Mircopulsation measurements of a Pc 5 wave event on July 14, 1982, in the afternoon magnetosphere are reported as observed by wave and particle instruments on board the Dynamics Explorer 1 (DE 1) spacecraft. The overall structure of the Pc event as noted in the low-energy particle and quasi-static electric field data seems to order the event into two distinct halves. The appearance is reminiscent of a wave packet and suggests a temporal or spatial variation of the micropulsation, which has a scale of 20 min or 3000 km. The wave packet structure is also well correlated with a variation in the pitch angle distribution of the low-energy plasma with single direction field-aligned flow associated with the maximum amplitude of the wave packet structure and bidirectional field-aligned flows associated with the nodal point of the wave packet structure.

The field-aligned velocities of the observed H+, He+, O+, N+, and O++ ions combined with the elliptical E¿B wave oscillation in the first half of the event produce a helical motion of the plasma along the field line. In the second half of the event although all ions species are still present, strong magnetospheric convection seems to have a significant effect on the field-aligned motions and Pc 5 oscillations of the low-energy plasma. The event is characterized in the low-energy plasma by a left-hand to near-linear polarized rotation of the plasma over the first half of the event. Variations of the eccentricity over the first half of the event which are indicated by both the quasi-static electric field detector and the low-energy particle detector suggest that the center of resonance lies just radially inside of the DE 1 orbit (L=4.7) and just outside of the dayside plasmapause, which appears to be located at L=4 as indicated by experiments on board the DE 2 spacecraft.

Comparisons of the measured Pc 5 wave period to the theoretical period derived from in situ evaluation of the plasma mass loading factor yield values of 190 s and 192 s, respectively. This is consistent with the center of resonance being nearly coincident with the De 1 orbit. The second half of the event occurs in a region of enhanced magnetospheric convection, which makes determination of the eccentricity of the wave difficult and harder to interpret. The wave is found to be right-hand or linearly polarized during this portion of the wave difficult and harder to interpret. The wave is found to be right-hand or linearly polarized during this portion of the event, which suggests DE 1 is just radially inward of the resonance center. However, disagreement between the measured period of 233 s and the derived period of 189 s does not necessarily support this interpretation. Density variations of plasma along the field line which are hemispherically asymmetric may explain the inconsistencies between the measured and derived period in this half of the event.