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The Dynasonde is a digital ionosonde which measures the amplitude and phase of radio echoes reflected from the ionosphere. In addition to the frequency and virtual range of each echo, one parameter of particular interest is the direction of arrival which allows horizontal structures in the ionosphere to be studied. Under suitable ionospheric conditions, namely where structures or strong gradients are present in the electronconcentration, echoes may be observed out to horizontal distances of several hundred kilometres. We describe an automated method for latitudinally mapping these gradients in F-region peak electronconcentration using the Dynasonde. Good agreement is found when the results are compared with a co-located incoherent scatter radar lending credibility to observations of electronconcentrationgradients by a Dynasonde alone. This is significant for sites where no supporting instruments exist. Although Dynasondes account for only a small fraction of digital ionosondes in use today, the techniques described in this paper could be extended to other digital ionosondes with similar directional capabilities. The combination of routine soundings, and the worldwide distribution of such instruments, would provide a powerful means to monitor ionospheric structures on a regular basis.

The dynasonde at Halley, Antarctica, is operated throughout the year making ionogram soundings every five minutes. The extensive database of observations from 1993 and 1994 has been processed to investigate ionogram echoes from mesospheric heights. The occurrence of these echoes shows a very clear seasonal trend with far more echoes observed during the winter. The echoes are shown to be predominantly dependent on the absence of direct solar illumination. The characteristics of the echoes are compared with similar observations from a northern hemisphere site at Tromso, Norway. The observations from Halley and Tromso are discussed in relation to Polar Mesosphere Summer Echoes (PMSE) which are seen at higher radio frequencies above Tromso. It is found that ionogram mesospheric echoes have different occurrence statistics from PMSE and there is no statistical evidence to suggest that the echoes observed during the summer are different from those observed at other times of year.