UW News

September 5, 1997

Ice Station SHEBA, Fact Sheet 2: SHEBA goal to improve climate predictions

In October a Canadian Coast Guard ice breaker will be frozen in the ice about 300 miles north of Prudhoe Bay and left to drift for a full year as part of the Surface Heat Budget of the Arctic Ocean (SHEBA) project. A multi-agency effort led by the National Science Foundation and the Office of Naval Research, the long-term goal of SHEBA is to better understand Arctic climate in order to improve forecasts of global climate change in the next 10 to 200 years.

Climate modelers come up with very different results when they simulate how global and Arctic climate could respond if the carbon dioxide in the Earth’s atmosphere were double what it was in the 1960s, a situation that is expected to occur in less than 100 years. Many models show that the arctic pack ice in winter — which today covers an area about the size of the United States — will shrink to almost nothing. Other models show only half of it disappearing.

To better predict what might happen, scientists need more data about how the snow, sea ice and water of the Arctic respond to such things as the amount of sunlight hitting these surfaces, the amount of sunlight that is absorbed and the amount reflected back, infrared radiation coming down from the atmosphere and heat coming up from water beneath the ice. SHEBA scientists plan to measure these energy transfers, the response of surfaces and a wide variety of related variables during a full year’s worth of melting and freezing.

SHEBA is the largest, most complex Arctic expedition ever sponsored by the National Science Foundation

More than 50 researchers from U.S. and international institutions are participating in this phase of the program, which costs $16.5 million (about $14 million from NSF, $2 million from the Office of Naval Research and $500,000 from the Japanese government).

The SHEBA project office is located at the University of Washington in Seattle and is directed by Dick Moritz of the UW’s Applied Physics Laboratory.

Overseeing the project for NSF is Mike Ledbetter, director of the foundation’s Arctic System Science Program.

Icebreaker will be frozen in place for 13 months

The Canadian Coast Guard ice breaker Des Groseilliers will be frozen to a large ice floe at approximately 75 N and 143 W. It will be “escorted” from the ice about 13 months later by the Louis S. St. Laurent. The two ice breakers and a number of other vessels are supporting the SHEBA efforts under an agreement with the Canadian Coast Guard and the Canadian Department of Fisheries and Oceans.

The Des Groseilliers will be the ice station’s “hotel,” power station and communications base. On the ice nearby will be a shipping container and about eight small buildings for science and three or four structures for camp support. On the ship and the ice around the station scientists will rely on numerous instruments ranging from simple meter sticks to a state-of-the-art cloud LIDAR (a laser version of radar).

It’s been a hundred years since scientists deliberately locked their ship in the ice for more than a year’s worth of work

With a planned duration of about 13 months, Ice Station SHEBA represents the longest period scientists have planned to work from a ship since Fridtjof Nansen’s Norwegian expedition locked into the pack ice off the New Siberian Islands in 1893 and drifted for 34 months until it reached Spitsbergen in 1896.

What makes SHEBA different from previous ice camps and stations? ( Measurements made over a full year.

( The sheer number of measurements using the latest technologies.

( The scale of the study area ranging from within three- to five-km of the ice breaker to an area about 100-km square.

( Working in conjunction with five cooperating programs to share data collected from satellites, research flights and at the site:

DOE’s Atmospheric Radiation Measurement Program

NASA’s First ISCCP Regional Experiment III Program

NASA’s RADARSAT Geophysical Processing System

ONR’s Submarine Science Ice Experiment

The Japanese government’s Japan Marine Science and Technology Center

SHEBA study area is 100 km square miles

Organizers will seek an ice floe three- to five-km wide for the ice station, with the actual study area extending to 100 km. Researchers will study a column that extends through the upper part of the Arctic Ocean (the upper halocline), the sea ice floating on the water and the lower atmosphere (below the troposphere).

The horizontal extent of the column is chosen such that the changes in surface temperature, ice thickness, snow depth and other measurements inside the column can be characterized accurately by statistical parameters, such as the average, the standard deviation, the mode or the extremes.

This type of column coincides well with the horizontal resolution of the most advanced global climate models. These models, for example, resolve the earth’s surface into a set of grid points, and each point in a high resolution model might represent a 100 km square of surface.

What processes is SHEBA going to study in detail?

The surface heat budget of the Arctic Ocean determines the state of the snow, ice and water at the surface. If the budget is positive, the snow, ice and water are gaining energy and warming. When ice or snow finally reach 0 C the excess energy goes into melting. In the opposite case, if the surface energy budget is negative, water freezes. Further heat loss cools the ice and snow as freezing continues at the base of the ice.

SHEBA will measure these processes and compare them to what climate models predict will happen under the same environmental conditions.

<emFeedback mechanisms particularly puzzling

Feedbacks between the surface of the ice pack, the albedo (the amount of sunlight reflected by different surfaces) and clouds are key puzzles in modeling the Arctic climate, for instance:

( The ice surface — The ice cover is highly heterogeneous: it can range in thickness from zero (open water or “leads”) to more than 10 meters; it can be flat or hummocked, ridged and broken; it can be covered with variable layers of snow. Each of these surfaces changes in a different way in response to heat from the sun, the atmosphere and the ocean, and stresses caused by the wind and water.

( The albedo of different surfaces — For example, cold dry snow reflects far more sunlight than open water which is almost black. As ice melts and turns to water, the albedo is reduced, thus allowing more sunlight to be absorbed, followed by more melting of ice, even more sunlight being absorbed, and so on. It might be sunny for many days in a row but there will far more warming and melting if there are numerous melt ponds on the surface and open water than if the pack is frozen solid with snow on top.

( Clouds — Statiform clouds are almost ubiquitous in the Arctic summer and strongly affect the surface radiation fluxes, reducing the incoming sunlight and enhancing the incoming longwave radiation. SHEBA scientists will observe the evolving cloud structure, the atmospheric structure (temperature, humidity) and radiation, to address questions such as: If the surface melts and albedo decreases, does this tend to enhance cloudiness or reduce it? If it enhances cloudiness, does having less sunlight outweigh the enhanced longwave radiation?

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