Abstract: In this project we made fundamental measurements of cloud optical and microphysical properties at Ross Island, Antarctica, using a versatile shortwave spectroradiometer (Panalytical, Inc.) acquired for atmospheric field research by the Scripps Institution of Oceanography (SIO). This instrument measures downwelling spectral irradiance at the Earth surface in the wavelength interval 350-2200 nm. From this data set one can retrieve properties of coastal Antarctic stratiform clouds including optical depth, thermodynamic phase, liquid water droplet effective radius, and ice cloud effective particle size. The instrument was installed at Arrival Heights, and measurements were made from 10 October 2012 to 4 February 2013. Spectral data recorded in one-minute averages, with some gaps for instrument maintenance and data backup, and some occasional down time when the site was inaccessible. Active satellite remote sensing data (CloudSat and CALIPSO) were used for validation and interpretation of the spectroradiometer retrievals (Scott and Lubin 2014). <br><br>There are two reasons why this measurement program remains timely. One straightforward reason involves the location of McMurdo Station, which is the US Antarctic Programs air transport entry point to the continent. Improvements in our knowledge of atmospheric physics in this region can eventually lead to improvements in numerical weather forecasting relevant to aviation. A second reason involves the recent advances in cloud microphysics for global climate model simulation. Mixed-phase cloud parameterizations have become very sophisticated, requiring validation with each new improvement. Traditional observational test cases - from the Arctic or mid-latitude storm systems - are often quite complex. A coastal Antarctic site at very high latitudes can provide more straightforward cases for testing current microphysical parameterizations. Over Ross Island aerosol and cloud nucleation sources are essentially all natural and oceanic, and cloud geometry is simple, while at the same time there is abundant supercooled cloud liquid water. <br><br>Ancillary meteorological data from the McMurdo Weather Office are also included here for help in interpreting the spectroradiometer data, including rawinsonde profiles, surface weather observations from the active ice runway, and automated FMQ19 surface weather measurements from Williams Field and Pegasus runway. For interpretation of clear sky or nearly cloud-free irradiance spectra (i.e., when a large fraction of the irradiance is directional from the Sun and not diffused by clouds), we recommend consulting Meywerk and Ramanathan (1999) for information about the Panalytical instruments cosine response.