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ERDC/CRREL TR-02-10
Deep Cold
Deep Cold (DC) differs from EC in that the long-term temperature trend is
more or less flat but punctuated with strong temperature fluctuations of shorter
duration. Even after the averaging and filtering operations, a fair degree of short-
term variability is apparent in Figure 5, attesting to the degree of variability from
a mean state at this time. During this period of almost no insolation, the Arctic
Slope experiences several major polar cold outbreaks, with very few contrasting
warm spells. Though several sites had record monthly maximum temperatures
above freezing, this season typically sees few anomalous warm spells. Essen-
tially, it is either cold or very cold. Intersite variability in temperature is largest
during DC, with coastal BET on average consistently the coldest site and IMN
the warmest. There is a fair degree of coherence in the temperature oscillations
among the sites, suggesting that the cold polar air mass outbreaks responsible for
the low temperatures extend across most of the network of sites. With the excep-
tion of WKU, the trend in maximum, minimum, and mean temperatures also
shows warmer conditions to the south, which also corresponds to warmer tem-
peratures with increasing elevation.
The persistent low temperatures at BET, FRA, and WKU during DC attest to
one of the signal features of cold-season climate at inland high-latitude regions--
extreme variability in microclimate dominated by infrared cooling during the
long and often clear winter night. Over a period of several days the resident air
mass comes into thermal equilibrium with the radiatively cooled snow surface
(Curry 1983). This pooling of very cold air produces a very strong temperature
inversion, similar to that seen at many locations in interior Alaska (Bowling et al.
1968). Once in place, this stable thermal environment resists vertical mixing and
typically persists until replaced with a more temperate air mass.
The last half of February is the coldest time of year at all sites, even though
the diurnal cycle is again becoming better established as solar radiation returns to
the Arctic Slope. This fact is apparent both in mean temperature and in the record
low temperatures, with the latter occurring in February at three of the five sites.
The record minimum temperature for the network for the period of record con-
sidered here, 46.1C (51F), occurred at FRA on 27 February 1997. Also, only
two sites, IMN and SAG, had February record maximum temperatures above
freezing.
Late Cold
With increasing insolation the Late Cold season (LC) is a period of more-or-
less steady warming, punctuated by strong polar cold outbreaks that often affect
the entire network, especially during March. While mean temperatures are
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