Abstract
Abstract. The dayside high-latitude trough is a persistent feature of the post-noon wintertime auroral ionosphere. Radio tomography observations have been used to map its location and latitudinal structure under quiet geomagnetic conditions (Kp≤2) near winter solstice. The trough is also a clear feature in the ion density distribution of the Coupled Thermosphere-Ionosphere-Plasmasphere model (CTIP) under similar geophysical conditions. Comparisons of the measured and modelled distributions show that the plasma production equatorward of the trough is mainly controlled by solar radiation, but there are also other processes maintaining the equatorward trough-wall that are open to debate. The poleward trough-wall is produced by particle precipitation, but the densities are significantly overestimated by the model. At the trough minimum the observed densities are consistent with low nighttime densities convecting sunward to displace the higher daytime densities, but this is not borne out by the CTIP model. The study shows the potential of combining radio tomography and modelling to interpret the balance of the physical processes responsible for large-scale structuring of the high-latitude ionosphere, and highlights the role of tomographic imaging in validating and developing physical models.
Highlights
The high latitude ionosphere is a structured medium containing irregularities in electron density over an extended range of horizontal spatial scales
Average density distributions from tomographic observations have been obtained that show the latitudinal characteristics of the dayside high-latitude trough in the post-magnetic-noon sector under quiet geomagnetic conditions near solar maximum
The latitudinal variations have been compared with those given by the Coupled Thermosphere-Ionosphere-Plasmasphere model (CTIP) model under similar conditions, revealing that:
Summary
The high latitude ionosphere is a structured medium containing irregularities in electron density over an extended range of horizontal spatial scales. Ground-based measurements by a network of ionospheric sounders made in December 1958 during the International Geophysical Year (IGY) are reported by Whalen (1987, 1989) These showed the trough to be located at latitudes poleward of 70◦ magnetic latitude during quiet conditions, but to expand to lower latitudes at times of higher activity. Observations by incoherent scatter radar of high-latitude dayside troughs during active conditions were reported by Evans et al (1983) and Holt et al (1984). In these studies the trough had migrated to lower latitudes, and its formation was attributed to plasma erosion associated with intense electric fields
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