A Raman lidar at Maïdo Observatory (Reunion Island) to measure water vapor in the troposphere and lower stratosphere: calibration and validation

Abstract

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...

Tropospheric ozone profiles by DIAL at Maïdo Observatory (Reunion Island): system description, instrumental performance and result comparison with ozone external data set

“…Figure 5 shows the comparison between LIO3T and eight ECC soundings collocated in time and space: two were performed in June 2013, four in May 2015 and two in July 2015. Note that these last six were part of the Maïdo ObservatoRy Gaz and Aerosols Ndacc Experiment (MORGANE) campaign that took place in May-July 2015 Duflot et al, 2016;Posny et al, 2016;Vérèmes et al, 2017). The integration time for the LIO3T profiles used here is 1 h (starting at the ECC sonde launch time) and corresponds roughly to the time for the balloon to travel the troposphere.…”

“…Since temperature measurements are now performed with the LI1200 system -also dedicated to water vapour measurement Vérèmes et al, 2017) -the previous LIO3T UR was modified into a system dedicated to the measurement of tropospheric O 3 (and aerosols): the LIO3T. Figure 2 sketches the experimental schematic of the O 3 DIAL part of the LIO3T and gives its main technical characteristics.…”

“…-the LI1200, a lidar dedicated to tropospheric water vapour (Hoareau et al, 2012;Dionisi et al, 2015;Vérèmes et al, 2017) and stratospheric-mesospheric temperature measurements (Morel et al, 2002;Keckhut et al, 2004Keckhut et al, , 2015Sivakumar et al, 2011a);…”

Two-year operation of the lidar1200: from fine-scale tropospheric structures to lower stratospheric water vapor detection

“…Mean profiles have been calculated and differentiated into three classes characterized by their integration time: 10, 40 and 240 minutes [3]. The measurement sessions have been averaged and processed with the algorithm used on a routine basis.…”

“…The GNSS technique has been chosen in order to improve the reliability of the calibration and the robustness of the water vapor measurement on a long-term perspective. This methodology has been successfully used in the 2013-2015 dataset [3].…”