Evidence linking rapid Arctic warming to mid-latitude weather patterns

Abstract

The effects of rapid Arctic warming and ice loss on weather patterns in the Northern Hemisphere is a topic of active research, lively scientific debate and high societal impact. The emergence of Arctic amplification--the enhanced sensitivity of high-latitude temperature to global warming--in only the last 10-20 years presents a challenge to identifying statistically robust atmospheric responses using observations. Several recent studies have proposed and demonstrated new mechanisms by which the changing Arctic may be affecting weather patterns in mid-latitudes, and these linkages differ fundamentally from tropics/jet-stream interactions through the transfer of wave energy. In this study, new metrics and evidence are presented that suggest disproportionate Arctic warming-and resulting weakening of the poleward temperature gradient-is causing the Northern Hemisphere circulation to assume a more meridional character (i.e. wavier), although not uniformly in space or by season, and that highly amplified jet-stream patterns are occurring more frequently. Further analysis based on self-organizing maps supports this finding. These changes in circulation are expected to lead to persistent weather patterns that are known to cause extreme weather events. As emissions of greenhouse gases continue unabated, therefore, the continued amplification of Arctic warming should favour an increased occurrence of extreme events caused by prolonged weather conditions.

Keywords: Arctic; extreme weather; jet stream.

Figure 1.

Five-year running means of near-surface air temperature anomalies (C, relative to 1970–1999) during autumn (Oct.–Dec., a) and winter (Jan.–Mar., b) for the Arctic (70° N to 90° N, cyan) and for the Northern Hemisphere mid-latitudes (30° N to 60° N, blue). Data were obtained from the NCEP Reanalysis, NOAA/ESRL Physical Sciences Division, Boulder, CO, http://www.esrl.noaa.gov/psd/.

Figure 2.

Arctic sea ice along with earlier and more extensive Eurasian snow cover in the autumn may favour the negative phase of the NAO/AO in winter. Snow is shown in white, sea ice in light blue, sea ice melt with blue waves, anomalous high and low geopotential heights with red ‘H’ and blue ‘L’, tropospheric polar jet stream in light blue with arrows, and stratospheric polar vortex in purple with arrows. Middle and right diagrams illustrate cold (warm) temperature anomalies associated with the negative phase of the winter NAO/AO, shown in blue (orange). Adapted from [16].

Figure 3.

(a,c,e,g) Seasonal anomalies in the 1000-to-500 hPa thickness during 2000 to 2013 relative to 1981 to 2010 (m). (b,d,f,h) Seasonal trends in |MCI| during 2000 to 2013 (year⁻¹×10⁵). Asterisks denote significant trends with a 95% confidence.

Figure 4.

Average seasonal 500 hPa geopotential height contours for the period 2000 to 2013. The contour used for the analysis of high-amplitude patterns for each season is indicated with a red box. Data were obtained from the NCEP Reanalysis, NOAA/ESRL Physical Sciences Division, Boulder, CO, http://www.esrl.noaa.gov/psd/.

Figure 5.

Master SOM of daily 5600-m 500 hPa height contours during 1948 to 2012 (a). The daily mean latitude of each contour is subtracted to obtain latitude anomalies. Monthly frequency distribution of days belonging in each SOM cluster (b). Data were obtained from the NCEP Reanalysis, NOAA/ESRL Physical Sciences Division, Boulder, CO, http://www.esrl.noaa.gov/psd/.

Figure 6.

(a) Number of days that belong in each node of the master SOM. (b) Mean latitude range (deg.) of contours in each node. (c) Difference in frequency of days (number of days relative to total days) from earlier to later periods. (d) Change in mean latitude range (deg.) from earlier to later period. (e) Relative contributions by each factor to annual-mean total change in the SOM-mean latitude range.