Arctic Summer Cyclones Churn Up Sea Ice
At the top of the world, intense summer cyclones have been raging in recent years, eating up sea ice and helping push the North Pole closer to ice-free summers.
In fact, a week-long cyclone just concluded, which Matthew Asplin, a PhD student at the University of Manitoba, monitored closely from Winnipeg. Asplin thirsts after severe weather in all its forms but finds special meaning in watching the Arctic.
“The polar regions are where we expect (and are seeing) the first signs of climate change,” he said.
And one of the changes might be summer cyclones, which appear to be getting more intense in recent years. Winter cyclones in the Arctic have historically been more intense than the summer ones.
Asplin and other scientists monitored the cyclone carefully last week since a rather large low pressure system has parked itself over the Arctic since May (see image at right), producing a very stormy melt season. As the cyclone raged, pressures reached 975 millibars, equal to that of Atlantic or Pacific storms. The storm must have produced some pretty rough waves in the ice-free waters of the Beaufort sea.
The cyclone was too short-lived to melt much sea ice, Asplin said. In general, cyclones can generate huge waves in open water that wash over ice to accelerate melting. The winds can cause the ice to move and deform.
The effect on sea-ice were visible during the Great Arctic Cyclone of 2012.
The Great Cyclone was the largest and deepest ever recorded in the Arctic. Atmospheric pressures reached a minimum of 975 millibars, and winds reached speeds rarely seen in August. The storm raged for almost two weeks.
All this happened in a year the sea ice reached a record minimum level on August 26. The ice cover in the Arctic last summer was 18 percent below the previous record from 2007.
Scientists wanted to figure out how much of a role the Great Cyclone, which began August 6, played in the loss of sea ice.
Not very much, according to a study published in Geophysical Research Letters in February. The Great Cyclone reduced sea ice by 58,000 square miles — the size of Bangladesh — but this was still only 4 percent of the typical ice cover. Even without the cyclone, 2012 would have set the record for minimum sea ice.
There is some evidence that more intense and frequent cyclones may be the new norm for the Arctic summer.
Scientists also do not know yet if climate change, which has affected many atmospheric processes in the Arctic, has anything to do with the weather.
So, they continue to study cyclones with special interest. This entire season from May onwards has been interesting because of the intense low pressures, Asplin said.
“It’s been very stormy,” he added.
Images: Cyclone over the Arctic in 2012. Credit: Jesse Allen and Robert Simmon/NASA Earth Observatory.
Sea level pressures over the Arctic. Between 1981 and 2010, high surface pressures have been the norm over the Arctic (left). In June 2013, intense low pressure has parked over the Arctic, producing stormy weather (right). Credit: Matthew Asplin.