Global electron density distributions from topside soundings

A global morphology of electron density distributions in the topside ionosphere during sunspot minimum as deduced from Alouette I and II ionograms is presented. Graphs are shown illustrating the variations of electron density with altitude (400 to 3000 km), dip latitude (±90°), local time (24 hours), and season (December and June solstices; equinox) for both quiet and disturbed geomagnetic field conditions. "Average" daytime and nighttime electron density distributions, based on the analysis of large quantities of Alouette I quiet-time data, are presented for the lower altitudes (less than 1000 km) and for low and middle dip latitudes for each season. Large-scale anomalous features are summarized and discussed with respect to their bottomside counterparts where such exist. Small-scale effects and physical explanations for the topside ionosphere behavior are discussed in companion papers.