Jökull - 01.12.1971, Page 17

TABLE 5.
Precipitation at Akureyri in per cent o£ precipitation at Bægisárjökull for days with various
prevailing wind directions.
Period N NE E SE S SW W NW Variable direction Total
1967 July 3— August 18 170 — — 35 46 21 0 43 33 46
1968 July—August 9 . . . 6 — - — 29 17 29 — 57 25
Total obs. period . 37 - - 35 45 18 27 43 45 38
precipitation and summer temperature in the
area might there£ore be used to construct the
mass balance for single years. Comparison of
data from the glacier and from Akureyri is
therefore of interest. Measured quantities on
the glacier and from the meteorological station
at Akureyri are summarized in Table 4. It is of
special interest to compare the values of pre-
cipitation and air temperature. The total pre-
cipitation on Akureyri for the months Septem-
ber to May is found to be respectively 24 and
20 percent of the specific winter balance for
the two glaciological years. The mutual pro-
portionality for the two years is fairly good. For
the observation periods during the summers of
1967 and 1968 the corresponding values were
46 and 25 percent respectively. The high value
for precipitation at Akureyri compared with
Bægsárjökull in the summer of 1967 might at
least partly be due to the dominating norther-
ly wincl as seen in Table 5. The table should
be compared with Table 2.
Tlie temperature gradient between Akureyri
and Bægisárjökull was found to be fairly low
and depending on the wind direction. For both
summer periods as a whole the lapse rate was
found to be on the average 0.65 °C per 100 m
during days with prevailing southerly to west-
erly winds and lower for wind directions from
the sea.
Further measurements on the glacier and a
closer comparison with neighbouring climatic
stations is needed to obtain reliable statistical
equations for construction of the past mass bal-
ance variations.
MASS BALANCE
AT BÆGISÁRJÖKULL 1966-67-68
Investigations of mass budget were carried
out by standard stratigraphic methods and
gravimetric snow surveys (see e.g. 0strem and
Stanley 1969). All changes of mass in the sur-
face layer are therefore referred to the time
of the formation of an observable “sumrner
surface” at the end of the balance year. The
techniques include snow pit stratigraphy, den-
sity measurements in the pits, snow-depth
sounding down to the summer surface (with
an aluminium rod along sounding profiles and
50 m separation between the soundings), and
measurements at accumulation and ablation
stakes.
The position of the sounding profiles, snow
pits and the ablation stakes is shown in Fig. 10.
The number of soundings was about 100 per
km2. The main winter balance was measured
both years in early May and the summer sur-
face was easily recognized. The distribution
of the winter balance is given in Fig. 11. The
maximum winter balance is found below the
mountain Jökulborgir due to orographic effects
and snow avalanches.
No detailed observations were done on the
JÖKULL 21. ÁR 15