FLUCTUATIONS IN BRIGHTNESS FROM QUIET-FORM AURORAS

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Abstract
Observations of brightness fluctuations in quiet-form auroras have been made from Saskatoon. The resulting data sequences were analyzed on the basis that they are physical realizations of second-order stationary stochastic processes. It is shown that these fluctuations occur almost always and that certain reciprocal frequencies dominate the fluctuation spectra. The spectral-density estimates invariably show one and sometimes two pronounced peaks in the reciprocal frequency range of 3–20 seconds. The scale size of the spatial fluctuations has been determined to be of the order of 50 kilometers. These spatial fluctuations are anisotropic. At times, a disturbance has been detected moving within a quiet form and the propagation speed has been measured. Simultaneous fluctuations in brightness at wavelengths of 3 914 Å and 4 861 Å have been observed and their nature is described. Examination of a simple model based on the precipitation of trapped electrons reveals that the observations can be explained only partially by such a mechanism.