Low-level stratus mask from Polarstern during MOSAiC

Daily files of low-level stratus (LLS) for the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition (Shupe et al., 2022). The LLS was detected following Griesche et al. (2020) based on near-range data from PollyXT (Engelmann et al., 2016) to extend the Cloudnet cloud properties derived for MOSAiC (Engelmann et al. 2023; doi:10.60656/59216bca3a304156) into the bild zone of the cloud radar (i.e. below 180 m altitude). The applied method was updated to the use of the attenuated backscatter (att bsc) instead of the signal-to-noise ratio to reduce the influence of changes in the system constant on the LLS detection. An LLS was identified when the att bsc exceeded a threshold of 4e-06 sr-1 m-1 below 180 m. Data issues caused by external drivers are documented in a separate issue tracking file (Griesche & Seifert, 2023; doi:10.5281/zenodo.7310858). Flagged data must be handled with care and should be excluded from statistical analyses. Issues tracking flags are identified by tethered balloon operation periods and experienced-eye observations of MOSAiC staff.