The southern-hemisphere mid-latitude day-time and night-time trough at low-sunspot numbers

The diurnal, seasonal, spatial and magnetic activity variations of the southern-hemisphere mid-latitude trough has been studied by using GPS and TOPEX satellite techniques during the low-sunspot number period of February 1995-February 1996. The ionospheric total electron content (TEC) values were obtained from the raw satellite data to observe the trough both locally in the Australian longitude region and globally over the world oceans. Various trough features were observed and investigated under different magnetic conditions, and were compared to the results of other researchers employing different techniques at Macquarie Island (-54.5degreesN; 154.95degreesE, geographic and the magnetic shell parameter (L) is 5.38). The ionization build-up on the equatorward trough wall, which has not been investigated since Foster (1993), is discussed in detail with the DeltaTEC parameter utilized to characterize it. Some of the GPS findings were continued with the TOPEX results. Comparisons with the model generated TEC plots indicated that the model did not reproduce the trough. Several day-time and night-time global TOPEX TEC maps, showing also the geomagnetic and dip equators, were constructed for the season of the 1995 autumnal equinox to observe the trough globally, the first time in the literature, with other large-scale ionospheric formations. The magnetic alignment of these large-scale ionospheric formations is obvious. On the night-time maps the empirical position of the trough were plotted for various local time values at K-p = 0 and 6, and indicated a very good agreement between the experimental and theoretical results. (C) 2003 Elsevier Ltd. All rights reserved.