An Arctic hurricane (or polar low) northeast of Scandinavia, with a characteristic eye and counter-clockwise swirl of clouds. They grey area in the upper left-hand corner is sea ice.
Credit: University of Dundee via Kent Moore
Santa better have hurricane insurance.
Every year, there are thousands of cyclones in the Arctic, some with hurricane-force winds. Before satellites spotted these storms, sailors would return from the North with tales of massive squalls appearing out of nowhere, creating waves up to 36 feet (11 meters) high.
A new study published online this week in the journal Nature Geoscience has found that these storms transport a significant amount of heat from the tropics to the Arctic and help power the Gulf Stream, the ocean current that shuttles warm water northeast from the Caribbean toward Europe. The Gulf Stream keeps the continent warmer than it would otherwise be, said Alan Condron, study co-author and oceanographer at the University of Massachusetts at Amherst.
These storms are technically known as polar lows but can be referred to as Arctic hurricanes, although that term usually refers to cyclones that form in the tropics. Like hurricanes, though, polar lows can be incredibly intense, with winds above 74 mph (118 kph), and have a central "eye" with swirling bands of clouds, Condron told OurAmazingPlanet. Unlike typical hurricanes, however, polar lows tend to be on average about 25 percent smaller in area and are shorter-lived, he said. [Infographic: How, When & Where Hurricanes Form]
Short-lived but wide-ranging
Polar lows are created when masses of frigid air move over warmer water, which creates instability in the atmosphere. That can lead to the development of small, strong storms powered by the transfer of heat from the ocean to the atmosphere, as well as by the interaction of warmer air to the north with cooler air to the south, said Kent Moore, an atmospheric physicist at the University of Toronto who wasn't involved in the research.
As the frigid air from one of these storms moves over the comparatively warmer water, the water cools and sinks. This sinking helps power the Gulf Stream, and more broadly, the global ocean conveyor belt, Condron said.
The storms "intensify the circulation of the ocean and are partly responsible for keeping Europe warm," he said.
Prior to this study, nobody had looked to see whether or not these brief cyclones — which usually last about 24 hours — might have a significant impact on the world's oceans and climate, Moore said.
"The authors were able to show these storms have a strong impact on ocean circulation," he said. "That's quite a surprising result since [the cyclones] are so short-lived." But thousands of short-lived storms add up, he added.
The air within polar lows can often be as cold as minus 4 degrees Fahrenheit (minus 20 degrees Celsius). They are capable of extracting 93 watts of heat per square foot (1,000 watts per square meter), enough to power two 45-watt light bulbs for every square foot of ocean surface, Moore said.
Condron estimates these Arctic hurricanes are responsible for about 5 percent of the heat transferred from the equator to the poles, he said. He and his co-author Ian Renfrew, from the University of East Anglia in England, were able to create a computer model that accurately recreated these powerful storms. Current climate models do not take the storm into account, which could lead to incomplete predictions, Condron said.
"These models may predict it will be too warm [to the south]," he said. "If we can run models that include these polar lows, it will improve our future forecast."