Cloud cover estimation using different methods exploiting solar radiation measurements at various sites in Antarctica
Authors: Frangipani Claudia , Cordero Raul , Gulisano Adriana M. , Lupi Angelo , Ochoa Hector A. , Rowe Penny , Vitale Vito 
Published: February 2023

Observations at the surface in Antarctica have always been challenging, but cloud observations are particularly scarce due to different factors, among which the polar night and lack of instruments and observers. One way to obtain information on cloud cover, and fill the gap, is through broadband radiation measurements thanks to methods based on the effect that clouds have on solar and terrestrial radiation. In this work three different algorithms have been studied and implemented: i) Long et al.[1] method, which exploits global and diffuse shortwave radiation components; ii) Kasten and Czeplak[2], based on global shortwave component alone; iii) APCADA[3] algorithm, which requires longwave downward radiation measurements and meteorological variables data, and is specially chosen as it yields results also at (polar) night. Different methods were selected to adapt to the data available at each site and to cross-check the results. The algorithms are tested on common-time data sets from three different stations: Marambio (64&#176;14&#8217;50&#8217;&#8217;S - 56&#176;37&#8217;39&#8217;&#8217;W), where upward and downward components for shortwave and longwave radiation are measured along with diffuse shortwave radiation; Professor Julio Escudero (62&#176;12&#8217;57&#8217;&#8217;S - 58&#176;57&#8217;35&#8217;&#8217;W) where downward shortwave and longwave radiation data are available; and Concordia (75&#176;05&#8217;59&#8217;&#8217;S - 123&#176;19&#8217;57&#8217;&#8217;E) where data on all components of both solar and terrestrial radiation are collected. Before any computation, data quality control is executed following tests[4] recommended by the Baseline Surface Radiation Network[5], showing good quality for all three data sets. Sky conditions depend on the location of the stations: Marambio and Escudero are coastal sites located on islands on opposite sides of the Antarctic Peninsula where cloudy skies are expected to occur, while Concordia is situated on the East Antarctic Plateau where the sky should be clearer. Such expectations are confirmed by the preliminary results obtained from the tested algorithms, indicating that clouds occur very often with almost scarce clear sky periods at the coastal stations.&#160;&#160;Bibliography[1] Long C. N., Ackerman T. P., Gaustad K. L., and Cole J. N. S. (2006): &#8220;Estimation of fractional sky cover from broadband shortwave radiometer measurements&#8221;, J. Geophys. Res. 111, doi: 10.1029/2005JD006475[2] D&#252;rr B. and Philipona R. (2004): &#8220;Automatic cloud amount detection by surface longwave downward radiation measurements&#8221;, J. Geophys. Res. 109, doi: 10.1029/2003JD004182[3] Kasten F., Czeplak G. (1980): &#8220;Solar and terrestrial radiation dependent on the amount and type of cloud&#8221;, Solar Energy 24, doi: 10.1016/0038-092X(80)90391-6[4] Long and Shi (2008): &#8220;An automated quality assessment and control algorithm for surface radiation measurements&#8221;, Open Atm. Science J. 2, doi: 10.2174/1874282300802010023[5] https://bsrn.awi.de/