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similar to those reached by solar protons. These energetic
electrons are accelerated primarily within the magnetosphere
(rather than on the Sun) and occur much more frequently than major
flare events. The presence or absence of the relativistic electron
fluxes appears to be strongly controlled by the existence of
high-speed solar-wind streams emanating from persistent coronal
holes, which in turn are strongly controlled by the solar activity
cycle. The extent to which precipitating relativistic electrons
actually enter the atmosphere is currently uncertain. As noted in
Chapter 3, if a significant amount of these ionizing particles
reaches the middle atmosphere, the long term effects on ozone
concentrations in the stratosphere could be significant (Callis et