The Arrival of High Energy Solar Protons

Solar Proton Event blasts the SOHO spacecraft

Solar proton events produce several major consequences at Earth:

  • High energy protons penetrate the Earth's magnetic field in the polar regions, crash into atmospheric particles and produce ion and electron pairs that temporarily increase the density in the lowest regions of the ionosphere. This causes absorption of short wave radio signals and wide-spread blackout of communications, called a polar cap absorption event.
  • Dangerous levels of high energy particle radiation build up in the magnetosphere that can damage spacecraft microelectronics and pose a serious threat to the safety of astronauts.

    Click here to find out how often solar proton events occur in space.

Minutes to Hours Later .....

Solar protons are accelerated to very high velocities in the explosive release of energy associated with a solar flare. These particles first make their way out of the corona. Then they cannot take a straight line path to the Earth but must travel along the Sun's extended magnetic field lines (called the interplanetary magnetic field or IMF). These field lines have a structure resembling the spiral traced out by a spinning lawn sprinkler, which is referred to as a Parker spiral.

The image on the right shows how flare location on the surface of the Sun affects the intensity and arrival time of the high speed solar particles at the Earth. In the first case, the flare occurred in the center of the Sun on a direct line-of-sight path to the Earth. In the second case, the flare site is on the limb of the Sun, directly connected to the Earth along a curved magnetic field line. The line plot in each case gives the history of the flux (in logarithmic units) as it arrives at Earth. The flare particles, blown out at the limb of the Sun, arrive more rapidly and in greater numbers (flux is almost 10 times higher) than those that began their journey from the center of the solar disk.

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