Publikationsdatum:
2017-04-04
Beschreibung:
An ocean analysis, assimilating both surface
and subsurface hydrographic temperature data into a
global ocean model, has been produced for the period
1958–2000, and used to study the time and space vari-
ations of North Atlantic upper ocean heat content (HC).
Observational evidence is presented for interannual-to-
decadal variability of upper ocean thermal fluctuations
in the North Atlantic related to the North Atlantic
Oscillation (NAO) variability over the last 40 years. The
assimilation scheme used in the ocean analysis is a uni-
variate, variational optimum interpolation of tempera-
ture. The first guess is produced by an eddy permitting
global ocean general circulation forced by atmospheric
reanalysis from the National Center for Environmental
Prediction (NCEP). The validation of the ocean analysis
has been done through the comparison with objectively
analyzed observations and independent data sets. The
method is able to compensate for the model systematic
error to reproduce a realistic vertical thermal structure
of the region and to improve consistently the model
estimation of the time variability of the upper ocean
temperature. Empirical orthogonal function (EOF)
analysis shows that an important mode of variability of
the wintertime upper ocean climate over the North
Atlantic during the period of study is characterized by a
tripole pattern both for SST and upper ocean HC. A
similar mode is found for summer HC anomalies but not
for summer SST. Over the whole period, HC variations
in the subtropics show a general warming trend while the
tropical and north eastern part of the basin have an
opposite cooling tendency. Superimposed on this linear
trend, the HC variability explained by the first EOF
both in winter and summer conditions reveals quasi-
decadal oscillations correlated with changes in the NAO
index. On the other hand, there is no evidence of cor- relation in time between the NAO index and the upper
ocean HC averaged over the whole North Atlantic
which exhibits a substantial and monotonic warming
trend during the last two decades of the analysis period.
The maximum correlation is found between the leading
principal component of winter HC anomalies and NAO
index at 1 year lag with NAO leading. For SST anom-
alies significant correlation is found only for winter
conditions. In contrast, for HC anomalies high corre-
lations are found also in the summer suggesting that the
summer HC keeps a memory of winter conditions.
Beschreibung:
This work has been supported by the EU
PREDICATE Project (Contract EVK2-CT-1999-00020) and the
EU ENACT Project (Contract EVK2-CT2001-00117)
Beschreibung:
Published
Beschreibung:
531-546
Beschreibung:
4A. Clima e Oceani
Beschreibung:
JCR Journal
Beschreibung:
restricted
Schlagwort(e):
Ocean dynamics
;
Ocean modelling
;
Ocean Reanalysis
;
data assimilation
;
Interannual variability
;
decadal variability
;
03. Hydrosphere::03.01. General::03.01.04. Ocean data assimilation and reanalysis
Repository-Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Materialart:
article
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