Warm air currents spur faster melting in Antarctica

Warm downslope winds are accelerating ice melt in Antarctica, a new survey finds. This could cause the break-up of the Larsen C ice shelf, raising sea levels much faster than anticipated. From the BBC: 

A new study has found an atmospheric melting phenomenon in the region to be far more prevalent than anyone had realised. 

This is the foehn winds that drop over the big mountains of the peninsula, raising the temperature of the air on the leeward side well above freezing. 

"The best way to consider these winds is how they translate to german now, which is 'hairdryer'," explained Jenny Turton from the British Antarctic Survey (BAS). 

"So, they're warm and they're dry and they're downslope. If you take the spring, the air over the ice shelf is usually minus 14 but during the foehn winds it’s above freezing.”

The effect on the ice that pushes east from the Peninsula out over the Weddell Sea is clear. It produces great ponds of brilliant blue melt water at the surface. 

Such warm, downslope winds are well known across the Earth, of course; and they all have a local name. 

The chinook winds, for example, that drop over the Rockies and Cascades in North America are the exact same thing. 

Foehn is just the title they garnered originally in Europe's Alps. And while their presence on the White Continent has also long been recognised, the BAS study is really the first effort to try to quantify their behaviour. 

Examining data from 2009 to 2012, Turton and colleagues identified over 200 foehn episodes a year. 

That makes them more frequent than anyone had thought previously. And the range is broader, too, with occurrences being recorded much further south on the Peninsula. 

This all means their melting influence on the eastern shelf ice has very likely been underestimated. 

"In summer, we expect some melt, around 2mm per day. But in spring we’re having an equal amount of melt as we are in summer during the foehn winds," Ms Turton told BBC News. 

"That's significant because it’s making the melt onset earlier. We kind of expect melt in January/February time; but we’re also seeing it sometimes in September/October, in particularly frequent foehn wind conditions."

Read the whole thing here.

Links for more information:
"Antarctica's troublesome 'hairdryer winds,' from the BBC: http://www.bbc.com/news/science-environment-39759329