Fróðskaparrit - 01.01.2002, Page 107

ARKTISKA FJALLAVEÐRIÐ í 2000 Á SORNFELLI
105
0 45 90 135 180 225 270 315 380
Winđ direction, degrees
Figure 9. Windchill as a
function ofwind direction at
tlie Sornfelli meteorological
station. The windchill values
are calculated hased on tlie
corrected air temperature data
for 2000.
for the Sund station was 7.3°C, a value
somewhat warmer than the Torshavn 1961 -
1990 annual mean of 6.5°C (Table 1).
The mean annual lapse rate was
-0.0077°C/m (Fig. 10). This value is well
above the standard value of -0.0065°C/m
(Ahrens, 2000) for oceanic regions, and
shows that the atmosphere in general is un-
stable. Winter lapse rates generally between
-0.007°C/m and -0.009°C/m, and summer
values of -0.004°C/m and -0.005°C/m are
recorded for temperatures close to the
ground surface in the Slættaratindur moun-
tain area, in the northern part of the Faroe
Islands, in the period 1995-2001 (Chris-
tiansen and Humlum, submitted). The sea-
sonal variation in the lapse rate (Fig. 10)
shows the atmosphere to be generally
unstable all the year, but with several sum-
mer periods with stable conditions, when
values above -0.0065°C/m occur. During
summer temperature inversions occurred
primarily during calm conditions, when the
Sornfelli mountain received more direct
insulation than the more shaded, lower
located Kaldbaksfjørður valley, where also
moist air and fog occurred at the coast.
Freezing, thawing and
growing indices at Sornfelli
The corrected air temperature (Fig. 6) was
used to calculate freezing, thawing and
growing degree days (FDD, TDD and
GDD) (Andersland and Ladanyi, 1994;
Molau and Mølgárd, 1996) at Sornfelli
(Fig. 11), based on daily mean air tempera-
tures. The annual TDD sum of 973 is much
larger than the 361 FDD sum, indicating a
positive ground thermal regime without
permafrost.
The annual sum of GDD is 160, which is
significantly less than found at the same al-
titude at the Slættaratindur area by Hum-
lum and Christiansen (1998b, Fig. 5: 178),
based on ground surface temperatures.
Discussion
The new concept of the Sornfelli meteoro-
logical station, with a heated cylinder hous-
ing the instruments in an advanced auto-