A 27‐day periodicity in outer zone trapped electron intensities

Data from the polar orbiting satellite 1963 38C show the existence of a 27-day periodicity in the intensities of trapped, ≥280-kev and ≥1.2-Mev electrons for L ≥3.5. This effect is seen for the four sequential solar rotations commencing October 6, 1963. The trapped energetic electron intensities are observed to undergo two large increases every 27 days and are shown to be intimately linked with the passage of the recently observed interplanetary magnetic field sector boundaries. It is also shown that these electron intensity increases are triggered by variations in the parameter β, the ratio of the directed solar wind kinetic energy density to the interplanetary magnetic field energy density. Equivalently, large variations in the Alfven Mach number MA are shown to be responsible for these trapped electron variations.

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