Observations of temperature inversions over central Arctic sea ice in summer

We analysed high-resolution tethersonde sounding data from the drifting ice station Tara in the Arctic Ocean in April to August 2007 to (a) better understand the multiple processes affecting the generation and properties of Arctic air temperature inversions and (b) to obtain insight into the vertical structure of the atmospheric boundary layer during the exceptional spring and summer 2007, which resulted in a historically low sea ice extent. A total of 95 profiles, up to the height of 2 km, were measured on 39 days. Inversions were present in 88% of the data, 13% of them being surface-based. Compared to winter, the occurrence and properties of summer inversions depended much less on surface net radiation and were mainly controlled by the surface melt and warm-air advection. Inversions occuring during snow/ice melt were located at low altitudes, frequently based at the surface, and were often as strong as winter inversions reported in previous studies. In general, the Tara inversions were shallow, and the deepest ones were observed when clouds occurred inside or partly above the inversion layer. Inversions were strongest under clear skies or in cases when the cloud top was above the inversion base. Related to cases of strong warm-air advection (up to 35 K day-1) in July, exceptionally high temperatures around the inversion top caused maximum inversion strengths up to 13 K. Inversions of this magnitude at this time of the year have been rarely documented previously.