Magazine article Oceanus

Ice, Wind & Fury

Magazine article Oceanus

Ice, Wind & Fury

Article excerpt

Tasiilaq, Greenland, Friday, Feb. 6, 1970. 6 p.m.

Dead silence falls over Tasiilaq.

Whatever midwinter daylight appeared briefly in this village on the southeast coast of Greenland is long gone, leaving the afternoon pitch black. A fresh layer of snow from the morning covers the ground, reflecting the darkness around it. The vacuum of space is clear, and stars glint behind snow-covered mountains.

But any hint of pastoral calm is about to be obliterated.

The temperature has plummeted to -4° Fahrenheit and is still falling. Suddenly the wind picks up, and in an instant the silence vanishes. Village dogs start barking furiously. Icy gusts whistle through the spaces between the boards of wooden huts, a banshee-like warning of the bombardment to come from ice balls, rocks, untethered sleighs-anything that is unsecured.

By now, every creature in Tasiilaq knows: A piteraq is colliding with the town, and going outside into the elements would be suicide.

Torrential winds

During a piteraq, a torrent of cold air suddenly sweeps down off the Greenland ice cap and thunders down the steep slopes of ice-covered mountains, an avalanche of freezing winds that can reach hurricane intensity and flood everything in its path below. These rivers of air gain even more velocity as they converge and rush through narrow coastal fjords, the steep-sided inlets named by the Norsemen who made landfall here in the 10th century.

With more than 2,000 inhabitants, Tasiilaq is the seventh-largest town in Greenland and the most populous community on the eastern coast. The 1970 piteraq in Tasiilaq had wind gusts estimated at 160 miles per hour that savaged the town into near ruin. Not all piteraqs are as devastating as that one, but strong winds with speeds above 40 miles per hour can occur as frequently as 15 times per year. They haunt Tasiilaq in all seasons except summer.

There is one telltale sign that a piteraq is coming: The sky suddenly becomes dear-indicating that the wind has shifted direction and is now coming from the mountains and the vast Greenland Ice Sheet beyond. After the 1970 storm, Tasiilaq created an official warning system that sounds an alarm when a piteraq is forecast and completely shuts down the town until the piteraq subsides.

So piteraqs are well-known to Greenlanders, but they have not been well-studied by scientists. That's not surprising for a phenomenon that occurs in such a remote, harsh environment. As a consequence, little is known about how they form and what their impacts are.

Our goal was to investigate some of these mysteries.

Filling in the gaps

With my Ph.D. advisor Fiamma Straneo and colleagues, we set about to do the first systematic study of piteraqs, also known as downslope wind events, or DWEs. To do this, we analyzed meteorological data collected at two weather stations in the area: one in Tasiilaq that has been operated by the Danish Meteorological Institute since 1958, and another one on a hill in nearby Sermilik Fjord, established by the University of Copenhagen in 1997. The data were collected every three hours at first, and more recently at hourly and ten-minute intervals.

These stations supplied a lot of data, but in only two locations. To gain insights into the larger-scale setting in which piteraqs form, we used a tool called reanalysis, which essentially helps fill in the missing pieces between and around our two weather stations. Created by the European Centre for Medium-Range Weather Forecast, it's a computer model that uses measurements from weather stations, satellites, radiosondes (balloons released into the air to collect data from the atmosphere), and other data sets. Then it factors in the laws of physics to connect the dots and reconstruct meteorological measurements where no observations exist.

With the reanalysis, we discovered that piteraqs are not simple meteorological events. They are created by a fascinating combination of factors and phenomena that includes the atmosphere, mountains, ice sheets, and fjords. …

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