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The ozonesonde is a small balloon-borne instrument that is attached to a standard radiosonde to measure profiles of ozone from the surface to 35 km with ~100-m vertical resolution. Ozonesonde data constitute a mainstay of satellite calibration and are used for climatologies and analysis of trends, especially in the lower stratosphere where satellites are most uncertain. The electrochemical-concentration cell (ECC) ozonesonde has been deployed at ~100 stations worldwide since the 1960s, with changes over time in manufacture and procedures, including details of the cell chemical solution and data processing. As a consequence, there are biases among different stations and discontinuities in profile time-series from individual site records. For 22 years the Jülich [Germany] Ozone Sonde Intercomparison Experiment (JOSIE) has periodically tested ozonesondes in a simulation chamber designated the World Calibration Centre for Ozonesondes (WCCOS) by WMO. In October-November 2017 a JOSIE campaign evaluated the sondes and procedures used in SHADOZ (Southern Hemisphere Additional Ozonesondes), a 14-station sonde network operating in the tropics and subtropics. A distinctive feature of the 2017 JOSIE was that the tests were conducted by operators from eight SHADOZ stations. Experimental protocols for the SHADOZ sonde configurations, which represent most of those in use today, are described, along with preliminary results. SHADOZ stations that follow WMO-recommended protocols record total ozone within 3% of the JOSIE reference instrument. These results and prior JOSIEs demonstrate that regular testing is essential to maintain best practices in ozonesonde operations and to ensure high-quality data for the satellite and ozone assessment communities.

Reprocessed ozonesonde data from eight SHADOZ (Southern Hemisphere ADditional OZonesondes) sites have been used to derive the first analysis of uncertainty estimates for both profile and total column ozone (TCO). The ozone uncertainty is a composite of the uncertainties of the individual terms in the ozone partial pressure (P O3 ) equation, those being the ozone sensor current, background current, internal pump temperature, pump efficiency factors, conversion efficiency, and flow-rate. Overall, P O3 uncertainties (ΔP O3 ) are within 15% and peak around the tropopause (15±3km) where ozone is a minimum and ΔP O3 approaches the measured signal. The uncertainty in the background and sensor currents dominate the overall ΔP O3 in the troposphere including the tropopause region, while the uncertainties in the conversion efficiency and flow-rate dominate in the stratosphere. Seasonally, ΔP O3 is generally a maximum in the March-May, with the exception of SHADOZ sites in Asia, for which the highest ΔP O3 occurs in September-February. As a first approach, we calculate sonde TCO uncertainty (ΔTCO) by integrating the profile ΔP O3 and adding the ozone residual uncertainty, derived from the McPeters and Labow [2012] 1-σ ozone mixing ratios. Overall, ΔTCO are within ±15 DU, representing ~5-6% of the TCO. TOMS and OMI satellite overpasses are generally within the sonde ΔTCO. However, there is a discontinuity between TOMS v8.6 (1998-2004/09) and OMI (2004/10-2016) TCO on the order of 10DU that accounts for the significant 16DU overall difference observed between sonde and TOMS. By comparison, the sonde-OMI absolute difference for the eight stations is only ~4DU.

Observations from long-term ozonesonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Réunion Island (21.1°S, 55.5°E) in June-August. Here we examine possible causes of the observed ozone variation at Réunion Island using hindcast simulations by the stratosphere-troposphere Global Modeling Initiative chemical transport model (GMI-CTM) for 1992-2014, driven by assimilated Modern-Era Retrospective Analysis for Research and Applications (MERRA) meteorological fields. Réunion Island is at the edge of the subtropical jet, a region of strong stratospheric-tropospheric exchange (STE). Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Réunion is driven by the large IAV of the stratospheric influence. The IAV of the large-scale, quasi-horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Réunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited to the lower troposphere near the surface in August - September.

The assessment of changes induced by human activities on Earth atmospheric composition and thus on global climate requires a long-term and regular survey of the stratospheric and tropospheric atmospheric layers. The objective of this paper is to describe the atmospheric observations performed continuously at Reunion Island (55.5 degrees east, 20.8 degrees south) for 15 years. The various instruments contributing to the systematic observations are described as well as the measured parameters, the accuracy and the database. The LiDAR systems give profiles of temperature, aerosols and ozone in the troposphere and stratosphere, probes give profiles of temperature, ozone and relative humidity, radiometers and spectrometers give stratospheric and tropospheric integrated columns of a variety of atmospheric trace gases. Data are included in international networks, and used for satellite validation. Moreover, some scientific activities for which this station offers exceptional opportunities are highlighted, especially air mass exchanges nearby dynamical barriers: (1) On the vertical scale through the tropical tropopause layer (stratosphere-troposphere exchange). (2) On the quasi-horizontal scale across the southern subtropical barrier separating the tropical stratospheric reservoir from mid- and high latitudes.

Rayleigh-Mie lidar measurements of stratospheric temperature and aerosol profiles have been carried out at Reunion Island (southern tropics) since 1993. Since June 1998, an operational extension of the system is permitting additional measurements of tropospheric ozone to be made by differential absorption lidar. The emission wavelengths (289 and 316 nm) are obtained by stimulated Raman shifting of the fourth harmonic of a Nd:YAG laser in a high-pressure deuterium cell. A mosaic of four parabolic mirrors collects the backscattered signal, and the transmission is processed by the multiple fiber collector method. The altitude range of ozone profiles obtained with this system is 3¿17 km. Technical details of this lidar system working in the southern tropics, comparisons of ozone lidar profiles with radiosondes, and scientific perspectives are presented. The significant lack of tropospheric ozone measurements in the tropical and equatorial regions, the particular scientific interest in these regions, and the altitude range of the ozone measurements to 16¿17 km make this lidar supplement useful and its adaptation technically conceivable at many Rayleigh-Mie lidar stations.

The total ionisation produced by ions stopped in nitrogen, methane and carbon dioxide has been measured in the energy range 25-375 keV using a chamber described previously. The chamber was operated alternately as a proportional counter and as an ionisation chamber to measure respectively the particle rate and the total ionisation produced. This procedure was repeated 20 to 40 times and a statistical treatment of the data was carried out. The average energy loss per ion pair (W-value), the associated standard deviation and the systematic error (+/- 2.5%) were determined for H+, He+, C+, N+, O+ and Ar+ ions stopping in the three gases. The W-value was found to be dependent on the velocity of the incident ions. For nitrogen gas, values range from 35 eV for 25 keV H+ to 84 eV for 25 keV O+. For methane, the values are 30.3 and 66.4 eV. For carbon dioxide, W-values range from 33.4 eV for 50 keV H+ to 135.9 eV for 25 keV Ar+. Finally, the Bragg additivity formula was tested for tissue-equivalent gas. The agreement between W-values calculated by this formula and those measured was found to be within 2% except for 25 keV O+ where the discrepancy is 10%.