Étude de la variabilité et la tendance de l'ozone stratosphérique au-dessus des tropiques et subtropiques sud

Ozone plays an important role on photochemical equilibrium of atmosphere and participate on radiative balance process between hemispheres (Mecke, 1931). In the troposphere, ozone determines the oxidizing capacity of major species and absorbs continuously in the stratosphere the harmful ultraviolet radiation (McMichael et al, 2003). Based on the above facts, it is important to monitor ozone continuously with consistency and accuracy. Global total column ozone (TCO) has depleted gradually since 1980 with an increase of chlorofluorocarbon concentrations in the stratosphere due to anthropogenic activities. In 1987, the Montreal protocol was formulated in order to regulate the emissions of substances that deplete ozone. Concentrations of these substances are observed to decrease ten years after the Montreal protocol. Thus we have been expecting an increase in ozone by now (UNEP/PNUE, 2009; WMO, 2010 and 2014). The current needs are to achieve consistent and reliable measurements in which their exploitation on adapted methods/models can help scientists to follow the ozone evolution and to estimate long term ozone trend. In this work, a variety of ozone products from different instruments was combined in order to create reliable and homogenous dataset to study the ozone variability and trend over the southern tropics and subtropics. The dataset application on wavelets method allowed to identify the dynamic parameters that control ozone variability and their periodicities. These include seasonal variations of climate, the quasi-biennial oscillations, the El-Niño Southern Oscillation and the 11-years solar cycle. The behavior of each parameter and its influence on ozone variability were analysed based on statistical method and the Trend-Run model. The contribution and response of each variable on ozone variability were quantified from the model. The obtained trends results exhibit an increase of total ozone from 1998 to 2012 with a rate varying between 0 and 2.78% par decade (depending of the site and region). The ozone increase was observed mainly above 22 km and it is more important over the subtropical region with respect to equatorial zone.L'ozone joue un rôle primordial sur l'équilibre photochimique de l'atmosphère et participe au processus d'équilibrage radiatif entre les deux hémisphères (Mecke, 1931). Dans la troposphère, l'ozone détermine la capacité oxydante de la majorité des gaz et absorbe continuellement dans la stratosphère les radiations ultraviolettes nocives (McMicheal et al., 2003). D'où l'intérêt de surveiller la variation de la couche d'ozone de façon régulière. Il a été constaté au début des années 80, une diminution inquiétante et progressive de la colonne totale de l'ozone dûe aux émissions anthropiques des substances riches en chlore, brome et fluor. Ce constat a conduit au Protocole de Montréal en 1987 dont l'objectif est de mettre en place une politique internationale visant à réduire les émissions des substances appauvrissant l'ozone. Dix ans après la signature du dit Protocole, la concentration de ces substances commence à diminuer dans l'atmosphère et la prospection d'un recouvrement progressif de la couche d'ozone demeure aujourd'hui un sujet d'actualité (UNEP/PNUE, 2009 ; OMM, 2010 et 2014). Les besoins d'aujourd'hui sont de réaliser des mesures continues et fiables de l'ozone dont leurs exploitation dans des méthodes et/ ou des modèles bien adaptés à la problématique aideront la communauté à suivre l'évolution de l'ozone et d'estimer les tendances à long terme. Dans ce travail, une variété de produits d'ozone issue de différents instruments a été combinée pour construire des bases des données fiables et homogènes afin d'étudier sa variabilité et d'estimer la tendance de l'ozone dans les régions tropicale et subtropicale sud. L'application de ces bases de données sur les ondelettes a permis d'identifier les principaux forçages qui contrôlent la variabilité de l'ozone et la période de retour associée à chaque forçage. Il s'agit des variations saisonnières du climat, les oscillations quasi-biennales, les oscillations australes El-Niño et l'activité solaire dont le cycle moyen est évalué à 11ans. Le comportement et l'influence de chacun de ces paramètres sur la viabilité de l'ozone sont étudiés. Cette étude est faite en s'appuyant sur des méthodes statistiques et sur le modèle Trend-Run. Avec ce modèle, la part de contribution et la réponse de chaque paramètre sur la variabilité de l'ozone sont quantifiées. Les résultats sur les tendances montrent une augmentation de la couche d'ozone avec un taux variant entre 0 et 2.78% par décade (selon la région et le site) sur la période 1998-2012. Cette amélioration est bien observée au-dessus de 22km, surtout aux subtropiques par rapport à la région équatoriale

Comparison of total column ozone obtained by the IASI-MetOp satellite with ground-based and OMI satellite observations in the southern tropics and subtropics

International audienceThis paper presents comparison results of the total column ozone (TCO) data product over 13 southern tropical and subtropical sites recorded from the Infrared Atmospheric Sounder Interferometer (IASI) onboard the EU-METSAT (European organization for the exploitation of METeorological SATellite) MetOp (Meteorological Operational satellite program) satellite. TCO monthly averages obtained from IASI between June 2008 and December 2012 are compared with collocated TCO measurements from the Ozone Monitoring Instrument (OMI) on the OMI/Aura satellite and the Dobson and SAOZ (Système d'Analyse par Observation Zénithale) ground-based instruments. The results show that IASI displays a positive bias with an average less than 2 % with respect to OMI and Dobson observations, but exhibits a negative bias compared to SAOZ over Bauru with a bias around 2.63 %. There is a good agreement between IASI and the other instruments, especially from 15 • S southward where a correlation coefficient higher than 0.87 is found. IASI exhibits a seasonal dependence, with an upward trend in autumn and a downward trend during spring, especially before September 2010. After September 2010, the autumn seasonal bias is considerably reduced due to changes made to the retrieval algorithm of the IASI level 2 (L2) product. The L2 product released after August (L2 O 3 version 5 (v5)) matches TCO from the other instruments better compared to version 4 (v4), which was released between June 2008 and August 2010. IASI bias error recorded from September 2010 is estimated to be at 1.5 % with respect to OMI and less than ±1 % with respect to the other ground-based instruments. Thus, the improvement made by O 3 L2 version 5 (v5) product compared with version 4 (v4), allows IASI TCO products to be used with confidence to study the distribution and interannual variability of total ozone in the southern tropics and subtropics. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry

Ozone Climatology obtained by a combination of MLS/AURA and SHADOZ ozonesondes profiles over southern tropic and subtropic

International audienceIn this paper a new ozone climatology (1998-2012) is presented over 8 southern tropic and subtropic sites. The climatology has been formed by combining data from Aura –MLS (Microwave Limb Sounder) and from SHADOZ (Southern Hemisphere ADditional OZonesondes) balloon sonde. Prior to combine the two observations, a preliminary study has been conducted to validate MLS profiles by comparison with ozonesondes. A satisfactory agreement is observed between MLS and ozonesonde measurements especially from 20 km to 30 km where the monthly relative difference between the two observations with respect to ozonesonde measurement is between 0.36% and 9.30%. The bias between the two observations decreases with the increase of altitude; from 20 km to 30 km the observed mean bias is assessed to be 3.69±1.13% with respect to SHADOZ observations. The presented climatology consists of monthly averages of ozone profiles for each site obtained from 1 km to 62 km. This climatology is established from hybrid profiles, normalized with the corresponding total column ozone (TCO) measured by Aura Ozone Monitoring Instrument, OMI satellite. Ozone below 26 km is based on ozonesonde while ozone above 29 km is based on MLS measurements. SHADOZ and MLS profiles are merged between 26 and 29 km where the best agreement (around 1%) between SHADOZ and MLS is observed. The obtained climatology captures with more accurately the principle behavior of ozone seasonal and spatial distributions; the integrated total ozone amounts from the presented climatology are consistent with the measured TCO from SAOZ (Système d'Analyse par Observation Zénitale) and Dobson at Reunion and Irene respectively

Studies on CO distribution over South Africa, Madagascar and Reunion Island using Tropospheric Emission Spectrometer (TES) data

International audienceCommunication about Studies on CO distribution over South Africa, Madagascar and Reunion Island using Tropospheric Emission Spectrometer (TES) dat

Influence of the dynamical activity on the inter-annual variability of ozone in the tropics

International audienceReunion Island (21 ◦ S - 55 ◦ E) is one of few tropical station of the Network for Detection of Atmospheric Com- position Change (NDAAC). The first measurements were carried out in 1992 and since 2012 a new observatory dedicated to atmospheric study have been commissioned (Maido Observatory 2200 m asl). The historical instru- ments are a UV-Vis spectrometer SAOZ that measures Total Column Ozone (TCO) continuously since 1993, and the balloon-borne ECC soundings, which are operational in the framework of the SHADOZ (Southern Hemisphere ADditional OZonesondes) network since 1998. More recently, a stratospheric ozone DIAL was installed early 2013 at the Maido observatory. This instrument has already performed more than 160 profiles over three years. Interannual variability and trend of ozone above this tropical site was investigated using a multi-linear regression analysis (Trend-run) on the de-seasonalised monthly mean SAOZ TCO and ECC profiles. Duration of measure- ments for the DIAL is currently too short to investigated inter-annual variability.Forcings representing the 11 years solar cycle, the El Nino Southern Oscillation, the Quasi- Biennial Oscillation have been used to perform reference analysis. The dynamical influence was studied by introducing of new proxies characteristics of wave activity (Eliassen-Palm flux), or the subtropical barrier location in regard to Reunion Island. The aim of this study is to estimate how the addition of new dynamical can improve the quality of the regression model and quantify the dynamic impact on this variability. The trend analysis has been estimated before and after 2000

Variability and Trend of Total Ozone Column from Brewer Spectrophotometer and Satellite Measurements Over South of Brazil

International audienceTotal ozone columns (TOC) have been measured in the South of Brazil, at Santa Maria, since 1992, by the use of three Brewer spectrometers: MKIV#081 from 1992 to 2000, MKII#056 from 2000 to 2002 and MKIII #167 from 2002 to the present. All the maintenance and observations have been made within the Brewer Brazilian network in the Southern Space Observatory (SSO). For the purpose of this study we combined all the Brewer datasets for comparison with satellite observations over the South of Brazil, i.e. TOMS (Total Ozone Mapping Spectrometer) aboard Nimbus-7 from 1979 to 1993, Meteor-3 between 1991 and 1994 and Earth Probe from 1996 to 2005) and OMI (Ozone Monitoring Instrument) aboard Aura (from 2004 till now). Similar to Brewer datasets, monthly values of TCO observations recorded by satellites over the Brazilian Southern Space Observatory in São Martinho da Serra (29.42 • S, 53.87 • W) are merged in one continuous 36-year time-series. On the merged datasets we applied the Trend-Run model (Bencherif et al., 2006; Begue et al, 2010), a multi-regression model based on the principle of breaking down the variations of ozone time-series into a sum of several forcings (seasonal cycles, QBO, ENSO, Solar cycles.. .). Besides to trend estimate, the trend-Run model enable to study TCO variability between 1979 and 2014. The trend values are derived from the residual terms as a linear function. A preliminary study has been conducted to validate the merged satellite data by comparing with Brewer measurement. A good agreement that is expressed by regression coefficient (R2) > 0.82 and 0.93 is observed between the ground-based (Brewer) and satellite TOMS and OMI data, respectively and the coefficient C2, used to quantify how well the fitting model describes the observed data, is 0.87. The results show a significative negative trend over the whole period (-1.39 ± 0.30%) per decade over the south of Brazil. In the present work, we also investigate and discuss the contributions of the main forcings as estimated by the model