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Disputation: Britta Schäfer

Doctoral candidate Britta Schäfer at the Department of Geosciences, Faculty of Mathematics and Natural Sciences, is defending the thesis Of ice crystals, clouds and climate: Measuring and modeling cold clouds in the Arctic for the degree of Philosophiae Doctor.

Britta Schäfer. Photo: Private

Britta Schäfer. Photo: Private

The PhD defence and trial lecture will be held in Auditorium 1 in The Geology Building. In some cases, it will be possible to attend the trial lecture and dissertation digitally, in that case a link to Zoom will be posted.

Trial lecture

Tuesday 4 June, 10:15-11:00, Aud 1, The Geology Building: 

Polar amplification of global warming

Conferral summary (in Norwegian)

Skyer i Arktis består ofte av en blanding av underkjølt flytende vann (ved temperaturer under frysepunktet) og is, og forholdet mellom disse to har stor betydning for skyenes effekt på stråling og klima. I avhandlingen er det brukt observasjoner til å bedre karakterisere forekomst og egenskaper til arktiske skyer, og modellregninger til å bedre forstå de fysiske prosessene i skyene. I doktorgradsarbeidet er det også sett på mulige endringer i arktiske skyer i et varmere klima.

Main research findings

Popular scientific article about Schäfer’s dissertation:

Of ice crystals, clouds and climate: Measuring and modeling cold clouds in the Arctic

Clouds are important elements in the atmosphere and the whole climate system as they transport water and impact incoming and outgoing radiation. They may consist of liquid water, ice or a mixture of both. Among other factors the relation between supercooled liquid water and ice in mixed-phase clouds is governing how much longwave radiation and thereby heat a cloud traps between itself and the surface. These effects are not only relevant in the Arctic, but especially important there, as shortwave radiation is absent from the Arctic during large parts of the year. 

The first part of this doctoral thesis uses both long-term lidar measurements and shorter-term intensive in-situ observations to characterize cold clouds in the Norwegian Arctic. The second part aims to better represent Arctic mixed-phase clouds in a regional weather model. This is achieved by using observationally-constrained aerosol concentrations and adding processes for so-called secondary ice production, i.e. mechanisms that create new ice particles based on existing ice. Finally, the optimized model is used to study how Arctic mixed-phase clouds may change in a warmer climate.

Photo: Illustration photo of clouds over Andenes, Northern Norway. The sketch in the top left corner is a conceptual draft of a mixed-phase cloud and how it affects outgoing longwave radiation. The figure in the lower right corner shows improved model simulations of the number of ice particles in a mixed-phase cloud (dotted line) in comparison with observations (boxes), an intermediate simulation (dashed line) and the default model (solid line). Figure, sketch and photo: Britta Schäfer.
Arctic clouds over Andenes in Nordland, Northern Norway. The top left sketch is a conceptual draft of a mixed-phase cloud and how it affects outgoing longwave radiation. The figure to the right  shows improved model simulations of the number of ice particles in a mixed-phase cloud (dotted line) in comparison with observations (boxes), an intermediate simulation (dashed line) and the default model (solid line). See larger version here. Illustration/figures: Britta Schäfer.

Photo and other information:

Press photo: Britta Schäfer, portrait; 1000px. Photo: Private

Other photo material: Figure with description and credit as specified in the article above, size 2500px.

Published May 21, 2024 3:31 PM - Last modified May 21, 2024 3:31 PM