I. McWhirter

First tristatic studies of meso‐scale ion‐neutral dynamics and energetics in the high‐latitude upper atmosphere using collocated FPIs and EISCAT radar

A unique experiment was undertaken during the nights of 27 and 28 February 2003. Tristatic Fabry-Perot Interferometer (FPI) measurements of the upper thermosphere were co-located with tristatic EISCAT radar measurements of the ionosphere. Tristatic measurements should remove assumptions of uniform wind fields and ion drifts, and zero vertical winds. The FPIs are located close to the 3 radars of the EISCAT configuration in northern Scandinavia. Initial studies indicate that the thermosphere is more dynamic and responsive to ionospheric forcing than expected. Mesoscale variations are observed on the scales of tens of kilometers and minutes. The magnitude of the upper thermosphere neutral wind dynamo field is on average 50% of the magnetospheric electric field and contributes an average magnitude of 41% of in-situ Joule heating. The relative orientations of the 2 dynamo field vectors produce a standard deviation of ±65% in the contribution of the neutral wind dynamo.

Combined ground-based optical support for the aurora (DELTA) sounding rocket campaign

The Japan Aerospace Exploration Agency (JAXA) DELTA rocket experiment, successfully launched from Andøya at 0033 UT on December 13, 2004, supported by ground based optical instruments, primarily 2 Fabry- Perot Interferometers (FPIs) located at Skibotn, Norway (69.3°N, 20.4°E) and the KEOPS Site, Esrange, Kiruna, Sweden (67.8°N, 20.4°E). Both these instruments sampled the 557.7 nm lower thermosphere atomic oxygen emission and provided neutral temperatures and line-of-sight wind velocities, with deduced vector wind patterns over each site. All sky cameras allow contextual auroral information to be acquired. The proximity of the sites provided overlapping fields of view, adjacent to the trajectory of the DELTA rocket. This allowed independent verification of the absolute temperatures in the relatively quiet conditions early in the night, especially important given the context provided by co-located EISCAT ion temperature measurements which allow investigation of the likely emission altitude of the passive FPI measurements. The results demonstrate that this altitude changes from 120 km pre-midnight to 115 km post-midnight. Within this large scale context the results from the FPIs also demonstrate smaller scale structure in neutral temperatures, winds and intensities consistent with localised heating. These results present a challenge to the representation of thermospheric variability for the existing models of the region.

Auroral spectral estimation with wide-band color mosaic CCDs

Optical aurora can be structured over a wide range of spatial and temporal scales with spectral features that depend on the energy of precipitating particles. Scientific studies typically combine data from multiple instruments that are individually optimized for spatial, spectral, or temporal resolution. One recent addition combines all-sky optics with color mosaic CCD (charge-coupled device) detectors that use a matrix of different wide-band micro-filters to produce an image with several (often three) color channels. These devices provide sequences of two dimensional multispectral luminosity with simultaneous exposure of all color channels allowing interchannel comparison even during periods with rapidly varying aurora. At present color auroral image data are primarily used for qualitative analysis. In this study a quantitative approach based on Backus–Gilbert linear inversion was used to better understand the effective spectral resolution of existing and proposed instruments. Two spectrally calibrated commercial detectors (Sony ICX285AQ and ICX429AKL) with very different color mosaics (RGB (red, green, blue) vs. CYGM (cyan, yellow, green, magenta)) were found to have very similar spectral resolution: three channels with FWHM (full-width halfmaximum)≈ 100 nm; a NIR (near infrared) blocking filter is important for stabilizing inversion of both three-channel configurations. Operating the ICX429AKL in a noninterlaced mode would improve spectral resolution and provide an additional near infrared channel. Transformations from arbitrary device channels to RGB are easily obtained through inversion. Simultaneous imaging of multiple auroral emissions may be achieved using a single-color camera with a triplepass filter. Combinations of multiple cameras with simple filters should provide∼ 50 nm resolution across most of the visible spectrum. Performance of other instrument designs could be explored and compared using the same quantitative framework.