Simulations of hydrographic properties in the north western North Atlantic Ocean in Coupled Climate Models

• Main Authors: M. F. De Jong, W. Hazeleger, H. M. Van Aken, C. A. Severijns, Royal Netherl, De Bilt, The Netherl
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: Irminger Sea; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.512.2918; http://www.knmi.nl/publications/fulltexts/revision_2_of_simulations_incl_figs1.pdf

The performance of Coupled Climate Models (CCMs) in simulating the hydrographic structure and variability of the northwestern North Atlantic Ocean, in particular the Labrador and Irminger Sea, has been assessed. This area plays an important role in the Meridional Overturning Circulation. Hydrographic properties of the pre-industrial run of eight CCMs used in the IPCC AR4 report are compared with observations from the AR7 World Ocean Circulation Experiment repeat section. The mean and standard deviation of 20 years of simulated data are compared in three layers, representing the surface waters, intermediate waters and deep waters. Two models simulate an extremely cold, fresh surface layer with model biases down to-1.7 psu and-4.0 °C, much larger than the observed ranges of variability. The intermediate and deep layers are generally too warm and saline, with biases up to 0.7 psu and 2.8 °C. An analysis of the maximum mixed layer depth shows that the low surface salinity is related to a convective regime restricted to the upper 500 dbar. Thus, intermediate water formed by convection is partly replaced by warmer water from the south. Model biases seem to be caused by the coupling to the atmospheric component of the CCM. Model drift during long spin up periods allows the initially small biases in water mass characteristics to become significant. Biases that develop in the control run are carried over to the 20th century runs which are initialized from the control runs. 2 1.