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Scientists have modeled the internal workings of lightning-filled “rocket dust storms” on Mars that rise at speeds 100 times faster than ordinary storms and inject dust high into the Martian atmosphere.
The Red Planet is a very dry and dusty place, with global storms that sometimes obscure the entire surface. Satellites orbiting Mars have seen persistent dust layers reaching very high altitudes, as much as 30 to 50 km above the ground, though scientists are at a loss to explain exactly how the dust got there.
Using a high-resolution model, researchers have shown that a thick blob-like dust pocket inside a storm may become heated by the sun, causing the surrounding atmosphere to warm quickly. Because hot air rises, these areas will shoot skyward super fast, much like a rocket launching into space, hence “rocket dust storms.”
“The vertical transport was so strong we want to come up with a kind of spectacular name, to give an idea of the very powerful rise,” said planetary scientist Aymeric Spiga from the Institut Pierre Simon Laplace in Paris, France, who is lead author on a paper describing the phenomena in the Journal of Geophysical Research: Planets on Jan. 14.
These speedily rising dust blobs can soar from near the surface to 30 or 40 km into the atmosphere in a matter of hours at speeds in excess of 10 meters per second (22 mph). This is far faster than the typical convection speeds in a dust storm of 0.1 meters per second (0.2 mph). Since the dust particles rub up against one another and create friction, the rocket dust storms may become charged with electrostatic forces, which could which could trigger fantastic lightning bolts.
Spiga and his team used detailed models of winds and dust on Mars to determine exactly how these rocket dust storms behave. Most previous models of Mars’ climate simulate large-scale global dust storms with fairly coarse resolution and so have not noticed the rocket storms. The team seeded their model with data from a dust storm observed by the OMEGA instrument aboard ESA’s Mars Express orbiting satellite and watched the rise of rocket storms.
Similar dust storms can’t happen on Earth. This is mainly because Mars’ atmosphere is about 100 times thinner than our own, meaning that it gets quickly and efficiently heated when dust particles absorb sunlight and then emit thermal radiation.
But a comparable phenomenon occurs in grey cumulonimbus thunderstorm clouds on Earth. The large accumulations of water particles in such clouds release latent heat, causing strong vertical motions and an extensive tall structure. Spiga’s team has used this Earthly analogy in the rocket dust storm’s more technical name, conio-cumulonimbus, from the Greek conious, which means dust.
“But I prefer to call them rocket dust storms,” Spiga said. “Then everyone knows what I’m talking about.”
Other researchers are impressed with the physical modeling done in the work. “I was a little surprised that such a small dust disturbance could remain intact over such long distances,” said planetary atmospheres scientist Scot Rafkin from the Southwest Research Institute in Boulder, Colorado. The mechanism could help explain how long-lasting layers of dust climb so high in the Martian atmosphere, he says.
Because they appear to be relatively rare, it may take a while to track down more rocket dust storms. But Spiga is hopeful they will be found by orbiting satellites, which may even image the lightning flashes inside them.
http://www.wired.com/wiredscience/2013/01/rocket-dust-storms/
