The Botany of Iceland - 01.12.1914, Blaðsíða 91

PHYSICAL GEOGRAPHY
275
699.2 mm.; at Beruijord during a period of 34 years, from 788.7 mm.
to 704.9 mm.; and at Akureyri, during one of 33 years, from 789 mm.
to 705.7 mm. The paths of the moving centres of depression lie especi-
ally frequently south of Iceland so that one centre of depression after
the other crosses the Atlantic from the west with a main direction of
east or north-east; sometimes nearer, sometimes further from Iceland.
This movement of low pressure centres causes the wind to veer to-
wards the sun, especially from S. or SE. through E. and NE. Table III
shows that at Stykkisholm, very freifuently the winds blow from S.
and SW. (such form 11 °/o and 10 % respectively) which is due to the
fact that Denmark Strait also provides a path for the moving centres
of depression; thev come from the south and cause on Iceland a veering
of the wind with the sun from SE. or S. through SW. It is probably
these centres of depression which cause the rather frequent winds from
the W. and SW. at Grímsey and Papey respectively. There may,
however, occur longer periods in which the winds of Iceland are
rather constant, the lowest atmospheric pressure over the North
Atlantic remaining at the same place. The wind-conditions are gen-
erally favourable for Iceland, the warm air from the Atlantic Ocean
is carried in over the land, while it is rare for cold winds to be
thus brought during winter. According to observations taken at
Stykkisholm on the west coast, the warmest winds there are the
SE., S. and SW. while the greatest cold is caused by the N., NE.
and E. winds. The difference between the temperature induced by
the warmest and by the coldest winds is on an average 9°—10° C.
in the months of December to April, and 4°—6° C. in the other
months. The temperature inay show great diíferences according to
whether norllierly or southerlj' and easterly winds are the prevalent
ones for any length of time; thus, the mean temperature at Stykkis-
holm in March 1856 was + 4.3° when southerly winds prevailed,
and in March, in the ice-year 1881, the mean temperature was
— 13.3° when easterly winds were prevalent.1 Conditions pertaining
to the atmospheric pressure over the Atlantic, whicli is specially
1 V. Willaume-Jantzen: Climat du littoral islandais, 1902. N. Hoffmeyer:
Die Vertheilung des Luftdruckes iiber den nord-atlantischen Ocean wahrend des
Winters und deren Einfluss auf das Klima von Europa (Zeitschrift fiir Meteorologie.
Wien, 1878. Bd. XIII. Nr. 22). N. Hoffmeyer: Etude sur les tempðtes de l’Atlantique
septentrional. Copenhague, 1880. G. Rung: Répartition de la pression atmos-
phérique sur l’ocean atlantique septentrional. Copenhague, 1894. V. Garde: Vind-
kort over den nordligste Del af Atlanterhavet (Nautisk-meteorologisk Aarbog for
1899. Kobenhavn, 1900. S. 25—46).