Dynasonde observations of electron concentration gradients above Tromsø

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.