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NASA finds the effects of lighting extend to the Van Allen belts

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  • David
    Bill Steigerwald Goddard Space Flight Center, Greenbelt, Md (Phone: 301/286-5017) RELEASE: 05-070 NASA FINDS LIGHTNING CLEARS SAFE ZONE IN EARTH S RADIATION
    Message 1 of 1 , Mar 8, 2005
      Bill Steigerwald
      Goddard Space Flight Center, Greenbelt, Md
      (Phone: 301/286-5017)

      RELEASE: 05-070


      Lightning in clouds, only a few miles above the ground, clears a safe
      zone in the radiation belts thousands of miles above the Earth,
      according to NASA-funded researchers. The unexpected result resolves a
      forty-year-old debate as to how the safe zone is formed, and it
      illuminates how the region is cleared after it is filled with
      radiation during magnetic storms.

      The safe zone, called the Van Allen Belt slot, is a potential haven
      offering reduced radiation dosages for satellites that require Middle
      Earth Orbits (MEOs). The research may eventually be applied to remove
      radiation belts around the Earth and other worlds, reducing the
      hazards of the space environment.

      "The multi-billion-dollar Global Positioning System satellites skirt
      the edge of the safe zone," said Dr. James Green of NASA's Goddard
      Space Flight Center, Greenbelt, Md. He is the lead author of the paper
      about the research published in the Journal of Geophysical Research.
      "Without the cleansing effect from lightning, there would be just one
      big radiation belt, with no easily accessible place to put
      satellites," he said.

      If the Van Allen radiation belts were visible from space, they would
      resemble a pair of donuts around the Earth, one inside the other, with
      the planet in the hole of the innermost. The Van Allen Belt slot would
      appear as a space between the inner and outer donut. The belts are
      comprised of high-speed electrically charged particles (electrons and
      atomic nuclei) trapped in the Earth's magnetic field. The Earth's
      magnetic field has invisible lines of magnetic force emerging from the
      South Polar Region, out into space and back into the North Polar
      Region. Because the radiation belt particles are electrically charged,
      they respond to magnetic forces. The particles spiral around the
      Earth's magnetic field lines, bouncing from pole to pole where the
      planet's magnetic field is concentrated.

      Scientists debated two theories to explain how the safe zone was
      cleared. The prominent theory stated radio waves from space, generated
      by turbulence in the zone, cleared it. An alternate theory, confirmed
      by this research, stated radio waves generated by lightning were
      responsible. "We were fascinated to discover evidence that strongly
      supported the lightning theory, because we usually think about how the
      space environment affects the Earth, not the reverse," Green said.

      The flash we see from lightning is just part of the total radiation it
      produces. Lightning also generates radio waves. In the same way
      visible light is bent by a prism, these radio waves are bent by
      electrically charged gas trapped in the Earth's magnetic field. That
      causes the waves to flow out into space along the Earth's magnetic
      field lines.

      According to the lightning theory, radio waves clear the safe zone by
      interacting with the radiation belt particles, removing a little of
      their energy and changing their direction. This lowers the mirror
      point, the place above the polar regions where the particles bounce.
      Eventually, the mirror point becomes so low; it is in the Earth's
      atmosphere. When this happens, the radiation belt particles can no
      longer bounce back into space, because they collide with atmospheric
      particles and dissipate their energy.

      To confirm the theory, the team used a global map of lightning
      activity made with the Micro Lab 1 spacecraft. They used radio wave
      data from the Radio Plasma Imager on the Imager for Magnetopause to
      Aurora Global Exploration (IMAGE) spacecraft, combined with archival
      data from the Dynamics Explorer spacecraft. IMAGE and Dynamics
      Explorer showed the radio wave activity in the safe zone closely
      followed terrestrial lightning patterns observed by Micro Lab 1.

      According to the team, there would not be a correlation if the radio
      waves came from space instead of Earth. They concluded when magnetic
      storms, caused by violent solar activity, inject a new supply of
      high-speed particles into the safe zone, lightning clears them away in
      a few days.

      Engineers may eventually design spacecraft to generate radio waves at
      the correct frequency and location to clear radiation belts around
      other planets. This could be useful for human exploration of
      interesting bodies like Jupiter's moon Europa, which orbits within the
      giant planet's intense radiation belt.

      The research team included Drs. Scott Boardsen, Leonard Garcia,
      William Taylor, and Shing Fung from Goddard; and Dr. Bodo Reinisch,
      University of Massachusetts, Lowell. For images and information about
      this research on the Web, visit:

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