Dispersive shear Alfvén waves on model Tsyganenko magnetic field lines Original Research Article

We present a theory of low-m dispersive shear Alfvén waves (SAWs) that are excited on magnetic field lines specified by the Tsyganenko 1996 magnetic field model. Our dispersive nonlinear model is applied to field lines near the midnight meridional plane and is parameterized by averaged quantities along a field line. For inner plasma sheet ambient parameters, dispersion is dominated by finite electron temperature and ion gyroradius effects that lead to a poleward propagating arc that is in general agreement with simultaneous CANOPUS and FAST satellite observations. The computed fundamental mode frequency is in the 1–4 mHz range, and is in agreement with the measured frequency of nightside magnetospheric field line resonances (FLRs). We conclude that dispersive Alfvén waves excited in a stretched magnetic topology can explain many features of FLRs observed within diffuse auroral precipitation (in Hβ) near the inner plasma sheet.