High-frequency and time resolution rocket observations of structured low- and medium-frequency whistler mode emissions in the auroral ionosphere

High bandwidth electric field waveform measurements on a recent auroral sou nding rocket reveal structured whistler mode signals at 400-800 kHz. These are observed intermittently between 300 and 500 km with spectral densities 0-10 dB above the detection threshold of 1.5 x 10(-11) V-2/m(2) Hz. The lac k of correlation with local particle measurements suggests a remote source. The Signals are composed of discrete structures, in one case having bandwi dths of about 10 kHz and exhibiting rapid frequency variations of the order of 200 kHz per 100 ms. In one case, emissions near the harmonic of the whi stler mode signals are detected simultaneously. Current theories of auroral zone whistler mode emissions have not been applied to explain quantitative ly the fine structure of these signals, which resemble auroral kilometric r adiation (AKR) rather than auroral hiss.