Variations of the occurrence rate of discontinuities in the interplanetary magnetic field

A statistical study of magnetic field discontinuities for the interval February to October 1968 using data from the NASA Goddard Space Flight Center/University of Rome experiment on Pioneer 8 has been conducted. High-resolution data (10-sec averages) have been employed, stringent criteria being utilized to select more than 16,000 events, about 50% being identified as disturbances that are probably tangential discontinuities (TD). Near 1 AU the average occurrence rate of discontinuities is about 3.6/hr, whereas that of tangentiallike discontinuities is about 1.6/hr. The rate of occurrence of discontinuities is found to be correlated with the directional change of the field across the discontinuity surface. The normal to the TD discontinuity plane is most often perpendicular to the Archimedean spiral field configuration. A decrease of the rate of occurrence of TD is found with increasing heliocentric distance and/or with decreasing heliographic latitude. Possible interpretations of the effect are discussed.

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