DIRECTION FINDING STUDY OF JOVIAN
HECTOMETRIC AND BROAD-BAND KILOMETRIC
RADIO EMISSIONS - EVIDENCE FOR THEIR
AURORAL ORIGIN
LADREITER HP
ZARKA P
LECACHEUX A
PLANETARY AND SPACE SCIENCE
v.42, n.11, NOV, 94, p.919-931
Taking advantage of the direction finding capabilities of the Ulysses unified
radio and plasma
wave (URAP) experiment we derive the source locations and emission
characteristics of the
Jovian hectometric (HOM)and broadband kilometric (bKOM) emissions. Unlike
previous
studies we additionally determine the systematic error-of the source
direction due to the
uncertainty of the antenna/receiver calibration parameters. To obtain maximum
accuracy when
doing direction fi nding, we use HOM and bKOM events observed close to the
Ulysses
encounter with Jupiter. It is found that both emissions have their sources at
the auroral zones
of Jupiter, at dipole L shells between 7 and 11 for HOM in the northern
hemisphere, and
between 9 and 15 for the bKOM radiation observed at high southern latitudes
after the
Ulysses Jupiter encounter. For the analyzed HOM events the source location is
usually
between 40 degrees and 130 degrees central meridian longitude (CML) and 2200
and 0600
local time (LT), but probably there exis t emissions from other longitudes
and local times too.
In contrast, the bKOM is emitted from a wide range of longitudes and local
times as well.
There is some evidence that both the kilometric and hectometric emissions are
composed of a
dominant component in the fast extraordinary (R-X) mode and a weaker ordinary
(L-O)
mode component. Due to the uncertainty in source direction determination the
emission's cone
half-angle (i.e. half-angle of the cone in which the emission is beamed)
cannot be accurately
determined. It is some 30 degrees-90 d egrees for the HOM and about 40
degrees-80
degrees for the bKOM. The source location of bKOM is likely to be associated
with open
magnetospheric field lines whereas the HOM is located at field lines that
connect the HOM
radio sources with the inner Jovian plasma sheet and/or outer plasma torus.
There is some
evidence that the bKOM radio emissions are correlated with ultraviolet
auroral activity.