Abstract. The term Z mode is space physics notation for the low-frequency branch of the extraordinary (X) mode. It is an internal, or trapped, mode of the plasma confined in frequency between the cutoff frequency fz and the upper-hybrid frequency f uh which is related to the electron plasma frequency fpe and the electron cyclotron frequency fce by the expression f; fz is a function of fpe and fce. These characteristic frequencies are directly related to the electron number density Ne and the magnetic field strength |B|, i.e., fpe (kHz) 2 ≈ 80.6Ne(cm −3 ) and fce (kHz) 2 ≈ 0.028|B|(nT). The Z mode is further classified as slow or fast depending on whether the phase velocity is lower or higher than the speed of light in vacuum. The Z mode provides a link between the short wavelength λ (large wave number k = 2π/λ ) electrostatic (es) domain and the long λ (small k) electromagnetic (em) domain. An understanding of the generation, propagation and reception of Z-mode waves in space plasma leads to fundamental information on wave/particle interactions, Ne, and field-aligned Ne irregularities (FAI) in both active and passive wave experiments. Here we review Z-mode observations and their interpretations from both radio sounders on rockets and satellites and from plasma-wave receivers on satellites. The emphasis will be on the scattering and ducting of sounder-generated Z-mode waves by FAI and on the passive reception of Z-mode waves generated by natural processes such as Cherenkov and cyclotron emission. The diagnostic applications of the observations to understanding ionospheric and magnetospheric plasma processes and structures benefit from the complementary nature of passive and active plasma-wave experiments.

No abstract

No abstract

No abstract

No abstract