Experimental verification of drift-shell splitting in the distorted magnetosphere

Data from an electron spectrometer on the synchronous-orbit satellite ATS 1 and data from an electron spectrometer and ion chamber on the elliptical-orbit satellite OGO 3 can be used experimentally to test drift-shell splitting in the nondipolar distorted magnetosphere as proposed by Roederer. Quiet-day pitch-angle distributions obtained by ATS 1 at 6.6 RE qualitatively confirm the shell splitting by showing that near noon the pitch-angle distribution is nearly isotropic, whereas near midnight the pitch-angle distribution is peaked toward small angles (parallel to the field). By using the Mead model magnetic field for calculating the drift shells for electrons of pitch angle α = 65° and α = 90°, as well as the measured pitch-angle distribution and measured radial gradient for electrons at local noon, the pitch-angle distribution can be calculated as a function of local time for the ATS 1 orbit. The agreement between calculated and measured fluxes is satisfactory not only in predicting the proper noon to midnight asymmetry (25 to 1 for 500- to 1000-kev electrons on February 15, 1967) but also in correctly predicting the pitch-angle distribution as a function of local time (when the pitch-angle distribution is isotropic at noon, it is nonisotropic with a 3 to 1 ratio between a α 65° and α = 90° at midnight). In one case (February 15, 1967), however an asymmetry is observed near local midnight with minimum count rate at 2200 LT, representing a departure from the symmetric Mead model.