Solar radiation over and under sea ice was measured by radiation station 2019R9, an autonomous platform, installed on drifting First-Year-Ice (FYI) in the Arctic Ocean during MOSAiC (Leg 1) 2019/20. The resulting time series describes radiation measurements as a function of place and time between 07 October 2019 and 17 June 2020 in sample intervals of 3 hours. The radiation measurements have been performed with spectral radiometers. All data are given in full spectral resolution interpolated to 1.0 nm, and integrated over the entire wavelength range (broadband, total: 320 to 950 nm). Two sensors, solar irradiance and upward reflected solar irradiance, were mounted on a on a platform about 1 m above the sea ice surface. The third sensor was mounted 0.5 m underneath the sea ice measuring the downward transmitted irradiance. Along with the radiation measurements, this autonomous platform consisted of a 5 m long thermistor chain with sensor spacing of 0.02 m and several other sensor packages, which measured water temperature, pressure and conductivity at hourly intervals. Ecology sensors measured backscatter strength, chlorophyll a and fluorescence of dissolved organic matter at hourly intervals. Oxygen sensors measured relative oxygen air saturation, and water temperature at hourly intervals. In addition, uncompensated and compensated conductivity of water as well as relative snow height was measured at hourly intervals. All times are given in UTC. The data set has been processed and contains quality flags for different kinds for erroneous data. Flag values are the sum of individual error codes. The value of 0 refers to no error. Quality flag, position: The geographic position is flagged +1 if the drift velocity, as derived from the GPS longitude and latitude, exceeds a threshold of 10 deg latitude or 50 deg longitude per time step; +2 if the position exceeds extreme values, such as longitude > 360 deg; +4 if the position is exactly 0.0. Quality flag, sun: If the suns position is close to the horizon, the radiometers measure a very noisy signal. Radiometer measurements and variables which are computed from them are flagged +1 if the sun elevation is below 10 degrees; +2 if the broad band albedo exceeds the threshold 1.05 .

The data set has been processed and contains quality flags for different kinds for erroneous data. Flag values are the sum of individual error codes. The value of 0 refers to no error. Quality flag, position: The geographic position is flagged +1 if the drift velocity, as derived from the GPS longitude and latitude, exceeds a threshold of 10 deg latitude or 50 deg longitude per time step; +2 if the position exceeds extreme values, such as longitude > 360 deg; +4 if the position is exactly 0.0.