Horizontal km Scale Variability of Arctic Sea Ice and Atmospheric Dynamics, Aerosol, Trace Gases and Radiation for Investigating Interaction Processes of the Earth System Compartments during the Melting Season (HELiPOD4ArtofMelt)

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The project HELiPOD4ArtofMelt has the overall aims to contribute to understanding the impact of warm-air intrusions on the Arctic atmosphere, and to understanding processes and feedback mechanisms determining the spatially inhomogeneous onset of Arctic sea ice melt. The method consists in the analysis of airborne field data obtained during the expedition Art of Melt of the Swedish ice breaker Oden in the Atlantic sector of the Arctic Ocean in May/June 2023. The helicopter borne sonde HELiPOD is deployed with a multitude of sensors for characterising the spatial distribution and properties of the sea ice surface, atmospheric dynamics, aerosol, trace gases and radiation budget within a range of up to 100 km around the Oden. Additional complementary sensors of the international participants of the Oden expedition are included in the HELiPOD, e.g. for investigating the water vapour isotopes to study evaporation, for determining ice nucleation particles to relate the observations to cloud properties, for measuring the carbon monoxide concentration, the soot concentration, and filter samplers for subsequent microscopic laboratory analyses. Long flight legs are performed at low altitudes in the range of 15-20 m to study the ocean-sea ice-air exchange processes, and vertical profiles are done to investigate atmospheric stability and the vertical distribution and variability of the parameters. The simultaneous data sets of the different parameters allow quantifying relations and interactions, e.g. an area of increased melt pond fraction can be related directly to changes in sensible and latent heat fluxes, modifications in aerosol particle size distribution and number concentration, and subsequent alteration of the surface energy balance on small spatial scales. In addition to the continuous measurements on the Oden, the HELiPOD data provide information on the spatial variability. After final postprocessing of the large data set, the spatial variability of the different parameters is determined to derive a three-dimensional picture on the scale from below 1 km to 100 km. A special focus of the analyses with the international partners is on the characterisation of so-called „atmospheric rivers“, circulation patterns that advect warm and moist air masses in the Arctic dome, to quantify properties and modification of the atmospheric boundary layer, e.g. changes in the vertical temperatue profiles and heat fluxes, which finally impact melting. Further, the processes and interactions contributing to the spatially and temporally inhomogeneous sea ice melting onset are investigated based on the airborne observations, continuous measurements aboard Oden, and taking into account the pan-Arctic measurement network of observatories in Svalbard, Greenland and northern Scandinavia.