Quarter-wave ULF pulsations

Recent theoretical work has predicted the possible existence of “quarter-wave” ULF pulsation resonances, in which the wave electric field has a near-node in one ionosphere and an antinode in the conjugate ionosphere. Eigenvalues are derived for quarter-wave toroidal and guided poloidal resonances for a range of L-values and plasma density distributions. From these eigenvalues, resonant periods can be obtained.Three pulsation events with anomalously long periods (when interpreted as half-waves) are examined in the light of these results. It is decided that only one event is a good candidate for quarter-wave status; this event seems likely to be a driven resonance effectively in the quarter-wave guided poloidal mode.