Influence of the North Atlantic on simulated atmospheric variability

An atmospheric general circulation model is used to investigate the influence of the North Atlantic Ocean on
atmospheric variability. The study covers the period from 1950 to 1994. The observed sea surface temperature
and sea ice extension are used to force the atmospheric model. Several configurations of the oceanic boundary
conditions were made to isolate the role of the North Atlantic and to study its non-linear interaction with forcings
from other oceanic basins. The multi-realization character of the experiments distinguishes between the internal
random part and the external forced part of the total variability. The potential predictability can thus be evaluated.
The response of the atmosphere is also studied with a modal approach in terms of hemispheric teleconnection
patterns. The North Atlantic Ocean has a direct influence on both the Northern Hemisphere annular mode and the
Pacific-North-America pattern, leading to a weak predictability. However the direct response is largely modulated
by forcings from other oceanic basins. The non-linearity of the system compensates the predictable component of
the annular mode induced by the North Atlantic forcing. Furthermore it reduces the forced component of the
Pacific-North-America pattern, increasing its chaoticity.