| Prospects for seasonal prediction of climate variability depend on the strength of feedbacks
between different components of the climate system. Sources for seasonal predictability of
surface atmospheric anomalies in middle latitudes have been previously sought in
teleconnections to the tropical phenomenon of El-Niño-Southern Oscillation and among
various extratropical drivers including sea surface temperature anomalies, Arctic sea ice
cover extremes, continental snow variability and tropospheric-stratospheric interactions.
However, impacts of extratropical subsurface ocean variability on atmospheric
teleconnections are poorly known. Here we use a lagged regression analysis between an
index of the observed summertime Atlantic water temperature (AWT) anomalies at the
entrance to the Barents Sea in the period 1982-2005 and the corresponding year-round
data from the National Centers for Environmental Prediction/National Center for
Atmospheric Research (NCEP/NCAR) reanalysis to show that subsurface oceanic heat
anomalies heading the Arctic Ocean are significant precursors of wintertime atmospheric
anomalies over mid-latitude Eurasia and North Pacific. In particular, warm AWT
anomalies precede an Arctic warming accompanied by a cooling over Eurasia. The
summertime oceanic anomalies explain about 40% of the variance in the surface
air temperature averaged over entire Eurasia from 35°to 45Ë N and 50% of the
variance in surface winds over the Far East Asia in the following winter. We find that
the remote tropospheric response arises from modification of planetary waves and
interaction of mean winds with synoptic eddies leading to a reorganization of the
mid-latitude storm tracks. The AWT anomalies explain about 60% of the variance in the
upper-tropospheric storm track activity averaged over the Pacific and Eurasia from 35Ë
to 55Ë N and in the lower-tropospheric poleward transient eddy heat flux over
western Eurasia. Finally, we show that the tropospheric response to the oceanic
forcing may involve interactions with the stratospheric polar vortex and appear in
quadrature with the concurrent anomalies associated with the North Atlantic Oscillation. |