Abstract
Abstract. In order to recognize the importance of ozone (O3) in the troposphere and lower stratosphere in the tropics, a DIAL (differential absorption lidar) tropospheric O3 lidar system (LIO3TUR) was developed and installed at the Université de la Réunion campus site (close to the sea) on Reunion Island (southern tropics) in 1998. From 1998 to 2010, it acquired 427 O3 profiles from the low to the upper troposphere and has been central to several studies. In 2012, the system was moved up to the new Maïdo Observatory facility (2160 m a.m.s.l. – metres above mean sea level) where it started operation in February 2013. The current system (LIO3T) configuration generates a 266 nm beam obtained with the fourth harmonic of a Nd:YAG laser sent into a Raman cell filled up with deuterium (using helium as buffer gas), generating the 289 and 316 nm beams to enable the use of the DIAL method for O3 profile measurements. The optimal range for the actual system is 6–19 km a.m.s.l., depending on the instrumental and atmospheric conditions. For a 1 h integration time, vertical resolution varies from 0.7 km at 6 km a.m.s.l. to 1.3 km at 19 km a.m.s.l., and mean uncertainty within the 6–19 km range is between 6 and 13 %. Comparisons with eight electrochemical concentration cell (ECC) sondes simultaneously launched from the Maïdo Observatory show good agreement between data sets with a 6.8 % mean absolute relative difference (D) between 6 and 17 km a.m.s.l. (LIO3T lower than ECC). Comparisons with 37 ECC sondes launched from the nearby Gillot site during the daytime in a ±24 h window around lidar shooting result in a 9.4 % D between 6 and 19 km a.m.s.l. (LIO3T lower than ECC). Comparisons with 11 ground-based Network for Detection of Atmospheric Composition Change (NDACC) Fourier transform infrared (FTIR) spectrometer measurements acquired during the daytime in a ±24 h window around lidar shooting show good agreement between data sets with a D of 11.8 % for the 8.5–16 km partial column (LIO3T higher than FTIR), and comparisons with 39 simultaneous Infrared Atmospheric Sounding Interferometer (IASI) observations over Reunion Island show good agreement between data sets with a D of 11.3 % for the 6–16 km partial column (LIO3T higher than IASI). ECC, LIO3TUR and LIO3T O3 monthly climatologies all exhibit the same range of values and patterns. In particular, the Southern Hemisphere biomass burning seasonal enhancement and the ozonopause altitude decrease in late austral winter–spring, as well as the sign of deep convection bringing boundary layer O3-poor air masses up to the middle–upper troposphere in late austral summer, are clearly visible in all data sets.
Highlights
Because of its interaction with solar and terrestrial radiation, ozone (O3) is an important contributor to the Earth’s radiative balance, and any changes in its atmospheric distribution contribute to the radiative forcing of climate change (Lacis et al, 1990)
This paper aims to provide a technical reference socle for further use of the O3 data provided by the LIO3T system: we first present the data processing, give a brief historical review of the tropospheric O3 lidar system when installed at the Université de la Réunion campus site (1998–2010) together with a description of the current LIO3T system installed at the Maïdo Observatory
A DIAL tropospheric O3 lidar was operating on the Université de la Réunion campus site from 1998 to 2010, providing 427 O3 profiles
Summary
Because of its interaction with solar and terrestrial radiation, ozone (O3) is an important contributor to the Earth’s radiative balance, and any changes in its atmospheric distribution contribute to the radiative forcing of climate change (Lacis et al, 1990). Reunion Island is a tropical island located in the southwestern part of the Indian Ocean at 20.8◦ S and 55.5◦ E It is seasonally impacted by biomass burning plumes transported from southern Africa, South America and south-eastern Asia which can significantly affect the free tropospheric concentrations of O3 and other pollutants like CO (Edwards et al, 2006 ; Duflot et al, 2010). It is affected by stratospheric intrusions associated with the dynamical influence of the subtropical jet stream (Baray et al, 1998; Clain et al, 2010) and the tropical cyclone deep convection (Leclair De Bellevue et al, 2006). The programme used to calculate the O3 profile, uncertainties and resolution is adapted from the stratospheric O3 programme DIAL (differential absorption lidar), which has been described and intercompared by Godin et al (1999) and is currently used for the stratospheric DIAL O3 retrievals at Reunion Island (NDACC affiliated)
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