Magnetic-Field-Aligned Electron-Density Irregularities in the Ionosphere and
Magnetosphere: their Detection, Generation and Significance

R. F. Benson


Electron-density irregularities perpendicular to the magnetic field B that are
maintained for long distances parallel to B are common in the ionosphere and
magnetosphere. They are referred to as Field-Aligned Irregularities (FAI). These
FAI are easily detected because they cause radio waves generated by ground-based
radars and ionosondes, and by rocket- and satellite-borne radio sounders, to be
scattered or ducted. They are generated both by natural processes and by
high-power radio waves during active experiments. Diffuse echoes in the
ionosphere (known as spread-F) and the magnetosphere (particularly in the
vicinity of the plasmapause) are attributed to FAI. A review will be given of
the observations, suggested generation mechanisms, and the significance of FAI.
Particular emphasis will be given to the sounders employed on the Alouette, ISIS
and IMAGE satellites.

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Laboratory for Solar and Space Physics Seminar Series, NASA Goddard Space Flight 
Center, Greenbelt, Maryland, U.S.A., 7 April 2006