ELECTRON-CONTENT MEASUREMENTS IN THE AURORAL-ZONE USING GPS - PRELIMINARY-OBSERVATIONS OF THE MAIN TROUGH AND A SURVEY OF THE DEGREE OF IRREGULARITY IN SUMMER

Ionospheric electron content was monitored from sites in or near Troms o, Norway, for six months of 1993, using the transmissions from the sa tellites of the Global Positioning System (GPS). The data have been us ed for preliminary studies of two important phenomena of the high-lati tude ionosphere: the main trough and the incidence of large irregulari ties. The latitude and motion of the trough were determined on several occasions during the spring period, and the results compared with pre vious data. Best agreement is with the formula of Collis and Haggstrom (1988). The incidence of large irregularities was surveyed during a f our-month period, approximately from the summer solstice to the autumn al equinox, and the variation with time of day and magnetic activity h as been determined. It was found that irregularities are considerably larger by night than by day, but that they are enhanced during both pe riods by increased magnetic activity. Statistical results are presente d. It is suggested that these irregularities are the same as the ''aur oral blobs'' previously studied by incoherent-scatter radar. (C) 1996 Elsevier Science Ltd