Interpreting Auroral Roar Fine Structure Measurements

Details Interpreting Auroral Roar Fine Structure Measurements Interpreting Auroral Roar Fine Structure Measurements

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm44a..03y&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM44A-03

Other

2467 Plasma Temperature And Density, 2471 Plasma Waves And Instabilities (2772), 2475 Polar Cap Ionosphere, 2483 Wave/Particle Interactions (7867), 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934)

Scientific paper

Fine structures of auroral radio emissions, such as AKR fine structures, have long been of intrest to geophysicists. Auroral roar is an emission observed near two and three times the electron cyclotron frequency in the auroral ionosphere. LaBelle et al. [1995] first observed that auroral roar has fine structure superficially similar to that of AKR, and Shepherd et al. [1998] identified multiplet structures drifting up and down in frequency within auroral roar. Yoon et al. [2000] showed that discrete frequency eigenmodes are a natural consequence of a cylindrical field-aligned density structure, and proposed these as the source of auroral roar fine structure. In December 2002, VIEW (Versatile Electromagnetic Wave Receiver) was installed at South Pole Station to record auroral roar and other radio emissions. The 1 MHz bandwidth of this receiver resolves the auroral roar fine structure, but only during selected time intervals, not continuously, due to the high data rate. Hundreds of examples drifting multiplets within auroral roar were captured during 2003 and 2004. Close study of the each example yields these parameters: f_h (the frequency of the highest-frequency multiplet); N (the number of multiplets); and δ f_n for n=1,...,N (the frequency spacings between each multiplet). Using the Yoon et al. [2000] eigenmode theory, we invert these measured parameters to determine L (the length scale of the assumed cylindrical density enhancements). The result is a statistical distribution of length scales L inferred from the ground-based auroral roar fine structure measurements. This measured distribution can be compared, for example, to rocket observations of the distributions of the length scales of density irregularities.

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