Jökull - 01.12.1969, Side 71

season, if any, that summer. This is exactly
what happened last year (1968).
American meteorologists are using infrared
sensing thermometers and measuring the sur-
face heat radiation of the water of Hudson Bay.
As a result they were generally able to rein-
force previous indications that the melt water
from the thawing pack-ice remains a clistinct
body significantly colder than the surrounding
waters almost until the autumn freeze up. This
indicates that once the icepack has reached the
coastal waters of northern Iceland the chances
that the following winter will bring ice into
these same waters are better than even, since
the cold ancl less saline surface waters will
freeze more easily than in average years (see
Fig. 3 and Fig. 8). To stop this trend a radica!
change in the atmospheric circulation is necess-
ary.
The ice-pack has pressure ridges reaching a
height of about 8 meters, while corresponding
pendants go to three to five times the height
of the ridges, below the normal bottom of the
ice-pack. These ridges and pendants tend to
increase the effects of the wind and the cur-
rents respectively.
It is evident that a great force is needed
to move an icemass of about 10,000 km3 several
hundreds of kilometers. A single low, even an
intense one, only breaks up the ice edge, but
does not move the ice-pack much. To move
such a rnass a longterm circulation in a pre-
vailing direction is needed. Once the ice-pack
has started to move and gathered momentum
it will neither be easily stopped nor diverted
from its course. The author has analysed over
30 maps depicting the average monthly surface
pressure, selected from November 1964 to Janu-
ary 1969, and the correlation between the pre-
vailing wind direction and the extent and the
position of the ice edge is quite striking.
There are several difficulties in mapping the
ice edge by the use of APT pictures. It is very
difficult to distinguish between ice and clouds
from a single picture; cloucls move however 20
to 2000 times faster than the ice-pack, and
with several pictures in chronological order it
becomes easy. The land in high latitude is only
clearly visible when it is covered with snow,
otherwise it is almost impossible to be sure
whether a dark area is sea or land. Melting
Fig. 8. August 11, 1968. The unusually cold
surface waters surrounding Iceland have cool-
ed the air to its condensation temperature;
the resulting fog over the coastal waters shows
off the dark land area quite distinctly. The
glaciers of Icelancl are easily seen. The ice
tongue has withdrawn to the north and is seen
extending through the gap between Spitsbergen
and Greenland reaching well south of Shannon
Island.
Fig. 9. August 18, 1968. In the evening sun-
light the extent of the ice-pack along the east
coast of Greenland is easily observed.
JÖKULL 19. AR 67