The Botany of Iceland - 01.12.1942, Page 37

THE PTERIDOPHYTA AND SPERMATOPHYTA OF ICELAND
35
when the temperature begins to decrease. The south-westem part will
now cool down more rapidly than the north country, and, consequently,
the month of September will show a fairly marked uniformity over the
whole country, with a temperature at about 7°C. In October a pre-
cipitous fall of the temperature is followed directly by the Icelandic
winter, and the position of the isotherms is again as in the months of
January—March.
The meteorological station Grímsstaðir, situated about 90 km and
80 km from the sea towards the N. and E. respectively, and at a height
of 385 m s. m., shows the afore-mentioned rise of temperature in April,
while from the beginning of August there is a constant gradual fall
into the month of December; but here, too, the climate has a more
continental character. The summer temperature of the air will rise
higher than at the coast and, if the temperature be reduced to sea
level, Grímsstaðir will be the warmest locality in Iceland in July, with
12.7°C. The winter shows a corresponding low fall of the temperature;
in Grímsstaðir the difference between the warmest and the coldest
month is 15°C, a difference notably larger than at the coast stations,
where it scarcely exceeds 12 degrees. (Cp. Iwan, 1931, tab. VII).
Frost-days.
The number of days with the temperature entirely above zero is
comparatively not very large, inasmuch as day-frosts will usually occur
till late in May and again set in in the month of September. Thus on
the Vestmanna islands, at Berufjörður and on Stykkishólmur only the
month of July has been entirely free of frost; and on Grímsey under
the Polar circle there may occur days with frost in all the months of
the year. July, for instance, has an average 2 days of frost.
The difference in the number of days with frost in the various parts
of Iceland is shown in the following table after Iwan, loc. cit., p. 37.
TABLE 5.
Station Years of observa- tion Temp. below zero the entire day Days with alternate frost and thaw Temp. above zero the entire day
Stykkishólmur 19 61 101 203
Berufjörður 20 38 117 210
Grímsey 20 71 118 176
Vestmannaeyjar 19 17 90 258
Grímsstaðir (7) (122) (113) (130)
3*