GEOPHYSICAL RESEARCH LETTERS,
VOL. 35,
L11701,
doi:10.1029/2008GL033273,
2008
http://www.agu.org/pubs/crossref/2008/2008GL033273.shtml
Is the observed NAO variability during the instrumental record unusual?
Semenov, V. M. Latif, J. Jungclaus, W. Park
Abstract
Observed multidecadal variability (30 yr
running means, trends, and moving standard deviations) of the North
Atlantic Oscillation (NAO) during the instrumental record is compared
to that simulated by two different coupled general circulation models
in extended-range control experiments. Simulated NAO exhibits strong
low frequency fluctuations, even on multi-centennial time scale.
Observed multi-decadal NAO variations agree well with the model
variability. Trend probability distribution functions, observed and
simulated, were not found to be different with statistical
significance. Thus, multi-decadal NAO changes similar to those observed
during the instrumental record, including the recent increase in
1965–1995, may be internally generated within the coupled
atmosphere-ocean system without considering external forcing.
GEOPHYSICAL RESEARCH LETTERS,
VOL. 35,
L11603,
doi:10.1029/2008GL034059,
2008
http://www.agu.org/pubs/crossref/2008/2008GL034059.shtml
Potential predictability of rapid changes in the Atlantic meridional overturning circulation
Hawkins, E., R. Sutton
Abstract
We explore the potential predictability
of rapid changes in the Atlantic meridional overturning circulation
(MOC) using a coupled global climate model (HadCM3). Rapid changes in
the temperature and salinity of surface water in the Nordic Seas, and
the flow of dense water through Denmark Strait, are found to be
precursors to rapid changes in the model's MOC, with a lead time of
around 10 years. The mechanism proposed to explain this potential
predictability relies on the development of density anomalies in the
Nordic Seas which propagate through Denmark Strait and along the deep
western boundary current, affecting the overturning. These rapid
changes in the MOC have significant, and widespread, climate impacts
which are potentially predictable a few years ahead. Whilst the flow
through Denmark Strait is too strong in HadCM3, the presence of such
potential predictability motivates the monitoring of water properties
in the Nordic Seas and Denmark Strait.
