March 20, 2006

NASA Radar Plane Gauges Arctic Snow Layer

By Deborah Zabarenko

WASHINGTON -- A radar-equipped NASA plane is flying low over the Arctic this week to measure the snow on top of sea ice, a finding with implications for polar bears and possibly humans, an ice scientist said on Monday.

Polar bears raise their young in snow dens sitting atop sea ice so the depth of that snow is critical to their survival, said Thorsten Markus of NASA's Goddard Space Flight Center outside Washington.

The temperature under a layer of snow rarely falls below freezing so polar bears often let snow drift around their bodies to form an insulating layer of warmth. Without enough snow on the sea ice, polar bears can't build their dens.

In recent years, polar sea ice has been retreating farther north in the summer months, leaving polar bears stranded in the open sea or on land in Alaska.

But as bad as this may be for the polar bears, it could have an impact on people and the global environment, Markus said in a telephone interview from Fairbanks, Alaska.

"NASA's objective is not so much polar bears, it's really climate change on the larger scale," he said. "The snow depth on the sea ice is a very, very important factor in the polar climate system."

Snow atop sea ice acts like a thick quilt on top of a thin blanket, slowing the transfer of heat from the comparatively warm water to the intensely cold atmosphere.

Snow is a much more efficient insulator than sea ice, Markus said. As little as 4 inches of snow has the thermal insulating power of more than 3 feet (1 meter) of sea ice.

"If the snow depth changes, it will have profound implications" on the way the water's relative warmth is transferred to the polar atmosphere, he said. "So it's really, really important."

Markus said climate models predict an increase in precipitation and global warming.

While the temperature of water under polar sea ice must be more than 32 degrees F (0 degrees C), the air can be dozens of degrees colder.

But measuring snow on top of Arctic sea ice is trickier than going out and plunging a ruler into the snow. For a start, few people are equipped to travel out onto the sea ice -- trying to do this by boat has inherent risks to humans -- and satellites meant to track weather often have a distorted view of the polar regions.

However, NASA's Aqua satellite has an instrument called an Advanced Microwave Scanning Radiometer meant to gauge snow depth. This week's radar flights are meant to confirm these satellite observations, Markus said.

The first of six planned radar flights in the area around Barrow, Alaska, flew on Saturday; the rest are set to take place by March 28, he said.

Flying at just 500 feet, the special plane carries instruments that bounce signals off the top and the bottom of the snow, which should give scientists an accurate idea of how deep the snow is, Markus said.