The data set contains measurements performed by the passive radiometer as part of the Microwave Radar and radiometer for Arctic Clouds (MiRAC; Mech et al., 2019) operated on board the Polar 5 research aircraft during 14 flights of the Airborne measurements of radiative and turbulent FLUXes of energy and momentum in the Arctic boundary layer (AFLUX; Mech et al., 2022) campaign, carried out in spring 2019 northwest of Svalbard (Norway). The measurement campaign is embedded in the Transregional Collaborative Research Centre TR 172 (ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3. The published data set consists of brightness temperature measurements at nadir view with respect to the aircraft's fuselage at six frequencies in the water vapor absorption band at around 183.31 GHz and at two additional channels at 243 and 340 GHz. It should be considered that the brightness temperatures have not been corrected for aircraft attitude. The data set has been quality-checked and is available in NetCDF format for each flight separately. Details on the instrument can be found in Mech et al. (2019) and on the dataset and its usage in Mech et al. (2022).