Astrid Bragstad Gjelsvik

• Dekhtyareva, Alena; Sodemann, Harald; Carlsen, Tim; Thurnherr, Iris; Johannessen, Aina Marie & Seidl, Andrew [Vis alle 14 forfattere av denne artikkelen] (2026). Spatially distributed measurements of aerosols and stable isotopes in water vapour and precipitation in coastal Northern Norway during the ISLAS2021 campaign. Earth System Science Data. ISSN 1866-3508. 18(4), s. 2573–2607. doi: 10.5194/essd-18-2573-2026. Fulltekst i vitenarkiv Vis sammendrag

  Precipitation from mixed-phase clouds at high-latitudes is difficult to represent correctly in numerical weather prediction models. Paired water vapour and precipitation isotope measurements provide a constraint on the integrated effect of evaporation and condensation processes, but have rarely been collected in a way that allows to use these for model validation and improvement. Here we present a collection of spatially distributed measurements of water isotopes in the different phases at high time resolution during the ISLAS2021 field campaign over the period 15 to 30 March 2021. The main observational site of this campaign was Andenes, Norway (69.3144° N, 16.1194° E). Isotopic measurements were conducted simultaneously at sea level and a mountain observatory, as well as additional coastal sites at distances of 120 km (Tromsø, Norway) and 1100 km (Bergen, Norway), enabling the assessment of spatial representativeness of vapour isotope measurements. Precipitation samples for water isotope analysis were collected on site at sub-event time resolution, and along a transect across the Vesterålen archipelago. These measurements were complemented by a suite of aerosol measurements, including ice-nucleating particles, and additional in situ and remote sensing observations of meteorological variables. During the two weeks of the ISLAS2021 field campaign, frequent alternations between mid-latitude and arctic weather systems were encountered, providing a range of different cases for more detailed process studies. The dataset is available at https://doi.org/10.1594/PANGAEA.984616 (Sodemann et al., 2025), and can serve as a test bed for assessing the spatial representativeness and sampling strategies for water isotope measurements on meteorological time scales. Furthermore, we anticipate our data to be useful in various aspects related to cloud microphysics, for example the quantification of riming processes in convective clouds, the role of ice nucleating particles in marine cold-air outbreaks, and on the condensation efficiency of mid-latitude storms.

• Gjelsvik, Astrid Bragstad; David, Robert Oscar; Carlsen, Tim; Hellmuth, Franziska; Hofer, Stefan & McGraw, Zachary [Vis alle 8 forfattere av denne artikkelen] (2025). Using a region-specific ice-nucleating particle parameterization improves the representation of Arctic clouds in a global climate model. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 25(3), s. 1617–1637. doi: 10.5194/acp-25-1617-2025. Fulltekst i vitenarkiv Vis sammendrag

  Projections of global climate change and Arctic amplification are sensitive to the representation of low-level cloud phase in climate models. Ice-nucleating particles (INPs) are necessary for primary cloud ice formation at temperatures above approximately −38 °C and thus significantly affect cloud phase and cloud radiative effect (CRE). Due to their complex and insufficiently understood variability, INPs constitute an important modelling challenge, especially in remote regions with few observations, such as the Arctic. In this study, INP observations were carried out at Andenes, Norway, in March 2021. These observations were used as a basis for an Arctic-specific and purely temperature-dependent INP parameterization, which was implemented into the Norwegian Earth System Model (NorESM). This implementation results in an annual average increase in cloud liquid water path (CLWP) of 70 % for the Arctic and improves the representation of cloud phase compared to satellite observations. The change in CLWP in boreal autumn and winter is found to likely be the dominant contributor to the annual average increase in net surface CRE of 2 W m−2. This large surface flux increase brings the simulation into better agreement with Arctic ground-based measurements. Despite the fact that the model cannot respond fully to the INP parameterization change due to fixed sea surface temperatures, Arctic surface air temperature increases by 0.7 °C in boreal autumn. These findings indicate that INPs could have a significant impact on Arctic climate and that a region-specific INP parameterization can be a useful tool to improve cloud representation in the Arctic region.

• Lund, Marianne Tronstad; Nordling, Kalle; Gjelsvik, Astrid Bragstad & Samset, Bjørn Hallvard (2023). The influence of variability on fire weather conditions in high latitude regions under present and future global warming. Environmental Research Communications (ERC). 5(6). doi: 10.1088/2515-7620/acdfad. Fulltekst i vitenarkiv Vis sammendrag

  Recent years have seen unprecedented fire activity at high latitudes and knowledge of future wildfire risk is key for adaptation and risk management. Here we present a systematic characterization of the probability distributions (PDFs) of fire weather conditions, and how it arises from underlying meteorological drivers of change, in five boreal forest regions, for pre-industrial conditions and different global warming levels. Using initial condition ensembles from two global climate models to characterize regional variability, we quantify the PDFs of daily maximum surface air temperature (SATmax), precipitation, wind, and minimum relative humidity (RHmin), and their evolution with global temperature. The resulting aggregate change in fire risk is quantified using the Canadian Fire Weather Index (FWI). In all regions we find increases in both means and upper tails of the FWI distribution, and a widening suggesting increased variability. The main underlying drivers are the projected increase in mean daily SATmax and decline in RHmin, marked already at +1 and +2 °C global warming. The largest changes occur in Canada, where we estimate a doubling of days with moderate-or-higher FWI between +1 °C and +4 °C global warming, and the smallest in Alaska. While both models exhibit the same general features of change with warming, differences in magnitude of the shifts exist, particularly for RHmin, where the bias compared to reanalysis is also largest. Given its importance for the FWI, RHmin evolution is identified as an area in need of further research. While occurrence and severity of wildfires ultimately depend also on factors such as ignition and fuel, we show how improved knowledge of meteorological conditions conducive to high wildfire risk, already changing across the high latitudes, can be used as a first indication of near-term changes. Our results confirm that continued global warming can rapidly push boreal forest regions into increasingly unfamiliar fire weather regimes.

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