Adaptation Actions for a Changing Arctic: Perspectives from the Barents Area
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Chapter 4 · Physical and socio-economic environment
Figure 4.8 Polar low off the Finnmark coast, 23 March 2011 (MET Norway / NOAA).
and Lien, 2010). Polar lows develop when cold air from the polar ice cap is forced out over the warmer waters of the North Atlantic Current such that the air is heated from below, which generates convective systems that bring storm force winds and heavy snowfall. Polar lows pose a serious risk to shipping owing to the rapid onset of storm force winds. They are associated with weather conditions that are well outside the operating limits for aircraft and for oil and gas drilling operations. Due to their limited predictability and the rapid onset of extreme weather conditions, polar lows are a priority concern for shipping and oil exploration. A study by Zahn and von Storch (2008) using NCEP/NCAR re-analysis data shows there was little change in polar low frequency between 1948 and 2005. A mapping study by Kvammen (2014) of the actual trajectories (Rojo et al., 2015) of the polar lows recorded at MET Norway from 1999 to 2013 also shows little change in their spatial distribution
area where sea ice shows the strongest seasonal variations). For the areas of maximum change, north and northeast of Novaya Zemlya this corresponds to a relative increase in maximum wind speed of 40%. Polar lows Polar lows are small (~100 km) maritime vortices with a short lifetime (several hours), accompanied by extreme weather conditions in the lower troposphere and so represent a threat to human life, coastal infrastructure and offshore activities (Figure 4.8).There are on average 13 polar low events per year in the Norwegian and Barents seas, mainly during the cold season (October to April), with a high number of events in March (Figure 4.9). The seasonal dependency of polar lows was first shown in a study at MET Norway in Tromsø from 1982 to 1985 (Lystad et al., 1986), and the same seasonality was confirmed in a more recent study for 2000 to 2009 (Noer
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Figure 4.9 Seasonal distribution of polar lows recorded at MET Norway for the first two decades of the 21st century (note different scales on axes) (MET Norway).
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