Sector Structure of the Quiet Interplanetary Magnetic Field.
Observations of the interplanetary magnetic field by the Imp-1 satellite have revealed a regular longitudinal sector structure in this field. The sectors co-rotate with the sun; as an average sector sweeps past the earth the magnitude of the interplanetary field decreases from greater than 6 gammas (1 gamma = 10(-5) gauss) to less than 4 gammas, and the daily sum of the geomagnetic activity index, Kp, decreases from 25 to less than 10.
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