Simultaneous observation of a Pc 1 pulsation by the Air Force Geophysics Laboratory Magnetometer Network and GEOS 1

Abstract

A Pc 1 event was observed simultaneously at the Air Force Geophysics Laboratory Magnetometer Network Newport station (L = 3, 1500–1600 MLT) and by GEOS 1 (L = 7, 1230–1310 MLT) on August 8–9, 1977, between 2325 and 0015 UT. Throughout the event the satellite and ground station were separated by at least 2.4 hours in local time and four L shells. At GEOS 1 the event had two frequency components, one just below and one just above the local He+ gyrofrequency. During the first part of the event these components are narrow‐banded. In the later stages of the event, the emissions observed in space are more broad‐banded. The first part of the event was observed on the ground; the lower‐frequency component was present, while the higher‐frequency component was detected only weakly. A comparison of wave spectra shows that the lower‐frequency component has the same frequency as a function of time in space and on the ground, but the temporal variations in the intensity and shape of the spectral peaks are different. Substorm onsets that occurred during the event are apparent as Pi 2 and PiB signatures in the ground‐based search coil data. These onsets may have affected the reception of the signal at Newport. We conclude that the source region was localized both in longitude and L shell, and on the basis of this conclusion we estimate the attenuation of the signal in the ionospheric duct to be 0.009–0.014 dB km−1.