J. M. Holmes

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

[1]xa0Ground 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 A[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 A[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.

Circumpolar ground‐based optical measurements of proton and electron shock aurora

Meridian scanning photometer (MSP) data are combined with global ultraviolet images from the Polar Ultraviolet Imager instrument to estimate the timing and propagation speed of shock auroras previously studied using solely space-based ultraviolet auroral imagery. The multispectral nature of the MSPs, including the presence of a Balmer beta channel, enables the discrimination between proton and electron aurora. Following a near-magnetic noon onset, the occurrence of auroral emissions created by shocked precipitating protons and electrons is observed to propagate tailward, along the auroral oval with speeds of several km/s, consistent with the shock propagation speed in the solar wind. In two cases, shock aurora propagation speeds along the auroral oval determined from satellite imagery are confirmed, to within calculated uncertainties, with ground-based timing. The majority of instruments detect low-energy discrete auroral arcs poleward of diffuse, higher-energy aurora. Evidence of a previously reported two-pulse proton aurora shock onset is detected at some, but not all, locations.

Rates, flux densities, and spectral indices of meteor radio afterglows

Using the narrowband all-sky imager mode of the LWA1 we have now detected 30 transients at 25.6 MHz, 1 at 34 MHz, and 93 at 38.0 MHz. While we have only optically confirmed that 37 of these events are radio afterglows from meteors, evidence suggests that most, if not all, are. Using the beam-forming mode of the LWA1 we have also captured the broadband spectra between 22.0 and 55.0 MHz of four events. We compare the smooth, spectral components of these four events and fit the frequency dependent flux density to a power law, and find that the spectral index is time variable, with the spectrum steepening over time for each meteor afterglow. Using these spectral indices along with the narrow band flux density measurements of the 123 events at 25.6 and 38 MHz, we predict the expected flux densities and rates for meteor afterglows potentially observable by other low frequency radio telescopes.