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Fwd: Article: Noxious Lightning

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  • Roger L. Bagula
    ... wrote: Noxious Lightning The worldwide distribution of lightning strikes. Each flash produces a tiny puff of NOx, individually negligible,
    Message 1 of 1 , May 1, 2007
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      --- In physical_sciences@yahoogroups.com, "Robert Karl Stonjek"
      <stonjek@...> wrote:

      Noxious Lightning


      The worldwide distribution of lightning strikes.
      Each flash produces a tiny puff of NOx, individually negligible,
      but adding up to as much as 20 trillion grams per year when summed
      over the entire globe.
      Credit: NASA


      Lightning is more than light and noise: It's an intense chemical
      factory that affects both local air quality and global climate. But
      how big is the effect? Researchers aren't sure. To answer the question
      they're developing a new technique to estimate the factory's output.

      Lightning is more than light and noise: It's an intense chemical
      factory that affects both local air quality and global climate. But
      how big is the effect? Researchers aren't sure. To answer the question
      they're developing a new technique to estimate the factory's output.

      "Atmospheric chemists are very interested in trace gases produced by
      lightning, particularly nitrogen oxides ('NOx' for short)," explains
      William Koshak, a lightning researcher at NASA's Marshall Space Flight
      Center. NOx includes nitric oxide (NO), a toxic air pollutant produced
      by automobile engines and power plants, and nitrogen dioxide (NO2), a
      poisonous reddish-brown gas with a sharp odor.

      "We know that lightning is the most important source of NOx in the
      upper troposphere, where our weather takes place," Koshak continues.
      "NOx indirectly influences our climate because it partly controls the
      concentration of ozone (O3) and hydroxyl radicals (OH) in the
      atmosphere. Ozone is an important greenhouse gas, and OH is a highly
      reactive molecule that controls the oxidation of several greenhouse
      gases."

      While the output from cars and industry can be measured, lightning is
      a wildcard in models of regional air quality and global climate
      because it is difficult to realistically model several important
      lightning characteristics--e.g., lightning energy and the
      thermochemical yield of NOx produced by a lightning stroke. As such,
      the global production rate of lightning NOx is still uncertain, and
      ranges anywhere from 2 to 20 teragrams per year (1 teragram = 1
      trillion grams).

      "Fortunately, space-based atmospheric chemistry measurements made by
      NASA's Aura satellite provide a 'top-down' constraint on global
      chemistry and climate models," Koshak says. "With these new
      constraints, the best estimate to date is closer to 6 teragrams per
      year. However, more work must be done to better model lightning and
      other chemical processes before full confidence in this estimate is
      achieved."

      To better understand lightning flash energy -- a critical parameter in
      lightning NOx production -- Koshak and his colleagues are using data
      from the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall
      Measuring Mission (TRMM) satellite and two arrays of ground
      instruments at NASA's Kennedy Space Center in Florida. LIS is a
      special camera that uses a very narrow spectral filter and other
      techniques to detect the lightning optical emissions during both day
      and night. The filter is centered near 777.4 nm, which is just below
      the deep red limit of human vision.

      Their results will be reported in Lightning charge retrieval:
      dimensional reduction, LDAR constraints, and a first comparison with
      LIS satellite data, a paper recently accepted for publication in the
      Journal of Atmospheric & Oceanic Technology of the American
      Meteorological Society. His co-authors are E. Philip Krider, Natalie
      Murray, and Dennis Boccippio.

      "The idea is to investigate what correlation may exist between the
      optical characteristics of flashes seen by LIS vs. ground-based
      lightning measurements at Kennedy. The ground-based sensors allow us
      to probe deep within the thundercloud to determine the geometry of the
      lightning channel, the charges deposited by the flash, and the energy
      of the flash. The key is to see if the space-based optical
      measurements can be related to the ground-based flash energy
      estimates. If this can be done, it would be possible to use sensors in
      space to remotely retrieve flash energetics over a much larger region
      of the globe," says Koshak.

      "It's a formidable task, and this is just a preliminary look," he says
      of the forthcoming paper. The cloud medium is variable and therefore
      scatters the light emitted from lightning in complex ways. Energetic
      flashes embedded deep within an "optically thick" thundercloud could
      appear relatively dim to a space sensor, while weak-energy flashes
      occurring near cloud-top could appear relatively bright. All these
      complexities must be unraveled, and it is "tricky business."

      Ultimately Koshak hopes to provide a technique that will use GLM data
      to estimate lightning flash energy. "In practice we'll do it in a
      statistical fashion. We would like to give the atmospheric chemistry
      modelers a realistic probability distribution function for lightning
      flash energies that they can use in their models to better simulate
      lightning (be it ground or cloud flashes)."

      From that, scientists will start to better understand the global
      production of one of the key pollutants in the atmosphere pertinent to
      global climate and air quality.

      Source: by Dave Dooling, Science@NASA
      http://www.physorg.com/news97160144.html

      Posted by
      Robert Karl Stonjek

      --- End forwarded message ---
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