Preprints
https://doi.org/10.5194/acp-2021-97
https://doi.org/10.5194/acp-2021-97

  23 Mar 2021

23 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

Ice and Mixed-Phase Cloud Statistics on Antarctic Plateau

William Cossich1,, Tiziano Maestri1,, Davide Magurno1,, Michele Martinazzo1, Gianluca Di Natale2, Luca Palchetti2, Giovanni Bianchini2, and Massimo Del Guasta2 William Cossich et al.
  • 1Physics and Astronomy Department, Alma Mater Studiorum - University of Bologna (I)
  • 2Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (I)
  • These authors contributed equally to this work.

Abstract. Statistics on the occurrence of clear skies, ice and mixed-phase clouds over the Concordia station, in the Antarctic Plateau, are provided for multiple time scales and analysed in relation to simultaneous meteorological parameters measured at the surface. Results are obtained by applying a machine learning cloud identification and classification code (named CIC) to 4 years of measurements between 2012–2105 of down-welling high spectral resolution radiances, measured by the Radiation Explorer in the Far Infrared-Prototype for Applications and Development (REFIR-PAD) spectroradiometer. The CIC algorithm is optimized for Antarctic sky conditions (clear sky, ice clouds, and mixed-phase clouds) and results in a total hit rate of almost 0.98, where 1.0 is a perfect score. Scene truth is provided by LiDAR measurements that are concurrent with REFIR-PAD. The CIC approach demonstrates the key role of far infrared spectral measurements for clear/cloud discrimination and for cloud phase classification. Mean annual occurrences are 72.3 %, 24.9 % and 2.7 % for clear sky, ice and mixed-phase clouds respectively, with an inter-annual variability of a few percent. The seasonal occurrence of clear sky shows a minimum in winter (66.8 %) and maxima (75–76 %) during intermediate seasons. In winter the mean surface temperature is about 9 °C colder in clear conditions than when ice clouds are present. Mixed-phase clouds are observed only in the warm season; in summer they amount to more than one third of total observed clouds. Their occurrence is correlated with warmer surface temperatures. In the austral summer, the mean surface air temperature is about 5 °C warmer when clouds are present than in clear sky conditions. This difference is larger during the night than in daylight hours, likely due to increased solar warming. A comparison of monthly mean results with cloud occurrence/fraction derived from gridded (Level-3) satellite products, from both passive and active sensors, emphasizes the difficulty of adequately inferring cloud/clear-sky properties in the Antarctic region and highlights the ability of the CIC/REFIR-PAD synergy to identify multiple cloud conditions and study their variability at different time scales.

William Cossich et al.

Status: open (until 18 May 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-97', Xianglei Huang, 31 Mar 2021 reply
  • RC2: 'Comment on acp-2021-97', Bryan A. Baum, 31 Mar 2021 reply
  • RC3: 'Comment on acp-2021-97', M. G. Mlynczak, 15 Apr 2021 reply

William Cossich et al.

William Cossich et al.

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Short summary
The presence of clouds over Concordia, in the Antarctic Plateau, is investigated. Results are obtained by applying a machine learning algorithm to measurements of the infrared radiation emitted by the atmosphere toward the surface. The clear sky, ice and mixed-phase cloud occurrence at different time scales is studied. A comparison with satellite measurements highlights the limitations and difficulties to observe the Antarctic region from space.
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