Trends in surface radiation and cloud radiative effect at four Swiss sites for the 1996–2015 period

• Published in: Atmospheric chemistry and physics Vol. 19; no. 20; pp. 13227 - 13241
• Main Authors: Nyeki, Stephan, Wacker, Stefan, Aebi, Christine, Gröbner, Julian, Martucci, Giovanni, Vuilleumier, Laurent
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 25.10.2019; Copernicus Publications
• Subjects: Cameras; Cloud properties; Clouds; Confidence intervals; Empirical analysis; Humidity; Long wave radiation; Mathematical analysis; Meteorological parameters; Radiation; Short wave radiation; Sky; Specific humidity; Temperature; Trends; Water vapor; Water vapour; Switzerland
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-19-13227-2019

The trends of meteorological parameters and surface downward shortwave radiation (DSR) and downward longwave radiation (DLR) were analysed at four stations (between 370 and 3580 m a.s.l.) in Switzerland for the 1996–2015 period. Ground temperature, specific humidity, and atmospheric integrated water vapour (IWV) trends were positive during all-sky and cloud-free conditions. All-sky DSR and DLR trends were in the ranges of 0.6–4.3 W m−2 decade−1 and 0.9–4.3 W m−2 decade−1, respectively, while corresponding cloud-free trends were −2.9–3.3 W m−2 decade−1 and 2.9–5.4 W m−2 decade−1. Most trends were significant at the 90 % and 95 % confidence levels. The cloud radiative effect (CRE) was determined using radiative-transfer calculations for cloud-free DSR and an empirical scheme for cloud-free DLR. The CRE decreased in magnitude by 0.9–3.1 W m−2 decade−1 (only one trend significant at 90 % confidence level), which implies a change in macrophysical and/or microphysical cloud properties. Between 10 % and 70 % of the increase in DLR is explained by factors other than ground temperature and IWV. A more detailed, long-term quantification of cloud changes is crucial and will be possible in the future, as cloud cameras have been measuring reliably at two of the four stations since 2013.