2005 LAYERED OCEAN MODEL WORKSHOP

Simulations of tropical Atlantic climate with coupled models suffer from severe biases. MICOM in the Atlantic has been coupled to the atmosphere model Speedy (T30, 7 layers) to study these biases (SPEEDO). The upper ocean thermal structure and associated atmospheric circulation proves to be strongly related to the strength of upper ocean mixing. The cold bias in the coupled model can be completely removed by enhancing the entrainment efficiency. Slightly deeper mixed layer reduce the upper ocean divergence resulting in realistic cold tongue development and realistic heat balances. Also, the annual cycle of SST, the thermocline structure, and the Atlantic Marine ITCZ improves markedly. The fully coupled model shows realistic low-frequency tropical Atlantic variability. The oceanic and atmospheric patterns and magnitudes of the meridional gradient mode and the eastern cold-tongue mode are comparable to observations. Other developments at KNMI will be shortly discussed as well.