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RESEARCH HIGHLIGHT
Sea Ice Conditions in the Arctic Ocean off the Coast of Alaska: 2002-2003
January 13, 2006
Sea ice in the Arctic Ocean off the coast of Alaska has been
receding since 2002. However, recent satellite images show that the
sea ice is closer to the Alaska coast this year than it was last
year (Figure 1). The advance toward the Alaska coast is counter to
what the greenhouse effect predict: that sea ice is supposed to
continue to move away from the Alaska coast as it shrinks. Although
it is generally agreed that the Arctic sea ice is shrinking, the
movement of sea ice away from the Siberian coast and toward Greenland
and Alaska is most likely due to natural causes such as a shift in wind pattern and many other factors.
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| Figure 1. These satellite maps show that summer sea ice is closer to the Alaska
coast this year than it was the last three years. This is evident by comparing five satellite images
taken in 2001-2005. |
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SEPTEMBER SEA ICE |
Spring Notes:
High pressure over Alaska and low pressure over north central Siberia facilitated advection
of the warm air masses over Chukotka into the Chukchi and East Siberian Sea regions.
The warm air advanced melt onset, and the ensuing ice-albedo feedbacks.
Spring winds promoted offshore ice advection in the E. Siberian and Laptev Seas, moving the thicker
winter ice toward the pole which was replaced by younger and thinner first year ice. |
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Summer Notes:
Low-pressure anomaly formed over the Beaufort Sea.
The Beaufort Gyre was weakened.
Less sea ice was advected from the Beaufort Sea into the Chukchi and E. Siberian Seas.
Ice divergence was enhanced, promoting more leads and lateral melt.
Prevailing winds compressed ice in the Beaufort Sea into the Canadian coast.
Summary:
Despite cooler than average summer air temperatures north of Alaska, the combined effects of early
melt onset and offshore ice advection, a weakened summer Gyre, greater ice divergence and lateral
melt, and prevailing westerly winds during summer, promoted diminished September ice extent in
the western Arctic |
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SEPTEMBER SEA ICE |
Spring Notes:
A lot of similarity to 2002, except the low pressure over north central Siberia was much deeper.
The deep low pressure system enhanced ice advection through the Transpolar Drift Stream.
Winds facilitated offshore ice advection in the Laptev and E. Siberian Seas.
Warm surface air over Chukotka was advected into the western Arctic.
Melt onset was advanced over a predominantly first-year ice pack (extreme ice retreat in autumn
2002). |
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Summer Notes:
Like summer 2002, lower than average pressure over the Beaufort Sea weakened the Beaufort Gyre.
Increased ice divergence promoted lateral melt of an otherwise thinner than average ice pack,
which was preconditioned by the extreme 2002-summer ice retreat, and then followed by enhanced
offshore ice advection during spring 2003.
Less sea ice was advected from the Beaufort Sea into the Chukchi and E. Siberian Seas.
Prevailing westerly winds compressed ice in the Beaufort Sea into the Canadian coast.
Summary:
Similar to 2002. Enhanced spring ice advection through the Transpolar Drift Stream further
compressed the sea ice into the eastern Arctic. |
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SEPTEMBER SEA ICE |
Spring Notes:
In contrast to 2002-2003, stronger than average high pressure conditions established over the
Arctic Ocean north of central Siberia.
The Beaufort Gyre had good integrity, helping to retain ice in the western Arctic.
Ice advection through the Drift Stream was inhibited, as was export through the Fram Strait.
The far northern position of the high-pressure system enhanced advection of slightly warmer
than average air from Chukotka into the coastal regions of the E. Siberian Sea and eastward,
promoting earlier melt onset dates along the Siberian coastal region.
Except for #4 above, these spring conditions would have tended to favor greater than average September
ice extent; however, see summer notes. |
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Summer Notes:
The spring high pressure anomaly over the north central Siberian region weakened and a high
pressure anomaly over Alaska developed.
Northeasterly winds advected the anomalously warm air over Alaska and Chukota into the Beaufort/Chukchi
Seas, greatly enhancing summer melt and advecting ice northward into a relatively discrete ice
edge.
In the Laptev Sea region, southerly winds promoted onshore ice advection and cooler than average
terrestrial temperatures, facilitating the preservation of September ice extent.
Northeastly winds in the Barents Sea region helped compress the sea ice edge well north of Spitzbergen.
Summary:
Summer conditions were primarily responsible for the extreme minimum September ice extent in the
western Arctic. |
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Spring Notes:
Dominant atmospheric pressure systems were not apparent in the 3-month (March-April-May) average
(perhaps monthly averages would be more illuminating).
A high-pressure zone over the southern Beaufort Sea enhanced westerly near shore ice advection
from the Beaufort toward the Chukchi.
Pronounced offshore ice advection in the Laptev Sea district bifurcated with an atypical component
directly toward the Beaufort Sea, facilitated by the anomalous southwest position of the Beaufort
Gyre.
Lower than average pressure over northern Eurasia, together with the high-pressure ridge over eastern
Siberia, established wind fields that drove offshore ice advection in central Siberia as well as
earlier melt onset by concurrent advection of warmer than average southern air. |
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Summer Notes:
A high-pressure ridge over Alaska extended northward, deep into the Arctic Ocean.
Associated wind fields advected warm southern air into the Chukchi and E. Siberian Seas, enhancing
summer melt, while southerly winds on the other side of the high pressure ridge advected cool
Arctic air and sea ice into the southeastern Beaufort Sea.
Higher than average pressure over the north Beaufort Sea enhanced the advection and convergence
of ice toward the Canadian coast.
Summary:
In central Siberia, offshore ice advection and warm southern airflow during spring facilitated
the minimal September ice cover. In the E. Siberian and Chukchi Seas, advection of warm
southern air during summer enhanced melt, while prevailing winds moved the ice northward. However,
in the eastern Beaufort Sea, ice was preserved in September by southward advection of both ice
and cool air during the summer months. |
Figure 2. Analysis of Sea Ice conditions in the Arctic Ocean off the coast of
Alaska: 2002-2005 (NASA Team sea ice concentration). |
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iarc.uaf.edu
