Rj. Leamon et al., MAGNETIC NULLS IN THE OUTER MAGNETOSPHERE OF JUPITER - DETECTIONS BY PIONEER AND VOYAGER SPACECRAFT, J GEO R-S P, 100(A2), 1995, pp. 1829-1835
First reported during the Ulysses flyby of Jupiter in February 1992, n
ull events are sporadic dropouts in the magnetic field strength detect
ed in the outer Jovian magnetosphere, with the magnitude of the field
strength decreasing to values that can be less than 0.2 nT. The events
occur in regions where the ambient field is primarily southward, that
is, aligned with the local planetary dipole field direction and are d
istinct from the field depressions encountered in the center of the ma
gnetodisk in the middle magnetosphere. They also appear distinct from
the field structures encountered at the magnetopause. Here we report a
survey of the occurrence of such events in the magnetic field data re
corded by the earlier Pioneer and Voyager spacecraft passages through
the Jovian system. All of the previous spacecraft to fly through the J
ovian magnetosphere recorded field null events on their inbound passes
where the field-magnitude dropped below 2 nT. There is little or no e
vidence of any field reversal in the center of events. Only Pioneer 11
, which was the only spacecraft to exit on the dayside of the magnetos
phere, recorded events on its outbound pass.