In the framework of the Multidisciplinary Observatory for the Study of Arctic Climate (MOSAiC) expedition, the tethered balloon system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) was deployed from a research camp on an ice floe drifting in the Fram Strait in Summer 2020. The BELUGA system consists of a 90 m³ helium-filled balloon with modular instrumentation. The present data set covers the meteorological measurements with an extended radiosonde package on 31 flights with mean altitudes of 1 km between 29 June and 27 July 2020. Lonardi et al. 2022 give an overview of the BELUGA observations during MOSAiC leg 4. A data descriptor by Pilz et al. (in preparation) describe the sensor package and the BELUGA operations in detail.