Abstract
Abstract. A tethered-balloon system (TBS) has been developed and is being operated by Sandia National Laboratories (SNL) on behalf of the U.S. Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) User Facility in order to collect in situ atmospheric measurements within mixed-phase Arctic clouds. Periodic tethered-balloon flights have been conducted since 2015 within restricted airspace at ARM's Advanced Mobile Facility 3 (AMF3) in Oliktok Point, Alaska, as part of the AALCO (Aerial Assessment of Liquid in Clouds at Oliktok), ERASMUS (Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems), and POPEYE (Profiling at Oliktok Point to Enhance YOPP Experiments) field campaigns. The tethered-balloon system uses helium-filled 34 m3 helikites and 79 and 104 m3 aerostats to suspend instrumentation that is used to measure aerosol particle size distributions, temperature, horizontal wind, pressure, relative humidity, turbulence, and cloud particle properties and to calibrate ground-based remote sensing instruments. Supercooled liquid water content (SLWC) sondes using the vibrating-wire principle, developed by Anasphere Inc., were operated at Oliktok Point at multiple altitudes on the TBS within mixed-phase clouds for over 200 h. Sonde-collected SLWC data were compared with liquid water content derived from a microwave radiometer, Ka-band ARM zenith radar, and ceilometer at the AMF3, as well as liquid water content derived from AMF3 radiosonde flights. The in situ data collected by the Anasphere sensors were also compared with data collected simultaneously by an alternative SLWC sensor developed at the University of Reading, UK; both vibrating-wire instruments were typically observed to shed their ice quickly upon exiting the cloud or reaching maximum ice loading. Temperature sensing measurements distributed with fiber optic tethered balloons were also compared with AMF3 radiosonde temperature measurements. Combined, the results indicate that TBS-distributed temperature sensing and supercooled liquid water measurements are in reasonably good agreement with remote sensing and radiosonde-based measurements of both properties. From these measurements and sensor evaluations, tethered-balloon flights are shown to offer an effective method of collecting data to inform and constrain numerical models, calibrate and validate remote sensing instruments, and characterize the flight environment of unmanned aircraft, circumventing the difficulties of in-cloud unmanned aircraft flights such as limited flight time and in-flight icing.
Highlights
Understanding microphysical properties of persistent Arctic mixed-phase stratiform clouds is a critical factor in accurately representing the radiative energy balance in climate models (e.g., Morrison et al, 2012; Jouan et al, 2012; Shupe et al, 2013)
The maximum supercooled liquid water content (SLWC) observed by the highest-altitude tethered-balloon system (TBS) SLWC sonde between 23:26 and 23:32 UTC was 0.14 g m−3, while the maximum SLWC observed by the lower-altitude sonde was 0.05 g m−3
The supercooled liquid water contents calculated by RAOB from the free-radiosonde flight at the altitudes of two vibrating-wire Anasphere SLWC sondes on the tethered balloon were both 0.14 g m−3
Summary
Understanding microphysical properties of persistent Arctic mixed-phase stratiform clouds is a critical factor in accurately representing the radiative energy balance in climate models (e.g., Morrison et al, 2012; Jouan et al, 2012; Shupe et al, 2013). In the past decade vibrating-wire-based supercooled liquid water content radiosonde flights have been conducted concurrently with a collocated microwave radiometer, ceilometer, and Kaband radar to validate the sonde-measured vertical profile of supercooled liquid water (e.g., Serke et al, 2014; King et al, 2016). Advancing this approach, supercooled liquid water content sondes from two manufacturers were operated on the ARM TBS at multiple altitudes within Arctic clouds simultaneously for over 200 h, in order to collect comparatively higher spatially and temporally resolved data than were available from radiosonde balloon flights. An overview of the tethered-balloon system is provided, followed by descriptions of the SLWC sondes and DTS system, subsequent flight results from Oliktok Point, and a discussion of future operational plans
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