Seasonal and Regional Variation of Pan-Arctic Surface Air Temperature Over the Instrumental Record

Historical surface air temperature (SAT) records from 59 Arctic stations north of 64°N show monthly anomalies of several degrees and large spatial teleconnectivity yet major seasonal and regional differences, based on time/longitude plots of SAT anomalies and Principal Component Analysis (PCA). Using monthly station data rather than gridded fields for this analysis highlights the importance of considering record length in calculating reliable Arctic change estimates; for example, we contrast PCA performed on 11 stations beginning in 1886, 20 stations beginning in 1912, and 45 stations beginning in 1936. While often there is a well-known interdecadal negative covariability in winter between Scandinavia and Baffin Bay in the historical SATs, long-term changes in the remainder of the Arctic are most evident in spring, with cool temperatures before 1920 and Arctic-wide warming in the 1990s. Summer anomalies are generally weaker than spring or winter but tend to mirror spring conditions before 1920 and in recent decades. Temperature advection in the trough-ridge structure in the positive phase of the Arctic Oscillation (AO) in the N. Atlantic establishes wintertime temperature anomalies in adjacent regions, while the zonal/annular nature of the AO in the remainder of the Arctic must break down in spring to promote meridional temperature advection. There are regional/decadal warm events during winter and spring in the 1930s to 1950s, but meteorological analysis suggests that these SAT anomalies are the result of intrinsic variability in region flow patterns. The mid-century events contrast with an Arctic-wide AO influence in the 1990s. We also present a conceptual model for decadal variability of the Arctic system consisting of chaotic behavior of the polar vortex. Regional feedbacks in the Arctic can act as partial multi-year memory for the vortex through amplification of ocean/sea-ice/land-vegetation changes, while the vortex in turn is often driven by north/south differences in radiational forcing from CO 2 , aerosols, solar absorption and volcanic influence. The preponderance of evidence supports the conclusion that warm SAT anomalies in spring for the decade for the 1990s had the greatest longitudinal extent in the instrumental record.