Jökull - 01.12.1969, Blaðsíða 15

Sea Ice Conditions and the Atmospheric
Circulation North of Iceland
HELGI BJÖRNSSON1
abstract
Maps of monthly meari pressure at sea level
and ice limits north of Iceland at the end of
the respective months are compared. For the
period considered, 1965—1968, the comparison
indicates that an intensification of the Barents
Sea low correspojids fairly close lo the develop-
ment of bad ice conditions at the northern
coast of Icela?id. On the other hand, an in-
tensification of tlie Icelandic loiv corresponds
to good ice conclitions.
The relation between the atmospheric cir-
culation and sea ice conditions has been studi-
ed by several authors. One can distinguish
between two different categories of approach.
One deals with the comparison of temporary
changes in the general air-circulation t.o the
extent of the pack ice iii the polar basin.
These investigations suggest that the deteriora-
tion of the ice conditions arouncl Iceland in
the last years has some connection with the
increasing frequency of the meridional type of
circulation in the last three to four decennia
(see for example Defant 1924, Lamb 1966,
Fletcher 1965). The other category deals with
the local circulation pattern from year to year
and its relation to fluctuations of ice abund-
ance (e. g. Wiese 1924).
Studying the effects of wind on the ice
conditions north of Iceland from year to year
it is necessary to consider the whole area from
the Arctic Ocean to Iceland. As known tliere
are two major drifts of ice in the Arctic Ocean
— The Pacific Gyral and The Transpolar Drift
(Fig. 1). The position and strength óf these
ts mainly determined by the long-term mean
air-circulation. Consequently short-term varia-
1) Now at Norges Vassdrags- og Elektrisitets-
vesen, Oslo.
tions superimposed on the long-term mean
air-circulation over the Arctic Ocean may be
assumed to affect these two drifts and the ice
conditions in the East Greenland Current
(EGC); not only from season to season but
also from year to year. Strubing (1968) has
discussed the relation between circulation pat-
terns over the Arctic Ocean and the ice condi-
tions in the EGC. His results are “that the years
with a greater/smaller amount of ice carried by
the EGC will have been preceded by a wind-
produced influx of ice from/into the region
of the Pacific Gyral into/from the area of
strongly/weakly developecl Transpolar Drift
Stream”. Although this procedure may give a
forecast of the ice masses carried l»y the EGG
one rnust additionally consider other progno-
stic parameters: the wind field over the EGC
and the ice forming processes in the current.
According to Voioinckel (1963) there is little
ice formation south of 80° N in the EGG.
But for the years 1962 ancl 1963 Wittmann
and Schule (1966) report that “there are much
greater quantities of new ice in the marginal
seas than previously believed, and generally
more new ice in the Eurasian Basin, where
increasing wind stresses near the Greenland
Sea tend to cause divergence or ice separation”.
In this connection one may note that the air
temperature over the EGC falls when northerly
winds increase. The air temperature over the
EGC is therefore strongly depending on the
air-circulation in the area.
In the following the air-circulation north of
Iceland and the corresponding ice conditions
will be considered. Pressure maps showing the
monthly mean pressure for the surface layer
(Deutscher Wetterdienst) and ice inaps show-
ing the ice conditions at the end of the re-
spective months (British Met. Office) are used
as a basis for this study (Fig. 2). One may
JÖKULL 19. ÁR 11