [more ▼]

After several decades of sustained increase, hydrogen chloride (HCl, the main reservoir for stratospheric chlorine) showed a maximum abundance around 1997. Since then, its decrease has been documented, characterized by short-term variability which was attributed to atmospheric circulation changes, affecting mainly the lower stratosphere (Mahieu et al., 2014). This notably led to a temporary increase of HCl over 2007-2011, complicating the determination of the long-term HCl trend and the accurate verification of the success of the Montreal Protocol for the protection of the stratospheric ozone layer. Studies have used other long-lived tracers to remove the effects of dynamical variability in the lower stratosphere (e.g., Stolarski et al., 2018), while other investigations have suggested that trends in the upper stratosphere were potentially more appropriate for the long-term characterization of the HCl decrease (e.g., Froidevaux et al., 2015; Bernath and Fernando, 2018), especially when dealing with satellite height-resolved data. In this contribution, we use FTIR (Fourier Transform InfraRed) data from the Jungfraujoch station (Swiss Alps, 3580 m a.s.l.), a site of the NDACC network (http://www.ndacc.org), to study the evolution of HCl in some detail. The SFIT-4 retrieval algorithm implementing the Optimal Estimation Method of Rodgers (2000) is employed, providing HCl columns with good sensitivity from the tropopause up to about 40 km altitude. Moreover, the vertical resolution is sufficient to determine independent partial columns for the lower and upper stratosphere. With the support of model simulations performed with the 3D-Chemistry Transport Model of the Belgian Assimilation System for Chemical ObsErvations (BASCOE; Chabrillat et al., 2018), driven by the ERA-Interim meteorological reanalysis, we investigate the post-peak trend of HCl in the lower and upper stratosphere. We also determine the magnitude of the uncertainties affecting the various trends, using bootstrap tools which are specifically developed to take into account the auto-correlation present in our geophysical data sets. [less ▲]

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See detailPOst-peak trend of upper stratospheric hydrogen chloride derived from ground-based FTIR solar spectra and model simulations
Mahieu, Emmanuel ULiege; Prignon, Maxime ULiege; Servais, Christian ULiege et al

Conference (2019, April 12)

After several decades of sustained increase, hydrogen chloride (HCl, the main reservoir for stratospheric chlorine) showed a maximum abundance around 1997. Since then, its decrease has been documented ... [more ▼]

After several decades of sustained increase, hydrogen chloride (HCl, the main reservoir for stratospheric chlorine) showed a maximum abundance around 1997. Since then, its decrease has been documented, characterized by short-term variability which was attributed to atmospheric circulation changes, affecting mainly the lower stratosphere (Mahieu et al., 2014). This notably led to a temporary increase of HCl over 2007-2011, complicating the determination of the long-term HCl trend and the accurate verification of the success of the Montreal Protocol for the protection of the stratospheric ozone layer. Studies have used other long-lived tracers to remove the effects of dynamical variability in the lower stratosphere (e.g., Stolarski et al., 2018), while other investigations have suggested that trends in the upper stratosphere were potentially more appropriate for the long-term characterization of the HCl decrease (e.g., Froidevaux et al., 2015; Bernath and Fernando, 2018), especially when dealing with satellite height-resolved data. In this contribution, we use FTIR (Fourier Transform InfraRed) data from the Jungfraujoch station (Swiss Alps, 3580 m a.s.l.), a site of the NDACC network (http://www.ndacc.org), to study the evolution of HCl in some detail. The SFIT-4 retrieval algorithm implementing the Optimal Estimation Method of Rodgers (2000) is employed, providing HCl columns with good sensitivity from the tropopause up to about 40 km altitude. Moreover, the vertical resolution is sufficient to determine independent partial columns for the lower and upper stratosphere. With the support of model simulations performed with the 3D-Chemistry Transport Model of the Belgian Assimilation System for Chemical ObsErvations (BASCOE; Chabrillat et al., 2018), driven by the ERA-Interim meteorological reanalysis, we investigate the post-peak trend of HCl in the lower and upper stratosphere. We also determine the magnitude of the uncertainties affecting the various trends, using bootstrap tools which are specifically developed to take into account the auto-correlation present in our geophysical data sets. [less ▲]

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See detailInvestigation of stratospheric circulation using long-lived tracers with WACCM, BASCOE CTM and a reanalysis of MLS observations
Minganti, Daniele ULiege; Chabrillat, Simon; Christophe, Yves et al

Poster (2019, April 12)

The stratospheric circulation is investigated using WACCM4 (Whole Atmosphere Community Climate Model version 4), together with BASCOE CTM (Belgian Assimilation System for Chemical Observations Chemistry ... [more ▼]

The stratospheric circulation is investigated using WACCM4 (Whole Atmosphere Community Climate Model version 4), together with BASCOE CTM (Belgian Assimilation System for Chemical Observations Chemistry-Transport Model) and a reanalysis of stratospheric composition observed by MLS: BRAM2 (BASCOE Reanalysis of AURA MLS release 2) over the period 2005-2015. Three different reanalyses of the wind fields (ERA-interim, JRA55 and MERRA2) are used to drive the CTM, providing an estimate of the uncertainties in our representation of the actual stratospheric circulation. We use a long-lived tracer (N2O), and the Transformed Eulerian Mean (TEM) framework to analyse the tracer budget. We focus on the residual advection (mainly vertical) and eddy mixing (mainly horizontal) contributions to the N2O variations, studying the mean annual cycle and variability in the higher stratosphere and how it is depicted in the different datasets. The BRAM2 mean annual cycle, for both the vertical and the horizontal terms, is nearly in the middle of the spread. WACCM is in good agreement concerning the vertical term but differs considerably from the other datasets in the horizontal (~mixing) term. WACCM present a smaller variability with respect to the reanalysis in the Tropical higher stratosphere, especially for the vertical term. The next step of our research is to perform such analysis with the newer version of WACCM (version 6) as well as new BASCOE CTM runs using other reanalysis products. Multi-decadal changes in the terms of the budget, and their space dependence, will be investigated as well. [less ▲]

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See detailImpact of lower stratospheric dynamical variability on total inorganic fluorine derived from ground-based FTIR, satellite and model data
Prignon, Maxime ULiege; Bernath, P. F.; Chabrillat, S. et al

Poster (2019, April 12)

Long-lived tracer concentrations in the lower stratosphere are affected by short time scale circulation variability as highlighted by recent papers (e.g., Mahieu et al., 2014). Many tracers, such as ... [more ▼]

Long-lived tracer concentrations in the lower stratosphere are affected by short time scale circulation variability as highlighted by recent papers (e.g., Mahieu et al., 2014). Many tracers, such as hydrogen chloride (HCl) or hydrogen fluoride (HF) have now been successfully used to investigate or identify this variability (e.g., Harrison et al., 2016) In this work, the main reservoirs of inorganic fluorine [i.e., HF, carbonyl fluoride (COF2) and carbonyl chloride fluoride (COClF)] and their sum (total inorganic fluorine, Fy) are used to investigate the lower stratospheric circulation changes. We use Fourier Transform InfraRed (FTIR) ground-based observations conducted in the framework of the NDACC network (http://www.ndacc.org) to derive column abundances of HF and COF2, thus providing a good proxy for Fy. To support this research, we also include satellite observations from HALOE (HF available) and ACE-FTS (HF, COF2 and COClF available). Moreover, we use the Chemical-Transport Model (CTM) BASCOE (Belgian Assimilation System for Chemical ObsErvations; Chabrillat et al., 2018) to evaluate the representation of the investigated circulation changes in state-of-the-art meteorological reanalyses. We also evaluate if WACCM4 (Whole Atmosphere Community Climate Model version 4) is able to reproduce these changes through a free dynamics and free chemistry run. Finally, SLIMCAT CTM (Chipperfield et al., 2015) simulations are included to provide information on the partitioning between the main Fy reservoirs. [less ▲]

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