The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013.

Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice.

That was what was happening on the left side of the animation (below) in late January 2013.

A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea.

“A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.”

In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles).

The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible.

While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.

(By Editorial, gCaptain)

Digest 뷰포트 해빙에서 1000킬로미터 균열 발생

Suomi NPP 위성의 적외선이미지센서(VIIRS)가 알래스카 북쪽 해안의 해빙에서 대규모 균열을 포착했다. 이 균열은 올해 1월 말에 시작되어 2월과 3월에 걸쳐 뱅크스 섬을 향해 서쪽으로 뻗어나갔다. 북극 빙하란 움직이지 않는 하나의 거대한 얼음판이 떠 있는 것이라고 생각하기 쉽지만, 사실 바람과 해류에 의해 끊임없이 이동하고 갈라지고 서로 부딪치는 작은 얼음들의 집합이다. 특히 여름에 빙하 조각 사이에서 쉽게 균열이 발생하며 이런 현상은 때로 한겨울에 일어나기도 한다.

(번역 정리 김지선)