Correlation Between Low Frequency Auroral Kilometric Radiation (AKR) and Auroral 
Structures

Katherine A. Pazamickas, James L. Green, Dennis L. Gallagher, Scott Boardsen,
Stephen Mende, Harald Frey, Bodo W. Reinisch


Auroral Kilometric Radiation (AKR) is a radio wave emission that has long been
associated with auroral activity. AKR is normally observed in the frequency
range from ~60 - 600 kHz. Low frequency AKR (or LF-AKR) events are characterized
as a rapid extension of AKR related emissions to 30 kHz or lower in frequency
for typically much less than 10 minutes. LF-AKR emissions predominantly occur
within a frequency range of 20 kHz - 30 kHz, but there are LF-AKR related
emissions that reach to a frequency of 5 kHz. This study correlates all
instances of LF-AKR events during the first four years of observations from the
IMAGE spacecraft's Radio Plasma Imager (RPI) instrument with auroral
observations from the wideband imaging camera (WIC) onboard IMAGE. The
correlation between LF-AKR occurrence and WIC auroral observations shows that in
the 295 confirmed cases of LF-AKR emissions, bifurcation of the aurora is seen
in 74% of the cases. The bifurcation is seen in the dusk and midnight sectors of
the auroral oval, where AKR is believed to be generated. The polarization of
these LF-AKR emissions has yet to be identified. Although LF-AKR may not be the
only phenomena correlated with bifurcated auroral structures, bifurcation will
occur in most instances when LF-AKR is observed. The LF-AKR emissions may be an
indicator of specific auroral processes sometimes occurring during storm-time
conditions in which field-aligned density cavities extend a distance of perhaps
5-6 RE tailward from the Earth for a period of 10 minutes or less.

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Submitted to Journal of Geophysical Research, July 2005