29 March 2026 | 13:15 - 15:00 CEST / UTC+2
Open Session - HYBRID
Room: Per Kirkeby Auditorium
Session Description:
This session focuses on the Arctic atmosphere, including aerosols, clouds and extreme weather. It examines how atmospheric processes interact with the ocean, ice and land, and how observations and models improve understanding and prediction of Arctic climate change.
Keynote: Dr. Kathy S. Law
Oral presentations:
Name: Aarni Vaittinen (Institute for Atmospheric and Earth System Research (INAR) / Physics, University of Helsinki)
Title of Presentation: Long-term measurements of aerosol particles and their formation at Ny-Ålesund, Svalbard
Abstract text: In the Arctic, new particle formation (NPF) is the source for up to 90 % of the cloud-forming particles in the troposphere. In NPF, precursor vapours nucleate to form small molecular clusters, which can then grow by further condensation and eventually act as cloud condensation nuclei. Precursor vapours that are known to initiate NPF include sulfuric acid (SA), methanesulfonic acid (MSA), iodic acid (IA) and other iodine oxoacids, ammonia, and highly oxidised organic compounds (HOMs). [1-2] // In the Arctic, the abundance of these precursor gases is tied to a variety of biological and physical processes. SA and MSA concentrations depend on the activity of oceanic phytoplankton, while air-sea ice -interactions impact the concentrations of iodine compounds. HOMs originate from terrestrial sources. Finally, the fauna acts as a strong source of ammonia. As the Arctic is rapidly changing due to climate change, ecosystem responses are expected to alter these gas emissions and can therefore impact the strength and occurrence of NPF in the future. [3] // We have been studying the NPF process across the Arctic for over a decade now, with measurements spanning across different ecosystems. In the High Arctic site of Ny-Ålesund, Svalbard, our measurements of aerosol particles and their precursors have been performed since 2014, and continuously since 2017. // While our past observations have already revealed aerosol formation driven by the clustering of SA and ammonia, our recent findings include the first-ever direct field observations of MSA-enhanced nucleation, as well as new details concerning the influence of iodine compounds on Arctic NPF. Here, we present our latest results, and the future directions for our research. // References // 1. Gordon H, et al. J Geophys Res Atmos. 2017;122:8739–8760. // 2. Kerminen VM et al. Environ Res Lett. 2018;13:103003. // 3. Schmale J, Baccarini A. Geophys Res Lett. 2021;48:e2021GL094198.
Name: Arundathi Chandrasekharan (Finnish Meteorological Institute)
Title of Presentation: Understanding Gaps in Arctic Aerosol Representation in Climate Models
Abstract text: The effects of climate change are especially strong in the Arctic compared to other parts of the world. To better understand and predict these changes, it’s important to accurately represent local processes in the Arctic environment. One such process that is important is the representation of local aerosol processes. A major hurdle has been the lack of measurement data, especially in the high Arctic to evaluate the performance of models in the Arctic. The MOSAiC expedition, which took place from September 20, 2019, to October 12, 2020, collected a full year of data, including aerosols, in the Arctic. This provides a great opportunity to learn more about these tiny particles. In this study, we use MOSAiC data to evaluate the Arctic aerosols in TM5, the aerosol-chemistry model of EC-Earth3. After analysing the performance of the current model, we then do sensitivity analysis to find out what are the missing or misrepresented Arctic relevant processes. We also look at aerosols in CMIP6 models to understand the general lay of the land when it comes to Arctic aerosols.We find that all the models we look at underestimate aerosol values throughout the year. We introduce a new formula for aerosol formation, which is dependent on concentration of sulphuric acid and methanesulfonic acid(MSA) as opposed to only sulphuric acid which is the case in the climate models we look at. We find the new method we introduce produces values closer to the observations in summer. During winter increasing aerosols from sea spray emissions values closer to measurements. Adding sources of aerosols, such as blowing snow or emissions from cracks in sea ice (leads) during winter, as well as including other factors that promote particle formation—like MSA—will help improve the models and our understanding of Arctic climate.
Name: Tiago Silva (University of Graz)
Title of Presentation: Spatio-Temporal Dynamics and a Diagnostic Framework for Piteraq Events in Southeast Greenland
Abstract text: Weather extremes are increasing in frequency across the Arctic. One such extreme event is the downslope windstorm, locally known as "piteraq” in the Tasiilaq region of Southeast Greenland. These severe windstorms occur multiple times per year, disrupting communities, damaging infrastructure, and occasionally claiming lives. Despite their severity, the mechanisms that trigger and intensify piteraq events remain poorly understood due to insufficient high-resolution analysis. Without this knowledge, forecasting accuracy and risk mitigation efforts fall short. This study addresses the question: What is the spatio-temporal climatology of piteraq events, and what specific physical mechanisms drive their formation and intensity?To detect and investigate the driving factors of piteraq events, we utilized more than 30 years of high-resolution Copernicus Arctic Regional Reanalysis and regional observational network data. We identified key atmospheric diagnostics that characterize synoptically driven downslope windstorms. Our contribution will explain how piteraq events form through the interaction between cold air masses from the Canadian Arctic and Greenland's frigid interior. This topographically amplified flow can generate hurricane-force winds that sweep across more than 500 km of South Greenland’s coast.Our work provides the first comprehensive spatio-temporal description of piteraq events. We will present our primary findings for the winter season, since the frequency, intensity, and thermodynamic mechanisms of piteraq events show seasonality. These results offer critical, data-driven insights for a multidisciplinary audience by revealing how these windstorms impact not only the Tasiilaq region but also the entire Irminger Sea — a vital corridor for fishing, shipping, and aviation. Ultimately, our diagnostic framework will build a basis to improve severe weather forecasting and enable more robust assessments of air-sea exchange processes that influence the North Atlantic climate dynamics.
Name: Jennie Spicker Schmidt (Aarhus Universitet)
Title of Presentation: A Novel Mechanism of Sea-Surface-Microlayer Formation Driven by Terrestrial Runoff: A Source of Ice Nucleating Particles in Arctic Coastal Waters
Abstract text: Aerosols, particularly biological aerosols, play a key role in Arctic cloud formation, influencing regional climate by modulating cloud properties. Persistent Arctic mixed-phase clouds are strongly affected by ice nucleating particles (INP), yet the sources, composition, and microbial producers of biological INPs remain largely unknown. As Arctic warming accelerates glacial melt and terrestrial runoff, understanding how these processes affect INP fluxes and atmospheric cloud properties becomes critical for improving climate models.Here, we investigate the contribution of terrestrial runoff to coastal marine and atmospheric INP pools in Young Sound fjord, NE Greenland, August 2022. Concentrations of INPs active at −10 °C were significantly elevated in the sea surface microlayer (SML) and river outlets compared to bulk seawater, exhibiting strong negative correlations with salinity and distance from freshwater inputs, indicating runoff as a major source of biological INPs to Arctic coastal waters. We further reveal a novel mechanism of SML formation driven by density contrasts between freshwater and marine waters, leading to accumulation of terrestrial particles and organic matter at the surface. Using flow cytometry, we identified riverine cell populations and their efficient transfer into the SML, substantially influencing its composition over at least 73 km from the river mouth. Flow cytometry, qPCR, and amplicon sequencing revealed diverse microbial communities in riverine, marine, and aerosol samples, linking biological INPs to terrestrial and freshwater origins. SourceTracker2 analysis confirmed that terrestrial runoff and direct aerosolization from soil and vegetation are major contributors to the atmospheric INP pool.Our findings show terrestrial environments are reservoirs of highly active biogenic INPs, with the coastal SML serving as a key interface for their atmospheric transfer, highlighting a pathway through which Arctic warming can impact cloud properties and regional climate feedbacks.
Name: Anna Voss (Institute of Flight Guidance, Technische Universität Braunschweig)
Title of Presentation: Uncrewed aerial system based investigation of ultrafine particles in the sub-arctic in spring and autumn 2025
Abstract text:The spatial distribution of aerosol particles in Polar Regions is driven by various factors, including long-range transport, air mass origin, local sources and new particle formation. Although ground-based monitoring networks provide valuable long-term data, they often cannot provide in-situ data of the vertical distribution of aerosol particles within the atmospheric boundary layer (ABL). For this purpose, uncrewed aerial systems (UAS) are essential tools to provide high-resolution in-situ data to gain a broader understanding of the spatial distribution of aerosol particles in the ABL.From 4 April 2025 to 12 April 2025 and 16 September to 30 September 2025, the Finnish Meteorological Institute (FMI) and TU Braunschweig operated five different UAS to conduct two intensive measurement campaigns in Pallas, Finland. Two fixed-wings, one vertical take-off and landing (VTOL) and two multirotor UAS were operated, depending on the objective of the measurement flight. The campaigns consisted of 246 measurement flights, reaching altitudes up to 2 km above ground level, with more than 80 hours of sampling time. The main goal of the study is to characterize aerosol properties, such as particle number concentration, size distribution, new particle formation, the vertical distribution of meteorological parameters and compare the data with the ground-based observatory Sammaltunturi. Preliminary results indicate new particle formation events linked to air mass transport, originating from the central Arctic in spring and local sources for new particle formation in autumn. While the spring campaign was mainly dominated by new particle formation the autumn campaign was dominated by low cloud formation. This campaign is part of continuous measurements by FMI conducted every spring and autumn to characterize changes in the subarctic ABL, the aerosol distribution and cloud microphysics. This presentation gives an overview of the seasonal variability of ultrafine aerosol particles in the sub-arctic in spring and autumn.