| There is a growing evidence that Arctic sea ice anomalies influence mid-latitude weather and
climate through coupled changes in the polar jet stream, planetary waves and storm tracks. In
particular, the wintertime atmospheric conditions over Eurasia are sensitive to disturbances of
sea ice cover in the Barents Sea. Our previous studies, based on a lagged regression analysis
between oceanic observations and atmospheric (NCEP/NCAR) reanalysis data in the period
1982–2006, indicate that more than 70 % of the interannual variance of the total
wintertime sea ice area in the Nordic (Greenland-Iceland-Norwegian and Barents)
seas region can be explained by Atlantic water temperature (AWT) anomalies at
the entrance to the Barents Sea in the preceding summer. When brought to the
surface, oceanic heat anomalies influence not only the sea ice cover in the Nordic
seas but also the local atmospheric conditions up to the tropopause level. The sea
ice and atmospheric anomalies persist in winter because of a feedback between
oceanically-driven wind anomalies and wind-driven AWT anomalies. A question is whether
remote effects of sea ice anomalies in the Nordic seas are modulated by interannual
variability in oceanic forcing. Here we show, using the same oceanic and atmospheric
datasets as in the previous studies, that the summertime AWT anomalies are indeed
significant precursors of a large-scale wintertime atmospheric variability. In particular,
positive AWT anomalies precede predominantly westerly wind anomalies in high
latitudes and easterly wind anomalies in middle latitudes. The mid-latitude wind
anomalies, while being generally equivalent barotropic in the upper troposphere, have a
strong low-level baroclinic contribution over Eurasia. The near-surface easterly wind
anomalies in this area are locally deflected southward, maintaining cold spots near
orography. As at the same time a strong warm anomaly is forced over the Barents and
Greenland Seas, the lower-tropospheric temperature anomalies exhibit a ‘warm
Arctic-cold Eurasia’ pattern. The ‘warm Arctic-cold Eurasia’ pattern coexists with a
hot spot in an anomalous equivalent-barotropic anticyclone that develops over the
Gulf of Alaska. An Eulerian analysis of synoptic variability indicates that these
teleconnections are related to reorganization of storm tracks. The AWT anomalies
explain as much as about 60 % of the variance in the upper-tropospheric storm
track activity averaged over the Pacific and Eurasia from 35˚ to 55˚ N and in
the lower-tropospheric poleward transient eddy heat flux over western Eurasia.
Interestingly, the AWT-related wintertime atmospheric anomalies are uncorrelated
with the concurrent anomalies associated with the North Atlantic Oscillation. This
increases a potential for seasonal prediction based on summer AWT anomalies. |