Statistical study of auroral roar emissions observed at South Pole Station

Details Statistical study of auroral roar emissions observed at South Pole Station Statistical study of auroral roar emissions observed at South Pole Station

Jul 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jgra..107.1140l&link_type=abstract

Journal of Geophysical Research (Space Physics), Volume 107, Issue A7, pp. SIA 17-1, CiteID 1140, DOI 10.1029/2001JA000319

Physics

Plasma Physics

2

Ionosphere: Auroral Ionosphere (2704), Ionosphere: Plasma Waves And Instabilities, Magnetospheric Physics: Auroral Phenomena (2407), Space Plasma Physics: Radiation Processes

Scientific paper

Auroral roar is a band-limited natural auroral radio emission observed at ground level in the auroral zone at frequencies near 3 MHz and 4.5 MHz, close to 2 and 3 times the electron gyrofrequency. Using semiautomated data analysis techniques, we generate a database of frequencies, amplitudes, and universal times of 2fce-auroral roar emissions observed at South Pole Station (74° invariant latitude) during 1999. These data confirm that auroral roar emissions are observed at ground level only during times when the ionosphere is not illuminated, and magnetic local time plays a significant role in controlling the occurrence rates of auroral roar emissions observed at ground level. Auroral roar occurrence rates and the ranges of auroral roar amplitudes and frequencies increase during times of high geomagnetic activity. The distribution of auroral roar frequencies is bimodal for large-amplitude events, which we interpret as evidence that a substantial fraction of the auroral roar emissions observed at ground level originate in the topside ionosphere. Finally, superposed epoch analyses of occurrences of auroral roar relative to substorm onsets inferred from magnetometer and VLF data show that auroral roar emissions occur favorably preceding such events rather than after them, consistent with previous case study and anecdotal evidence.

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