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Optical observations of 557.7 nm and 630.0 nmemissions from discrete auroral arcs in the post-noon sector have been relatedto localised field-aligned enhancements in the spatial distribution of E- andF-layer electron density respectively seen in images reconstructed byionospheric tomography. Results from two case studies are presented in whichmeridian scanning photometer and all-sky camera observations on Svalbard havebeen compared to electron-density structures found by tomographic inversion ofmeasurements made by reception of radio signals at a chain of four stations athigh latitude. The F-layer features are long-lived and show exact correspondenceto the red-line emissions. Transient arcs in green-line intensity result inE-region structures that are resolved in one case, but not in another where thedynamic auroral forms are separated by less than one degree of latitude. Thesignature of an inverted-V precipitation event is clearly evident in oneexample.  <b>Key words. </b>Ionosphere (Auroral ionosphere) ·Magnetospheric physics (Auroral phenomena) · Radio science (Ionosphericphysics

Probing discrete auroral arcs by ionospheric tomography