Abstract
Wave data from the DE 1 spacecraft for 50 sudden commencements were analyzed for amplitude and spectral modifications and correlated with data from ground‐based observatories. Changes in wave activity were identified in 14 of the events studied. The changes, which were commonly observed at frequencies below the local electron gyrofrequency, exhibited a complex structure both in frequency and in time and varied considerably among events. The typical event lasted 1–10 min with a maximum narrowband amplitude increase or decrease of 10–30 dB. The onset time of the wave growth was correlated with the arrival of the magnetic disturbance at the spacecraft. Changes were most commonly observed at L shells in the range 3 < L < 6. Growth was observed on the nightside as well as the dayside, and no clear local time dependence was found. In several cases, growth at frequencies above the local gyrofrequency was noted and identified as auroral kilometric radiation.
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