Sweeping sands across the Sahara and other dune expanses are blown by more than just wind, scientists have discovered. Powerful electric fields spring up near the desert floor and propel sand grains into the air. By accounting for this electricity, researchers say they can design better climate change models, and even explain features of the dust on Mars.Scientists have long been at a loss to explain why sand sweeping across the desert doesn't bounce higher when the wind gets stronger. But when researchers at the University of Michigan made the first calculations ofelectricity's role in this dance of particles, they were finally able to match their models with observations.As wind forces sand to scrape over Earth's surface in a process called saltation, the friction causes the sand particles to pick up loose electrons from the ground, giving them a negative charge and leaving the surface with a positive charge, the researchers found. "It's sort of like when you stroke your cat and feel little sparks, or run a balloon on your head to make your hair stand up," said Jasper Kok, a graduate student in applied physics at the University of Michigan, who led the study with his advisor, Michigan atmospheric scientist Nilton Renno.
The research will be published in the January 11 issue of the journal, Physical Review Letters.
The separation ofcharges
creates an electric field that can reach strengths of 100,000 to
200,000 volts per meter at a centimeter from the surface.
This field in
turn draws even more sand up into the air because the positively
charged ground particles are attracted to the floating negative ones.
The electric field also explains why the skipping particles do not reach greater heights when the wind blows faster.
"Now we think that as the
wind speed increases, so does the electricity, and they sort of cancel
each other out," Kok said. "The bouncing sand is electrically attracted
to the surface. We were very excited when we plotted that graph and it
all matched up."
Sculpting dunes
Saltation is the force that forms sand dunes, sculpts rocks and causes erosion.
&quo......
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Sea floor records ancient Earth
Climate change and phenomena
Study explains rainforest similarities
Did comets cause killer cold spell ?
Ancient tsunami 'hit New York'
Prehistoric jungles laughed at global warming
Massive ice chunks break up in Antarctica
Animal Language
Global warming could change Earths tilt
