Ulysses paper

Geophys. Res. Lett., 24, 2387-2390, 1997

Abstract:
We present a single example of a previously unidentified type of upstream wave structure, found several minutes ahead of a forward propagating, oblique interplanetary shock observed on day 6, 1992, using Ulysses magnetometer data. The wave appears as an isolated high frequency wavepacket associated with a larger scale compressive structure. In the region between the wavepacket and the shock the magnetic field is moderately, but significantly, compressed and deflected suggesting the existence of a foreshock. The wavepacket is dispersive and wavelet analysis shows a near linear decrease in frequency from 0.3 to 0.1 Hz, continuing across the large scale structure which is assumed to be the source of these waves. We suggest that the feature is similar in nature to the shocklet and associated discrete wavepacket commonly found in planetary foreshocks, but further examples are required before a definite conclusion can be reached.

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