Abstract. 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 Stratospheric

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 Stratospheric 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 a.s.l.: it hosts various instruments for atmospheric measurements, including LiDAR systems, spectro-radiometers and in situ gases and aerosols measurements.

This new high-altitude Maïdo station allows:
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.
2. To develop in-situ measurements of the atmospheric composition for climate change survey, in a reference site in the tropical/subtropical region of the Southern Hemisphere.
3. To offer trans-national access to host experiments or measurement campaigns for focused process studies

Abstract.A new lidar system devoted to tropospheric and lower stratospheric water vapor measurements has been installed at the Maïdo altitude station facility of Réunion island, in the southern subtropics.To evaluate the performances and the capabilities of the new system with a particular focus on UTLS (Upper Troposphere Lower Stratosphere) measurements, the Maïdo Lidar Calibration Campaign (MALICCA) was performed in April 2013.Varying the characteristics of the transmitter and the receiver components, different system configuration scenarios were tested and possible parasite signals (fluorescent contamination, rejection) were investigated. A hybrid calibration methodology has been set up and validated to insure optimal lidar calibration stability with time. In particular, the receiver transmittance is monitored through the calibration lamp method that, at the moment, can detect transmittance variations greater than 10-15 %. Calibration coefficients are then calculated through the hourly values of IWV (Integrated Water Vapor) provided by the co-located GPS. The comparison between the constants derived by GPS and Vaisala RS92 radiosondes launched at Maïdo during MALICCA, points out an acceptable agreement in terms of accuracy of the mean calibration value (with a difference of approximately 2-3 %), but a significant difference in terms of variability (14 % vs. 7-9 %, for GPS and RS92 calibration procedures, respectively).We obtained a relatively good agreement between the lidar measurements and 15 co-located and simultaneous RS92 radiosondes. A relative difference below 10 % is measured in the low and middle troposphere (2-10 km). The upper troposphere (up to 15 km) is characterized by a larger spread (approximately 20 %), because of the increasing distance between the two sensors.To measure water vapor in the UTLS region, nighttime and monthly water vapor profiles are presented and compared. The good agreement between the lidar monthly profile and the mean WVMR profile measured by satellite MLS (Microwave Limb Sounder) has been used as a quality control procedure of the lidar product, attesting the absence of significant wet biases and validating the calibration procedure.Due to its performance and location, the MAIDO H 2 O lidar will become a reference instrument in the southern subtropics, insuring the long-term survey of the vertical distribution of water vapor. Furthermore, this system allows the investigation of several scientific themes, such as stratospheretroposphere exchange, tropospheric dynamics in the subtropics, and links between cirrus clouds and water vapor.

The Maïdo high-altitude observatory located in Reunion Island (21 ∘ S, 55.5 ∘ E) is equipped with the Lidar1200, an innovative Raman lidar designed to measure the water vapor mixing ratio in the troposphere and the lower stratosphere, to perform long-term survey and processes studies in the vicinity of the tropopause. The calibration methodology is based on a GNSS (Global Navigation Satellite System) IWV (Integrated Water Vapor) dataset. The lidar water vapor measurements from November 2013 to October 2015 have been calibrated according to this methodology and used to evaluate the performance of the lidar. The 2-year operation shows that the calibration uncertainty using the GNSS technique is in good agreement with the calibration derived using radiosondes. During the MORGANE (Maïdo ObservatoRy Gaz and Aerosols NDACC Experiment) campaign (Reunion Island, May 2015), CFH (Cryogenic Frost point Hygrometer) radiosonde and Raman lidar profiles are compared and show good agreement up to 22 km asl; no significant biases are detected and mean differences are smaller than 9% up to 22 km asl.

International audienceThe first operations at the new High-altitude Maïdo Observatory at La Réunion began in 2013. The Maïdo Lidar Calibration Campaign (MALICCA) was organized there in April 2013 and has focused on the validation of the thermodynamic parameters (temperature, water vapor, and wind) measured with many instruments including the new very large lidar for water vapor and temperature profiles. The aim of this publication consists of providing an overview of the different instruments deployed during this campaign and their status, some of the targeted scientific questions and associated instrumental issues. Some specific detailed studies for some individual techniques were addressed elsewhere. This study shows that temperature profiles were obtained from the ground to the mesopause (80 km) thanks to the lidar and regular meteorological balloon-borne sondes with an overlap range showing good agreement. Water vapor is also monitored from the ground to the mesopause by using the Raman lidar and microwave techniques. Both techniques need to be pushed to their limit to reduce the missing range in the lower stratosphere. Total columns obtained from global positioning system or spectrometers are valuable for checking the calibration and ensuring vertical continuity. The lidar can also provide the vertical cloud structure that is a valuable complementary piece of information when investigating the water vapor cycle. Finally, wind vertical profiles, which were obtained from sondes, are now also retrieved at Maïdo from the newly implemented microwave technique and the lidar. Stable calibrations as well as a small-scale dynamical structure are required to monitor the thermodynamic state of the middle atmosphere, ensure validation of satellite sensors, study the transport of water vapor in the vicinity of the tropical tropopause and study their link with cirrus clouds and cyclones and the impact of small-scale dynamics (gravity waves) and their link with the mean state of the mesosphere

Abstract. The Maïdo high-altitude observatory located in Reunion Island (21°S, 55.5°E) is equipped with Lidar1200, an innovative Raman lidar designed to measure the water vapor mixing ratio in the troposphere and the lower stratosphere. The calibration methodology is based on a GNSS (Global Navigation Satellite System) IWV (Integrated Water Vapor) dataset and 20 lamp measurements. The mean relative standard error on the calibration coefficient is around 2.7%. Two years of lidar water vapor measurements from November 2013 to October 2015 are now processed. By comparing CFH (Cryogenic Frost point Hygrometer) radiosonde profiles with the Raman lidar profiles, the ability of the lidar to provide accurate measurements is possible up to 22 km. The ability of measuring water vapor mixing ratios of a few ppmv in the lower stratosphere is demonstrated with a 48-hours integration time period, an absolute error lower than 0.8 ppmv and a relative error less than 20%. 25This Raman lidar is dedicated to provide regular profiles of water vapor measurements with a high vertical resolution and low uncertainties to international networks; in the wider interest of research on stratosphere-troposphere exchange processes and on the long-term survey of water vapor in the upper troposphere and lower stratosphere in the Southern Hemisphere. A strategy of data sampling and filtering is proposed to meet these objectives with regard to the altitude range requested. 10-min time integration and 65-90 m vertical resolution ensure a vertical profile reaching 10 km, but more than 2800 minutes and a vertical 30 resolution of 150-1300 m are necessary to reach the lower stratosphere with an uncertainty less than 20%. 1 IntroductionTo monitor potential climate changes, observations of essential climate variables (ECV) such as atmospheric water vapor (Bojinski et al., 2014) are necessary. Long-term series allow the international community to progress on important climatological issues, such as the contributions of stratospheric water vapor to decadal changes in the rate of global warming 35 (Solomon et al., 2010). Selection criteria are important for the certification of networks. These criteria include: long-term stability and regularity. When supplying the databases, very precise and detailed metadata files of the physical quantities have to be provided. And most importantly, an uncertainty has to be associated to the data. This last exercise is realized through the examination of the data processing algorithms and calibration methodologies. This rigor is essential to monitor efficiently the Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2017Discuss., doi:10.5194/amt- -32, 2017 (Immler et al., 2010). One of the challenging ECV to measure is water vapor mainly in the upper troposphere and lower stratosphere (GCOS, 2003). Water vapor is the main greenhouse gas. The factors influencing its spatio-temporal variability are various: convection, precipitations, temperature (Kennett and Toumi, 2005), transport and dynamical processes from eddies to synop...

Abstract. A new lidar system devoted to tropospheric and lower stratospheric water vapor measurements has been installed at the Maïdo altitude station facility of La Reunion Island, in the southern subtropics. The main objectives of the MAïdo LIdar Calibration Campaign (MALICCA), performed in April 2013, were to validate the system, to set up a calibration methodology, to compare the acquired water profiles with radiosonde measurements and to evaluate its performances and capabilities with a particular focus on the UTLS measurements. Varying the characteristics of the transmitter and the receiver components, different system configuration scenarios were tested and possible parasite signals (fluorescent contamination, rejection) were investigated. A hybrid calibration methodology has been set up and validated to insure optimal lidar calibration stability with time. In particular, the receiver transmittance is monitored through the calibration lamp method that, at the moment, can detect transmittance variations greater than 10–15%. Calibration coefficients are then calculated through the hourly values of IWV provided by the co-located GPS. The comparison between the constants derived by GPS and Vaisala RS92 radiosondes launched at Maïdo during MALICCA, points out an acceptable agreement in terms of accuracy of the mean calibration value (with a difference of approximately 2–3%), but a significant difference in terms of variability (14 vs. 7–9%, for GPS and RS92 calibration procedures, respectively). We obtained a relatively good agreement between the lidar measurements and 15 co-located and simultaneous RS92 radiosondes. A relative difference below 10% is measured in low and middle troposphere (2–10 km). The upper troposphere (up to 15 km) is characterized by a larger spread (approximately 20%), because of the increasing distance between the two sensors. To measure water vapor in the UTLS region, nighttime and monthly water vapor profiles are presented and compared. The good agreement between the lidar monthly profile and the mean WVMR profile measured by satellite MLS has been used as a quality control procedure of the lidar product, attesting the absence of significant wet biases and validating the calibration procedure. Thanks to its performance and location, the MAIDO H2O lidar is devoted to become a reference instrument in the southern subtropics, allowing to insure the long-term survey of the vertical distribution of water vapor, and to document scientific themes such as stratosphere–troposphere exchange, tropospheric dynamics in the subtropics, links between cirrus clouds and water vapor.

Today, resilience in the face of cyclone risks has become a crucial issue for our societies. With climate change, the risk of strong cyclones occurring is expected to intensify significantly and to impact the way of life in many countries. To meet some of the associated challenges, the interdisciplinary ReNovRisk programme aims to study tropical cyclones and their impacts on the South-West Indian Ocean basin. This article is a presentation of the ReNovRisk programme, which is divided into four areas: study of cyclonic hazards, study of erosion and solid transport processes, study of water transfer and swell impacts on the coast, and studies of socio-economic impacts. The first transdisciplinary results of the programme are presented together with the database, which will be open access from mid-2021.