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Abstract. A novel fiber-optic distributed temperature sensing instrument, the Fiber-optic Laser Operated Atmospheric Temperature Sensor (FLOATS), was developed for continuous in situ profiling of the atmosphere up to 2 km below constant-altitude scientific balloons. The temperature-sensingsystem uses a suspended fiber-optic cable and temperature-dependent scattering of pulsed laser light in the Raman regime to retrieve continuous3 m vertical-resolution profiles at a minimum sampling period of 20 s.FLOATS was designed for operation aboard drifting super-pressure balloons inthe tropical tropopause layer at altitudes around 18 km as part of theStratéole 2 campaign. A short test flight of the system was conductedfrom Laramie, Wyoming, in January 2021 to check the optical, electrical, andmechanical systems at altitude and to validate a four-reference temperaturecalibration procedure with a fiber-optic deployment length of 1170 m. During the 4 h flight aboard a vented balloon, FLOATS retrieved temperatureprofiles during ascent and while at a float altitude of about 19 km. TheFLOATS retrievals provided differences of less than 1.0 ∘Ccompared to a commercial radiosonde aboard the flight payload during ascent.At float altitude, a comparison of optical length and GPS position at thebottom of the fiber-optic revealed little to no curvature in the fiber-opticcable, suggesting that the position of any distributed temperaturemeasurement can be effectively modeled. Comparisons of the distributedmore »temperature retrievals to the reference temperature sensors show strongagreement with root-mean-square-error values less than 0.4 ∘C. Theinstrument also demonstrated good agreement with nearby meteorologicalobservations and COSMIC-2 satellite profiles. Observations of temperatureand wind perturbations compared to the nearby radiosounding profiles provide evidence of inertial gravity wave activity during the test flight. Spectral analysis of the observed temperature perturbations shows that FLOATS is an effective and pioneering tool for the investigation of small-scale gravity waves in the upper troposphere and lower stratosphere.« less

Abstract. Current climate models have difficulty representing realistic wave–mean flow interactions, partly because the contribution from waves with fine vertical scales is poorly known. There are few direct observations of these waves, and most models have difficulty resolving them. This observational challenge cannot be addressed by satellite or sparse ground-based methods. The Strateole-2 long-duration stratospheric superpressure balloons that float with the horizontal wind on constant-density surfaces provide a unique platform for wave observations across a broad range of spatial and temporal scales. For the first time, balloon-borne Global Navigation Satellite System (GNSS) radio occultation (RO) is used to provide high-vertical-resolution equatorial wave observations. By tracking navigation signal refractive delays from GPS satellites near the horizon, 40–50 temperature profiles were retrieved daily, from balloon flight altitude (∼20 km) down to 6–8 km altitude, forming an orthogonal pattern of observations over a broad area (±400–500 km) surrounding the flight track. The refractivity profiles show an excellent agreement of better than 0.2 % with co-located radiosonde, spaceborne COSMIC-2 RO, and reanalysis products. The 200–500 m vertical resolution and the spatial and temporal continuity of sampling make it possible to extract properties of Kelvin waves and gravity waves with vertical wavelengths as short as 2–3 km. The results illustrate themore »difference in the Kelvin wave period (20 vs. 16 d) in the Lagrangian versus ground-fixed reference and as much as a 20 % difference in amplitude compared to COSMIC-2, both of which impact estimates of momentum flux. A small dataset from the extra Galileo, GLONASS, and BeiDou constellations demonstrates the feasibility of nearly doubling the sampling density in planned follow-on campaigns when data with full equatorial coverage will contribute to a better estimate of wave forcing on the quasi-biennial oscillation (QBO) and improved QBO representation in models.« less

In the Stratéole 2 program, set to launch in November 2018, instruments will ride balloons into the stratosphere and circle the world, observing properties of the air and winds in fine detail.