Observations of Auroral Roar Emissions at Resolute Bay, Sondrestrom, and South Pole Station

Details Observations of Auroral Roar Emissions at Resolute Bay, Sondrestrom, and South Pole Station Observations of Auroral Roar Emissions at Resolute Bay, Sondrestrom, and South Pole Station

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm32a19l&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SM32A-19

Physics

2407 Auroral Ionosphere (2704), 2471 Plasma Waves And Instabilities, 2704 Auroral Phenomena (2407), 6984 Waves In Plasma

Scientific paper

Auroral roar is one of three types of auroral radio emissions observable at ground level in the LF/MF/HF part of the radio spectrum (30 Hz--30 MHz). It occurs at approximately 3.0 and 4.5 MHz, and it is believed to be generated through mode conversion of upper hybrid waves excited by unstable auroral electron distribution functions in the F-region auroral ionosphere at points where the upper hybrid frequency matches cyclotron harmonics. Recent auroral roar data from Resolute Bay (84o corrected geomagnetic latitude), Sondrestrom (74o cgm) and South Pole (-74o cgm) are of high enough quality to allow automated statistical analysis of the emission frequencies, local times, amplitude, and seasonal dependences. The resulting statistical data sets reveal several interesting effects. For example, analysis of the frequencies of auroral roars observed at Sondrestrom and South Pole Station implies that a significant fraction of the auroral roar events detected at ground level originates in the topside of the ionosphere. A similar analysis of data from Resolute Bay reveals a high-frequency cutoff near 3 MHz. The seasonal dependence of the auroral roars at South Pole Station likewise provides indirect but independent evidence that the source altitude is in the auroral F-region. The Resolute Bay data show that the distribution of events in local time depends on both latitude and geomagnetic activity level. The effects observed in these studies provide further clues about the source location and the origin of time variations of the auroral roar emissions, which are significant because they represent the most local, easily observed examples of mode conversion radiations which are ubiquitous elsewhere in the solar-terrestrial environment.

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