Fróðskaparrit - 01.01.1998, Page 171

SEINHOLOSENA VEÐURLAGIÐ ELVDITIL JARÐFORMANDIVIRKSEMI f FØROYUM ] 77
the North Atlantic Drift. Rapid variations
in weather (often within few hours) are
characteristic of the present Faroese cli-
mate. In Tórshavn, close to sea level, the
MAAT is 6.5°C (AD 1961-1990), with
year-to-year variations of 0.5-1.5°C. Au-
gust is the warmest month with 10.5°C and
January the coldest with 3.2°C. The annual
mean precipitation is less than 900 mm w.e.
in the west (Mykines), increasing to almost
2,800 mm w.e. in the mountainous northern
and eastern part of the islands (Hansen,
1990; Søgaard, 1996). As an average, pre-
cipitation is registered in Tórshavn on 3 out
of 4 days. Fog is common and relative hu-
midity is high throughout the year. The
dominant wind direction is from the W, SW
and S. In many places, however, the topog-
raphy causes a local air flow pattern. The
average wind speed is high, 7.2 m/s (AD
1961-1995; data obtained by the Danish
Meteorological Institute) at exposed
Akraberg, southem Suðuroy, and has
shown an increasing trend since the early
AD 1970s, for the time being with a culmi-
nation AD 1989 to 1993. During this five-
year period the average wind speed at
Akraberg was no less than 10.5 m/s. In the
classical Koppen system (Kðppen, 1918),
the Faroe Islands fall within the type Cfc, a
moist, temperate climate with cool sum-
mers. This, however, only applies for alti-
tudes close to sea level.
Knowledge on the mountain climate of
the Faroe Islands is poor as most meteoro-
logical stations are located at low altitudes.
Above 200-300 m a.s.l. the widespread oc-
currence of small-scale pattemed ground
phenomena (Fig. 3), solifluction features
and deflation surfaces, suggests a mountain
climate characterised by extreme humidity
and strong winds rather than extreme cold
(Christiansen, 1988; Humlum and Chris-
tiansen, in press). Adopting a standard ver-
tical lapse rate of about O.OOóS^Cm1, the
modern mean winter air temperature in the
highlands is expected to lie between -3°C
and 0°C, with mean annual temperatures in
the range of 1°C to 4°C (Hansen, 1990).
In the northern hemisphere the principal
premise for distinguishing the Arctic zone
is frequently treelessness, so that all areas
lying north of the treeline are regarded as
part of the Arctic zone or tundra (Tuhka-
nen, 1987). In low-relief regions the ‘tree-
line’ may take the form of a 50-100 km
wide zone (French, 1996), while in high-re-
lief areas this boundary is well-defined, ap-
proximately coinciding with a mean air
temperature of 10°C for the warmest
month. On the Faroe Islands the warmest
month is slightly above 10°C at sea level,
and the modern treeline is located 0-100 m
above sea level, so from this point of view
the major part of the Faroese landscape is
clearly within the Arctic or periglacial do-
main.
Late 20th century mountain climate
In 1995 a limited meteorological pro-
gramme was begun in the highest mountain
massif in the Faroe Islands, the Slættaratin-
dur region, northem Eysturoy, to obtain in-
formation on the effect of altitude, topo-
graphic shadow, aspect and distance from
the sea (Humlum and Christiansen, in
press). From May 1995 to May 1996 five
daily measurements were carried out at