The New York Times
03-20-07
Lightning and Climate Change
By HENRY FOUNTAIN
Nitrogen oxides, the reactive gases that contribute to smog near the ground and
help regulate ozone far above it, are not made by cars and industry alone. A lot
of NOx, as the various gases are collectively known, is made by lightning.
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Chris Gash
Atmospheric scientists would like to know how much, to better understand
processes related to pollution and climate change. But only indirect
measurements have been made, by taking air samples from storm clouds.
It took lightning researchers to make the first direct measurements — touching
off lightning by sending a small rocket into an electrically charged thundercloud at
the International Center for Lightning Research and Testing in Camp Blanding,
Fla.
“We put that lightning through a bottle,” said Martin A. Uman, a University of
Florida professor and co-director of the center, describing the experimental
process. “Then we sucked the air out and measured the nitrogen oxides.”
When the rocket is launched, it travels about 1,000 feet into the air, trailing a thin
copper wire that is attached to the test chamber. The rocket sets off a discharge
in the cloud, acting, as Dr. Uman put it, “like the top of the Empire State Building,”
which frequently induces lightning.
There is a wave of what is called continuous-current lightning through the cloud,
and lightning travels down the wire to the test chamber, where it jumps a oneinch gap between two electrodes. The intense heat of the arc ionizes nitrogen
and oxygen, which recombine in various forms as the air cools. By knowing the
length of the arc, and precisely measuring the NOx produced, the researchers
came up with a number.
For the record, lightning produces 2 to 3 times 1020 molecules of NOx per meter
of lightning per coulomb (a unit of charge), Dr. Uman, M. Mahbubur Rahman of
Uppsala University in Sweden and others report in Geophysical Research
Letters.
Atmospheric scientists had long assumed that most of the NOx was created by
powerful “return” strokes, what most people think of as lightning. But the research
shows that discharges within clouds, which are much less dramatic, play a
greater role.
“It’s not the bright, impulsive thing you see” that’s creating all the NOx, Dr. Uman
said. “It’s the tail end of what you see.”
Decoding a Neighbor’s Call
A couple of years ago, researchers at the University of Montana discovered that
black-capped chickadees are pretty clever. The birds, they found, encode their
warning calls to other chickadees with information about the degree of threat
posed by a particular nearby predator.
The lead researcher in that study, Christopher N. Templeton, who has moved on
to the doctoral program at the University of Washington, now reports that if
chickadees are clever, red-breasted nuthatches are cleverer still. The
nuthatches, which are about the same size and share many of the same habitats
as chickadees, don’t have to depend on warning calls of their own — they can
eavesdrop on the chickadees to get the information they need.
Mr. Templeton and Erick Greene, another of the original researchers who is an
associate professor of biology at the University of Montana, used an
experimental setup that was similar to that used with the first study, recording
chickadee calls in response to different predators and playing them back for
nuthatches.
A chickadee’s call is shorter — with fewer “dees” at the end — if the predator is a
great horned owl or some similar large, slower-moving bird. The call is longer if
the predator is a smaller nimble bird like a northern pygmy owl, which is more of
a threat. Chickadees respond to the greater threat by more “mobbing” behavior,
approaching the predator and harassing it by making noise.
The researchers found that nuthatches responded with agitation and mobbing
behavior as well, and that, just as among chickadees themselves, the behavior
was stronger if the call was longer. The findings are being published in The
Proceedings of the National Academy of Sciences.
While it is not unknown for one species to eavesdrop on another, the researchers
say this is the first example of one species learning to decode the information in
another’s calls.
The Color of Fertile Soil
Gardeners know a general rule of thumb about soil: the darker it is, the more
organic matter it contains.
That may be enough information if all you are growing is some tomatoes and
zukes in the backyard. But soil scientists need more specific information about
organic carbon content — data from across a landscape — to better understand
how certain processes, like erosion and the exchange of carbon with the
atmosphere, affect it throughout a region.
Direct laboratory analysis of many soil samples for carbon content is expensive,
though, so over the years researchers have tried indirect means, including
remote sensing. Another approach is a more refined version of darker-is-better:
judging soil by its color.
Scientists have used color for decades to broadly categorize different kinds of
soils; a comparison method called the Munsell color system has even been
developed to do that. But Skye A. Wills of the University of Maryland and
colleagues at Iowa State University wanted to see if they could use color
measurements in the field to rapidly and accurately predict organic carbon
content.
They tested soils from northeastern Iowa using both color chips from the Munsell
system and a spectrophotometer, which analyzes the frequency of light (and thus
the color) reflected off a surface. Their findings were published in The Soil
Science Society of America Journal.
They found that their approach could work, although there are limitations. For
one thing, the best predictor of carbon content came from factoring in both
Munsell and spectrophotometer data along with information about the depth of
the sample. And while the method proved reliable for farmland, the researchers
say more work is needed make it useful for prairie soils.
Bacteria With a Taste for Oil
Scientists at Nankai University in China have sequenced the genome of an oileating bacterium found in a deep reservoir in Northern China. The bug,
Geobacillus thermodenitrificans NG80-2, breaks down long-chain alkanes, and
the scientists report in The Proceedings of the National Academy of Sciences
that they have identified the key enzyme responsible. It’s called LadA, and the
researchers say it may be useful in cleaning up oil spills.