Jökull - 01.12.1971, Page 9

General characteristics
of the weather situation
At the end of June and in July 1967 the
air circulation was rather cyclonic but winds
were of northerly or variable direction and
iight strength except on June 26 and 27 when
the northern wind reached strong breeze for
some hours. July in 1967 was extremely cold,
foggy and with frequent rainfall. In August
light south to westerly winds prevailed. The
only period of anticyclonic circulation during
the summer of 1967 was observed in July 12—
15. In July 14 the relatively strong and dry
southerly wind may be characterized as foehn.
In 1968 the end of June was cold with fre-
quent snowfall. The first half of July had
rather light winds and the temperature was at
or below normal. From July 2 to 6 an anti-
cyclone was developed over the western part
of Iceland. During these days relatively dry
southerly winds were blowing and the insola-
tion reached its maximum for the summer.
From the middle of July and throughout the
observation period southwesterly to westerly
winds prevailed with a trend to increased
strength and air temperature above normal.
Advective, climatic factors
Although wind directions are to some extent
influenced by the local topography the wind
roses in Table 2 for the prevailing wind direc-
tion in a day illustrate clearly the advective
effects of the climatic controls present near the
northern coast of Iceland. The wind roses for
the relative humidity and the air temperature
point out the significant sources of heat and
moisture at the glacier. Northerly winds bring
cold air with high relative humidity to the
glacier, the cloudiness is high, fog and pre-
cipitation are frequent. Southerly winds bring
relatively warm air to the glacier, humid dur-
ing passage of cyclones but otherwise relatively
dry with great daily ranges of relative humi-
dity and air temperature (see Fig. 5 and Fig. 6).
Table 2 illustrates further the effect of the
different wind frequency in the two summers.
The difference between July 1967 and July
1968 is striking. An interesting observation is
that in spite of relatively low frequency of
northerly winds in July 1968 compared with
July 1967, winds from this direction brought
LlI
>
CLOUDINESs'loctas) “
Fig. 7. Frequency curve of daily average of
cloud amount.
7. myncl. Tíðni dagsmeðaltals skýjahtdu i 8.
hlutum himins.
relatively high amounts of precipitation and
north was the only direction which brought
snow. This emphasizes the importance of the
proximity of the sea for the nourishment of
the glacier.
Statistics on precipitation and fog for both
summer periods is summarized in Table 3.
Precipitation was mainly in form of rain and
drizzle and snowfall was only observed in two
days each year. Unmeasurable traces of pre-
cipitation were very frequent in July 1968.
The given amounts of precipitation can only
be taken as indicating values as will be discuss-
ed later.
Characteristic features of the cloud climate
for both sumrner periods are illustrated in Fig.
7. It appears that for the observation period
in 1967 there is a marked maximum of days
with dense overcast and few days with clear
sky. In the observation period in 1968 days
with clear sky were relatively less frequent
than the year before. This difference is a result
of less frequent northerly wind directions in
the summer of 1968.
The advective dependence of the tempera-
ture climate is further illustrated by the histo-
grams in Fig. 8. In July 1967 the main mode
lies between 4 to 5 °C and about 35 percent
JÖKULL 21. ÁR 7