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The dayside high-latitude trough is a persistent feature of the post-noonwintertime auroral ionosphere. Radio tomography observations have been usedto map its location and latitudinal structure under quiet geomagneticconditions (<i>K<sub>p</sub></i>≤2) near winter solstice. The trough is also a clearfeature in the ion density distribution of the CoupledThermosphere-Ionosphere-Plasmasphere model (CTIP) under similar geophysicalconditions. Comparisons of the measured and modelled distributions show thatthe plasma production equatorward of the trough is mainly controlled bysolar radiation, but there are also other processes maintaining theequatorward trough-wall that are open to debate. The poleward trough-wall isproduced by particle precipitation, but the densities are significantlyoverestimated by the model. At the trough minimum the observed densities areconsistent with low nighttime densities convecting sunward to displace thehigher daytime densities, but this is not borne out by the CTIP model. Thestudy shows the potential of combining radio tomography and modelling tointerpret the balance of the physical processes responsible for large-scalestructuring of the high-latitude ionosphere, and highlights the role oftomographic imaging in validating and developing physical models

The dayside high-latitude trough under quiet geomagnetic conditions: Radio tomography and the CTIP model