Spaced measurements and progress in understanding space plasma waves

Measuring plasma wave properties with spatially separated antennae observes wavelength, propagation speed, and direction as well as frequency. This ap proach has been pivotal to progress in understanding three phenomena in spa ce plasmas. The first is lower hybrid solitary waves, which are waves with cylindrical symmetry propagating inside a density cavity. The second is ele ctron phase-space holes, which are propagating vortices in phase space. The third is called broadband ELF (extra low frequency) electric fields and is an important but poorly understood wave process essential to transverse io n acceleration. (C) 2000 American Institute of Physics. [S1070-664X(00)9120 5-9].