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Arctic-centered character with nearly equal contributions from the Atlantic and
Paci
c sectors. In contrast,
the differences between positive and negative AO
composites de
ned from monthly values of Principal Components from the same
period have similar magnitudes in the Paci
c and Arctic, but have additional large
NAO signature in the Atlantic sector. Thus Arctic changes of decadal scales are
more symmetric with the pole than suggested by the standard AO index de
nition.
Change point analysis of the AO shows that a shift in value near 1989 is an
alternative hypothesis to a linear trend. Analysis of zonal and meridional winds by
longitudinal sectors shows the importance of the standing wave pattern in inter-
preting the AO, which supplements the view of the AO as a simple zonal average
(annular) mode
. Thus the Arctic Oscillation should be considered as a physical
phenomenon connected with the enhancement of circumpolar vortex and relevant
mass and temperature changes in the stratosphere.
By the end of the 1980s
”
the beginning of the 1990s a very strong NAO
enhancement resulted in powerful transport of warmer and fresher Norwegian
Atlantic waters to the north of the Fram Strait and the Barents Sea. Entering the
Arctic, the sub-layer of Atlantic waters was becoming thinner, warming (by about
2
—
°
20 %). At smaller depths, the cold
haloclyne (which thermally isolates the sea ice cover from the warm Atlantic layer
located below) shifted towards the euro-asiatic basin, which resulted in substantial
changes of mass and energy balances of the ice cover surface. This and other
phenomena have been studied within a number of recent programs such as ASP
(Arctic Studies Program), ISAC (International Study of Arctic Change), SEATCH
(NOAA Study of Environmental Arctic Change), etc. The climatic impact of
polynyas is of particular interest (Schrank 2007).
Alekseev (1998) has emphasized that the Arctic is in many respects a key part of
the global climatic system, where the strongest natural
C) and increasing its horizontal extent (
*
fluctuations of climatic
characteristics develop. The global impact of the Arctic is primarily accomplished
through the Arctic Ocean, which is capable of changing its structure circulation
regime under the in
fl
uence of changes in fresh water, salt and heat exchange with
the non-polar parts of the global system. The freshened upper layer and sea ice
located above it turn out to be the most active components, with fresh water, heat
and salt transport being the major processes responsible for coupling between the
high-latitude environment and its lower-latitude parts.
Speci
fl
c features of the arctic atmosphere such as phenomena of Arctic Haze as
well as extended cloudiness and radiation, have been studied during the period of
the First GARP (Global Atmospheric Research Programme) Global Experiment
—
FGGE (Kondratyev et al. 1992; Kondratyev 1999).
Important progress has been achieved in the
field of arctic climate diagnostics.
Basic features of arctic climate dynamics have been demonstrated, such as strong
space and time variability of various scales. For example, it was shown, that as far
as inter-annual lower troposphere variations are concerned, before the 1980s neg-
ative anomalies had prevailed, while later on, for the whole troposphere, positive
temperature anomalies were typical. However, the total polar atmosphere energy
(potential plus internal) during the previous 40 years has not changed.
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