Three bolts from the blue
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Fundamental questions about atmospheric
Martin Uman of the University of Florida asked these questions
yesterday at the opening of the International Conference for
Atmospheric Electricity. While most of the scientists will share
what they have learned in their specific areas of study, Uman
instead decided to ask a few general questions about atmospheric
electricity. Uman hopes to motivate discussion among all the
conference scientists so they will work together to solve these
"I'm asking these questions because nobody ever worries about putting it all together," Uman said.
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Left: The ozone hole at the Earth's South Pole. The TOMS (Total Ozone Mapping Spectrometer) false-color image shows low levels of ozone in blue, high levels in red. This time-elapsed image shows the ozone hole as it develops each year between late August and early October.
Increasing concentrations of nitric oxide and other chemicals in the Earth's atmosphere contribute to the ozone hole over Antarctica. Although most of this nitric oxide is produced by human activity, lightning also produces a small but significant amount. Still, estimates vary about exactly how much nitric oxide is produced by lightning.
"The literature about NO production is confusing,"
said Uman. "Everyone cites different production levels,
so it's still an unsolved mystery."
Right: Moonrise over the Earth's atmosphere. This fragile-looking shell protects us from powerful radiation coming from space.
Also, scientists don't really know what sort of electrical discharges produce nitric oxide. Although it is well established that lightning produces some nitric oxide, other electrical discharges such as sprites could also be a source.
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According to current models, only the most powerful lightning strikes generate enough energy to produce sprites. Uman questioned whether these models are accurate representations of the energy needed to genera
"The models don't agree with the all the measurements,
so there's a big debate over which is wrong," said Uman.
"Are the models wrong, or do we need to get better measurements?"
Left: A red sprite photographed by a team at the University of Alaska, Fairbanks. Sprites are emitted near the tops of thunderclouds and reach up into the ionosphere.
"The transmission line model is a case of a model that works, but probably shouldn't," Uman said.
The transmission line model for lightning shows a smooth upward curve of current. Lightning, however, is not a smooth and steady phenomena.
"Lightning is a mess," said Uman. "The transmission line model is the oldest and simplest model about lightning, so it shouldn't work. Lightning is much more complicated than that."
Lightning does not follow a simple path across the sky. For instance,
Right: Lightning often exhibits complex patterns in the sky. Credit: Australian Severe Weather/ Michael Bath.
Uman asked these questions because he believes most theorists are too intent on developing their own models. By posing these questions at the International Conference on Atmospheric Electricity, Uman hopes to stimulate further thought about the physics of lightning. When these questions are answered, they could fundamentally alter our understanding of how electricity interacts with the atmosphere. Web Links Human Voltage (June 18, 1999) Scientists discuss biology, safety, and statistics of lightning strikes.
News shorts from Atmospheric Electricity Conference (June 16, 1999) Poster papers on hurricanes and tornadoes summarized.
Soaking in atmospheric electricity (June 15, 1999) 'Fair weather' measurements important to understanding thunderstorms.
Lightning position in storm may circle strongest updrafts (June 11, 1999) New finding could help in predicting hail, tornadoes
Lightning follows the Sun (June 10, 1999) Space imaging team discovers unexpected preferences
Spirits of another sort (June 10, 1999) Thunderstorms generate elusive and mysterious sprites.
Getting a solid view of lightning (June 9, 1999): New Mexico team develops system to depict lightning in three dimensions.
Learning how to diagnose bad flying weather (June 8, 1999): Scientists discuss what they know about lightning's effects on spacecraft and aircraft.
Three bolts from the blue (June 8, 1999): Fundamental questions about atmospheric electricity posed at conference this week.
Lightning Leaders Converge in Alabama (May 24, 1999): Preview of the 11th International Conference on Atmospheric Electricity.
What Comes Out of the Top of a Thunderstorm? (May 26, 1999): Gamma-rays (sometimes).
Lightning research at NASA/Marshall and the Global Hydrology and Climate Center.
45th Weather Squadron at Patrick AFB,
lightning reference page.
Australian Severe Weather has a large collection of storm pictures, most from Down Under.
Atmospheric Structure - a chart at the University of Wisconsin at Stevens Point describing the Earth's different atmospheric layers
National Severe Storms Laboratory, Norman, OK
National Severe Storms Laboratory Photo Library, where we got a lot of the neat pictures for these lightning conference stories.
More Space Science Headlines - NASA research on the web
NASA's Earth Science Enterprise Information on Earth Science missions, etc.
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