Session 7E - Space and Basic.
ORAL session, Thursday morning, November 14
Majestic Ballroom, Adam's Mark
Compressional Alfvén waves in the terrestrial magnetospheric cavity constitute a discrete spectrum of global modes which can resonate with specific components of the continuum spectrum of standing shear Alfvén wave field line resonances (FLRs). The compressional modes are excited by solar wind impulsive perturbations and the experimental evidence suggests that their resonance absorption results in FLR intensifications and is responsible for the optical emissions from discrete auroral arc structures. We investigate the effect of the ponderomotive force of standing shear Alfvén waves on the nonlinear saturation of FLRs. In the low \beta magnetospheric plasmas the FLR saturation occurs due to a nonlinear phase slip between the compressional mode driver and the shear wave filed. Ponderomotive force also leads to density depletions at the ionospheric ends of the resonator, nonlinear narrowing of FLR up to meridional scales comparable to the electron inertia scale length or to the scale of ion cyclotron radius. At these scales the parametric decay instability of the shear Alfvén wave takes place which is responsible for the FLR structuring comparable to scales comparable to those embedded within temporally modulated discrete auroral arcs. Observational features related to the effects of shear Alfvén wave dispersion will be discussed.