High-Latitude Boundary of the Outer Radiation Zone at 1000 km

Particle detectors on the Alouette satellite have been used to determine the average high-latitude boundary of the outer radiation zone at 1000 km as a function of local time. The boundary for electrons with energies greater than 40 kev is approximately symmetrical with respect to the noon–midnight meridian and occurs at the highest latitude near local noon, shifting between 4° and 5° to its lowest value near local midnight. There is very little difference in the average boundaries of so-called trapped and precipitated electrons. The results are discussed in terms of measurements of electrons with similar energies in the equatorial plane and models of the earth's magnetic field.