| Abstract: Numerical simulations of the Atlantic
Ocean during the period 1950 to 1989, using a sigma coordinate, free surface
numerical model, show long-term variabilities in the upper ocean subtropical
gyre similar to those obtained from observations. The simulations
show how westward propagating planetary waves, originated in the eastern
North Atlantic, affect interdecadal variabilities of ocean properties such
as the Bermuda sea level, the Gulf Stream position and strength, and subsurface
temperature anomalies in the weatern North Atlantic. Special attention
is given to the dramatic sea level drop at Bermuda in the early 1970s,
which is accompanied by cooling of subsurface layers in the western North
Atlantic and a northward shift and weakening of the Gulf Stream.
Following these events, between 1970 and 1980, the cold temperature anomalies
in the upper layers of the western North Atlantic slowly propagated eastward
and downward; the strongest propagating signal in the model is found at
200-m depth, suggesting that advection of anomalies downstream by the Gulf
Stream current and changes in winter mixing are involved. Significant
correlations were found between the sea level anomalies at Bermuda and
sea level anomalies in the eastern North Atlantic up to eight years earlier.
Sensitivity experiments with different atmospheric forcing fields are used
to study the ocean response to observed sea surface temperature and wind
stress anomalies. It is shown that on decadal timescales, the ocean
model responds in a linear fashion to the combined effect of SST and wind
stress anomalies, a fact that might be exploited in future climate prediction
studies. |