Jökull - 01.12.1991, Page 3

Temperature Conditions in Iceland 1901-1990
MARKÚS Á. EINARSSON
Icelandic Meteorological Office
Bústaðavegi 9, 150 Reykjavík, Iceland
ABSTRACT
Methods used to compute monthly mean tempera-
tures in Iceland since 1901 are shortly described.
Revised values are foundfor 32 selected weather sta-
tions starting continuous operation during the period
1901-1939, 7 ofwhich were already active in 1901.
Main characteristics of the mean temperature
1901-1990 are briefly discussed. A seasonal division
based on these temperature characteristics is pro-
posed. Mean temperature for the 50-year period
1936-1985 is described, primarily regional variations.
Finally, considerable temperature variations in
Iceland 1901-1990 are discussed.
INTRODUCTION
Considerable temperature variations have occurred in
Iceland during this century. The first two decades
were cold followed by an unusually warm period,
1926-1946. Those and other variations will be
described in detail later in this paper.
Several factors, meteorological as well as geo-
graphical, influence temperature conditions in Ice-
land to a great extent. The country is located approx-
imately between 63.4°N and 66.5°N, the northern-
most points reaching the Arctic Circle. At these lati-
tudes there is a considerable annual deficit in the total
radiation balance. Consequently, a transfer of heat
from lower latitudes is carried out by oceanic and
atmospheric circulations.
Iceland is situated near the border between warm
and cold ocean currents. The warm Irminger Current
encircles the south, west and partly the north coast
but on the other hand a branch of the cold East
Greenland Current, known as the East Iceland
Current, flows in a southerly and southeasterly direc-
tion along the east coast. Off the northwest and
southeast coast a temperature front is found between
these two different currents. It is obvious that the
oceanographic conditions must influence weather
and climate considerably, both directly at the coasts
and also because all air masses arrive in Iceland after
having passed over the sea. In addition sea ice some-
times reaches the north and northeast coast, particu-
larly in late winter, with cooling effects.
As with ocean currents warm and cold air masses
often meet near Iceland. Cyclones formed on the
polar front pass frequently, often with sudden tem-
perature changes, and in some cases cold or warm
periods may last for weeks, depending on the main
location of the low pressure centres.
Further, it should be mentioned that Iceland is a
very mountainous country which in many ways may
influence temperature.
For many reasons it is of interest to study temper-
ature conditions and variations in Iceland during this
century. For that purpose 32 weather stations, all in
continuous operation since 1939 or earlier, were
selected (Fig.l). Seven of them were already operat-
ing in the year 1901. A summary of methods used to
compute monthly mean temperatures at different
times is given in the following.
METHODS FOR COMPUTING MONTHLY
MEAN TEMPERATURES
During the first five decades of this century the main
hours of observation at Icelandic climatological
JOKULL, No. 41, 1991
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