HR: 0800h
AN: SM51A-1275 [Abstracts]
TI: Io-Jupiter Interaction, Millisecond Bursts and Field Aligned Potentials.
AU: Zarka, P
EM: philippe.zarka@obspm.fr
AF: LESIA, Observatoire de Meudon
5, place Jules Janssen
, Meudon Cedex, F-92195
France
AU: Hess, S
EM: sebastien.hess@obspm.fr
AF: LESIA, Observatoire de Meudon
5, place Jules Janssen
, Meudon Cedex, F-92195
France
AU: Hess, S
EM: sebastien.hess@obspm.fr
AF: CETP, Centre universitaire
10-12 avenue de l'Europe, Velizy, F-78140
France
AU: * Mottez, F
EM: fabrice.mottez@cetp.ipsl.fr
AF: CETP, Centre universitaire
10-12 avenue de l'Europe, Velizy, F-78140
France
AB:
Jovian millisecond (or S-)bursts are intense impulsive Jovian decametric radiations
drifting in frequency in tens of milliseconds.
Most of the theories about their origin
comprise an interpretation of the frequency drift.
Previous analyses suggest that S-bursts are cyclotron-maser emission
in the flux tube connecting Io's wake to Jupiter.
In this model, electrons are accelerated from Io to Jupiter.
Near Jupiter, an electron loss cone distribution appears due to a mixture
of accelerated and mirror reflected adiabatic electrons. It is unstable, so that
electron-cyclotron waves are amplified.
We have performed an automated analysis of 230 high resolution dynamic spectra of S-bursts,
providing 5.106 frequency drift measurements.
Our data is fully consistent with the above scenario.
In addition, we confirm with a large number of points that the frequency drift df/dt(f)
is negative and smaller (in absolute value) at higher frequencies, consistent with
the adiabatic theory. We find a typical energy of 4 keV for the emitting electrons.
We reformulate the adiabatic model including parallel electric fields, and search
for correspondig signatures in the data.
A statistical analysis suggests for the first time the existence of a distributed
potential drop of about 3 kV in the region of emission.
In addition, we have found in 36 cases (out of 230) stable localized
potential jumps of about 1 keV. These results are the first direct
measurements of electric potential variations along the Io flux tube.
We expect that these electric potential variations are
closely connected with the existence of nearly field aligned Alfvénic currents.
DE: 2704 Auroral phenomena (2407)
DE: 6219 Io
DE: 6220 Jupiter
DE: 7807 Charged particle motion and acceleration
DE: 7847 Radiation processes
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005