Jörg Wegener


Modes of North-Atlantic climate variability.


ABSTRACT:

According to Rowan T. Sutton and Miles R. Allen (hereafter: SA) there
is a chance to enhance the predictability of decadal climate
variability over the northern European sector. This enhancement
supposedly originates from the horizontal advection of SST ("Sea
Surface Temperature") anomalies along the Gulf Stream and North
Atlantic Current (NAC).  SA suggest that fluctuations in SST which
arise from advection might be predictable, and so would be their
impact on the atmosphere.  The described advection mechanism is
subject of this work, analyzing mainly NCEP/NCAR and COADS datasets of
various meteorological and oceanographic parameters. This issue is
investigated by means of statistical tools like EOF- and timeseries
analysis, especially Dietmar Dommenget's rotated DEOFs: a technique
which fits a spatial first-order autoregressive (AR(1)) process as a
null hypothesis to the data.  These analyses should clarify whether a
primary mode of advection exists or whether it is solely the
atmospheric imprint on the ocean which generates a sham advection.
The findings of SA could partly be confirmed, although a few remarks
about the statistical reliability of their analyses are made.
Applying an AR(1)-model, which divides its driving noise into a NAO
and a non-NAO part, it is shown that the former locally contributes
more than 40% to the explained variance of SST variability. The
maximum contributions align with the major areas of the NAC, where SA
suggest the propagation of SST anomalies. It is shown that this signal
is strongly influenced by the atmospheric forcing and that the latter
generates an advection-like pattern.