Jökull - 01.12.1969, Page 72

Fig. 10. The position of
the ice edge is shown at
several dates from Au-
gust 10 to December 27,
1968. This composite
picture is compiled from
APT pictures and air-
craft reports. The quest-
ion is: will we be able
to forecast the movement
of the ice edge in the
future?
snow from the land near the coastline will
frequently show up as an apparent break in
the icet'ield, wliile big leads (polynyas) in the
ice-pack give evidence of great internal stresses,
that are not easily explained. New ancl trans-
parent ice is not discernible in the pictures.
Flowever snow that falls on top of ice of this
kind will make it immediately visiltle. This can
cause some confusion since the ice edge may
seern to have advanced inexplicably far in a
short time, and quite rapidly in spite of gentle
wind speed. This kind of ice tends to break up
easily and moves then much more rapidly than
the main ice-pack.
Conclusion: By using APT pictures ancl
mapping the position of the ice edge, when-
ever possible, and also using average monthly
surface pressure maps, revised every 10 days or
so, it should be possible to forecast the move-
ment of the icefield 10 to 15 days ahead. These
forecasts would be based upon Zubov’s rule:
V = fqAp
where V is the drift of the ice in kilometers
per month.
Ap is the pressure gradient in millibars per
kilometer, calculated from an average monthly
surface pressure map, and
ttj is called the isobaric coefficient.
The rule is based on an empirical approach
so one would probably have to find a new
value for a{. In the preliminary studies the
value 13,000 was used.
REFERENCES
Gordienko, P. A. 1961: The Arctic Ocean. Sci-
entific American, May 1961.
68 JÖKULL 19. ÁR