Jökull - 01.12.1953, Blaðsíða 26

four points in the two metres profile. Each
experiment consisted of two or more readings
of these instruments, readings of incoming and
reflected radiation (by means of Epply Pile also
built by the author), silver and black radiation
thermometers, cloud cover and various ablation
stakes set up near the mast. In addition an ord-
inary meteorological record was maintained.
The experiments were carried out over clean
ice, dirty ice and ice covered with small dirt
cones and at bi-hourly intervals throughout the
day and night.
The work was hindered by many small ad-
versities. The weather was often bad; the engi-
nes activating the airscrews were often difficult
to start and one radiation thermometer was
broken by the wind, but in all some sixty tests
were successfully compleated.
Ablation-wns measured at bamboo rods drilled
into the ice, a mark being made at the surface
position on the stake each time the stake was
read. To facilitate ablation readings at more
permanent stakes the long canes were painted
with black and white for each alternate 10 cm
length and red for the 90 to 100 crris.
The drill for the holes in the ice was made
after the Ahlmann type and though somewhat
arduous in operation was successful down to
2p2 metres. With modificadon it is now hoped
to use this for much greater depths. The drill
brace was a simple cranked handle in a ’U’ shape
with facility for screwing in the drill bit on
extension rods. The bit was a metre length o’f
mild steel tubing of U/4" diameter.
The densities of ice samples were found by
measuring the change in volume in a graduated
cylinder. Grit particles were filtered in the
field but brought back to England for measur-
ing under a microscope. This method is amp-
lified in the section on Densities and Glacial
clirt.
OBSER VA TIONS.
Micro Meteorological observátions were ini-
tially made at three areas:
I. of clean ice free from hummocks and
channels.
II. of dirt covered ice free from hummocks and
channels.
III. of ice with many small dirt cones.
All areas were on the snout of the glacier
between 1 and 2 kms. from the ice edge. There
was no other grouping of these ”type” areas
between the snout and region of Esjufjöll. The
slope of the snout and the proximity of the
sandur caused almost constant katabatic winds
so that Esjufjöll may have been the better site
for work though the 20 kms. distance from the
ice eclge and the mountain nunataks were
thought to be possible causes of anomaly and
thus not desirable for initial work on debris and
the mechanics of its deposition.
The dirt covered ice was ribboned with minor
streams which changed course almost daily and
so modified the pattern of distribution and
thickness of the dirt cover that readings taken
over this dirt covered ice could not be compared
from day to day. To a much lesser degree, and
at a slower rate, changes occurred in the sur-
face conditions of the dirt-coned ice so that
after 4 weeks a second site was found for the
observations over dirt-coned ice (i. e. type III.
above).
Since only one mast was available it was not
possible to take simultaneous observations over
the clifferent type areas so that the mast was
erected each week at the site which had not been
previously investigated under the weather condi-
tions then prevailing. It was hoped by making
these changes to achieve observations over the
different areas with a representative range of
different combinations of sun, cloud, humidity
and wind.
The dominance of wind, cloud cover and
humidity, combined with the difficulties of
constant maintenance of apparatus, gave oppor-
tunity for sufficient observations only when
there was a cold wind blowing and in conditions
which were overcast and very moist.
Wind. The following summary indicates the
wind speeds experienced over the different
areas.
See Fig. 2.
Clean Ice. Velocity at 2 metres.
Max. 30.1 ft./sec.
Min. 11.7 ft./sec.
Mean of 13 Tests: Roughness Parameter 0.2
cms.
Dirt cone Area I. Velocity at 2 metres.
Max. 24.2 ft./sec.
Min. 10.5 ft./sec.
Mean of 20 Tests: Roughness Parameter 1.61
cms.
Dirt Cone Area II. Velocity at 2 metres.
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