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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 distributed 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. 

Profiles of stratospheric aerosol size distributions have been measured using balloon‐bornein situoptical particle counters, from Laramie, Wyoming (41°N) since 1971. In 2019, this measurement record transitioned to the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, Colorado (40°N). The new LASP Optical Particle Counter (LOPC), the fourth generation of instruments used for this record, is smaller and lighter (2 kg) than prior instruments, measures aerosols with diameters ≥0.3–30 μm in up to 450 size bins, with a flow rate of 20 L min⁻¹. The improved size resolution enables the complete measurement of size distributions, and calculation of aerosol extinction without fittinga prioridistribution shapes. The higher flow provides the sensitivity required to measure super‐micron particles in the stratosphere. The LOPC has been validated against prior Wyoming OPCs, through joint flights, laboratory comparisons, and statistical comparisons with the Wyoming record. The agreement between instruments is generally within the measurement uncertainty of ±10%–20% in sizing and ±10% in concentration, and within ±40% for calculated aerosol moments. The record is being continued with balloon soundings every 2 months from Colorado, coordinated with measurements of aerosol extinction from the SAGE III instrument on the International Space Station. Comparisons of aerosol extinction from the remote andin situplatforms have shown good agreement in the stratosphere, particularly for wavelengths <755 nm and altitudes <25 km. For extinction wavelengths ≥1,021 nm and altitudes above 25 km SAGE III/International Space Station extinction has a low bias relative to thein situmeasurements, yet still within the ±40% uncertainty.

 

Abstract. The tropical tropopause layer (TTL; 14–18.5 km) is the gateway formost air entering the stratosphere, and therefore processes within thislayer have an outsized influence in determining global stratospheric ozoneand water vapor concentrations. Despite the importance of this layer thereare few in situ measurements with the necessary detail to resolve the fine-scale processes within this region. Here, we introduce a novel platform forhigh-resolution in situ profiling that lowers and retracts a suspendedinstrument package beneath drifting long-duration balloons in the tropics.During a 100 d circumtropical flight, the instrument collected over a hundred 2 km profiles of temperature, water vapor, and aerosol at 1 m resolution, yielding unprecedented geographic sampling and verticalresolution. The instrument system integrates proven sensors for water vapor,temperature, pressure, and cloud and aerosol particles with an innovativemechanical reeling and control system. A technical evaluation of the systemperformance demonstrated the feasibility of this new measurement platformfor future missions with minor modifications. Six instruments planned fortwo upcoming field campaigns are expected to provide over 4000 profilesthrough the TTL, quadrupling the number of high-resolution aircraft andballoon profiles collected to date. These and future measurements willprovide the necessary resolution to diagnose the importance of competingmechanisms for the transport of water vapor across the TTL. 

The method to derive aerosol size distributions from in situ stratospheric measurements from the University of Wyoming is modified to include an explicit counting efficiency function (CEF) to describe the channel‐dependent instrument counting efficiency. This is motivated by Kovilakam and Deshler's (2015,https://doi.org/10.1002/2015JD023303) discovery of an error in the calibration method applied to the optical particle counter (OPC40) developed in the late 1980s and used from 1991 to 2012. The method can be applied to other optical aerosol instruments for which counting efficiencies have been measured. The CEF employed is the integral of the Gaussian distribution representing the instrument response at any one aerosol channel, the aerosol counting efficiency. Results using the CEF are compared to previous derivations of aerosol size distributions (Deshler et al., 2003,https://doi.org/10.1029/2002JD002514) applied to the measurements before and after Kovilakam and Deshler's correction of number concentration for the OPC40 calibration error. The CEF method is found, without any tuning parameter, to reproduce or improve upon the Kovilakam and Deshler's results, thus accounting for the calibration error without any external comparisons other than the laboratory determined counting efficiency at each aerosol channel. Moments of the new aerosol size distributions compare well with aerosol extinctions measured by Stratospheric Aerosol and Gas Experiment II and Halogen Occultation Experiment in the volcanic period 1991–1996, generally within ±40%, the precision of OPC40 moments, and in the nonvolcanic period after 1996, generally within ±20%. Stratospheric Aerosol and Gas Experiment II and Halogen Occultation Experiment estimates of aerosol surface area are generally in agreement with those derived using the new CEF method.