The tethered balloon system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) was operated during MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) leg 4 in July 2020. The balloon was started from an ice floe close to RV Polarstern between 29 June 2020 and 27 July 2020. BELUGA consists of a 90m3 helium-filled balloon with modular instrumentation: An ultrasonic anemometer package, a broadband radiation package with upward and downward-looking pyranometers and pyrgeometers, and an aerosol package. Lonardi et al. (in preparation) give an overview of the BELUGA operation during MOSAiC leg 4. The data processing routines are described in Pilz et al. (in preparation). The present data set covers the turbulence measurements of the ultrasonic anemometer recorded on eight days between 10 and 26 July 2020.