Helge Drange (1-4), Ingo Bethke (1), Tore Furevik (2-3), Mats Bentsen
(1,2,4), Odd Helge Ottera (1,2)
Affiliation: (1) Nansen Environmental and Remote Sensing Center,
Bergen, Norway, (2) Bjerknes Centre for Climate Research, Bergen, (3)
Geophysical Institute, University of Bergen, (4) Nansen-Zhu
International Research Centre, Beijing, China
The Bergen Climate Model (BCM), consisting of the GCMs ARPEGE and MICOM, has been developed, tested and evaluated over the last 5 years as part of the Bjerknes Centre for Climate Research in Bergen. In BCM version 1, both fresh water and heat flux adjustments were used. In BCM v2, no flux adjustments are applied, and this system is a part of the (rather extensive) Fourth Assessment Report of the IPCC scheduled for 2007.
Here we focus on how MICOM, in uncoupled and coupled mode, has been used to identify the formation, propagation and decay of hydrodynamic anomalies in the Atlantic-Arctic region. Special focus is on the fresh water budget, a quantity that is of critical importance for the variability and stability of the Atlantic Meridional Overturning Circulation.
In general, coupled atmosphere-sea ice-ocean climate models forced with increasing greenhouse gas concentrations predict enhanced evaporation in the tropics and enhanced precipitation in the extra- tropics. The additional precipitation and continental run-off into the North Atlantic and Arctic drainage regions, and melting of Arctic sea ice and glaciers, have led to the expectation of a gradual freshening of the northern North Atlantic, with a weakened Atlantic Meridional Overturning Circulation as a result. A six-member BCM ensemble is used to demonstrate that the North Atlantic may become more saline despite increased precipitation, melting of sea ice and glaciers, and a significantly fresher Arctic Ocean.