Is the plasmapause a preferred source region of electromagnetic ion cyclotron waves in the magnetosphere?

It has generally been assumed in the past that the plasmapause is a preferr ed region for the generation and propagation of electromagnetic ion cyclotr on (EMIC) waves in the Earth's magnetosphere. One assumption invoked the ov erlap of the expanding cold plasmapause with the inner edge of the hot ring current during storm recovery to provide favourable conditions for EMIC in stability. The plasmapause was also expected to provide a convenient gradie nt for guiding the waves from equatorial sources to higher latitudes. The p aper commences from a historic perspective and reviews the development of t he ideas from the 1960s that relate the source of EMIC waves to the plasmap ause. CRRES spacecraft observations of EMIC wave events over L = 3.5-8 and associated plasmapause locations indicate that the plasmapause is a region of wave generation and propagation, with significant wave power seen in the plasmatrough, but is not necessarily the preferred region. Other results s how that wave occurrence predominates in the afternoon and increases with r adial distance and a He+ slot is seen in the data. These agree with earlier AMPTE-CCE results from Anderson et al. (J. Geophys. Res. 97 (1992) 3075, 3 089). New results from CRRES show all wave polarisations (left-hand, linear , and right-hand) are seen within 8 degrees of the equator whereas linear p redominates over 20-30 degrees latitude. Waves are observed in background p lasma densities of 4-300 cm(-3). Wave frequencies above the He+ cyclotron f requency are concentrated outside the plasmapause in lower density regions of 2-30 cm(-3). (C) 2001 Elsevier Science Ltd. All rights reserved.