Quiet‐time electron increases: A measure of conditions in the outer solar system

One possible explanation for the increases in the intensity range of 3‐ to 12‐Mev interplanetary electrons that McDonald et al. (1972) have labeled as ‘quiet‐time electron increases’ is discussed. It is argued that the electrons in quiet‐time increases are galactic in origin but that the observed increases are not the result of any variation in the modulation of these particles in the inner solar system. It is suggested instead that quiet‐time increases may occur when more electrons than normal penetrate a modulating region that lies far beyond the orbit of the earth. The number of electrons penetrating this region may increase when field lines that have experienced an unusually large random walk in the photosphere are carried by the solar wind out to the region. As evidence of this increased random walk, it is shown that five solar rotations before most of the quiet‐time increases occur there is an extended period when the amplitude of the diurnal anisotropy (measured by the Deep River neutron monitor) is relatively low. A delay time of five rotations implies that the proposed modulating region lies at ∼30 AU from the sun if the average solar‐wind speed is assumed to be constant at ∼400 km/sec over this distance. The implications for the correlation between periods of low‐amplitude diurnal anisotropy and quiet‐time increases on interplanetary conditions out to ∼30 AU and some possible models for the proposed modulating region are also considered.