Empirical Trace Gas Gradients in the Arctic and Polar Dome Location

The Arctic or polar front has long been recognized as a transport barrier for mid-latitude air masses travelling into the high Arctic. A measurement based identification of the polar dome is difficult due to the temporal and spatial variability and a lack of consistent measurements in the lower few kilometers of the Arctic. Particularly the climatological role of the dome as a transport boundary for pollution tracers has not yet been fully addressed on the basis of in-situ measurements. We present aircraft based trace gas measurements in the Arctic during NETCARE 2014 and 2015 with the Polar 6 aircraft of Alfred Wegener Institute (AWI) covering an area from Spitsbergen to Alaska (134°W to 17°W and 68°N to 83°N). Based on CO and CO₂ measurements we analyze the distribution of these tracers in different coordinate systems and identify the dome location on the basis of trace gas gradients. Based on this analysis significant differences between winter/spring (NETCARE 2015) and summer (NETCARE 2014) appear. During winter/spring the dome is characterized by an almost isentropic distribution of CO and CO₂, whereas in summer diabatic processes introduce isentropic gradients. Based on kinematic 10-day back trajectories we analyze the transport to the high Arctic during spring (NETCARE 2015) and summer (NETCARE 2014), respectively. Consistent with the tracer measurements the analysis of trajectories revealed two major transport regimes with contributions of mid-latitude air ranging from 15%-56% with the North American continent being the dominant source region of the air masses for the summer campaign.