Variability and signal propagation from high resolution information

The work will be aimed at improving the present understanding and description of seasonal and interannual variability of the water masses that flow into and within the Nordic Seas and Arctic Ocean. The variability of the extent and fluxes of sea ice will also be investigated.
PT5 description

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
(4): variability and trends related to the ice cover and ice transport in the Arctic Sea and Nordic Seas

In Norway, little attention has so far been paid to examine and understand how the variability of the regional circulation is affected by the variability of the North Atlantic ocean circulation. Hence, one goal 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 lengths of the available time series from the sets of high resolution information 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.

The inflow of Atlantic Water (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. We will describe and analyze to what degree the variability is forced by oceanic teleconnections through signal propagation, and local atmospheric forcing. 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. Further, 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.

Trends in the ice coverage of the Arctic Ocean is recognized as being an important indicator of climate change in Norteast Europe 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. We will take advantage of the relevant high quality information that has been made available in the recent years from, e.g., upward-looking sonar, passive microwave data, and model simulations. Results 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). Here, 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 results.

Arne Melsom
Last modified: Fri Mar 30 13:14:37 GMT 2001