Jökull - 01.12.1969, Síða 12

Fig. 1. Mean
values, extremes
and the cumula-
tive frequency
distribution of
temperature in
the four seasons
during 1846—
1968.
variations in different seasons. According to
Icelandic tradition the winter is defined as
the period December to March, spring is April
and May, summer June to September and
autumn October and November.
Fig. 1 shows the cumulative l’requency
distribution of the temperature in the four
seasons, mean values and extrenres. The normal
values 1931 — 1960 are also shown on the figure
as all meteorological services now refer to this
period as the normal period.
The winter shows the greatest variation, the
difference between the coldest and mildest
winter is 12.5° C, while corresponding figures
for the spring and autumn are 6.5° C and
6.8° C, but the difference between the warm-
est and coldest summer is only 4.5° C. An-
other characteristic feature in the winter figur-
es is a left tailed distribution, while the other
seasons are fairly symmetric.
These distributions are liere used to classify
very cold, cold, normal, warm and very warm
seasons.
Tlie frequency 0.1 is taken as the limit for
very cold or very warm seasons, values between
the marks 0.1 and 0.25 form the groups of
warm and colcl and the 50% in the middle
of the distribution are here called normal.
Table 2 gives these limits for the different
seasons.
Figure 2 shows the season temperature for
the whole period of 123 years. Here again we
see clearly that the temperature variations are
greatest in the wintertime. The winters also
show clear periocls of different climate. One can
without hesitation speak of a period of warm
winters after 1920. The average temperature of
the winters 1921 to 1968 is 1.0° C over the
general mean 1846—1968, and the frequency of
warm ancl very warm winters is here 0.54. No
winter after 1920 belongs to the group of very
cold winters, and only three are cold, 1936,
1951 and 1968. The last 3 winters have all
been below the general average, but it is not
yet sufficiently justified to state that the periocl
of warm winters ended in 1965.
TABLE2
Stykkishólmur Weather Station
Temperature limits, °C
Seasons Very cold Cold Normal Warm Very warm
Winter . -3.1 -3.0, - 2.2 -2.1, -0.2 -0.1, 0.8 0.9
Spring 0.9 1.0, 1.8 1.9, 3.9 4.0, 4.7 4.8
Summer 7.7 7.8, 8.2 8.3, 9.2 9.3, 9.6 9.7
Autumn 0.8 0.9, 1.7 1.8, 3.2 3.3, 3.8 3.9
8 3ÖKLILL 19. ÁR