Strateole-2: High-resolution observations of the tropical tropopause layer with long-duration balloons
<p>Strateole-2 is a project aimed at studying the coupling between the troposphere and the stratosphere in the deep tropics. The project originality pertains to the use of long-duration ballons, which can fly for several months at 18 or 20 km altitude. The first Strateole-2 campaign took place from November 2019 to February 2020: 8 balloons with various instrumental configurations were released in the lower stratosphere from Seychelles Islands, in the Indian Ocean.<br>This first campaign was primarily devoted to testing all systems (balloons, gondolas, and instruments) developed for the project, and was very successful: the balloons flew for 85 days onaverage over the whole tropical band, and most instruments performed nominally. In-situ meteorological measurements performed every 30-s on each flight provide a unique description of gravity-wave activity in the tropics and its relation to deep convection. The first observations of aerosols and water vapor onboard long-duration balloons were also achieved, which e.g. highlighted the tape recorder signal in the tropical lower stratosphere. Very innovative instruments also premiered during the campaign: RACHuTS, a light reeled payload, for instance performed 50 high-resolution vertical profiles of temperature, aerosols and water vapor down to 2km below the balloon, crossing several times the cold-point tropopause. ROC collected hundreds of temperature profiles down to the middle troposphere through GPS radio-occultations. Last, one balloon also carried a nadir-pointing backscatter lidar, which has described the underlying convection at unprecedented temporal resolution. An overview of the flights and first results will be presented.<br>Two forthcoming balloon campaigns are planned within Strateole-2, in 2021-22 and 2024-25. Each will release 20 balloons.&#160;</p>