Effects of regional-scale and convective transports on tropospheric ozone chemistry revealed by aircraft observations during the wet season of the AMMA campaign

The African Monsoon Multidisciplinary Analyses (AMMA) fourth airborne campaign was conducted in July–August 2006 to study the chemical composition of the middle and upper troposphere in West Africa with the major objective to better understand the processing of chemical emissions by the West African Monsoon (WAM) and its associated regional-scale and vertical transports. In particular, the french airborne experiment was organized around two goals. The first was to characterize the impact of Mesoscale Convective Systems (MCSs) on the ozone budget in the upper troposphere and the evolution of the chemical composition of these convective plumes as they move westward toward the Atlantic Ocean. The second objective was to discriminate the impact of remote sources of pollution over West Africa, including transport from the middle east, Europe, Asia and from southern hemispheric fires. Observations of O<sub>3</sub>, CO, NO<sub>x</sub>, H<sub>2</sub>O and hydroperoxide above West Africa along repeated meridional transects were coupled with transport analysis based on the FLEXPART lagrangian model. The cross analysis of trace gas concentrations and transport pathways revealed 5 types of air masses: convective uplift of industrial and urban emissions, convective uplift of biogenic emissions, slow advection from Cotonou polluted plumes near the coast, meridional transport of upper tropospheric air from the subtropical barrier region, and meridional transport of Southern Hemisphere (SH) biomass burning emissions. O<sub>3</sub>/CO correlation plots and the correlation plots of H<sub>2</sub>O<sub>2</sub> with a OH proxy revealed not only a control of the trace gas variability by transport processes but also significant photochemical reactivity in the mid- and upper troposphere. The study of four MCSs outflow showed contrasted chemical composition and air mass origins depending on the MCSs lifetime and latitudinal position. Favorables conditions for ozone production were found for MCSs with increased MCS lifetime (>1.5 days), which allowed for more H<sub>2</sub>O<sub>2</sub> formation, and with trajectories crossing the 10° N latitude, which increased CO transport to the upper troposphere. The upper tropospheric concentrations sampled in the MCS outflow regions showed mixed origins including local vertical convective transport, and uplifting of air from the low troposphere over the middle-east related to the summer Asian low pressure system or from the southern hemispheric fires

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

Maïdo observatory: a new high-altitude station facility at Reunion Island (21° S, 55° E) for long-term atmospheric remote sensing and in situ measurements

Since the nineties, atmospheric measurement systems have been deployed at Reunion Island, mainly for monitoring the atmospheric composition in the framework of NDSC/NDACC (Network for the Detection of <i>Stratospheric</i> Change/Network for the Detection of Atmospheric Composition Change). The location of Reunion Island presents a great interest because there are very few multi-instrumented stations in the tropics and particularly in the southern hemisphere. In 2012, a new observatory was commissioned in Maïdo at 2200 m above sea level: it hosts various instruments for atmospheric measurements, including lidar systems, spectro-radiometers and in situ gas and aerosol measurements. <br><br> This new high-altitude Maïdo station provides an opportunity:<br> 1. to improve the performance of the optical instruments above the marine boundary layer, and to open new perspectives on upper troposphere and lower stratosphere studies;<br> 2. to develop in situ measurements of the atmospheric composition for climate change surveys, in a reference site in the tropical/subtropical region of the southern hemisphere;<br> 3. to offer trans-national access to host experiments or measurement campaigns for focused process studies

A Climate Observatory in South West Indian Ocean: The Maïdo Observatory in La Réunion. Current achievements and Future Prospects

International audienceObservatories of the climate system are essential to assess future climate predictions that are central and fundamental requirements for determining future mitigation strategies. such observing platforms are very few ones in the tropical southern hemisphere. Cnrs, Université de la réunion, région réunion and the european FeDer program support together the construction of a high- altitude observatory which is operational since October 2012 in La Réunion (South West Indian Ocean, 2160 m asl, latitude 21°S, longitude 55°E). The Maïdo observatory takes over from its predecessor programs at sea level over the island who started long-term observation data of atmospheric chemical composition since 1994. the Maïdo observatory is an ideal platform to sample the atmosphere with different techniques (in-situ analysers, radiosounding, passive and active remote sensing) and to record surface measurements and vertical profiles from ground to the mesosphere over a subtropical latitude band poorly sampled by other international programs. The Maïdo observatory hosts lidars, one UV spectrometer, one radiosonding station, Ftir spectrometers, microwave radiometers, one lightning antenna, cameras, one Gnss station, microbarometers, etc. these devices sample many atmospheric parameters (e.g., meteorological parameters, reactive and greenhouse gases, aerosols, lightning and transient luminous events, infrasounds, etc). part of this very extensive range of instruments is approved and belongs to international networks like nDaCC (network for the Detection of atmospheric Composition Change), sHaDOZ (southern Hemisphere aDditional OZonesondes), tCCOn (total Carbon Column Observing network), and WWLLN (World Wide Lightning Location Network). in-situ analysers regroup measurements of reactive and greenhouse gases, and aerosols measurements approved by or applying to networks like GAW/WMO (Global Atmospheric Watching / World Meteorological Organization), iCOs (integrated Carbon Observing system). The Maïdo observatory is currently the only way to provide regular remote and in-situ atmospheric observations at subtropical latitudes and at high resolutions (seconds in time, few tenths of meters vertically) over a marine-remote region poorly sampled by other programs. it provides data for users in science and policy including air quality forecasting, verification of CO2 emissions and Kyoto monitoring, numerical weather prediction, and validation of global chemical transport model, global climate chemical model and satellite products. since its participation in on-going european projects (nOrs, aCtris-2, arise-2), and thanks to the start of delivery of data in near real time, the Maïdo observatory will largely contribute to the Copernicus atmosphere Monitoring services (CaMs). the Maïdo observatory is open to transnational access thanks to its participation in european programmes like aCtris-2 and enVriplus. this presentation will give an overview of results achieved so far and a number of highlights to illustrate the promise Maïdo observatory data hold for the future, allowing new applications and analysis for a broad community of users

SHADOZ (Southern Hemisphere Additional Ozonesondes) Ozone Climatology. 4. Tropospheric and Lower Stratospheric Profiles (2005-2009) with Comparisons to OMI Total Ozone

International audienceWe present a regional and seasonal climatology of SHADOZ ozone profiles in the troposphere and tropical tropopause layer (TTL) based on measurements taken during the first five years of Aura, 2005-2009, when new stations joined the network at Hanoi, Vietnam; Hilo, Hawaii; Alajuela/Heredia, Costa Rica; Cotonou, Benin. In all, 15 stations operated during that period. A west-to-east progression of decreasing convective influence and increasing pollution leads to distinct tropospheric ozone profiles in three regions: (1) western Pacific/eastern Indian Ocean; (2) equatorial Americas (San Cristóbal, Alajuela, Paramaribo); (3) Atlantic and Africa. Comparisons in total ozone column from soundings, the Ozone Monitoring Instrument (OMI, on Aura, 2004-) satellite and ground-based instrumentation are presented. Most stations show better agreement with OMI than they did for EP/TOMS comparisons (1998-2004; Earth-Probe/Total Ozone Mapping Spectrometer), partly due to a revised above-burst ozone climatology. Possible station biases in the stratospheric segment of the ozone measurement noted in the first 7 years of SHADOZ ozone profiles are re-examined. High stratospheric bias observed during the TOMS period appears to persist at one station. Comparisons of SHADOZ tropospheric ozone and the daily Trajectory-enhanced Tropospheric Ozone Residual (TTOR) product (based on OMI/MLS) show that the satellite-derived column amount averages 25% low. Correlations between TTOR and the SHADOZ sondes are quite good (typical r2 = 0.5-0.8), however, which may account for why some published residual-based OMI products capture tropospheric interannual variability fairly realistically. On the other hand, no clear explanations emerge for why TTOR-sonde discrepancies vary over a wide range at most SHADOZ sites