brittsc

• 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.

• Dammann, Stian Leer-Salvesen; Schäfer, Britta; David, Robert Oscar & Storelvmo, Trude (2025). Observations and Model Simulations of Phase Heterogeneity in Arctic Clouds. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 130(13). doi: 10.1029/2024JD042714. Fulltekst i vitenarkiv Vis sammendrag

  Mixed-phase clouds (MPCs) play a key role in Earth's radiation budget particularly in the Arctic where they are ubiquitous year-round. An important characteristic of MPCs is how the cloud phases are mixed, which affects interactions between ice and liquid. Observations show that phase tends to be nonuniform with ice and liquid forming spatially separated single-phased “pockets” not accounted for in climate models. These pockets may vary in size from the micron-scale to several hundred kilometers making them notoriously difficult to study, and the factors influencing cloud-phase heterogeneity remain uncertain. We quantify size distributions of phase pockets in an observed and modeled Arctic MPC occurring 12 November 2019 in Ny-Ålesund, Svalbard. The case is simulated with the Weather Research and Forecasting model constrained with representative aerosol concentrations following measurements from the Ny-Ålesund Aerosol Cloud Experiment. We find that phase pockets exhibit broad size distributions with the smallest pockets occurring most frequently. Observations reveal mean pocket lengths of 2 km, whereas the simulated pockets are about 5 times longer on average. Simulated pocket size distributions are highly sensitive to prescribed aerosols. Moreover, we observe a pronounced increase of 6.5 km in the mean length of mixed-phase pockets when secondary ice production is enhanced in simulations. These results shed light on the link between cloud microphysics and the in-cloud distribution of phase and provide a potential framework for representation of sub-grid scale phase variability in climate models.

• Schäfer, Britta; David, Robert Oscar; Hodnebrog, Øivind & Storelvmo, Trude (2025). Response of an Arctic Mixed-Phase Cloud to Ice-Nucleating Particle Perturbations and Warming. Geophysical Research Letters. ISSN 0094-8276. 52(10). doi: 10.1029/2024GL114467. Fulltekst i vitenarkiv Vis sammendrag

  The Arctic is warming faster than any other region on Earth. This warming affects Arctic clouds, both directly and through changes in aerosol concentrations, triggering feedbacks that may further amplify the warming. Here we present simulations of a wintertime cloud case from Ny-Ålesund with parameterizations optimized for representing secondary ice production (SIP). We compare cloud phase and its impact on radiation in present-day conditions with simulations where we perturb (a) ice-nucleating particle concentrations (INPC) and (b) atmospheric and surface temperatures using a pseudo-global-warming approach. Increasing the INPC leads to cloud thinning and reduced downward longwave radiation at the surface (SDLR). Intriguingly, with warming we find an increase in cloud ice due to increased rime splintering (RS) and subsequent SIP, which also leads to reduced SDLR. This can be explained by an upward shift in the temperature region where RS is active to higher altitudes where more liquid water is present.

• Schäfer, Britta; David, Robert Oscar; Georgakaki, Paraskevi; Pasquier, Julie Thérèse; Sotiropoulou, Georgia & Storelvmo, Trude (2024). Simulations of primary and secondary ice production during an Arctic mixed-phase cloud case from the Ny-Ålesund Aerosol Cloud Experiment (NASCENT) campaign. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 24(12), s. 7179–7202. doi: 10.5194/acp-24-7179-2024. Fulltekst i vitenarkiv Vis sammendrag

  The representation of Arctic clouds and their phase distributions, i.e., the amount of ice and supercooled water, influences predictions of future Arctic warming. Therefore, it is essential that cloud phase is correctly captured by models in order to accurately predict the future Arctic climate. Ice crystal formation in clouds happens through ice nucleation (primary ice production) and ice multiplication (secondary ice production). In common weather and climate models, rime splintering is the only secondary ice production process included. In addition, prescribed number concentrations of cloud condensation nuclei or cloud droplets and ice-nucleating particles are often overestimated in Arctic environments by standard model configurations. This can lead to a misrepresentation of the phase distribution and precipitation formation in Arctic mixed-phase clouds, with important implications for the Arctic surface energy budget. During the Ny-Ålesund Aerosol Cloud Experiment (NASCENT), a holographic probe mounted on a tethered balloon took in situ measurements of number and mass concentrations of ice crystals and cloud droplets in Svalbard, Norway, during fall 2019 and spring 2020. In this study, we choose one case study from this campaign that shows evidence of strong secondary ice production and use the Weather Research and Forecasting (WRF) model to simulate it at a high vertical and spatial resolution. We test the performance of different microphysical parametrizations and apply a new state-of-the-art secondary ice parametrization. We find that agreement with observations highly depends on the prescribed cloud condensation nuclei/cloud droplet and ice-nucleating particle concentrations and requires an enhancement of secondary ice production processes. Lowering mass mixing ratio thresholds for rime splintering inside the Morrison microphysics scheme is crucial to enable secondary ice production and thereby match observations for the right reasons. In our case, rime splintering is required to initiate collisional breakup. The simulated contribution from collisional breakup is larger than that from droplet shattering. Simulating ice production correctly for the right reasons is a prerequisite for reliable simulations of Arctic mixed-phase cloud responses to future temperature or aerosol perturbations.

• Pasquier, Julie T.; David, Robert Oscar; Freitas, Gabriel; Gierens, Rosa; Gramlich, Yvette & Haslett, Sophie [Vis alle 44 forfattere av denne artikkelen] (2022). The Ny-Ålesund Aerosol Cloud Experiment (NASCENT) Overview and First Results. Bulletin of The American Meteorological Society - (BAMS). ISSN 0003-0007. 103(11), s. E2533–E2558. doi: 10.1175/BAMS-D-21-0034.1. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The Arctic is warming at more than twice the rate of the global average. This warming is influenced by clouds which modulate the solar and terrestrial radiative fluxes, and thus, determine the surface energy budget. However, the interactions among clouds, aerosols, and radiative fluxes in the Arctic are still poorly understood. To address these uncertainties, the Ny-Ålesund AeroSol Cloud ExperimeNT (NASCENT) study was conducted from September 2019 to August 2020 in Ny-Ålesund Svalbard. The campaign’s primary goal was to elucidate the life cycle of aerosols in the Arctic and to determine how they modulate cloud properties throughout the year. In-situ and remote sensing observations were taken on the ground at sea-level and at a mountaintop station, and with a tethered balloon system. An overview of the meteorological and the main aerosol seasonality encountered during the NASCENT year is introduced, followed by a presentation of first scientific highlights. In particular, we present new findings on aerosol physicochemical properties which also include molecular properties. Further, the role of cloud droplet activation and ice crystal nucleation in the formation and persistence of mixed-phase clouds, and the occurrence of secondary ice processes, are discussed and compared to the representation of cloud processes within the regional Weather Research and Forecasting model. The paper concludes with research questions that are to be addressed in upcoming NASCENT publications.

• Schäfer, Britta; Carlsen, Tim; Hanssen, Ingrid; Gausa, Michael & Storelvmo, Trude (2022). Observations of cold-cloud properties in the Norwegian Arctic using ground-based and spaceborne lidar. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 22(14), s. 9537–9551. doi: 10.5194/acp-22-9537-2022. Fulltekst i vitenarkiv Vis sammendrag

  Abstract. The role of clouds in the surface radiation budget is particularly complex in the rapidly changing Arctic. However, despite their importance, long-term observations of Arctic clouds are relatively sparse. Here, we present observations of cold clouds based on 7 years (2011–2017) of ground-based lidar observations at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in Andenes in the Norwegian Arctic. In two case studies, we assess (1) the agreement between a co-located cirrus cloud observations from the ground-based lidar and the spaceborne lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite and (2) the ground-based lidar's capability to determine the cloud phase in mixed-phase clouds from depolarization measurements. We then compute multiyear statistics of cold clouds from both platforms with respect to their occurrence, cloud top and base height, cloud top temperature, and thermodynamic phase for the 2011–2017 period. We find that satellite- and ground-based observations agree well with respect to the coincident cirrus measurement and that the vertical phase distribution within a liquid-topped mixed-phase cloud could be identified from depolarization measurements. On average, 8 % of all satellite profiles were identified as single-layer cold clouds with no apparent seasonal differences. The average cloud top and base heights, combining the ground-based and satellite measurements, are 9.1 and 6.9 km, respectively, resulting in an average thickness of 2.2 km. Seasonal differences between the average top and base heights are on the order of 1–2 km and are largest when comparing fall (highest) and spring (lowest). However, seasonal variations are small compared with the observed day-to-day variability. Cloud top temperatures agree well between both platforms, with warmer cloud top temperatures in summer. The presented study demonstrates the capabilities of long-term cloud observations in the Norwegian Arctic from the ground-based lidar at Andenes.

• Schäfer, Britta; Baumgarten, Gerd & Fiedler, Jens (2020). Small-scale structures in noctilucent clouds observed by lidar. Journal of Atmospheric and Solar-Terrestrial Physics. ISSN 1364-6826. 208(105384). doi: 10.1016/j.jastp.2020.105384. Fulltekst i vitenarkiv Vis sammendrag

  Noctilucent clouds (NLC) are mesospheric ice clouds occurring in the summer hemisphere at high latitudes and an altitude of about 83km. This region is the coldest of the earth’s atmosphere and is characterized by the presence of wave interaction and dissipation. The processes involved here lead to a variety of structures and instabilities that become visible in noctilucent clouds and are observed by different instruments. In this work high-resolution lidar measurements are used to give a wide overview of the structures at small scales below the Brunt–Väisälä period of 5min. For the first time a large amount of NLC profiles from lidar with a temporal resolution of 1s is analyzed in detail, covering about 1400h during the summer from 2011 to 2018. A new categorization focusing on small-scale structures is introduced, and occurrence statistics for these categories in the season of 2014 are performed. Both wave structures with periods below 10min and thin layers of 100m thickness are commonly found. When taking simultaneous wind measurements into account, we find that structures often are advected by the wind.

Se alle arbeider i NVA

• Schäfer, Britta (2023). Festival til hyllest for mangfold og klimakamp. Fulltekst i vitenarkiv Vis sammendrag

  Fulltekst på https://www.dt.no/festival-til-hyllest-for-mangfold-og-klimakamp/o/5-57-2058615

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