Earth’s Fiercest Winds

The most powerful winds on Earth were caught in action on Sept. 16, 2009. That’s when the sun peaked over the horizon and lit up this Antarctic scene of atmospheric ferocity. Here are some pretty neat details from NASA’s Earth Observatory:

“The scene provides at least two indications of the bay’s persistent and fierce katabatic winds—downslope winds that blow from the interior of the ice sheet toward the coast. One is the windswept ground in the mountainous terrain. In many places, there is a pattern of bare rock and snow drifts that suggests the winds have scoured snow from upwind (inland-facing) slopes and deposited it on the lee sides.

“The second sign of the strong winds appears in the open waters of Terra Nova Bay. Parallel white streamers are composed of newly formed sea ice, probably frazil—crystals just millimeters wide—and congealed frazil, called “grease ice” because it resembles an oil slick on the water. The ice is continually pushed out to sea by the strong offshore winds, leaving a pocket of open water, a polynya.”

Image credit: NASA

A Stormy Sky Over Brazil

On Oct. 6, 2009 the International Space Station (ISS) Expedition 20 crew looked toward the Earth’s limb (the hazy blue line on the horizon) and snapped this impressive photograph of stormy weather over Brazil. A huge amount of detail has been captured by the station’s Nikon D2Xs digital camera as a part of the ongoing ISS Crew Earth Observations experiment.

Cumulonimbus clouds in various stages of development can be seen in the unstable air of the tropics, causing thunderstorms. Ring-like patterns in the large-scale structure of the stormy cloud cover is evident, possibly generated by the storm activity. The snaking 2,100 mile (3,380 km) long Rio Madeira (Madeira River) in the Amazon Basin can also be seen, glinting in reflected sunlight.

Image credit: NASA/JSC Gateway to Astronaut Photography of Earth.

Katabatic Winds Rake Antarctica’s Terra Nova Bay

Just days away from the beginning of the Southern Hemisphere’s spring, Antarctica’s Inexpressible Island and the Northern Foothills Mountains were illuminated by a glimmer of sunlight from a low angle when the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured this image on September 16, 2009. The seaward slopes of the mountains are gleaming white, and they cast long shadows inland over the Nansen Ice Sheet. Terra Nova Bay appears in shadow.

The scene provides at least two indications of the bay’s persistent and fierce katabatic winds—downslope winds that blow from the interior of the ice sheet toward the coast. One is the windswept ground in the mountainous terrain. In many places, there is a pattern of bare rock and snow drifts that suggests the winds have scoured snow from upwind (inland-facing) slopes and deposited it on the lee sides.

The second sign of the strong winds appears in the open waters of Terra Nova Bay. Parallel white streamers are composed of newly formed sea ice, probably frazil—crystals just millimeters wide—and congealed frazil, called “grease ice” because it resembles an oil slick on the water. The ice is continually pushed out to sea by the strong offshore winds, leaving a pocket of open water, a polynya.

The winds are responsible for making this location an ideal spot for Adélie penguins, which have a colony on Inexpressible Island and at other sites around Terra Nova Bay. Unlike Emperor penguins, which breed on sea ice, Adélie penguins nest on ice-free land, which must be accessible to them via open water and close to their marine food supply. The Adélie penguin’s habitat requirements are so specific that scientists have used fossils from ancient Adélie penguin colonies to re-create the climate and ice conditions in the Ross Sea stretching back 45,000 years.

Dust over the Arabian Sea

The shift from summer heat to winter’s chill in the mountains of southwest Asia leads to regular dust storms over the Arabian Sea. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired this photo-like image on November 9, 2009. It is remarkably similar to images captured in late October and November in 2008, 2007, 2006, and previous years. In 2009, as in other years, distinct plumes of dust blow from the desert between the Makran Mountains and the Arabian Sea.

Wind and weather patterns in southwestern Pakistan and southeastern Iran are largely driven by the summer and winter monsoons. In the winter, the cloudless, dry air over southwest Asia cools. The cool, dense air sinks. Air over the Arabian Sea, meanwhile, is warm. The warm air rises, and the cool air from the continent rushes in to take its place. The movement of air from the land to the Arabian Sea creates strong winds that generate the dust storms seen every year.