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October 1997

Science Briefing

ATD is sending four specially packaged Flux-PAMs and a new GPS-based sounding system into the frozen North as part of NSF's Surface Heat Budget of the Arctic Ocean (SHEBA) project. During October, Ned Chamberlain, Tom Horst, Kurt Knudson, John Militzer, and Steve Semmer are each spending about two weeks on either of two Canadian Coast Guard icebreakers on the Beaufort Sea, about 400 kilometers (250 miles) north of Prudhoe Bay, supervising deployment of the instruments out on the ice close to longitude 75 degrees north, latitude 143 degrees west (see map). The instruments will collect data for the next year as one of the ships, the Des Grosseilliers(pronounced Day-GROSS-sea-a), freezes into the pack ice with researchers and technicians aboard and drifts with the Arctic currents. Supplies and staff will be flown in and out via Twin Otter and helicopter.

Jim Moore and Lia Pennington (JOSS) have been on board the Des Grosseilliers this month setting up SHEBA's on-line data catalog, developed by JOSS's Nimal Gamage and colleagues. The catalog will be run both on the ship and at a mirror site in Boulder, with satellite communications linking the two.

An international project coordinated by the University of Washington's Applied Physics Laboratory, SHEBA will track the transfer of energy between the ocean, sea ice, and atmosphere during a full year of freezing and melting. Project goals include better interpretation of satellite remote-sensing data from the Arctic and a better understanding of how sea ice interacts with the rest of the global climate system.

The four Flux-PAMs stations needed some repackaging to withstand a year of high winds (up to 30 meters per second--67 miles per hour--in storms) and low temperatures (down to -50 degrees Celsius, or -58 degrees Fahrenheit), along with three months of darkness. Flux-PAMs (portable automated mesonet) surface meteorological stations record standard surface variables: winds, temperature, humidity, and pressure. In addition, they measure vertical transport fluxes of long- and short-wave radiation, sensible heat, and momentum.

For SHEBA, the stations' solar-charged batteries were replaced with propane-powered thermoelectric generators. The generators, their fuel bottles, and storage batteries go into an insulated box with the station's electronics so the generator can keep the electronics warm enough to operate. The whole unit is mounted on a rugged sled (the kind used for towing behind snowmobiles). With their towers folded and loaded on top, the sled-mounted stations can be moved to different surfaces (such as new ice, multiyear ice, and melt ponds). John Militzer headed the project that made the stations iceworthy.

SHEBA also marks the debut of ATD's new GPS-Loran Atmospheric Sounding System (GLASS). There's no loran coverage near the Beaufort sea, and the available Omega radio navigation system, less accurate than GPS, is being phased out. This gave ATD the boost to develop a rawindsonde capable of using GPS (Global Positioning System) as well as loran. "GPS will work virtually anywhere," explains Ned Chamberlain, who wrote the new software for GLASS.

Shown here is the original projected location (top diamond) and possible 15-month drift path (arrow and second diamond) for the SHEBA research camp. The shaded region encloses 90% of the spread of possible final positions, based on a statistical model of randomly varying ice motion. The bold line depicts the average southward extent of 50% ice coverage in September. (Illustration from SHEBA Science Plan, courtesy SHEBA Project Office.)

The Arctic setup for GLASS includes sleds fitted with bag launchers--tubes of flexible fabric that protect the balloons while they're being readied for release. GLASS data (temperature, humidity, pressure, and winds) will be used on site and also transmitted off the ship via the GPS global telecommunications system for incorporation in forecasting models.

You can follow SHEBA's progress on the web. Recent news from the Web site: The Canadian Coast Guard icebreaker Des Grosseilliers reached the SHEBA "home ice floe" at latitude 75 degrees 17 minutes north, longitude 142 degrees 42 minutes west at 14:35 ADT on 2 October. The prevailing ice thickness at the site was about two meters under hummocks, and varied down to under one meter under the (frozen) melt ponds.

At 19:00 on 5 October, the air temperature was -22 degrees Celsius and winds were from the northwest at 10 knots. The four Flux-PAMs were brought out on the ice to be prepped for setup that day, looking "like four boxy versions of R2D2."


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Edited by Bob Henson, bhenson@ucar.edu

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