Agulhas

Principal Investigator

Dr S S Drijfhout
Royal Netherlands Meteorological Institute (KNMI)
P O Box 201
3730 AE De Bilt
The Netherlands

drijfhou@knmi.nl

Project description

Interannual and interdecadal climate variability in Europe is associated with thermohaline circulation anomalies in the ocean and anomalous convection and production of North Atlantic Deep Water (NADW). Such circulation anomalies can be forced in the North Atlantic itself, by a coupled ocean-atmosphere instability. Also, they can be forced elsewhere. Ocean anomalies can induce local atmospheric anomalies. which, through a 1 teleconnection may affect the production of NADW and climate variability above Europe, such as the North Atlantic Oscillation (NAO). Also, the global thermohaline circulation (THC) advects temperature anomalies northward into the North Atlantic. These anomalies are advected subsurface, but outcrop on the Northern North Atlantic where they can affect the atmosphere. Interocean exchange of between the Indian and South Atlantic Ocean controls the northward heat flux that is associated with this flow. Interbasin exchange of water around the Cape of Agulhas is thought to be a key link in the maintenance of the global THC. This so called Agulhas leakage occurs on an intermittent basis. It is largely determined by the shedding of Agulhas Rings which is extremely variable on the interannual timescale. As a result, Agulhas Rings seem to be the most likely source of South Atlantic circulation anomalies that influence the THC and climate variability above Europe. Also, they are an important source for South Atlantic SST anomalies.

This special project is part of a larger programme in which the relation between variable interocean exchange in the Agulhas Retroflection region, the Atlantic thermohaline circulation and climate variability above Europe are investigated. To this end, we have developed (are developing) numerical ocean and atmosphere models to investigate

1) The transfer from Indian Ocean Water from Agulhas Rings to the Conveyor Belt in the South Atlantic

2) The pathways of the Conveyor Belt in the South Atlantic.

3) The origins of (SST) variability in the South Atlantic.

4) The possible relation between South Atlantic ocean variability and coupled variability in the North Atlantic

5) Analysis of South Atlantic covariability from the COADS dataset and NCEP and ERA reanalysis.

Ultimately, a hindcast module will be developed which uses data-assimilation in both atmospheric and ocean model.

For more details, please refer to the last progress report.

Additional information

Project started in 1996.