Snow and ice spanning the horizons, formidable weather conditions, never-ending
darkness and sub-zero temperatures are concepts often associated with
arctic regions. But during the summer months, when solar energy blazes
intently 24 hours a day, conditions shift to the other extreme supporting
temperatures that can climb into the 90s. The effect of this heat at northern
latitudes has prompted some scientists to study the impact that climate
has on polar sea ice, and the effect any resulting change may have on
the atmosphere and global climate change.
Arctic sea ice observations have been collected over the last hundred
years and include information from whaling records, arctic residents,
pilot reports and scientifically recorded measurements. The addition of
high resolution satellite imagery has now made it possible to focus on
more extreme cases of atmospheric response, giving a broader view to climate
modeling efforts.
Uma Bhatt of the Frontier Research System for Global Change located at
the International Arctic Research Center (IARC) at the University of Alaska
Fairbanks (UAF) is working with a team of researchers on a project funded
through a National Oceanic and Atmospheric Administration (NOAA)/IARC
joint initiative examining atmospheric responses to sea ice conditions
over northern and mid-latitudes. Their study is one of the few to examine,
in detail, the atmospheric response to sea ice during the summer months.
An atmospheric model integrated with observed sea ice conditions
during August of 1995. Grey represents climatological ice conditions and
red shows how much the ice cover has been reduced. Yellow lines represent
changes in the storm tracking (northward shift) induced by the reduced
ice cover.
Possible Feedbacks from Ocean to Air
When sea ice melts during the summer, solar radiation is able to reach
the water’s surface and be absorbed, causing the ocean to warm and
store heat in its upper layers. This causes even more sea ice to melt,
exposing more open water, resulting in more warm water and the cycle continues.
In climate studies, this spiral of decreasing sea ice levels is referred
to as a positive feedback. That’s why the largest observable response
to long summer days, in reality or in simulations, occurs in August—with
very little response in June and July.
Bhatt and her colleagues have found there is an increase in convective
cloud formation, such as dense cumulus or heavy cumulonimbus clouds, above
the open water when sea ice is diminished. As warm moisture rises from
the ocean creating convective clouds, lower-forming stratus clouds decrease.
These cloud changes effect radiation levels reaching the surface because
the clouds serve to block some of the sun’s rays from reaching ocean
waters. Thus, clouds become the primary buffer, which is a negative feedback.
The negative feedback from cloud cover is weaker than the positive albedo
feedback of decreased sea ice, leaving an aggregate increase in the sun’s
effect during the summer. Bhatt suggests there are other negative feedback
mechanisms in nature that can lessen the melting sea ice. For example,
change in pressure patterns over sea ice.
A growing number of other modeling studies indicate that the atmospheric
response to sea ice during the winter months leads to circulation changes
in the atmosphere that can force an increase of ice formation anomalies,
which would provide a counter to the initial ice reduction anomalies.
Colder atmosphere causes more heat loss from the ocean, and as the water
cools more ice is formed. This ice is thin and can be moved around and
piled up by the winds, creating more open water, resulting in more heat
loss, leading to more ice formation.
Faster Running Ensembles
Recent expansions and upgrades to ARSC systems have allowed Bhatt and
her colleagues to run simulations faster and with multiple ensembles.
An ensemble is a specific set or collection of data. In each ensemble,
the sea ice boundary is fixed, but the initial variables, such as pressure,
temperature and winds are changed.
“The need for an adequate number of ensembles is becoming more evident,”
says Bhatt. “We were able to run our experiment simulation 51 times,
each with different initial conditions, but with the same sea ice and
sea surface temperature boundary condition.”
The mid-atmosphere response to enhanced sea ice extremes in the Okhotsk
Sea. The blues represent lower geopotential heights (or cooler temperatures)
while reds represent higher geopotential heights.
The capability to run 51 ensembles increases scientific
understanding and produces more meaningful results. In numerous other
large climate model experiments, it is generally possible to run only
10 to 15 ensembles.
Other researchers involved in this project include Mike Alexander of the
National Oceanic and Atmospheric Administration and the Cooperative Institute
for Research in Environmental Sciences, Mike Timlin of the University
of Illinois, Jack Miller of the Institute of Northern Engineering at the
University of Alaska Fairbanks and John Walsh, President’s Professor
of Global Climate Change at IARC.
State and National Resource…
The Arctic Region Supercomputing Center supports high performance computational
research in science and engineering with an emphasis on high latitudes
and the Arctic.
The center provides high performance computational, visualization, networking
and data storage resources for researchers within the University of Alaska,
other academic institutions, the Department of Defense and other government
agencies. ARSC is located on the UAF main campus in Fairbanks, Alaska.
Arctic Region Supercomputing Center
PO Box 756020, Fairbanks, AK 99775 | voice: 907-450-8600 | email:
