Surface Climate and SnowWeather Relationships of the Kuparuk Basin
37
the Arctic Slope during Early Cold (EC). Focusing on one representative site, it
is found that this bump occurs to some extent in all years of the period of record.
These annual late EC warming events result from nearly stationary or slowly
propagating and vertically stacked low-pressure systems over southern Alaska
that advect warm air northward to the Arctic Coast. Such events typically bring
from several hours to several days of above-freezing temperatures to the Arctic
Slope after a significant amount of snow has accumulated and produce a high-
density stratum in the snow cover, capping the accumulated EC snowpack and
protecting it from subsequent wind erosion.
The observed patterns of temperature and wind have important ramifications
for the winter snow cover of the Kuparuk Basin, which plays a central role in the
hydrology, ecology, and surface energy balance of the region. The seasonal dif-
ferences in the temperature patterns between the Brooks Range and the coast
explain why the snow cover forms first in the foothills and last near the coast, the
presence of an ice-free ocean moderating early-winter coastal temperatures suffi-
ciently to retard the formation of the snowpack. Similarly the occurrence of
above-freezing temperatures near the Brooks Range more than a month before
similar temperatures are experienced at the coast leads to a disappearance of
snow in the south considerably earlier than at the coast.
The low wind speeds experienced across the network in October and
November, particularly in the southern parts of the region, help to explain the
presence of thick but low-density layers in the base of the pack throughout this
area. These layers show signs of having been deposited in low wind conditions,
and their presence is one of the reasons the pack is such a good insulator, retard-
ing heat loss from the ground throughout the winter. The insulating value of these
basal layers is greatly enhanced when they metamorphose into depth hoar, which
has the lowest thermal conductivity of any type of snow (Sturm and Johnson
1992, Sturm et al. 1997). This metamorphic transition is virtually assured by the
cold winter climate and low winter precipitation values of the Arctic Slope. What
is surprising is that these low-density snow layers, which are at risk of erosion
during later high-wind events, are not eroded most of the time. Their persistence
can be in part ascribed to the unusual thaw observed each winter in November as
well as the generally low winds observed in much of EC. The thaw has been
observed to create an icy cap at the top of the snowpack that resists wind erosion.
We are unsure what happens in years when there is no thaw, but we note that a
close and critical connection exists between the snow cover and the weather. This
connection relies not only on the broader features of the weather but may depend
also on some of the subtler aspects.
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