Temperature climatology with Rayleigh lidar above Observatory of Haute-provence : dynamical feedback

International audienceRayleigh lidar in synergy with satellite observations (SSU and AMSU) allow insuring an efficient monitoring and showing that cooling has continued. New approach for trend detection has been developed allowing a better estimate of changes due to radiative forcing. Stratospheric Warmings and gravity waves contribute to insure a dynamical feedback of the long-term changes

Observation par GOMOS/ENVISAT de l’ozone dans la stratosphère tropicale : validation par le réseau SHADOZ, climatologie et variabilité

The work presented in this manuscript is devoted to the analysis and the interpretation ofobservations in the tropics from the stellar occultation instrument GOMOS on board ENVISAT. We mainly focus on O3 datasets from GOMOS level 2 data processing, version GOPR 6.0cf (and IPF 5.0) between August 2002 and December 2008. A validation study was performed and a satisfactory agreement was observed between GOMOS and SHADOZ in the 21-30 km altitude range. We recommend using GOMOS measurements with caution below 21 km in the tropics. Furthermore, the altitude registration of the GOMOS profiles is accurate. The O3 differences between GOMOS and SHADOZ do not depend on the spatial and temporal coincidence criteria. We also evaluate the stability of GOMOS measurements. A singular isentropic transport event from the Antarctic polar vortex to the subtropics shows the ability of GOMOS to capture and to reproduce ozone structures. Our results illustrate that the ozone enhancement observed in the subtropical lower stratosphere is linked to a polar filament. It originates from the vortex edge region rather than the vortex core during ozone depletion. Finally, analyzing correlations between GOMOS observations and simulations from the high-resolution model MIMOSA, we established a first basis to extract ozone fields from the model.Le travail présenté dans ce manuscrit est consacré à l’analyse et à l’interprétation des observations au-dessus des tropiques de l’instrument à occultation stellaire GOMOS embarqué sur ENVISAT. On se focalise essentiellement sur les données d’O3 GOMOS de niveau 2 issues du processeur GOPR 6.0cf (et IPF 5.00) entre Août 2002 et Décembre 2008. Une validation des observations GOMOS a été menée et un accord satisfaisant est observé entre GOMOS et SHADOZ de 21 km à 30 km. Pour les régions tropicales, il est recommandé d’utiliser les mesures GOMOS avec précaution pour les altitudes inferieures à ~21 km. De plus, l’estimation de l’altitude des profils GOMOS est fiable. Les différences relatives calculées entre les profils coïncidents GOMOS et SHADOZ sont indépendantes des variables spatio-temporelles. On étudie également la stabilité des mesures GOMOS. Un cas d’étude singulier de transport isentropique du vortex polaire en Antarctique vers les subtropiques montre qu’on peut étudier des structures et des variations des concentrations de l’ozone, à partir des observations GOMOS. Nos résultats montrent que l’augmentation d’ozone observée dans la basse stratosphère subtropicale est liée à un filament polaire. Celui-ci se produit durant la phase de destruction d’ozone et provient de la périphérie et non pas du cœur du vortex. Enfin, en analysant les corrélations entre les observations du spectomètre GOMOS et les simulations du modèle à haute résolution MIMOSA, nous avons établi une première base pour extraire des champs d’ozone du modèle

Observation par GOMOS/ENVISAT de l’ozone dans la stratosphère tropicale : validation par le réseau SHADOZ, climatologie et variabilité

The work presented in this manuscript is devoted to the analysis and the interpretation ofobservations in the tropics from the stellar occultation instrument GOMOS on board ENVISAT. We mainly focus on O3 datasets from GOMOS level 2 data processing, version GOPR 6.0cf (and IPF 5.0) between August 2002 and December 2008. A validation study was performed and a satisfactory agreement was observed between GOMOS and SHADOZ in the 21-30 km altitude range. We recommend using GOMOS measurements with caution below 21 km in the tropics. Furthermore, the altitude registration of the GOMOS profiles is accurate. The O3 differences between GOMOS and SHADOZ do not depend on the spatial and temporal coincidence criteria. We also evaluate the stability of GOMOS measurements. A singular isentropic transport event from the Antarctic polar vortex to the subtropics shows the ability of GOMOS to capture and to reproduce ozone structures. Our results illustrate that the ozone enhancement observed in the subtropical lower stratosphere is linked to a polar filament. It originates from the vortex edge region rather than the vortex core during ozone depletion. Finally, analyzing correlations between GOMOS observations and simulations from the high-resolution model MIMOSA, we established a first basis to extract ozone fields from the model.Le travail présenté dans ce manuscrit est consacré à l’analyse et à l’interprétation des observations au-dessus des tropiques de l’instrument à occultation stellaire GOMOS embarqué sur ENVISAT. On se focalise essentiellement sur les données d’O3 GOMOS de niveau 2 issues du processeur GOPR 6.0cf (et IPF 5.00) entre Août 2002 et Décembre 2008. Une validation des observations GOMOS a été menée et un accord satisfaisant est observé entre GOMOS et SHADOZ de 21 km à 30 km. Pour les régions tropicales, il est recommandé d’utiliser les mesures GOMOS avec précaution pour les altitudes inferieures à ~21 km. De plus, l’estimation de l’altitude des profils GOMOS est fiable. Les différences relatives calculées entre les profils coïncidents GOMOS et SHADOZ sont indépendantes des variables spatio-temporelles. On étudie également la stabilité des mesures GOMOS. Un cas d’étude singulier de transport isentropique du vortex polaire en Antarctique vers les subtropiques montre qu’on peut étudier des structures et des variations des concentrations de l’ozone, à partir des observations GOMOS. Nos résultats montrent que l’augmentation d’ozone observée dans la basse stratosphère subtropicale est liée à un filament polaire. Celui-ci se produit durant la phase de destruction d’ozone et provient de la périphérie et non pas du cœur du vortex. Enfin, en analysant les corrélations entre les observations du spectomètre GOMOS et les simulations du modèle à haute résolution MIMOSA, nous avons établi une première base pour extraire des champs d’ozone du modèle

Convective gravity wave propagation and breaking in the stratosphere: comparison between WRF model simulations and lidar data

International audienceIn this work we perform numerical simulations of convective gravity waves (GWs), using the WRF (Weather Research and Forecasting) model. We first run an idealized, simplified and highly resolved simulation with model top at 80 km. Below 60 km of altitude, a vertical grid spacing smaller than 1 km is supposed to reliably resolve the effects of GW breaking. An eastward linear wind shear interacts with the GW field generated by a single convective thunderstorm. After 70 min of integration time, averaging within a radius of 300 km from the storm centre, results show that wave breaking in the upper stratosphere is largely dominated by saturation effects, driving an average drag force up to −41 m s-1 day-1. In the lower stratosphere, mean wave drag is positive and equal to 4.4 m s-1 day-1. In a second step, realistic WRF simulations are compared with lidar measurements from the NDACC network (Network for the Detection of Atmospheric Composition Changes) of gravity wave potential energy (Ep) over OHP (Haute-Provence Observatory, southern France). Using a vertical grid spacing smaller than 1 km below 50 km of altitude, WRF seems to reliably reproduce the effect of GW dynamics and capture qualitative aspects of wave momentum and energy propagation and transfer to background mean flow. Averaging within a radius of 120 km from the storm centre, the resulting drag force for the study case (2 h storm) is negative in the higher (−1 m s-1 day-1) and positive in the lower stratosphere (0.23 m s-1 day-1). Vertical structures of simulated potential energy profiles are found to be in good agreement with those measured by lidar. Ep is mostly conserved with altitude in August while, in October, Ep decreases in the upper stratosphere to grow again in the lower mesosphere. On the other hand, the magnitude of simulated wave energy is clearly underestimated with respect to lidar data by about 3–4 times. Keywords. Meteorology and atmospheric dynamics (mesoscale meteorology middle atmosphere dynamics waves and tides

Recent dynamic studies on the middle atmosphere at mid- and low-latitudes using Rayleigh Lidar and other technologies

International audienc

Climatology and comparison of ozone from ENVISAT/GOMOS and SHADOZ/balloon-sonde observations in the southern tropics

International audienceIn this paper, the stellar occultation instrument GOMOS is compared with ozonesondes from the SHADOZ network. We only used nighttime O3 profiles and a requirement selection at 8 Southern Hemisphere stations. 7 years of GOMOS datasets (GOPR 6.0cf and IPF 5.0) and 11 years of balloon-sondes are used in this study. A monthly distribution of GOMOS O3 mixing ratios is performed in the upper-troposphere and in the stratosphere (15-50 km). A comparison with SHADOZ is done in the altitude range from 15 km to 30 km. In the 21-30 km altitude range, a satisfactory agreement is observed between GOMOS and SHADOZ although some differences are observed depending on the station. The range for monthly differences is generally decreasing with increasing height and is within ±15%. It is found that the agreement between GOMOS and SHADOZ degrades below ~20 km. The median differences are nearly within ±5% particularly above 23 km. But a large positive bias is found below 21 km compared to SHADOZ

Temperature variability and trends in the UT-LS over a subtropical site: Reunion (20.8° S, 55.5° E)

International audienceThis paper mainly focuses on the trends and variability of the UT-LS temperature using radiosonde observations carried out over 16 years (January 1993 to December 2008) from a southern subtropical site, Reunion (20.8° S, 55.5° E), using a linear-regression fitting model. Two kinds of tropopause definitions, namely, cold point tropopause (CPT) and lapse rate tropopause (LRT) are used. In order to characterize and quantify the relationship between regional oceanic forcing and temperature at UT-LS, we took into account the Indian Ocean Dipole (IOD) for the estimation of temperature trends. Results show that the main component is the Annual Cycle (AC), particularly at tropopause (CPT, LRT) and in the lower stratosphere (LS) where more than 26.0±2.4% of temperature variability can be explained by AC. The influence of IOD on the variability of the temperature is at highest ratio at CPT and LS, with respectively 12.3±7.3% and 13.1±5.9%. The correlations between IOD and temperature anomalies at UT-LS are barely significant, which are found to be in close agreement with the results obtained by Rosenlof et al. (2008) over the western tropical Pacific Ocean. The temperature trend in the LS reveals a cooling of about −0.90±0.40 K per decade. The cooling trend at LS is found to be in close agreement with the others studies. Trend estimates in the LS suggest that IOD forcing contributes to increasing cooling by about 0.16±0.05 K per decade. Past works have shown that the additional carbon dioxide increase has a minor effect in the LS, and suggested that other effects than ozone and carbon dioxide changes have to be considered, in order to explain the observed temperature changes in the LS. From this study, we can suggest that the SST changes can be considered also, in addition to effects due to ozone and carbon dioxide changes, in order to explain the observed temperature changes in the LS. As a consequence, our results support the assumption that the Indian Ocean may have a slight impact on temperature variability and on temperature change in the LS over Reunion

On the use of a regression model for trend estimates from ground based atmospheric observations in the Southern Hemisphere

International audienceThe present reports on the use of a multi-regression model adapted at Reunion University for temperature and ozone trend estimates. Depending on the location of the observing site, the studied geophysical signal is broken down in form of a sum of forcings that explain most of its variability. The trend values are then derived from the residual terms as linear function. The paper discusses different case studies by using different parameterisation, and reports on retrievals of temperature and ozone trend estimates over different sites in the southern hemisphere: South Africa (Durban and Upinhton), Reunion Island and Argentian (Buenos-Aires

Stratospheric ozone variability and anomalies as derived from ground-based observations over southern Africa

International audienceCommunication about Stratospheric ozone variability and anomalies as derived from ground-based observations over southern Afric

Total ozone variability and trend estimates from ground-based and satellite observations in the southern subtropics

International audienceDespite its low abundance in the atmosphere, ozone is an important component that prevents solar UV from reaching the Earth's surface. It contributes to the radiative balance, and hence has impact on climate change. The long-term evolution of stratospheric ozone depends on changes of both stratospheric and tropospheric constituents such as ozone-depleting substances, greenhouse gases, water vapor, and aerosols. It also depends on changes in the troposphere and in the stratosphere caused by natural variability and anthropogenic forcing (WMO, 2006). As reported by many authors, air penetrates into the stratosphere primarily through the tropical tropopause, while the tropical stratosphere is a region of major exchange with mid-latitude regions through the subtropical barriers (Portafaix et al., 2003; Bencherif et al., 2003; Semane et al., 2006; Bencherif et al., 2007). The present contribution reports on a comparative study on total ozone observations obtained from ground-based and satellite measurements over subtropical sites. The study examines the climatology and variability of total ozone. It is based on more than 15 years of continuous observations at four sites in the southern subtropics: Reunion Island (21°S, 55.5°E), Bauru (22°S, 49°O), Irene (25.5°S, 28.1°E) and Springbok (29.6°S, 17.9°E). Depending on the observational periods of each instrument, ground-based total ozone measurements are compared with satellite datasets, in terms of daily and monthly variations. The study focuses on comparisons with total ozone values measured from space by TOMS (Total Ozone Mapping Spectrometer), OMI (Ozone Monitoring Spectrometer) and by IASI (Infrared Atmospheric Sounding Interferometer) on the MetOp satellite. The obtained monthly-mean time-series of total ozone are analyzed by a multi-regression model named Trend-Run (Bencherif et al., 2006; Bègue et al., 2010). It is a trend model based on the linear multi-regression principal, i.e., the ozone signal is broken into a sum of several forcings (seasonal cycles, QBO, ENSO, IOD, Solar cycles, ...) that explain most of its variability. The trend values are then derived from the residual terms as a linear function