Ponderomotive effects in magnetospheric hydromagnetic waves (*)

The ponderomotive force (PMF) is a ubiquitousnonlinear wave effect arising in plasma physics when applied wave fields orplasma parameters have significant spatial gradients. Some basic properties ofthe PMF are described as they relate to ULF hydromagnetic waves in themagnetosphere. Examples are given of recent results obtained using bothanalytical and numerical techniques for waves from the lowest frequencies(determined by the dimensions of the magnetosphere) up to the vicinity of theion cyclotron frequency. These results include the possibilities that the PMFmay transport plasma over large distances in the magnetosphere, and that the PMFmay energize magnetospheric ions significantly. In particular the PMF may play arole in transporting and energizing O⁺ ions from the ionosphere intothe body of the magnetosphere. The PMF can also generate nonlinear couplingbetween the slow magnetosonic mode and the other hydromagnetic modes. Thisshould lead to limitation of density enhancements and, notably in the case ofstanding Alfvén waves, to spatial harmonic generation, secularly growingfrequency shifts, and saturation of driven wave fields. Some implications ofthese results for the magnetosphere are discussed