Nomokonova, Tatiana (2020). Arctic cloud properties derived from ground-based sensor synergy at Ny-Ålesund. PhD thesis, Universität zu Köln.

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Contemporary climate models show that clouds are one of the key components in the climate of the Arctic region experiencing rapid surface warming. Modeling of the cloud impact on the Arctic amplification is still uncertain not only because cloud life cycle is defined by large number of processes, but also because the clouds are closely related to other components of the Arctic climate, such as atmospheric water vapor, ocean, sea ice, and long-range air transport. In order to better understand the role of clouds in the Arctic, in June 2016 the French-German Arctic research station situated in Ny-Ålesund, Norway was complemented with a W-band cloud radar within the Transregional Collaborative Research Center (TRR 172) "Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC)³". This observation site became one of a few Arctic sites capable of state-of-the-art cloud profiling with high temporal and spatial resolution. This thesis summarizes the cloud macro and microphysical properties of clouds based on the first two and a half years of cloud measurements at Ny-Ålesund. The total occurrence of clouds was found to be ~81%. The most predominant type of clouds is multi-layer clouds with the frequency of occurrence of 44.8%. Single-layer clouds occur 36% of the time. The most common type of single-layer clouds is mixed-phase with a frequency of occurrence of 20.6%. The total occurrences of single-layer ice and liquid clouds are 9% and 6.4%, respectively. A comparison of cloud occurrence at Ny-Ålesund with a numerical weather prediction model revealed an overestimation in the occurrence of single layer ice clouds and underestimation of the occurrence of mixed-phase clouds. The cloud properties were further related to occurrence of anomalous atmospheric conditions often caused by transport of relatively warm and moist air from the North Atlantic and circulation of dry and cold air in the Arctic region. Dry anomalies are related to about 30% less cloud occurrence with respect to normal conditions. In contrast, during moist conditions the cloud occurrence typically reaches 90-99%. Excess and shortage in water vapor typically increases and decreases the amount of condensed water in cloud, respectively. The changes in cloud properties during moist and dry anomalies in turn affect the surface cloud radiative effect (CRE). In winter, spring, and autumn the net surface CRE is dominated by the longwave (LW) CRE and, therefore, during these seasons dry and moist conditions are related to lower and higher cloud related surface warming in Ny-Ålesund, respectively. In summer, shortwave CRE becomes dominant and moist conditions cause stronger surface cooling relative to normal cases, while dry conditions tend to reduce the cloud related surface cooling.Moist anomalies show significant positive trends varying for different seasons from 2.8 to 6.4%/decade. In contrast, the occurrence of dry anomalies has been declining at rates from -12.9 to -4%/decade. A novel technique for the estimation of LW CRE developed within this study shows that the long-term trends in the thermodynamic conditions at Ny-Ålesund are related to significant positive trends in longwave CRE of 3.4 and 2.2 W/(m² decade) in winter and autumn, respectively. In summer, a negative trend of -1.8 W/(m² decade) was found, while no significant trends were found for the spring season. The database with cloud profiles obtained within this work can be used for an evaluation of numerical weather prediction models, while radiative cloud properties estimated from reanalysis models can be evaluated with long-term LW CRE retrieved with the developed method.

Item Type: Thesis (PhD thesis)
CreatorsEmailORCIDORCID Put Code
Nomokonova, Tatianatnomokon@uni-koeln.deUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-113774
Date: 2020
Language: English
Faculty: Faculty of Mathematics and Natural Sciences
Divisions: Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects: Earth sciences
Natural sciences and mathematics
Uncontrolled Keywords:
Arctic cloudsEnglish
Ground-based remote sensingEnglish
Cloud radiative effectEnglish
Date of oral exam: 15 May 2020
NameAcademic Title
Löhnert, UlrichProf. Dr.
Neggers, Roel A. J.Prof. Dr.
Funders: German Research Foundation, Transregional Collaborative Research Center (TRR 172)
Projects: (AC)ᶟ
Refereed: Yes


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