Cloud cover estimation at various sites in Antarctica using different methods based on broadband radiation measurements

Surface observations in Antarctica have always been challenging but cloud observations are particularly scarce due to the lack of observers and instruments and the strict limitation caused by the polar night. This work aims at testing and finding methods that can fill the gap of information on cloud cover, based on solar or terrestrial broadband radiation measurements. In particular, the results from Long et al.[1] method, exploiting solar radiation measurements, and Dürr and Philipona[2] APCADA algorithm and Town et al.[3] methods, both based on terrestrial radiation measurements, will be shown. The methods are chosen to make use of shortwave and longwave radiation components, specially the latter because it can yield information throughout the year and not only during months of daylight, as methods based on shortwave radiation do. Studied data sets are from different coastal sites: Marambio (64°14’50’’S - 56°37’39’’W), Professor Julio Escudero (62°12’57’’S - 58°57’35’’W) and Jang Bogo (74°37’38’’S - 164°14’16’’E). Another analysed data set comprises measurements taken at DomeC (75°05’59’’S – 123°19’57’’E). Since stations can be equipped with different instruments that could record only some of the broadband radiation components, investigating different methods allows to adapt to the actually available data. It also means that is possible to cross-check results when more than one method can be used, like in the case of Marambio. Before data sets are used as input, they undergo quality check controls[4] as recommended by the Baseline Surface Radiation Network[5], when applicable. Preliminary results show that Marambio and Escudero stations thought to be similar, for their latitude and close distance, actually differ from one another when it comes to frequency of occurrence of clear and cloudy sky conditions.

Bibliography

[1] Long et al. (2006): “Estimation of fractional sky cover from broadband shortwave radiometer measurements”, J. Geophys. Res. 111, doi: 10.1029/2005JD006475
[2] Dürr and Philipona (2004): “Automatic cloud amount detection by surface longwave downward radiation measurements”, J. Geophys. Res. 109, doi: 10.1029/2003JD0041823
[3] Town et al. (2007): “Cloud Cover over the South Pole from Visual Observations, Satellite Retrievals, and Surface-Based Infrared Radiation Measurements”, Journal of Climate 20, doi: 10.1175/JCLI4005.1
[4] Long and Shi (2008): “An automated quality assessment and control algorithm for surface radiation measurements”, Open Atm. Science J. 2, doi: 10.2174/1874282300802010023
[5] https://bsrn.awi.de/