A model based method for obtaining the open/closed field line boundary from the cusp auroral 6300 Å[OI] red line

Ground based optical instruments are invaluable tools for studies of processes associated with the cusps and auroral morphology. In this work we present a method for obtaining the magnetic latitude of the open/closed field line boundary (OCB) from the cusp 6300 Å[OI] auroral red line using a meridian scanning photometer. The method which is based on a pre‐defined reference cusp aurora produced by the GLOW model is examined with respect to uncertainties, and we describe how a set of equations describing the error is constructed. The method is applicable to data from optical instruments located at high latitude observation sites such as Svalbard and Antarctica. Equations describing both errors and the mapping altitude for transforming the OCB from instrument centered coordinates to magnetic latitude for instrumentation located in Svalbard (Longyearbyen) are presented. Further, by applying the GLOW model we present results illustrating the great variability in the altitude profile of the atomic oxygen 6300 Å[OI] red line emission in the cusp. A simple calculation showing how a poleward neutral wind will change the latitudinal shape of the cusp aurora is also performed. Key Points The cusp aurora is highly variable in altitude and may vary by more than 100 km The neutral wind changes the shape of the cusp aurora considerably It is possible to determine the OCB from the cusp aurora within a set of errors