Continuous temperature profiles within the tropical tropopause layer with fiber optic distributed temperature sensing aboard long duration constant altitude balloons in Stratéole 2

A balloon-borne fiber optic distributed temperature sensing instrument named the Fiber-optic Laser Operated Atmospheric Temperature Sensor, or FLOATS, was used to retrieve continuous vertical temperature profiles spanning approximately 1.6 km within the tropical UTLS as part of the Stratéole 2 2021 balloon mission. In one isopycnic flight, flying at 18.5 km over the Indian Ocean and the Maritime continent, FLOATS retrieved nearly 22 days of temperature profiles with a sampling period of less than 10 minutes. The superpressure balloon flight demonstrated the applicability of distributed temperature sensing for ambient atmospheric temperature measurements and for analysis of dynamics within the UTLS. The temperature retrievals show good agreement with on-board reference sensors demonstrating the effectiveness of the in-flight calibration procedures. Comparisons to nearby meteorological soundings and COSMIC-2 temperature profiles were conducted for validation and to survey energy fluxes on the fiber optic cable including solar radiative heating and radiative cooling at night. Temperature perturbations retrieved from the FLOATS profiles are used to investigate small-scale and large-scale dynamics within the tropical tropopause layer.