The background wind matches averages presented previously by Sica et al. Smaller scale curvature and divergence features are also discernable and are discussed. Introduction There has been considerable experimental and theoretical interest in the small-scale structure of thermospheric wind and temperature fields at auroral latitudes. Eastes et al. The Walterscheid et al.
Interference fringes formed by the etalon are conjugate with the sky.
For each individual photon recorded by the IPD a spectral bin is calculated using both its detected position and the plate spacing prevailing at detection time. Prior to sky observations the instrument records a calibration map of the detector which encodes, for each pixel location, the etalon gap required to maximize the transmitted intensity at that pixel of a monochromatic source at the nominal observing wavelength. The appropriate spectral channel to assign to a photon detection during sky observations is then given by the difference between the current plate spacing and that spacing at which transmission maximizes for the detection location. Each detected photon is added to the total for its allocated spectral channel so that, at the end of each scan through one order in plate spacing, the photon totals represent a spectrum spanning one free spectral range in wavelength. Here, we have allocated a total of 25 zones mapping onto the sky as sectors of four concentric, annular, rings centered about the zenith.