Some aspects of plasmapause probing by whistlers

A guide to the whistler literature is presented, with emphasis on whistler probing of plasma structure and motions near the plasmapause. Whistler probing experiments have identified several types of variations in plasmasphere radius with local time, including (1) variations of a few tenths of an earth radius over ∼ 20° longitude that appear to originate on the nightside of the earth during substorms; (2) a secondary maximum in plasmasphere radius near noon; (3) the duskside plasmasphere bulge. A variety of remarkable and as yet incompletely understood VLF propagation effects occur in the vicinity of the plasmapause, including a decrease in received whistler activity outside the boundary and unusual propagation features such as echoing above the half‐equatorial gyrofrequency on paths just outside the plasmapause. Whistlers provide important information on magnetospheric conditions during wave‐particle interaction periods, for example, on equatorial electron densities and path magnetic shell parameters needed in modeling studies of observed interactions.