Sea ice impacts on polar surface weather types in the North American Arctic

Summer and autumn sea ice conditions in the Western Arctic have rapidly changed in recent years, while increases in lower tropospheric air temperature and moisture have concurrently been observed across much of the high northern latitudes during the autumn (October to December) and winter (January to March) months. However, the spatiotemporal relationships between this region's ice cover and North American climate are not particularly well understood. This study employs a synoptic climatological weather typing scheme known as the Spatial Synoptic Classification (SSC) to holistically evaluate temperature and moisture characteristics throughout the terrestrial North American Arctic (NAA) associated with the Western Arctic sea ice freeze-up dates from 1979 to 2013. Monthly climatologies and linear trends of autumn/winter-dominant SSC weather types in the region, Moist Polar (MP) and Dry Polar (DP), are assessed and statistically linked to the freeze dates. Results suggest that the MP weather types are increasing, at the expense of DP types, across much of the domain. The apparent NAA transition to MP conditions is positively correlated with the timing of the Western Arctic freeze-up, and far more MP days occur during late-freeze versus early-freeze years, especially at the most northerly weather stations. Positive near-surface temperature anomalies and northerly low-level winds across the Western Arctic Ocean during late minus early freeze years potentially connect delayed ice formation to a changing NAA climate.