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The elliptic orbit satellite Explorer 12 made possible the routine survey of the heart of the outer radiation zone as well as the region of transition between the magnetosphere and interplanetary space on the sunward side of the earth by means of a variety of particle and magnetic field detectors. The data received from the SUI detectors during the entire 112-day lifetime have been comprehensively analyzed. Salient features observed include: confirmation of the enhancement of soft electron fluxes and diminution of hard electron fluxes in the outer zone during magnetically disturbed times; the outward motion of the outer zone hard electron maximum during periods of enhancement; confirmation of the general Chapman and Ferraro picture of a well-defined magnetosphere with compression of the geomagnetic field during the initial phases of magnetic storms; the existence of a layer of quasi-thermalized plasma immediately outside the magnetosphere; confirmation of the result of Frank and Van Allen that the contours of constant counting rate for electrons with E ≥ 40 kev tend to protrude outward near 90° from the subsolar point and draw closer to the earth on the night side; and general support for the result of Gringauz, Kurt, Moroz, and Shklovskii that there exists a region beyond some 8Re on the night side of the earth dominated by very-low-energy electrons.
J. W. Freeman (Fri,) studied this question.