Balloon-borne lidar observations of cirrus in the tropics

Tropical cirrus clouds have a strong impact on the Earth’s climate, modulating both the radiative budget and the amount of water vapor transported to the stratosphere. They are still challenging to observe : ground-based and airborne observations have a limited coverage, and if space-borne sensors provide invaluable continuous observations at the global scale, they lack sensitivity to optically thin clouds. To tackle this issue and better characterize the tropical cirrus coverage, a new light-weight microlidar, named BeCOOL (Balloon-borne Cirrus and convective overshOOT Lidar), has been designed to fly onboard long duration super-pressure balloons in the lower stratosphere (~20 km), right above the clouds. Three of those have been recently flown during the Strateole-2 project, between October 2021 and January 2022. Comparisons with CALIPSO’s lidar observations highlight the microlidar’s unprecedented sensitivity to very thin cirrus that are below the detection capabilities of space-borne sensors.