Jökull - 01.12.1969, Page 67

Greenland current is supposed to carry from
the Arctic into the North-Atlantic Ocean must
be a rather crude one, since the satellite pic-
tures indicate large variations in the amount o£
the annual coverage of ice in this area.
Information on sea ice is now compiled from
observations and reports from ground stations,
ships, aircraft and pictures from weather satel-
lites. For brevity these pictures will henceforth
be callecl APT pictures (Automatic Picture
Transmission).
Up to the present the APT pictures received
at Keflavik Airport have come from the ESSA
Satellites. They orbit the earth approximately
from pole to pole at heights between 1400 ancl
1500 km. The gridding of areas north of 60
degrees latitude demands great precision, and
even so, some adjustments are usually necessary.
Pictures can yet only be taken over the day-
light zone of the eartli. This means tlrat we
can only get pictures of the ice edge from
Pebruary to November. (For further technical
information see: APT Users Guide, published
by U. S. Dept. of Commerce.) The area under
discussion lies between 60° N and 80° N. It is
bounded by the east coast of Greenland in the
West and 10° E in the East.
Sea ice conditions off and at the north coast
of Iceland are here divided into three categories.
When this classification was made three prim-
ary factors were considered as most important,
namely the amount of ice coverage, the diffi-
culty for shipping and finally the estimated
cooling effect on the sea off the north coast
(this factor affects the fishing).
The three categories are:
1. New ice less than 1 year old forrned hv
freezing of the surface waters at and off the
north coast o£ Iceland, sometimes mixed with
a few icefloes that may Iiave been broken off
the main icefield by intense storms. This ice
coverage amounts usually to 1/10 or less and
normally causes srnall difficulties for shipping
except into certain harbours. Coqling effect of
the sea is negligible. These conditions are not
nnusual for the north coast.
2. The icefield has been driven by persistent
northeasterly winds southwards along the east
coast of Greenland. When the wind turns to
prevailing westerly direction f. ex. for a month
or so, the icefield breaks up and drifts rapidly
Fig. 2. March 24, 1965. Persistent ancl rather
strong north and northeasterly winds from the
beginning of November 1964 to the end of
January 1965 drove the ice-pack southward. In
the beginning of February 1965 the wind direc-
tion changed to westerly. This caused the ice-
pack to break up somewhat and drift rapidly
eastward. A nortlierly wind prevailing during
the montli of March drove tliis broken icefield
to the nortli coast of Iceland.
east wards. The coverage is usually 1 to 3 tenths
and can cause difficulties for shipping along
the north coast. The cooling effect is consider-
able, but depends on the duration of the ice.
This kind of ice usually disappears rapidly
once the wind direction becomes east or south-
erly. The year 1965 is a case in point.
3. The ice tongue between Spitsbergen and
East-Greenland has been clriven by northerly
winds all the way from Shannon Island to the
north coast of Iceland. Wlien seen on the APT
picture the coverage is 10/10 and seems to reach
all the way from the North Pole to Iceland.
This is usually caused by a combination of a
strong north-wind along the east coast o£ Green-
lancl for several months and a prevailing east-
erly wind over the southern Denmark Strait.
JÖKULL 19. ÁR 63