THE DYNAMICS OF THE POLEWARD EDGE OF THE TROUGH DEDUCED USING DATA FROM A MERIDIONAL CHAIN OF VERTICAL-INCIDENCE SOUNDING STATIONS

Data from four ionospheric stations located along the 90-degrees-E mer idian in the range 55-70-degrees of corrected geomagnetic latitude, we re used to construct latitude-time electron density distributions in t he F2-layer peak for 17 winter nights of 1982-1983. It is concluded th at under stationary convection conditions the poleward edge of the tro ugh during the nighttime displaces only 0.5-1-degrees/h, that is, sign ificantly less than obtained from existing analytical models of the io nospheric trough. When the stationarity is upset (due to the developme nt of a substorm or abrupt changes of the north-south component of the IMF), the poleward edge of the trough is observed to displace abruptl y equatorward. In the substorm expansion phase these displacements can amount to 4-5-degrees in less than an hour. Such displacements of the poleward edge in the evening hours can characterize the dynamics of t he inner edge of the plasma sheet.