Etude des tendances d'ozone et de dioxyde d'azote dans la stratosphère tropicale

The tropical region is the main entry point of the chemical species in the troposphere lifted into the stratosphere. They are then redistributed to higher latitudes via the Brewer Dobson. Thus any change of stratospheric constituents in the tropics will have an impact on their distribution at mid latitudes. Long series of O3 and NO2 columns in the tropics are available from 2 SAOZ stations (UV-Vis spectrometers): at Bauru (22°S-49°W) since 1995 and in La Réunion (21°S-55°E) since 1993. The most significant modulation for both components is the seasonal cycle (40%). A multiple regression analysis of O3 and NO2 columns at Bauru and La Reunion has quantified the impact of solar and geophysical parameters on their variability. Following this analysis, the cycles of the most influential parameters are, in decreasing order: the Quasi-Biennal Oscillation with 40% for both species, the El-Niño Southern Oscillation with 25% for O3 and 20% for NO2, the solar flux with 15 and 18%, and the aerosols with 20 and 12%. After subtracting these influences, the residual variations of O3 are not significant. Those of NO2 indicate an increase from 2001 to 2006, followed by a decrease in 2007. From variations of the Eddy heat flux, variations in average intensity of meridional exchange through the southern subtropical barrier have been identified since 2001. These distortions have been detected through the modulation of the 2 tropical stations equivalent latitude. Taking into account these changes yields to an increase in the concentration of NO2 in the tropics (3%/dec) consistent with the one estimated of N2O (2.5%/dec), the gas source of nitrogen oxides in the stratosphereLa région tropicale est le principal point d'entrée des espèces troposphériques dans la stratosphère. Elles sont ensuite redistribuées vers les hautes latitudes via la circulation de Brewer Dobson. Toute modification des constituants stratosphériques aux tropiques aura un impact sur leur distribution aux moyennes latitudes. Les colonnes d'O3 et de NO2 aux tropiques sont disponibles à partir des stations SAOZ (spectromètres UV-Vis): à Bauru (22°S-49°W) depuis 1995 et à La Réunion (21°S-55°E) depuis 1993. Une analyse par régression multiple des variations des colonnes a permis de quantifier l'impact de paramètres géophysiques et solaires sur leurs variabilités. Ainsi, le cycle saisonnier correspond à 40% de leurs modulations. Les cycles les plus influents sur les variations de ces espèces sont par ordre décroissant: l'Oscillation Quasi-Biennale avec 40%, le couplage El-Niño et Oscillation Australe avec 25% pour l'O3 et 20% pour le NO2, le Flux solaire avec 15 et 18%, et les aérosols avec 20 et 12%. Après soustraction de ces influences, les variations résiduelles d'O3 sont non significatives. Celles de NO2 indiquent une augmentation des colonnes de 2001 à 2006, suivie d'une diminution en 2007. À partir des variations du flux de chaleur turbulente, des variations d'intensité des échanges méridionaux au travers de la barrière subtropicale ont pu être identifiées à partir de 2001. Ces déformations sont constatées à travers les modulations de la latitude équivalente des 2 stations. La prise en compte de ces variations a permis de détecter une augmentation de NO2 aux tropiques (3%/dec) cohérente avec celle de N2O (2.5%/dec), gaz source des oxydes d'azote dans la stratosphère

Etude des tendances d'ozone et de dioxyde d'azote dans la stratosphère tropicale

The tropical region is the main entry point of the chemical species in the troposphere lifted into the stratosphere. They are then redistributed to higher latitudes via the Brewer Dobson. Thus any change of stratospheric constituents in the tropics will have an impact on their distribution at mid latitudes. Long series of O3 and NO2 columns in the tropics are available from 2 SAOZ stations (UV-Vis spectrometers): at Bauru (22°S-49°W) since 1995 and in La Réunion (21°S-55°E) since 1993. The most significant modulation for both components is the seasonal cycle (40%). A multiple regression analysis of O3 and NO2 columns at Bauru and La Reunion has quantified the impact of solar and geophysical parameters on their variability. Following this analysis, the cycles of the most influential parameters are, in decreasing order: the Quasi-Biennal Oscillation with 40% for both species, the El-Niño Southern Oscillation with 25% for O3 and 20% for NO2, the solar flux with 15 and 18%, and the aerosols with 20 and 12%. After subtracting these influences, the residual variations of O3 are not significant. Those of NO2 indicate an increase from 2001 to 2006, followed by a decrease in 2007. From variations of the Eddy heat flux, variations in average intensity of meridional exchange through the southern subtropical barrier have been identified since 2001. These distortions have been detected through the modulation of the 2 tropical stations equivalent latitude. Taking into account these changes yields to an increase in the concentration of NO2 in the tropics (3%/dec) consistent with the one estimated of N2O (2.5%/dec), the gas source of nitrogen oxides in the stratosphereLa région tropicale est le principal point d'entrée des espèces troposphériques dans la stratosphère. Elles sont ensuite redistribuées vers les hautes latitudes via la circulation de Brewer Dobson. Toute modification des constituants stratosphériques aux tropiques aura un impact sur leur distribution aux moyennes latitudes. Les colonnes d'O3 et de NO2 aux tropiques sont disponibles à partir des stations SAOZ (spectromètres UV-Vis): à Bauru (22°S-49°W) depuis 1995 et à La Réunion (21°S-55°E) depuis 1993. Une analyse par régression multiple des variations des colonnes a permis de quantifier l'impact de paramètres géophysiques et solaires sur leurs variabilités. Ainsi, le cycle saisonnier correspond à 40% de leurs modulations. Les cycles les plus influents sur les variations de ces espèces sont par ordre décroissant: l'Oscillation Quasi-Biennale avec 40%, le couplage El-Niño et Oscillation Australe avec 25% pour l'O3 et 20% pour le NO2, le Flux solaire avec 15 et 18%, et les aérosols avec 20 et 12%. Après soustraction de ces influences, les variations résiduelles d'O3 sont non significatives. Celles de NO2 indiquent une augmentation des colonnes de 2001 à 2006, suivie d'une diminution en 2007. À partir des variations du flux de chaleur turbulente, des variations d'intensité des échanges méridionaux au travers de la barrière subtropicale ont pu être identifiées à partir de 2001. Ces déformations sont constatées à travers les modulations de la latitude équivalente des 2 stations. La prise en compte de ces variations a permis de détecter une augmentation de NO2 aux tropiques (3%/dec) cohérente avec celle de N2O (2.5%/dec), gaz source des oxydes d'azote dans la stratosphère

Étude des tendances d'ozone et de dioxyde d'azote dans la stratosphère tropicale

La région tropicale est le principal point d'entrée des espèces troposphériques dans la stratosphère. Elles sont ensuite redistribuées vers les hautes latitudes via la circulation de Brewer Dobson. Toute modification des constituants stratosphériques aux tropiques aura un impact sur leur distribution aux moyennes latitudes. Les colonnes d O3 et de NO2 aux tropiques sont disponibles à partir des stations SAOZ (spectromètres UV-Vis): à Bauru (22S-49W) depuis 1995 et à La Réunion (21S-55E) depuis 1993. Une analyse par régression multiple des variations des colonnes a permis de quantifier l'impact de paramètres géophysiques et solaires sur leurs variabilités. Ainsi, le cycle saisonnier correspond à 40% de leurs modulations. Les cycles les plus influents sur les variations de ces espèces sont par ordre décroissant: l'Oscillation Quasi-Biennale avec 40%, le couplage El-Niño et Oscillation Australe avec 25% pour l'O3 et 20% pour le NO2, le Flux solaire avec 15 et 18%, et les aérosols avec 20 et 12%. Après soustraction de ces influences, les variations résiduelles d'O3 sont non significatives. Celles de NO2 indiquent une augmentation des colonnes de 2001 à 2006, suivie d'une diminution en 2007. À partir des variations du flux de chaleur turbulente, des variations d'intensité des échanges méridionaux au travers de la barrière subtropicale ont pu être identifiées à partir de 2001. Ces déformations sont constatées à travers les modulations de la latitude équivalente des 2 stations. La prise en compte de ces variations a permis de détecter une augmentation de NO2 aux tropiques (3%/dec) cohérente avec celle de N2O (2.5%/dec), gaz source des oxydes d'azote dans la stratosphère.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Comparison and merging of ozone profile data from various measurement techniques at NDACC Alpine station

International audienceWithin the Network for the Detection of Atmospheric Composition Changes (NDACC), various remote sensing techniques are used in addition to in situ ozone sounding measurements for the long-term evaluation of the ozone vertical distribution. These techniques, using e.g. microwave spectrometers, Fourier Transform Infrared spectrometers or laser radiation (lidars), are very different in terms of vertical distribution, time sampling and precision, which can present some difficulties for the validation of satellite data or the products of the European Monitoring atmospheric composition & climate Service (MACC). A methodology was developed for the integration of profile ozone data from various sources in order to provide consistent ozone vertical distribution time series as well as tropospheric and stratospheric ozone partial columns. This methodology was developed for measurements performed in the stations forming the Alpine station (e.g. Haute-Provence Observatory OHP – France, Bern – Switzerland, Jungfraujoch – Switzerland). Ozone measurements from the ozone DIAL lidar instrument and ozone sondes at OHP, the microwave spectrometer at Bern and the FTIR spectrometer at the Jungfraujoch station were used for this purpose

A new methodology for integrating ground-based ozone profile data

A new methodology is developed for integrating complementary ground-based data sources to provide consistent ozone vertical distribution time series as well as tropospheric and stratospheric ozone partial columns. Primary results are presented for the Alpine station of the Network for the Detection of Atmospheric Composition Changes (NDACC). Ozone measurements from the lidar at Haute-Provence Observatory, the microwave spectrometer at Bern and the FTIR spectrometer at the Jungfrauch station are used for this purpose. First step is to evaluate the validity domain of ozone profile data considered here by assessing instrumental error and vertical resolution. Each instrument has its own vertical resolution; therefore adjustments need to be done for the creation of an homogeneous data set. Indeed, because of the higher resolution of lidar measurements, smoothing of the data is necessary for the comparison with FTIR and microwave measurements. However, smoothing the data induces a loss of scientific information. Therefore a compromise has to be established and discussed. The various intercomparisons provide an evaluation of the differences due to instrumental error and atmospheric variability. The statistical method used for combining the different measurements in order to obtain ozone vertical profile time series consistent with total ozone measurements is then discussed

Intercomparison of stratospheric ozone profiles for the assessment of the upgraded GROMOS radiometer at Bern

Since November 1994, the GROund-based Millimeter-wave Ozone Spectrometer (GROMOS) measures stratospheric and lower mesospheric ozone in Bern, Switzerland (47.95° N, 7.44° E). GROMOS is part of the Network for the Detection of Atmospheric Composition Change (NDACC). In July 2009, a Fast-Fourier-Transform spectrometer (FFTS) has been added as backend to GROMOS. The new FFTS and the original filter bench (FB) measured parallel for over two years. In October 2011, the FB has been turned off and the FFTS is now used to continue the ozone time series. For a consolidated ozone time series in the frame of NDACC, the quality of the stratospheric ozone profiles obtained with the FFTS has to be assessed. The FFTS results from July 2009 to December 2011 are compared to ozone profiles retrieved by the FB. FFTS and FB of the GROMOS microwave radiometer agree within 5% above 20 hPa. A later harmonization of both time series will be realized by taking the FFTS as benchmark for the FB. Ozone profiles from the FFTS are also compared to coinciding lidar measurements from the Observatoire Haute Provence (OHP), France. For the time period studied a maximum mean difference (lidar - GROMOS FFTS) of +3.8% at 3.1 hPa and a minimum mean difference of +1.4% at 8 hPa is found. Further, intercomparisons with ozone profiles from other independent instruments are performed: satellite measurements include MIPAS onboard ENVISAT, SABER onboard TIMED, MLS onboard EOS Aura and ACE-FTS onboard SCISAT-1. Additionally, ozonesondes launched from Payerne, Switzerland, are used in the lower stratosphere. Mean relative differences of GROMOS FFTS and these independent instruments are less than 10% between 50 and 0.1 hPa

Long-term evolution of tropical stratospheric O₃ and NO₂ Columns

The tropical region is the main entry point of the chemical species in the troposphere lifted and transported by convection in the stratosphere through the tropopause and redistributed to higher latitudes via the Brewer Dobson circulation. Thus any change in the distribution of stratospheric constituents in the tropics will have an impact on their concentration at mid-latitudes. Long time series of O3 and NO2 columns in the tropics are available from 2 SAOZ UV-visible spectrometers stations: in Bauru (Brazil, 22°S, 49°W) since 1995 and in La Réunion (21°S, 55°E) in the Indian Ocean since 1993. The most significant modulation for both components at both stations is the seasonal cycle (~40%). A multiple regression analysis of ozone and NO2 columns at Bauru and la Reunion has quantified the impact of solar and geophysical parameters of their variability. Following this analysis, the cycles of the most influential parameters in the tropics are (in decreasing order): the Quasi-Biennal Oscillation (QBO) with 40 % for both species, the El-Niño Southern Oscillation (ENSO) with 25% for O3 and 20% for the NO2, the solar flux with 15% and 18%, and finally the stratospheric aerosols with 20% and 12%. After subtracting these influences, the long-term residual variations of ozone are not significant. In contrast, NO2 shows a significant increase at both stations between 2001-2006, followed by a decrease after 2007. Same analysis has been applied to a merged satellite data set above the stations with GOME (1995-2002) - SCIAMACHY (2003-2011) for NO2 columns and EPTOMS (1995-2004) - OMI TOMS (2005-2011) for O3 columns. The long-term residual variations of those data present similar behaviour as SAOZ. From variations of the Eddy heat flux, variations in average intensity of meridional exchange through the southern subtropical barrier related to the amplitude of planetary waves over the entire Southern Hemisphere have been identified since 2001. These distortions of amplitude of planetary waves, affecting all longitudes, have been detected through the modulation of the two tropical stations's equivalent latitude. After taking into account this influence, the NO2 residual trend in the tropics is shown to be of 3%/decade only, that is consistent with the known increase by 2.5%/decade, of N2O the source of nitrogen oxides in the stratosphere

Long-term evolution of tropical stratospheric O3 and NO2 Columns

The tropical region is the main entry point of the chemical species in the troposphere lifted and transported by convection in the stratosphere through the tropopause and redistributed to higher latitudes via the Brewer Dobson circulation. Thus any change in the distribution of stratospheric constituents in the tropics will have an impact on their concentration at mid-latitudes. Long time series of O3 and NO2 columns in the tropics are available from 2 SAOZ UV-visible spectrometers stations: in Bauru (Brazil, 22°S, 49°W) since 1995 and in La Réunion (21°S, 55°E) in the Indian Ocean since 1993. The most significant modulation for both components at both stations is the seasonal cycle (~40%). A multiple regression analysis of ozone and NO2 columns at Bauru and la Reunion has quantified the impact of solar and geophysical parameters of their variability. Following this analysis, the cycles of the most influential parameters in the tropics are (in decreasing order): the Quasi-Biennal Oscillation (QBO) with 40 % for both species, the El-Niño Southern Oscillation (ENSO) with 25% for O3 and 20% for the NO2, the solar flux with 15% and 18%, and finally the stratospheric aerosols with 20% and 12%. After subtracting these influences, the long-term residual variations of ozone are not significant. In contrast, NO2 shows a significant increase at both stations between 2001-2006, followed by a decrease after 2007. Same analysis has been applied to a merged satellite data set above the stations with GOME (1995-2002) - SCIAMACHY (2003-2011) for NO2 columns and EPTOMS (1995-2004) - OMI TOMS (2005-2011) for O3 columns. The long-term residual variations of those data present similar behaviour as SAOZ. From variations of the Eddy heat flux, variations in average intensity of meridional exchange through the southern subtropical barrier related to the amplitude of planetary waves over the entire Southern Hemisphere have been identified since 2001. These distortions of amplitude of planetary waves, affecting all longitudes, have been detected through the modulation of the two tropical stations's equivalent latitude. After taking into account this influence, the NO2 residual trend in the tropics is shown to be of 3%/decade only, that is consistent with the known increase by 2.5%/decade, of N2O the source of nitrogen oxides in the stratosphere

Construction of merged satellite total O₃ and NO₂ time series in the tropics for trend studies and evaluation by comparison to NDACC SAOZ measurements

Long series of ozone and NO2 total column measurements at the Southern tropics are available from two ground-based SAOZ (Système d'Analyse par Observation Zenithale) UV-visible spectrometers operated within the NDACC (Network for the Detection of Amtospheric Composition Change) deployed in Bauru in S-E Brazil and Reunion Island in the S-W Indian Ocean in 1995 and 1993 respectively. Although at the same latitude, the data show larger columns of both species above the South American continent than above the Indian Ocean. For verifying the reliability of these data before carrying out trend analysis, they have been compared to satellites observations available during the same period. However, since no single satellite was operating from 1995 until present, the comparison requires the building of a composite, called merged satellites series. As systematic differences exist between the individual data sets because of the many differences between instruments, spectral ranges, absorption cross-sections, and retrieval procedures used, the building of such a composite requires thorough evaluation and normalisation of each. From comparisons with SAOZ, the merged satellite data set build with EP-TOMS from 1995 to 2004 and OMI-TOMS from 2005 to 2012 are found best for ozone in the Southern tropics. After correction for biases with SAOZ, both are confirming the larger ozone columns reported by SAOZ above South America compared to the Indian Ocean shown to origin from ozone production by lightning NOx (LNOx) over the continent in the summer and the advection from Africa of ozone produced by biomass burning emissions in the winter. For NO2, best matching the SAOZ is a combination of GOME GDP4 1996-2003 and SCIAMACHY 2003-2012 products, after correction for the photochemical diurnal change of the concentration of the species between the SAOZ twilight observations and the time of satellites overpasses. The merged data series built from the data of these two satellites fully confirms the larger NO2 column reported by SAOZ above the South American continent as well as and its seasonality. The 35% larger column above Brazil in the summer is shown to be due to the NOx production in the upper troposphere by the frequent lightning during the thunderstorm season, whereas the winter maximum is shown to come from the larger exchange of NOx rich air with mid-latitudes in the lower stratosphere due to the more equatorial latitude of the subtropical jet above South America compared to the Indian Ocean

Evaluation of ozone total column and vertical distribution recovering trends at NDACC Northern mid-latitude station

Since the mid-eighties, stratospheric ozone has been monitored at Observatoire de Haute-Provence (OHP - 44°N, 6°E) by a variety of instruments. Ozone total column measurements are provided by Dobson and DOAS spectrometers since respectively 1983 and 1992 while ozone vertical distribution is obtained by lidar, sondes and Umkehr measurements since respectively 1985, 1984 and 1983. In addition to the ozone data obtained at OHP, satellite ozone measurements from SAGE II, MLS and GOMOS are used for the study of the short term and long term evolution of ozone total column and vertical profile at the station. First, the coherence of ozone time series is evaluated from the analysis of the differences with satellite and ground-based coincident ozone records. This analysis shows generally non significant drifts between the various measurements, especially in the 20 - 40 km range. The stratospheric ozone total column and vertical profile trends are then estimated using the equivalent effective stratospheric chlorine (EESC) time series and two linear trend functions to simulate the change in the trends of ozone depleting substances. To that aim, a multiple linear regression model is used with different explanatory variables such as the quasi-biennial oscillation (QBO), the Northern Atlantic oscillation (NAO), solar flux, eddy heat flux, stratospheric aerosols optical depth and trend function. The computed trends from the ozone column at OHP indicate a clear signal of ozone recovery after 1997. Likewise, significant positive trends of the ozone vertical distribution are estimated in the 15 - 45 km altitude range after 1997. The influence of the various proxies on the medium and short term ozone variability is also analyzed, indicating that the QBO and eddy heat flux have contributed to the large ozone levels observed in 2010. In the lower stratosphere, the regression model is less efficient in reproducing ozone variability and other proxies are tested such as equivalent latitude in order to represent the advection of polar and tropical air masses over OHP during the winter and springtime