Geoscience Reference
In-Depth Information
commonly well developed in high latitudes during the polar night when anthropo-
genic heat supply is a major component of the energy balance. Most UHI studies
have been carried out at in middle and lower latitudes, but work has also been
undertaken at Fairbanks, Alaska (Benson and Bowling,
1975
; Bowling,
1986
;
Magee, Curtes, and Wendler,
1999
) and at Barrow, Alaska (Hinkel et al.,
2003
).
Barrow (71°N) is on the Arctic coast and has a mostly indigenous Inupiat popu-
lation numbering about 4,600 people. Hourly air and soil temperature data were
logged at fifty-four sites in a 150 km
2
area during 2001-2002. During December-
March the average air temperature at the official Barrow station is −25.3°C, and
the 2001-2002 winter was typical. The coldest sites are farthest from the landfast
ice-covered ocean and the settlement area. The UHI effect averaged 2.2°C. It
peaked at 5-6°C in January-February when the air temperature was below about
−30°C, presumably when there was maximum use of energy for domestic heating.
There is a strong relationship between UHI intensity and wind speed; for winds
less than 2 m s
−1
the UHI effect averaged 3.2°C and fell to about 1°C for winds
of 4-6 m s
−1
. Maximum UHI intensity was observed from late evening to early
morning.
8.6.2
Ice Fog
Detailed studies of ice fog characteristics were carried out at Fairbanks, Alaska in
the 1960s by Benson (
1970
). The most notable feature of its formation involves the
injection of hot supersaturated exhaust air into a very cold (less than −35°C) satu-
rated air mass. This forms ~10 μm diameter ice crystals in contrast with the roughly
30 μm diameter crystals that form as “diamond dust” in suspension at about −40°C.
Low temperatures at Fairbanks conducive to ice fog development are associated
with radiational cooling over the extensive valley flats, forming a “cold air lake.”
Strong inversions form with temperature gradients of 0.2-0.3°C m
−1
in the lowest
50 m. In the 1960s the main water source for the ice fogs was cooling water from
power plants, which exceed the total from other fuel combustion sources by a fac-
tor of two. The ice fogs are shallow with an average thickness of 10 m and rarely
exceed 30 m. There were 5-6 ice fog episodes in each of the two winters studied by
Benson, but the colder winter had more ice fog days (forty days in 1961-1962, com-
pared with twenty-five days in 1962-1963), and one episode lasted fifteen days. The
area affected averages 60 km
2
, with extreme events covering up to 200 km
2
. Apart
from the effects on visibility, anthropogenically produced ice fogs can have serious
health effects owing to pollutants such as lead, chlorine, bromine, and sulfate that
are adsorbed by the ice crystals.
Focus Questions and Exercises
1) What are the major difficulties in obtaining reliable estimates of the mass bal-
ance of the Greenland ice sheet?
