ULF waves: 1997 IAGA division 3 reporter review

Abstract

Abstract. Highlights of studies of ULF waves from 1995 to early 1997 are presented. The subjects covered include (1) Pc 3±5 waves excited by sources in the solar wind, with emphasis on the role of the magnetospheric cavity in modifying the external source and establishing its own resonances, and the role of the plasmapause in magnetohydrodynamic wave propagation; (2) Pi 2 waves, with emphasis on the plasmaspheric resonances and possible alternative excitation by plasmasheet source waves; (3) the spatial structure of internally excited long-period waves, including a kinetic theory for radially con®ned ring current instability and groundbased multipoint observation of giant pulsations; (4) amplitude-modulated Pc 1±2 waves in the outer magnetosphere (Pc 1±2 bursts) and in the inner magnetosphere (structured Pc 1 waves or pearls); and (5) the source region of the quasi-periodic emissions. Theory and observations are compared, and controversial issues are highlighted. In addition, some future directions are suggested.

Global distribution of EMIC waves derived from THEMIS observations

“…As will be shown, the wave activity in the nightside is very weak, and will not be a major target of this investigation. Third, Pc3–4 waves associated with the field line resonance are observed at low latitude and connected to the inner magnetosphere ( L < 6) [ Takahashi , 1998]. At L = 6, the minimum frequency of our investigation is 0.15 Hz and still lies above the maximum frequency of Pc3–4 waves.…”

“…We should also note that other types of waves may appear in this spectral range, and possibly add uncertainty to the present analysis. They are Pc3–5 and Pi2 waves [ Takahashi , 1998] and we discuss their characteristics compared with EMIC waves below. First, Pc4–5 waves driven by solar wind usually occur in the dayside, outer magnetosphere ( L > 6) including those waves generated by Kelvin‐Helmholtz instability [e.g., Claudepierre et al , 2008].…”