The first flights of the Strateole-2 technology demonstration campaign: Observing the global equatorial tropopause with long-duration balloons

Abstract:

Strateole-2 is an international initiative aimed at advancing knowledge of the global tropical tropopause. The originality of the project stems from the use of superpressure balloons (SPB) that fly for several months at altitudes of 18-20 km, sampling a stratospheric air mass directly and continuously, in a way that cannot be achieved with any other land-based or satellite observing system. SPBs are advected by the wind on constant-density surfaces, and therefore behave as quasi-Lagrangian tracers. A preparatory campaign was held beginning in November 2019. Eight SPBs were launched from Mahé, Seychelles Islands, and flew until late February 2020, achieving a mean flight duration of nearly 3 months in the tropics (85 days). Several balloons achieved more than one full circumnavigation of the Earth. Five different instrument configurations carried by the balloons provided information on the physics, dynamics, particle counts, and greenhouse gas composition of the sampled air parcels. Some instruments also sampled the atmospheric profile below the balloons, such as the Radio OCcultation instrument (ROC2), which provided more than 50 profiles per day of the upper troposphere / lower stratosphere, and the RaCHUTS reel-down in-situ sensor that sampled the tropical tropopause layer. Real-time in-situ measurements were assimilated by Numerical Weather Prediction centers. Preliminary results from several of the instruments will be described. The same instruments will be flown during two forthcoming campaigns in late 2021 and late 2024, with 20 balloons each, to further investigate wave generation by convection, wave driving of the QBO, and transport at the tropical tropopause. Observations will also contribute to the validation of recent spaceborne wind-lidar observations provided by the Aeolus mission.