Submitted to J. Geophys. Res., 103, 29633-29642, 1998
Abstract:
The interplanetary shock observed by Ulysses on day 109 of 1992 occurred at
a time of unusual interplanetary magnetic field conditions when the field
was closely aligned with the radial direction for nearly a day ahead of the
shock. There were several intervals of wave activity in the upstream
region, the first occurring on day 108, and the second two intervals on day
109 leading up to the shock. In addition just ahead of the shock the
background field magnitude decreased to a value close to zero and
superimposed on this decrease were a number of field magnitude
enhancements. The downstream region was populated by large amplitude
compressive waves. A combination of spectral and wave analysis techniques
were used to characterise the different intervals of wave activity. The
waves on day 108 and the first interval of wave activity on day 109, are
consistent with generation by an ion beam instability, but the waves on day
109 increased in amplitude as the shock was approached, suggesting that
these waves were directly produced by the shock.
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