"Waghorn" wrote in message
news:d8cv29
A 30-35 day oscillation has been reported in the literature in
association with N Atlantic sector blocking and retrogression of the
jet,this may be a harmonic of a 70 day signal.
Causes may be an internal oscillation involving barotropic interaction
with topography,probably unlikely in the Atlantic,

.... the short-range (synoptic / day-to-day scale) effect of the
Greenland land/ice mass on N. Atlantic disturbances is accepted (i.e.
the Kap Farvel / Cape Farewell distortion), and I believe that in recent
years, the whole subject of the interaction with the Northern
Hemispheric broadscale flow has been investigated and found to be a
fertile subject. Your mention of topography had 'little bells' ringing
at the back of my mind of a study that was published several years ago
that directly linked the presence of Greenland with distortions in the
long-wave pattern, but after a search, I can't come up with that
particular entry. However, I did come up with :-

http://folk.uio.no/jegill/papers/pet...004_tellus.pdf

"Numerical simulations of Greenland's impact on the Northern Hemisphere
winter circulation" from which the following is extracted (from the
Conclusion):-
quote The present study shows that Greenland has a significant impact
on the general circulation of the Northern Hemispheric extratropics, at
both lower and mid-tropospheric levels. Due to the presence of
Greenland, the storm tracks are shifted southward over the North
Atlantic and thus the mountain contributes to less precipitation at the
western coast of Norway and over the North Atlantic. Greenland has a
damming effect on the air mass on its west side, which is cooled down by
radiative heat loss during the polar winter, leading to less
geopotential thickness in the area and thus less 500-hPa geopotential
height than in the simulation without Greenland. The cold air also
causes increased baroclinicity over North America leading to an increase
in cyclone activity. On the east side of Greenland, the mountain causes
higher sea level pressure which is associated with increased
geopotential height at the 500-hPa level. The study demonstrates that
Greenland’s impact on the general circulation is fundamentally different
from the impact of the Rocky Mountains and the Tibetan Plateau. Unlike
the case of the classic Rossby wave where westerlies impinge on a major
mountain range and a trough is created downstream of the mountain,
Greenland’s impact seems mainly to be a perturbation of the flow on the
upstream side of the mountain generated by damming of cold low-level air
masses. /quote

If I understand aright, then we are not looking at the classic
'Rossby-wave' type of distortion of the pattern, but an indirect control
on same due to changes in the temperature regimes either side of
Greenland.

Whilst searching, I also came upon a few links relating climatological
regime changes over Greenland (from Ice core evidence) and the Asian
monsoon - this implies quite complex and fundamental teleconnections
north-to-south as well as west-to-east: who'd be a climate scientist!



Martin.