Katabatic Winds

Dear Fellow Explorers,

I'm writing to you under some pretty tough conditions—we hit a nasty wind storm today. Winds are reaching 80 knots; that's 92 mph. The waves are kicking up and splashing over the side, half our crew is sea sick, and—well, let's just say we haven't gotten much work done!

This storm isn't exactly a surprise. We are trying to collect some sediment samples and seafloor images from the ocean floor around Cape Denison, which is known as the windiest spot in Antarctica. And Antarctica itself is the windiest place on Earth!

In fact, Antarctica holds the record among continents for sustained wind speeds; wind speeds can reach 200 mph here. Most research teams, like ours, learn to deal with the wind; other teams actually spend their days in Antarctica studying wind.

The winds of Antarctica, however, are a tough study—even in places where winds are a little less extreme, the wind often damages the weather stations used to measure it. The wind blows snow into and out of precipitation gauges. It kicks up blinding blizzards that keep cargo and personnel transports prisoner. High winds and blizzards keep research teams holed up in their tents for hours or even days, unable to venture into the field.

Why are the winds of Antarctica so powerful? Antarctica's temperature patterns are part of the reason. On warmer continents, air temperature usually decreases as distance above land increases; in other words, the higher you get, the colder the air. When you climb a hill or a mountain, it gets colder toward the top, right? But in Antarctica, it's a bit different. Antarctica's interior region is the high Polar Plateau, an area covered with a thick ice sheet. This massive ice sheet cools the air above it; as a result, all the air above the Polar Plateau is very cold. The coldest, most dense air is closest to the ground; the higher the air, the farther it is from the cold ice sheet. That means that air temperature rises (instead of decreasing) with distance above land. This is called a temperature inversion, because it is the inverse, or opposite, of more common temperature patterns on warmer continents.

Cold air is more dense, or heavier, than warm air; that's why warm air rises and cold air sinks! (Think of how hot an attic can get in the summer.) The Polar Plateau is covered with so much ice that it is always cold; this means that it is always cooling the air above it. As a result, a mass of very cold, dense air sits on top of the Polar Plateau. This cold, dense air wants to sink, so it flows down from the high continental interior toward the lower coast, just as a stream flows down a mountain. These interior winds of cold, dense air are called inversion winds.

As you can see, most of the inversion winds flow fairly evenly down a gentle slope. However, some of the landscape is not a gentle slope; winds can be channeled by the rugged landforms of ice and mountains. Picture liquid being poured into a funnel—when the air flow of interior winds converges, more air is being compressed into a smaller channel space. The air flow gets stronger, turning into fast-flowing winds called katabatic winds. These katabatic winds roar toward the coast of Antarctica. Fairly quiet conditions turn instantaneously, with katabatic winds reaching speeds of 15 to 20 meters per second (50 to 66 ft/sec)!

Things are getting pretty wild here on board—I had better go and help everyone lash things down. We try to stow our equipment and samples safely at all times, just in case we run into heavy seas. But there are always a few things we have overlooked that we need to tie down—microscopes, cabinet doors, computers, my shift-mates....

All the best,