Geophys. Res. Lett., 25, 23, 4297 - 4300, 1998
Examination of 770 days of heliospheric magnetic field data recorded within polar solar wind by the Ulysses spacecraft revealed a number of occasions when the wave power decreased by more than an order of magnitude for several hours. These power dropouts were found to be associated with intervals when the magnetic field was closely aligned with the radial direction. A case by case study showed that there was no obvious signature in bulk plasma parameters. A statistical study of 24 intervals when the field was close to radial for at least 6 hours showed that the wave power in those intervals was significantly lower than that outside. There were no significant power changes when the field lay close to either the Parker spiral or an arbitrary direction. Although they are likely to be of solar origin, the exact source for these events is not clear.
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