Analysis of a rapid increase of stratospheric ozone during late austral summer 2008 over Kerguelen (49.4° S, 70.3° E)

This paper reports on an increase of ozone event observed over Kerguelen (49.4° S, 70.3° E) in relationship with large-scale isentropic transport. This is evidenced by ground-based observations (co-localised radiosonde and SAOZ experiments) together with satellite global observations (Aura/MLS) assimilated into MOCAGE, a Méteo-France model. <br><br> The study is based on the analyses of the first ozonesonde experiment never recorded at the Kerguelen site within the framework of a French campaign called ROCK that took place from April to August 2008. <br><br> Comparisons and interpretations of the observed event are supported by co-localised SAOZ observations, by global mapping of tracers (O<sub>3</sub>, N<sub>2</sub>O and columns of O<sub>3</sub>) from Aura/MLS and Aura/OMI experiments, and by model simulations of Ertel Potential Vorticity initialised by the ECMWF (European Centre for Medium-Range Weather Forecasts) data reanalyses. <br><br> Satellite and ground-based observational data revealed a consistent increase of ozone in the local stratosphere by mid-April 2008. Additionally, Ozone (O<sub>3</sub>) and nitrous oxide (N<sub>2</sub>O) profiles obtained during January–May 2008 using the Microwave Limb Sounder (MLS) aboard the Aura satellite are assimilated into MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle), a global three-dimensional chemistry transport model of Météo-France. The assimilated total O<sub>3</sub> values are consistent with SAOZ ground observations (within ±5%), and isentropic distributions of O<sub>3</sub> match well with maps of advected potential vorticity (APV) derived from the MIMOSA model, a high-resolution advection transport model, and from the ECMWF reanalysis. <br><br> The event studied seems to be related to the isentropic transport of air masses that took place simultaneously in the lower- and middle-stratosphere, respectively from the polar region and from the tropics to the mid-latitudes. <br><br> In fact, the ozone increase observed by mid April 2008 resulted simultaneously: (1) from an equator-ward departure of polar air masses characterised with a high-ozone layer in the lower stratosphere (near the 475 K isentropic level), and (2) from a reverse isentropic transport from the tropics to mid- and high-latitudes in the upper stratosphere (nearby the 700 K level). The increase of ozone observed over Kerguelen from the 16-April ozonesonde profile is thus attributed to a concomitant isentropic transport of ozone in two stratospheric layers: the tropical air moving southward and reaching over Kerguelen in the upper stratosphere, and the polar air passing over the same area but in the lower stratosphere

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

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

Seasonal variation of gravity wave activity at midlatitudes from 7 years of COSMIC GPS and Rayleigh lidar temperature observations

International audience7-year series of gravity wave (GW) potential energy at mid-latitude stratosphere (10 .. 50 km) is constructed by combining temperature profiles provided by COSMIC GPS satellite constellation and Rayleigh lidar operating at Haute Provence observatory in Southern France. The combined series are used to evaluate the representation of GW in MERRA reanalysis. The seasonal and zonal variabilities of GW activity are diagnosed using zonal wind and wind divergence provided by ERA-Interim reanalysis. The spatiotemporal distribution of GW activity is found strongly dependent on the zonal wind variation, wind divergence and topography. We show that anomalies in the wind divergence can serve as a proxy for locating synoptic-scale enhancements of GW. The analysis provides evidence for orographic GW excitation and the results are compatible with geostrophic adjustement being an additional source of stratospheric GW. The seasonal GW variability can be largely explained by interaction with the mean flow and wave propagation

Temperature trends observed in the middle atmosphere and future directions

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Middle Atmosphere Variability and Model Uncertainties as Investigated in the Framework of the ARISE Project

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