Summer atmospheric circulation anomalies over the Arctic Ocean and their influences on September sea ice extent: A cautionary tale

Abstract

AbstractNumerous studies have addressed links between summer atmospheric circulation patterns and interannual variability and the downward trend in total September Arctic sea ice extent. In general, low extent is favored when the preceding summer is characterized by positive sea level pressure (SLP) anomalies over the central Arctic Ocean north of Alaska. High extent is favored when low pressure dominates. If such atmospheric patterns could be predicted several months out, these links provide an avenue for improved seasonal predictability of total September extent. We analyze detrended September extent time series (1979–2015), atmospheric reanalysis fields, ice age and motion, and Atmospheric Infrared Sounder data, to show that while there is merit to this summer circulation framework, it has limitations. Large departures in total September extent relative to the trend line are preceded by a wide range of summer circulation patterns. While patterns for the four years with the largest positive departures in September extent have below average SLP over the central Arctic Ocean, they differ markedly in the magnitude and location of pressure and air temperature anomalies. Differences in circulation for the four years with the largest negative departures are equally prominent. Circulation anomalies preceding Septembers with ice extent close to the trend also have a wide range of patterns. In turn, years (such as 2013 and 2014) with almost identical total September extent were preceded by very different summer circulation patterns. September ice conditions can also be strongly shaped by events as far back as the previous winter or spring.