On the local-time dependence of outer radiation zone electron (E>1.6 Mev) intensities near the magnetic equator

A study of approximately 10 months of Explorer 14 observations of energetic electrons (E >1.6 Mev) in the outer radiation zone near the geomagnetic equator ∣λm∣ < 25° shows that, if the omnidirectional intensity measurements are organized in a B-L system based on surface measurements of the geomagnetic field, a large local-time dependence of intensities on a given L shell is observed beyond L ≃ 6. The ‘average’ isoflux contour Jo = 102 (cm2 sec)−1 in an L-local time coordinate system is at L ≃ 10 (maximum L) near the local noon meridian and at L ≃ 8 (minimum L) near the local midnight meridian. For the contours of higher intensities (and hence smaller radial distances), this local-time variation weakens; for Jo = 104 (cm2 sec)−1, maximum L ≃ 7 near local noon, minimum L ≃ 6 near local midnight. A geostationary satellite at 6.6RE (earth radii) should observe an average diurnal variation in electron (E >1.6 Mev) intensity by a factor ∽50. At higher magnetic latitudes, ∣λm∣ 25°, near local noon the electron (E >1.6 Mev) intensity profiles were often not monotonically decreasing with increasing radial distance beyond ∼5RE as were the profiles at lower magnetic latitudes but displayed frequent secondary peaks of intensity from 5 to 12RE, which may be indicative of an acceleration mechanism for energetic electronsE≳1 Mev in the local day part of the magnetosphere. The diurnal variations of electron (E >1.6 Mev) intensities observed near the geomagnetic equatorial plane are consistent with the expected distortion of the geomagnetic field in these regions by the solar wind.