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In recent years, the oceanographic community has gained
access to information that constitutes a formidable leap
for our science. This information includes data from
remote sensing instruments such as satellite altimetry and
ice thickness from upward looking sonar, in situ
observations like hydrography from SeaSoar-CTD and current
measurements from VM-ADCP, and model simulations of the
ocean circulation that produce results with an increasing
level of details. The expression "high resolution
information" is here used as a reference to the joint sets
of information just listed. In Task 5, we seek to take
advantage of these advances in order to arrive at an
enhanced understanding and improved description of
processes relevant to the ocean climate of the Nordic Seas
and the Arctic Sea. The work planned for Task 5 includes
studies of (1) variability in the transports of the
northern branches of the Gulf Stream system due to oceanic
teleconnections by signal propagation, (2) variability in
the fluxes and paths of Atlantic Water that enters the
Nordic Seas, (3) variability related to the front between
Atlantic Water and Arctic Water in the Nordic Seas, and
(4) variability and trends related to the ice cover and
ice transport in the Arctic Sea and Nordic Seas.
In Norway, there is a tradition for regional model studies
of the ocean circulation. Little attention has been paid
to examine and understand how the variability of the
regional circulation is affected by the variability of the
circulation of the North Atlantic Ocean. Hence, one goal
here is to investigate the relations between anomalous
events in the North Atlantic Ocean and variability of the
flux of Atlantic Water into the Nordic Seas. The length of
the available time series from the joint sets of high
resolution observations and simulations fall short of the
period required for studying decadal variability. Hence,
we will use these sets in a study of seasonal and
interannual variability and episodic events during the
last 10-20 years.
One of the model simulations involved has a global
perspective on the mesoscale, and it is therefore
considered pertinent for examination of variability of
transports of mass and heat in the mixed layer of the
Atlantic Ocean along the pathways in the Gulf Stream
system towards the Nordic Seas. However, this model is
unfit to describe variability within the Nordic Seas, and
uses open boundaries at the Greenland-Iceland-Scotland
ridge with specified lateral fluxes. In subtask 5.1, we
will use supplementary results from another model that is
truly Atlantic/Arctic and has a focus with high resolution
in the region of AW inflow to the Nordic Seas. The models
in question are the NLOM [Wallcraft, 1991] and the MICOM
[Bleck and Boudra, 1986], respectively.
In order to gain further understanding of AW inflow
variability, in situ measurements and observations from
remote sensing instruments will also be studied. These
data are valuable for examinations of variability and
events in their own right. In the present effort, we shall
seek to combine the observational data and model output in
order to obtain an improved description and understanding
by a synthesis of these sets of information. The
observations should also prove helpful in sorting out any
discrepancies between the two model simulations.
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The inflow of AW to the Nordic Seas may be considered as
being divided between two pathways, an eastern branch and
a western branch. Flow along the two pathways may differ
both in the characteristics of the water masses as they
enter the Nordic Seas, and in the modifications of AW by
mixing with adjacent water masses while in the Nordic
Seas. In the first phase, we will describe and analyze to
what degree the variability is forced by oceanic
teleconnections through signal propagation, and local
atmospheric forcing (subtasks 5.1 and 5.2). Particular
attention will be paid to the period 1992-present, for
which simulation results high quality altimeter data, data
from hydrography crossections, and current measurements
are all available. The work to be carried out in subtasks
5.1 and 5.2 will be coordinated and performed as a
collaborative effort. Here, we will address the question
of whether the widely different AW transport values that
has been reported are related to oceanic variability or
observational inaccuracies, or a combination of the two.
While the warm and salty water masses of the northeastern
Atlantic Ocean are generally recognized as a key feature
of the climate of Northwestern Europe, trends in the ice
coverage of the Arctic Ocean is recognized as being an
important indicator of climate change in these and other
regions. Also, sea ice is by itself important for the
climate, since there is a strong feedback in the heat
fluxes between the atmosphere and ocean related to melting
and freezing of ice. In subtask 5.3 we will work towards
an improved description and understanding of sea ice
variability using the relevant high quality information
that has been made available in the recent years from,
e.g., upward-looking sonar, passive microwave data (SMMR
and SSM/I), and model simulations using MICOM coupled to
NERSC's Hibler ice model [Drange and Simonsen, 1996;
Drange, 1999; Bentsen et al., 1999]. The study will also
include ocean variables in the Arctic Sea. Results from
subtask 5.2 may provide clues about relations between
variability of AW and variability related to Arctic sea
ice and hydrography due to signal propagation. The
interannual variability of the ice thickness will be given
particular attention, and results should prove valuable in
order to sort out the widely different trends that have
been reported in the literature.
Variability in the AW inflow to the Nordic Seas and
variability in the East Greenland Current related to
events in the Arctic Ocean have the potential for strongly
influencing processes in the frontal zone between these
water masses in the Nordic Seas. Obviously, the local
winds are also important in this context. A process study
of the mixing of water masses across this front will be
undertaken in a separate task (Principle Task 4). In
subtask 5.4 we aim at describing the seasonal and
interannual variability of the position and strength of
this front.. Again, the work will be performed using a
combination of observational data and model output from
MICOM. Results from MICOM have previously been used in
conjuncture with observations in a study of fluxes through
the boundaries of the Greenland Sea basin [Chierici et
al., 1999]. Results from subtasks 5.2 and 5.3 will
certainly be relevant for subtask 5.4, and a collaborative
effort will be undertaken on this basis.
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