Abstract:
Aspects of the circulation and convection in the Irminger Sea are investigated using a variety
of in-situ, satellite, and atmospheric reanalysis products.
Westerly Greenland tip jet events are intense, small-scale wind phenomena located east
of Cape Farewell, and are important to circulation and convection in the Irminger Sea.
A climatology of such events was used to investigate their evolution and mechanism of
generation. The air parcels constituting the tip jet are shown to have a continental origin,
and to exhibit a characteristic deflection and acceleration around southern Greenland. The
events are almost invariably accompanied both by a notable coherence of the lower-level
tip jet with an overlying upper-level jet stream, and by a surface cyclone located in the lee
(east) of Greenland. It is argued that the tip jet arises from the interplay of the synopticscale
flow evolution and the perturbing effects of Greenland’s topography upon the flow.
The IrmingerGyre is a narrow, cyclonic recirculation confined to the southwest Irminger
Sea. While the gyre’s existence has been previously documented, relatively little is known
about its specific features or variability. The mean strength of the gyre’s circulation between
1991 and 2007 was 6.8 ± 1.8 Sv. It intensified at a rate of 4.3 Sv per decade over the
observed period despite declining atmospheric forcing. Examination of the temporal evolution
of the LSW layer thickness across the Irminger Basin suggests that local convection
formed LSW during the early 1990s within the Irminger Gyre. In contrast, LSW appeared
outside of the gyre in the eastern part of the Irminger Sea with a time lag of 2-3 years,
consistent with transit from a remote source in the Labrador Sea.
In the winter of 2007-08 deep convection returned to both the Labrador and Irminger
seas following years of shallow overturning. The transition to a convective state took place
abruptly, without going through a preconditioning phase, which is contrary to general expectations.
Changes in the hemispheric air temperature, tracks of storms, flux of freshwater
to the Labrador Sea, and distribution of pack ice all conspired to enhance the air-sea heat
flux, resulting in the deep overturning.
