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Climate 2016, 4(4), 48; doi:10.3390/cli4040048

Cloud Fraction of Liquid Water Clouds above Switzerland over the Last 12 Years

1
Institute of Applied Physics, University of Bern, Bern 3012, Switzerland
2
Oeschger Centre for Climate Change Research, University of Bern, Bern 3012, Switzerland
3
School of Ocean and Earth Science Technology, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Yang Zhang
Received: 6 July 2016 / Revised: 9 September 2016 / Accepted: 18 September 2016 / Published: 22 September 2016
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Abstract

Cloud fraction (CF) plays a crucial role in the Earth’s radiative energy budget and thus in the climate. Reliable long-term measurements of CF are rare. The ground-based TROpospheric WAter RAdiometer (TROWARA) at Bern, Switzerland continuously measures integrated liquid water and infrared brightness temperature with a time resolution of 6–11 s since 2004. The view direction of TROWARA is constant (zenith angle 50 ), and all radiometer channels see the same volume of the atmosphere. TROWARA is sensitive to liquid water clouds while the microwave signal of ice clouds is negligible. By means of the measurement data we derived CF of thin liquid water clouds (1); thick supercooled liquid water clouds (2); thick warm liquid water clouds (3) and all liquid water clouds (4). The article presents the time series and seasonal climatologies of these four classes of CF. CF of thick supercooled liquid water clouds is larger than 15% from November to March. A significant negative trend of 0 . 29 % ± 0 . 10 %/yr is found for CF of thin liquid water clouds. No trends are found for the other classes (2, 3, 4) since their strong natural variability impedes a significant trend. However, CF of warm liquid water clouds increased by about + 0 . 51 % ± 0 . 27 %/yr from 2004 to 2015. Finally, we performed a Mann-Kendall analysis of seasonal trends which gave several significant trends in the classes 1, 2 and 3. View Full-Text
Keywords: cloud fraction; ground-based microwave radiometry; integrated liquid water; long-term monitoring; trend analysis; climatology; liquid water cloud; supercooled liquid water cloud cloud fraction; ground-based microwave radiometry; integrated liquid water; long-term monitoring; trend analysis; climatology; liquid water cloud; supercooled liquid water cloud
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Hocke, K.; Navas Guzmán, F.; Cossu, F.; Mätzler, C. Cloud Fraction of Liquid Water Clouds above Switzerland over the Last 12 Years. Climate 2016, 4, 48.

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