Associations between circulation pattern frequencies and sea ice minima in the western Arctic

In this study, a synoptic climatological approach is employed to assess the relationship between the frequency of circulation patterns (CPs) and the latitude of mid-September sea ice minima in the western Arctic. Fifteen CPs are created via principal component analysis and cluster analysis from daily NCEP/NCAR reanalysis sea-level pressure (SLP) fields across a grid from 50 to 90◦N and 150◦E–100◦W from 1979 to 2011. The frequency of these CPs are statistically compared with the latitude of the sea ice minimum from passive microwave data for each of 11 equally-spaced longitudes (176◦W to 126◦W) extending into the Chukchi and Beaufort Seas. Monthly frequencies for each of the 15 CPs from March to September, signifying the melt season, for each year are correlated with the ice minimum for that September. These monthly frequencies are then entered into a stepwise multiple linear regression (SMLR) and collectively, CP frequencies explain 40–79% of the total ice retreat variance across the longitudes. The frequency of one cluster, CP 11, representing a broad high pressure area over the Beaufort Sea, is highly correlated with the latitude of the sea ice minima; June and August frequencies of this pattern are the initial predictors at 8 of the 11 longitudes and explain 22–32% of the variance. This pattern has occurred more frequently from 2007 onwards; compared with a June mean occurrence of 9 days during 1979–2006, CP 11 occurred 16 times in June 2007, and on average more than 17 days per month during June 2008–2011. The Arctic Dipole (AD), Arctic Oscillation (AO), and Pacific-North American (PNA) pattern indices are significantly correlated with CPs 11–13 frequencies throughout certain summer months, further indicating strong relationships between summer circulation and sea ice minima in the region.