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A large retreat of sea-ice in the 'stormy' Atlantic Sector of the Arctic Ocean has become evident through a series of record minima for the winter maximum sea-ice extent since 2015. Results from the Norwegian young sea ICE (N-ICE2015) expedition, a five-month-long (Jan-Jun) drifting ice station in first and second year pack-ice north of Svalbard, showcase how sea-ice in this region is frequently affected by passing winter storms. Here we synthesise the interdisciplinary N-ICE2015 dataset, including independent observations of the atmosphere, snow, sea-ice, ocean, and ecosystem. We build upon recent results and illustrate the different mechanisms through which winter storms impact the coupled Arctic sea-ice system. These short-lived and episodic synoptic-scale events transport pulses of heat and moisture into the Arctic, which temporarily reduce radiative cooling and henceforth ice growth. Cumulative snowfall from each sequential storm deepens the snow pack and insulates the sea-ice, further inhibiting ice growth throughout the remaining winter season. Strong winds fracture the ice cover, enhance ocean-ice-atmosphere heat fluxes, and make the ice more susceptible to lateral melt. In conclusion, the legacy of Arctic winter storms for sea-ice and the ice-associated ecosystem in the Atlantic Sector lasts far beyond their short lifespan.

The in situ tests of first ever autonomous aerosol and cloud backscatter LIDAR (light detection and ranging) systems implemented on buoys for Arctic observations has been achieved in 2015 within the French EQUIPEX IAOOS project. The environmental and operational constraints were met by adopting a concept of a fibered microjoule lidar system using a laser diode. Two systems have been developed with and without polarization analysis capability. A specific optical design was used for polarization discrimination. These systems were integrated in buoys and tested in the Arctic in 2014 and 2015 at latitudes higher than 80°N. Data were transmitted through an Iridium space link. Measurements have been obtained 90% of the time from the non-polarized system in 2014 over 8 months as the first fully equipped buoy drifted from the Barneo Russian camp close to the North Pole toward Svalbard. A polarized system was then tested over a short period in winter 2015 north of Svalbard during the Norwegian campaign N-ICE. In April and May 2014, the unattended lidar measurements showed a large occurrence of aerosols and haze. The average attenuated scattering ratio for non-cloudy profiles during this period was about 2.2. Aerosols could reach an altitude of 5km on average, whereas over the rest of the period low level clouds (below 1000 m) were prevailing with an average attenuated scattering ratio of about 10 3 . The main features of the developed lidar instruments and first results are presented here.