Standing shear Alfven waves driven by the Jupiter dipole wobbling

Abstract:

We present Galileo observations of 10 h periodic variations of azimuthal
and radial magnetic fields in the Jovian magnetotail (at X<-40 R_J, where the
Jupiter Solar Equatorial (JSE) system is used). The radial magnetic field
variations correspond to the magnetotail flapping motion generated by the
diurnal Jupiter dipole wobbling. The azimuthal magnetic field variations are
phase shifted with respect to the radial variations by a quarter of the period.
The azimuthal magnetic field has maximum in the magnetotail neutral sheet and
its amplitude is comparable with the amplitude of the radial magnetic field. We
suggest that azimuthal variations represent the manifestation of shear waves
standing along magnetotail flux tubes and driven by the dipole wobbling. The
large amplitude of observed azimuthal variations could be attributed to the
shear wave standing along the resonant flux tube. We have found that azimuthal
magnetic field variations are associated with flat plasma density profiles
across the magnetotail current sheet. We suggest that the flattening of the
plasma density profile is due to the action of the ponderomotive force induced
by standing shear waves.