Abstract

Melt season frequencies of the Beaufort Sea High (BSH) have a profound effect on western Arctic climate, making the interannual spatial and temporal monitoring of this polar anticyclone important. This manuscript presents two automated synoptic climatological analyses using a two-step cluster procedure to classify daily mean sea level pressure (MSLP) over 180-120°W and 70-85°N with an emphasis on identifying BSH patterns. Separate raw and anomaly MSLP circulation pattern (CP) classifications are compared in order to assess the spatial characteristics of the BSH and its monthly frequency changes during the melt season from 1979 to 2012. Analysis of both classifications shows clear advantages to using the anomaly approach in terms of assessing temporal and spatial changes, particularly in light of the documented recent atmospheric circulation changes that have been observed over the region. Associations between the June anomaly circulation pattern (ACP) 5, a +4hPa BSH pattern situated between 155°W and 135°W, and June indices of atmospheric teleconnections such as the Arctic Dipole and Arctic Oscillation are statistically significant. There is also a statistically significant link to the downstream Greenland Blocking Index; suggesting that the BSH may be intricately related to climatic variability outside the analysed domain as well. Further, ACP 5 occurred nearly 3weeks more often during the melt season in recent massive Arctic Sea ice loss years (2007-2012) compared with the climatology (1979-2006). Recent increases in June ACP 5 frequencies account for a large proportion of this pattern's long-term frequency changes. © 2014 Royal Meteorological Society.