Water vapor observations up to the lower stratosphere through the Raman lidar during the MAïdo LIdar Calibration Campaign

Abstract

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.

Multiple subtropical stratospheric intrusions over Reunion Island: Observational, Lagrangian, and Eulerian numerical modeling approaches

“…The intensive measurement campaign MALICCA‐1 (1 April to 20 April 2013) provided detailed data set of water vapor profiles on a short period. The main goal of the campaign was to set the best instrumental configuration for the Raman lidar system and to evaluate its data [ Dionisi et al ., ; Keckhut et al ., ]. This campaign allowed also to conduct scientific studies on various topics: moistening of the lower stratosphere, cirrus clouds, among others, and STE including the case study documented in this paper.…”

“…The Raman water vapor lidar system which operated at Saint‐Denis from 2002 to 2005 [ Hoareau et al ., ] has been very significantly upgraded after being transferred to the Maïdo station in 2012. Some critical points detected in the previous system have been improved and optimized [ Hoareau et al ., ; Dionisi et al ., ]. The new Raman system has been designed to monitor the water vapor in the troposphere and in the lower stratosphere and, simultaneously, the temperature in the stratosphere and in the mesosphere.…”

Water Vapor Profiles up to the UT/LS from Raman Lidar at Reunion Island (21°S, 55°E) : Technical Description, Data Processing and Comparison with Sondes

“…The MALICCA-1 campaign data set shows a good agreement between water vapor lidar measurements and other almost simultaneous and collocated measurements (Vaisala RS92, MLS satellite) [3]. The relative difference between lidar profiles and fifteen radiosoundings was lower than 10% for the low and mid-troposphere and between 10 and 20% for the upper troposphere.…”

“…The relative difference between lidar profiles and fifteen radiosoundings was lower than 10% for the low and mid-troposphere and between 10 and 20% for the upper troposphere. Two integration methods has been tested : 240 minutes for an absolute error of approximately 2 ppmv from 17 to 20 km, and 1 ppmv at 20 km for a monthly integration, which demonstrates the ability of the lidar to measure quantities of only few ppm in the UT/LS [3]. The monthly water vapor average profile measured by MLS matches well in the lower stratosphere with the lidar average profile of MALICCA-1 [3].…”

“…Such FOV induces a geometrical obturation that is similar for both channels and allows to reduce PMT saturation and to retrieve water vapor mixing ratio down to the ground. Details on the different tests and the final choice of the optical configuration are given in [3].…”