ASCOS was an interdisciplinary expedition to the central Arctic on the icebreaker Oden from 1 August to 9 September 2008. The expedition focused on processes relating to cloud formation in the summer Arctic and included observations of marine biology and chemistry, atmospheric chemistry, physical oceanography, aerosol chemistry and physics, and meteorology. The soundings in this dataset were ... released in principle every six hour from the helipad of Oden, roughly 12 m above the sea surface. All soundings include profiles of pressure, temperature and humidity, and also wind speed and direction from GPS. Sub-sets of the soundings also include either ozone or radioactivity profiles. The sounding schedule started and ended in the Greenland Sea and soundings were also carried out in transit to a 20-day ice-drift period around N87 W5 from 13 August to 2 September, when Oden was drifting with the ice; more than half of the soundings come from this time period.