Étude de la variabilité de la vapeur d'eau dans la troposphère et la basse stratosphère en région (sub)tropicale et des processus associés

In a context of climate change, it is important to study distribution processes and the trends of trace atmospheric gases such as ozone and water vapor. The Maïdo atmospheric observatory, located at 2160 m in height, hosts a set of atmospheric in-situ and remote sensing instruments, including the Lidar1200 providing vertical water vapor profiles. This thesis aims to provide a thorough work of validation, evaluation and analysis of the Lidar1200 data. Comparisons with radiosoundings allowed to validate the water vapor profiles of the lidar from the lower troposphere up to an altitude of 22 km if a sufficient number of data is integrated. At a smaller temporal scale, the Lidar1200 is able to follow temporally structures in the range of a hundred of meters thick up to a dozen of kilometers in altitude. The data analysis show the potential of the lidar in monitoring the water vapor in the lower stratosphere on a long term with one to two points of measurements by month. The database 2013-2015 brings information on the seasonal variability of the water vapor over Reunion Island. The water vapor data allow to study various atmospheric processes including stratosphere-troposphere exchanges. Signatures of stratospheric intrusions were observed on quasi-simultaneous and co-localized ozone and water vapor observations realized by two lidars of the Maïdo Observatory during the measurement campaign MALICCA-1 (MAïdo LIdar Calibration CAmpaign, Reunion Island), on April 4, 2013, suggesting stratospheric intrusions with multiple origins.Dans un contexte de changement climatique, il est important d'étudier les processus de distribution et les tendances des gaz à l'état de traces dans l'atmosphère tels que l'ozone et la vapeur d'eau. L'observatoire atmosphérique du Maïdo, situé à 2160 m, héberge un ensemble d'instruments de mesures atmosphériques in-situ et par télédétection, dont le Lidar1200, pour la mesure de profils verticaux de vapeur d'eau. La validation, l'évaluation et une première exploitation des données du Lidar1200 font l'objet de cette thèse. Des comparaisons avec des radiosondages ont permis de valider les profils de vapeur d'eau du lidar depuis la basse troposphère jusqu'à 22 km d'altitude dès lors qu'un nombre suffisant de données est intégré. À courte échelle de temps, le Lidar1200 est capable de suivre temporellement des structures de l'ordre de la centaine de mètres d'épaisseur jusqu'à une dizaine de kilomètres d'altitude. L'analyse des données montre le potentiel du Lidar1200 de surveillance de la vapeur d'eau à long-terme dans la basse stratosphère avec un ou deux points de mesure par mois. La base de données 2013-2015 apporte des informations sur la variabilité saisonnière de la vapeur d'eau au-dessus de La Réunion. Les données de vapeur d'eau permettent de documenter divers processus atmosphériques dont les échanges stratosphère-troposphère. Des signatures d'intrusion stratosphérique ont été observées sur des observations lidar quasi simultanées et co-localisées d'ozone et de vapeur d'eau pendant la campagne de mesure MALICCA (MAïdo LIdar Calibration Campaign, La Réunion), le 4 avril 2013, suggérant un processus d'intrusion stratosphérique avec plusieurs origines

Validation of the Water Vapor Profiles of the Raman Lidar at the Maïdo Observatory (Reunion Island) Calibrated with Global Navigation Satellite System Integrated 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

Tropical Cyclones and Fertility : New Evidence from Madagascar

Does exposure to tropical cyclones affect fertility? This paper tackles this issue byexploiting geolocated microdata from the Malagasy Demographic and Health Surveytogether with wind field data generated by tropical cyclones hitting Madagascar duringthe 1985-2009 period. The mothers’ fertility history available in the microdata allowsus to construct a panel dataset indicating if a mother gave birth during a given yearand if she has been exposed to a tropical cyclone. By means of panel regressions, thatallows a full control of unobserved heterogeneities, we then estimate the causal effect oftropical cyclone shocks on female likelihood of giving birth. We find evidence that theeffect of tropical cyclone exposure on motherhood is significantly negative. In particular,being exposed to wind speed of 100 km/h implies a fall in the probability of giving birthof 25.6 points in the current year together with further decline of 5.9 and 2.0 pointsrespectively one and two years after being exposed. Alternative specifications of ourbaseline model provide further insights. First, we find mixed evidence of intensificationeffects. Second, we find no evidence of non-linearities in the effect. Third, the negativeeffect is stronger before 1998. Fourth, the effect of tropical cyclone on motherhood ispersistent since in an extended model estimated coefficients are significantly negativeup to seven years after being exposed. The estimated effect is shown to be robust tothe use of alternative formulation of the wind speed variable but also to an alternativetreatment of geolocated data

Spatial and seasonal variability of clouds over the southwest Indian Ocean based on the DARDAR mask product

International audienceWe present a characterization of the variability of clouds over the South‐West Indian Ocean between 2007 and 2010. Cloud occurrence is derived from the DARDAR (raDAR/liDAR) mask, a synergistic product based on CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) and CloudSat measurements. It provides a target classification for hydrometeors. We demonstrate that this product is suitable for studying the vertical, spatial and seasonal cloud distribution in the South‐West Indian Ocean. The variability of cloud occurrence increases approaching the tropics: the average maximum amplitude of monthly occurrence is ∼7% between 30°S and 60°S and ∼14% between 10°S and 30°S. The 10‐30°S latitudinal band exhibits the largest contrasts: summer (winter) total cloud occurrence is mainly driven by high‐ (low‐) level clouds. The vertical distribution of clouds differs on either side of 55°E and this is related to a land‐ocean contrast and to large‐scale influence. In winter, east of 55°E, the maximum of cloud occurrence corresponds to warm and mixed‐phased precipitating clouds associated with the Mascarene High. In summer, west of 55°E, the vertical distribution of cloud occurrence is driven by deep convection associated with the Inter Tropical Convergence Zone and the Near Equatorial Trough. The vertical distribution of cloud occurrence shows an interannual variability that is related to El Niño events. The influence of other oscillation modes should be further investigated

Profiling of aerosols and clouds in Reunion Island (21°S, 55.5°E)

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Long-Range Transport of Water Channelized through the Southern Subtropical Jet

In this study, an air mass (containing a cirrus cloud) was detected by light detection and ranging (lidar) above São Paulo (Brazil) in June 2007 and tracked around the globe, thanks to Lagrangian calculations as well as ground-based and satellite observations. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data were also used to provide locations of occurrence of cirrus around the globe and extract their respective macro physical parameters (altitude and temperature). An analysis of the air mass history based on Lagrangian trajectories reveals that water coming from the Equator is channelized through the southern subtropical jet for weeks. In this case, the back-trajectories showed that the cirrus cloud detected at São Paulo was a mixture of air masses from two different locations: (1) the active convective area located around the Equator, with transport into the upper troposphere that promotes cirrus cloud formation; and (2) the South Pacific Ocean, with transport that follows the subtropical jet stream (STJ). Air masses coming from equatorial convective regions are trapped by the jet, which contributes to maintaining the lifetime of the cirrus cloud for a few days. The cloud disappears near the African continent, due to a southern excursion and warmer temperatures, then reappears and is detected again by the lidar system in São Paulo after 12 days. The observed cloud is located at a similar altitude, revealing that sedimentation is small or compensated by radiative uplift

Monitoring the water cycle in the UT/LS with Raman lidar

International audienceRaman water vapor Lidar start to investigated 20 years ago on existing lidars in the frame of the NDACC network located in South of France (44°N, 6°E) and in Reunion Island (21°S, 55°E) with elasting scatter to register simultaneously cristal particules. From this experiment, a nex system have been designed to monitor the water vapor in the whole troposphere up to the lower stratosphere. Measurements have been validated with CFH and Vaisala radiosondes. Measuring quantities of a few ppmv in the lower stratosphere is achiveded. Calibration methodology have been developped and tested during the campaign MALICCA (MAïdo LIdar Calibration CAmpaign). The lidar water vapor profiles are calibrated with water vapor columns obtained from a collocated GNSS receiver. New methodologies of data averaging have been developped, for a long-term monitoring and studies of water transport around the tropopause. Few cases studies are presented to illustrated lidar capabilities

Validation of the Water Vapor Profiles of the Raman Lidar at the Maïdo Observatory (Reunion Island) Calibrated with Global Navigation Satellite System Integrated Water Vapor

International audienceThe 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