Low-level jet characteristics over the Arctic Ocean in spring and summer

Low-level jets (LLJ) are important for turbulence in the stably stratified atmospheric boundary layer, but their occurrence, properties, and generation mechanisms in the Arctic are not well known. We analysed LLJs over the central Arctic Ocean in spring and summer 2007 on the basis of data collected in the drifting ice station Tara. Instead of traditional radiosonde soundings, data from tethersonde soundings with a high vertical resolution were used. The Tara results showed a lower occurrence of LLJs (46 +/- 8%) than many previous studies over polar sea ice. Strong jet core winds contributed to growth of the turbulent layer. Complex relationships between the jet core height and the temperature inversion top height were detected: substantial correlation (r = 0.72; p < 0.01) occurred when the jet core was above the turbulent layer, but when inside the turbulent layer there was no correlation. The most important forcing mechanism for LLJs was baroclinicity, which was responsible for the generation of strong and warm LLJs, which on average occurred at lower altitudes than other jets. Baroclinic jets were mostly associated with transient cyclones instead of the climatological air temperature gradients. Besides baroclinicity, cases related to inertial oscillations and gusts were detected. As many as 49% of the LLJs observed were associated with a frontal passage, which provides favourable conditions for baroclinicity, inertial oscillations, and gusts. Further research needs on LLJs in the Arctic include investigation of low-level jet streams and their effects on the sea ice drift and atmospheric moisture transport.