Développement et mise en oeuvre de LiDAR embarqués sur bouées dérivantes pour l'étude des propriétés des aérosols et des nuages en Arctique et des forçages radiatifs induits

To improve our knowledge of the processes and interactions which occur in Arctic between atmosphere, sea ice and ocean, an EQUIPEX funding was granted to the IAOOS project. This improvement will be reached by deploying a network of multi-instrumented buoys. For the atmospheric analyses an innovative backscattering LiDAR meeting with constraints of the project and arctic environment has been developed. An analytical model of signal to noise ratio in clear sky led to the instrumental key parameters, and numerical simulations helped in improving the system performances. An evolutive prototype has been realized within the tight planning of this EQUIPEX. The first whole equiped buoy was deployed close to the north pole in April 2014 and worked until the beginning of December 2014. A second deployment of two buoys, including a polarized version, was then realized within the N-ICE campaign from January to June 2015. These first campaigns gave first statistics of aerosols and clouds distribution in the central arctic region with an autonomous LiDAR. First results show frequent aerosols layers in mid-troposphere during spring, as well as a high occurence of very low clouds. LiDAR measurements were also used to estimate downwelling longwave and shortwave at surface. Results obtained from these first deployments and comparisons with analysis and outputs from the WRF model show a first overview of what can be expected from this network of multi-instrumented buoys in the central arctic region.Afin de mieux comprendre les processus et les interactions entre l'atmosphère, la glace de mer et l'océan en arctique, un financement EQUIPEX a permis de développer et déployer le projet IAOOS (Ice-Atmosphere-Ocean-Observing-System) de réseau de bouées multi-instrumentées. Pour la partie atmosphère un LiDAR rétrodiffusion innovant a été développé pour répondre aux contraintes du projet et de l'environnement arctique. Un modèle analytique du rapport signal sur bruit en air clair a permis de préciser les paramètres clés de la conception. Des simulations numériques ont ensuite permis d'affiner les performances du système. Un prototype évolutif a été réalisé dans le planning serré de cet EQUIPEX, avant la mise en œuvre d'une première bouée complète au Pôle Nord en avril 2014, qui a fonctionné jusqu'en décembre 2014. Un second déploiement de deux bouées a ensuite été réalisé à l'occasion de la campagne N-ICE de janvier à juin 2015, dont l'une était équipée d'une version polarisée du LiDAR. Les deux campagnes ont permis d'obtenir des premières statistiques de la distribution des aérosols et des nuages en arctique central avec un système LiDAR autonome. Les premiers résultats montrent la présence de couches d'aérosols assez fréquentes au printemps dans la moyenne troposphère et des nuages bas très fréquents. Les mesures LiDAR ont été utilisées pour effectuer une estimation des flux infrarouge et visible descendants. Les résultats des deux premiers déploiements et les comparaisons avec des analyses et des sorties du modèle WRF fournissent des premiers éléments sur l'apport que pourra présenter ce réseau de bouées multi-instrumentées en région centrale arctique

Observations of Tropical Tropopause Layer clouds from a balloon-borne lidar

Tropical Tropopause Layer (TTL) clouds have a significant impact on the Earth’s radiative budget and regulate the amount of water vapor entering the stratosphere. During the Strateole-2 observation campaign, three microlidars were flown onboard stratospheric superpressure balloons from October 2021 to late January 2022, slowly drifting only a few kilometers above the TTL. These measurements have unprecedented sensitivity to thin cirrus and provide a fine-scale description of cloudy structures both in time and space. Case studies of collocated observations with the space-borne lidar Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show a very good agreement between the instruments and highlight the unique ability of the microlidar to detect optically very thin clouds below CALIOP detection capacity (optical depth τ < 2 · 10−3). Statistics on cloud occurrence show that TTL cirrus appear in more than 50 % of the microlidar profiles and have a mean geometrical depth of 1 km. Ultrathin TTL cirrus (τ < 2 · 10−3) have a significant coverage (16 % of the profiles) and their mean geometrical depth is below 500 m

Development and deployment of autonomous LiDAR set on drifting buoys to study aerosols and clouds Arctic properties, and induced radiative forcing

Afin de mieux comprendre les processus et les interactions entre l'atmosphère, la glace de mer et l'océan en arctique, un financement EQUIPEX a permis de développer et déployer le projet IAOOS (Ice-Atmosphere-Ocean-Observing-System) de réseau de bouées multi-instrumentées. Pour la partie atmosphère un LiDAR rétrodiffusion innovant a été développé pour répondre aux contraintes du projet et de l'environnement arctique. Un modèle analytique du rapport signal sur bruit en air clair a permis de préciser les paramètres clés de la conception. Des simulations numériques ont ensuite permis d'affiner les performances du système. Un prototype évolutif a été réalisé dans le planning serré de cet EQUIPEX, avant la mise en œuvre d'une première bouée complète au Pôle Nord en avril 2014, qui a fonctionné jusqu'en décembre 2014. Un second déploiement de deux bouées a ensuite été réalisé à l'occasion de la campagne N-ICE de janvier à juin 2015, dont l'une était équipée d'une version polarisée du LiDAR. Les deux campagnes ont permis d'obtenir des premières statistiques de la distribution des aérosols et des nuages en arctique central avec un système LiDAR autonome. Les premiers résultats montrent la présence de couches d'aérosols assez fréquentes au printemps dans la moyenne troposphère et des nuages bas très fréquents. Les mesures LiDAR ont été utilisées pour effectuer une estimation des flux infrarouge et visible descendants. Les résultats des deux premiers déploiements et les comparaisons avec des analyses et des sorties du modèle WRF fournissent des premiers éléments sur l'apport que pourra présenter ce réseau de bouées multi-instrumentées en région centrale arctique.To improve our knowledge of the processes and interactions which occur in Arctic between atmosphere, sea ice and ocean, an EQUIPEX funding was granted to the IAOOS project. This improvement will be reached by deploying a network of multi-instrumented buoys. For the atmospheric analyses an innovative backscattering LiDAR meeting with constraints of the project and arctic environment has been developed. An analytical model of signal to noise ratio in clear sky led to the instrumental key parameters, and numerical simulations helped in improving the system performances. An evolutive prototype has been realized within the tight planning of this EQUIPEX. The first whole equiped buoy was deployed close to the north pole in April 2014 and worked until the beginning of December 2014. A second deployment of two buoys, including a polarized version, was then realized within the N-ICE campaign from January to June 2015. These first campaigns gave first statistics of aerosols and clouds distribution in the central arctic region with an autonomous LiDAR. First results show frequent aerosols layers in mid-troposphere during spring, as well as a high occurence of very low clouds. LiDAR measurements were also used to estimate downwelling longwave and shortwave at surface. Results obtained from these first deployments and comparisons with analysis and outputs from the WRF model show a first overview of what can be expected from this network of multi-instrumented buoys in the central arctic region

IAOOS microlidar development and firsts results obtained during 2014 and 2015 arctic drifts

International audienceThe development of a first ever autonomous aerosol and cloud backscatter lidar system for on-buoy arctic observations has been achieved in 2014, within the French EQUIPEX IAOOS project developed in collaboration with LOCEAN at UPMC. This development is part of a larger set-up designed for integrated ocean-ice-atmosphere observations. First results have been obtained from spring to autumn 2014 after the system was installed at the North Pole at the Barneo Russian camp, and in winter-spring 2015 during the Norwegian campaign N-ICE 2015. The buoys were taking observations as drifting in the high arctic region where very few measurements have been made so far. This project required the design and the conception of an all-new lidar system to fit with the numerous constraints of such a deployment. We describe here the prototype and its performance. First analyzes are presented

Balloon-borne lidar observations of tropical cirrus cloudsand comparison with CALIOP

International audienceKey component of the climate system, tropical cirrus clouds modulate both the Earth’s radiativebudget and the amount of water vapor transported to the stratosphere. The range of optical depth ofsuch clouds pans several orders of magnitude, from thick opaque cirrus detrained from deepconvection to ultra thin ones just below the stratosphere. Although sub-visible cirrus clouds havebeen largely documented from CALIOP space-borne lidar, its detection lower limit is an obstacle toaccurately quantify the tropical cirrus coverage. The microlidar BeCOOL (Balloon-borne Cirrus andconvective overshOOT Lidar) has been designed to tackle this issue. Between October 2021 andJanuary 2022, in the framework of Strateole-2 project, three BeCOOL microlidars have been flownonboard super-pressure balloons in the lower tropical stratosphere (~20 km). Case studies ofcollocated observations with CALIOP, along with statistical comparisons, highlight the very goodagreement between the two lidars and the enhanced sensitivity of BeCOOL to ultra thin clouds. Thishigher sensitivity is achieved thanks to the low speed of the balloons and the small distance to theobserved clouds, which allow to integrate the observations over a longer time. BeCOOL’sobservations reveal the structure and the significant coverage of optically ultra thin clouds undetectedfrom space

Balloon-borne lidar observations of tropical cirrus cloudsand comparison with CALIOP

International audienceKey component of the climate system, tropical cirrus clouds modulate both the Earth’s radiativebudget and the amount of water vapor transported to the stratosphere. The range of optical depth ofsuch clouds pans several orders of magnitude, from thick opaque cirrus detrained from deepconvection to ultra thin ones just below the stratosphere. Although sub-visible cirrus clouds havebeen largely documented from CALIOP space-borne lidar, its detection lower limit is an obstacle toaccurately quantify the tropical cirrus coverage. The microlidar BeCOOL (Balloon-borne Cirrus andconvective overshOOT Lidar) has been designed to tackle this issue. Between October 2021 andJanuary 2022, in the framework of Strateole-2 project, three BeCOOL microlidars have been flownonboard super-pressure balloons in the lower tropical stratosphere (~20 km). Case studies ofcollocated observations with CALIOP, along with statistical comparisons, highlight the very goodagreement between the two lidars and the enhanced sensitivity of BeCOOL to ultra thin clouds. Thishigher sensitivity is achieved thanks to the low speed of the balloons and the small distance to theobserved clouds, which allow to integrate the observations over a longer time. BeCOOL’sobservations reveal the structure and the significant coverage of optically ultra thin clouds undetectedfrom space

Balloon-borne lidar observations of tropical cirrus cloudsand comparison with CALIOP

International audienceKey component of the climate system, tropical cirrus clouds modulate both the Earth’s radiativebudget and the amount of water vapor transported to the stratosphere. The range of optical depth ofsuch clouds pans several orders of magnitude, from thick opaque cirrus detrained from deepconvection to ultra thin ones just below the stratosphere. Although sub-visible cirrus clouds havebeen largely documented from CALIOP space-borne lidar, its detection lower limit is an obstacle toaccurately quantify the tropical cirrus coverage. The microlidar BeCOOL (Balloon-borne Cirrus andconvective overshOOT Lidar) has been designed to tackle this issue. Between October 2021 andJanuary 2022, in the framework of Strateole-2 project, three BeCOOL microlidars have been flownonboard super-pressure balloons in the lower tropical stratosphere (~20 km). Case studies ofcollocated observations with CALIOP, along with statistical comparisons, highlight the very goodagreement between the two lidars and the enhanced sensitivity of BeCOOL to ultra thin clouds. Thishigher sensitivity is achieved thanks to the low speed of the balloons and the small distance to theobserved clouds, which allow to integrate the observations over a longer time. BeCOOL’sobservations reveal the structure and the significant coverage of optically ultra thin clouds undetectedfrom space

Extensive coverage of ultrathin tropical tropopauselayer cirrus clouds revealed by balloon-bornelidar observations

International audienceTropical tropopause layer (TTL) clouds have a significant impact on the Earth’s radiative budgetand regulate the amount of water vapor entering the stratosphere. Estimating the total coverage of tropical cir-rus clouds is challenging, since the range of their optical depth spans several orders of magnitude, from thickopaque cirrus detrained from convection to sub-visible clouds just below the stratosphere. During the Strateole-2observation campaign, three microlidars were flown on board stratospheric superpressure balloons from October2021 to late January 2022, slowly drifting only a few kilometers above the TTL. These measurements have un-precedented sensitivity to thin cirrus and provide a fine-scale description of cloudy structures both in time and inspace. Case studies of collocated observations with the spaceborne Cloud-Aerosol Lidar with Orthogonal Polar-ization (CALIOP) show very good agreement between the instruments and highlight the Balloon-borne Cirrusand convective overshOOt Lidar’s (BeCOOL) higher detection sensitivity. Indeed, the microlidar is able to de-tect optically very thin clouds (optical depth τ < 2 × 10−3) that are undetected by CALIOP. Statistics on cloudoccurrence show that TTL cirrus appear in about 50 % of the microlidar profiles and have a mean geometricaldepth of 1 km. Ultrathin TTL cirrus (τ < 2 × 10−3) have a significant coverage (23 % of the profiles), and theirmean geometrical depth is 0.5 km

Characterisation and surface radiative impact of Arctic low clouds from the IAOOS field experiment

International audienceThe Ice, Atmosphere, Arctic Ocean Observing System (IAOOS) field experiment took place from 2014 to 2019. Over this period, more than 20 instrumented buoys were deployed at the North Pole. Once locked into the ice, the buoys drifted for periods of a month to more than a year. Some of these buoys were equipped with 808 nm wavelength lidars which acquired a total of 1805 profiles over the course of the campaign. This IAOOS lidar dataset is exploited to establish a novel statistic of cloud cover and of the geometrical and optical characteristics of the lowest cloud layer. Cloud frequency is globally at 75%, 5 and above 85% from May to October. Single layers are thickest in October/November and thinnest in the summer. Meanwhile, their optical depth is maximum in October. On the whole, the cloud cover is very low, with the great majority of first layer bases beneath 120 m. In the shoulder seasons, surface temperatures are markedly warmer when the IAOOS profile contains at least one low cloud than when it does not. This temperature difference is statistically insignificant in the summer months. Indeed, summer clouds have a shortwave cooling effect which can reach −60 W m −2 and balance out their longwave warming 10 effect

Study of Aerosol Properties North of Svalbard from Autumn 2014 to Spring 2015 Using Combined V4 CALIOP Data, Ice-based IAOOS Lidar Observations and Trajectory Analyses.

International audienceProperties of aerosol have been analyzed at the regional scale over the high Arctic north of Svalbard between October 2014 and June 2015 using the new version 4 (V4) CALIPSO (Cloud and Aerosol Lidar and Infrared Pathfinder Satellite Observations) data. Systematic trajectories have been performed for all identified aerosol layers. Results have been compared with lidar observations from IAOOS (Ice-Atmosphere-Ocean Observing System) drifting platforms. Space‒borne observations indicate a maximum in aerosol occurrence at the end of winter attributed to low‒level (0-2 km) and mid‒tropospheric (2-5 km) particles mostly identified by the CALIPSO Lidar CALIOP (Cloud and Aerosol Lidar with Orthogonal Polarization) as highly depolarizing. Another maximum was observed in October‒December due to clean marine particles below 2 km as well as smoke and depolarizing particles above. The 532 nm aerosol extinction was a factor 2 lower compared to average values previously reported using CALIOP V3 dataset. Aerosols originated mostly in Russia/Europe at all altitudes, and also North America above 2 km. CALIOP aerosol subtype classification is discussed from case studies allowing to identify aerosols close to IAOOS platforms and follow their transport. Adjustments of the aerosol classification involving arctic diamond dust are proposed. Cloudy parts of trajectories are identified for further aerosol-cloud interaction analyses