Evaluation of ARM tethered-balloon system instrumentation for supercooled liquid water and distributed temperature sensing in mixed-phase Arctic clouds

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. Sondecollected 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 TBSdistributed 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 inflight icing.

Data collected with CTEMPs DTS available upon request from [e-mail].

由桑迪亚国家实验室（Sandia National Laboratories）代表美国能源部（U.S. Department of Energy）大气辐射测量（Atmospheric Radiation Measurement，ARM）用户设施开发并运行的系留气球系统（Tethered-Balloon System，TBS），旨在收集混合相北极云层中的现场大气测量数据。自2015年起，在阿拉斯加奥利科特克角（Oliktok Point）ARM先进移动设施3号（Advanced Mobile Facility 3，AMF3）的受限空域内，已定期进行系留气球飞行，作为AALCO（奥利科特克云中液态评估，Aerial Assessment of Liquid in Clouds at Oliktok）、ERASMUS（使用无人机系统评估常规大气探测测量，Evaluation of Routine Atmospheric Sounding Measurements using Unmanned Systems）和POPEYE（奥利科特克角剖面测量以增强YOPP实验，Profiling at Oliktok Point to Enhance YOPP Experiments）野外考察活动的一部分。该系留气球系统采用充氦34立方米的风筝和79立方米及104立方米的浮标，以悬挂用于测量气溶胶粒子尺寸分布、温度、水平风速、气压、相对湿度、湍流以及云粒子特性的仪器，并用于校准地面遥感仪器。采用振动丝原理（由Anasphere Inc.开发）的超冷却液态水含量（Supercooled Liquid Water Content，SLWC）探针，在TBS中混合相云层内的多个高度运行超过200小时。探针收集的SLWC数据与AMF3的微波辐射计、Ka波段ARM天顶雷达和能见度仪计算得到的液态水含量、以及AMF3无线电探空飞行得到的液态水含量进行了比较。Anasphere传感器收集的现场数据还与英国雷丁大学（University of Reading）开发的一种替代SLWC传感器同时收集的数据进行了比较；两种振动丝仪器通常在离开云层或达到最大冰载荷时迅速释放冰。光纤系留气球上的温度传感测量结果也与AMF3无线电探空温度测量结果进行了比较。综合结果表明，TBS分布的温度传感和超冷却液态水测量结果与遥感以及基于无线电探空的这两种特性的测量结果在合理范围内一致。从这些测量和传感器评估中可以看出，系留气球飞行是一种有效的数据收集方法，可用来为数值模型提供信息和约束，校准和验证遥感仪器，以及表征无人机飞行环境，从而克服了云中无人机飞行所面临的困难，如飞行时间有限和飞行中结冰等问题。使用CTEMPs DTS收集的数据可应请求从[e-mail]获取。