Open AccessStriated auroral kilometric radiation emission: A remote tracer of ion solitary structures
Author(s) -
Mutel R. L.,
Menietti J. D.,
Christopher I. W.,
Gurnett D. A.,
Cook J. M.
Publication year - 2006
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2006ja011660
Subject(s) - physics , narrowband , ion , maser , instability , atomic physics , radiation , frequency drift , astrophysics , optics , computational physics , quantum mechanics , mechanics , phase locked loop , phase noise
We describe the statistical properties of narrowband drifting auroral kilometric radiation (“striated” AKR) based on observations from the Cluster wideband receiver during 2002–2005. We show that the observed characteristics, including frequency drift rate and direction, narrow bandwidth, observed intensity, and beaming angular sizes are all consistent with triggering by upward traveling ion solitary structures (“ion holes”). We calculate the expected perturbation of a horseshoe electron distribution function by an ion hole by integrating the resonance condition for a cyclotron maser instability (CMI) using the perturbed velocity distribution. We find that the CMI growth rate can be strongly enhanced as the horseshoe velocity distribution contracts inside the passing ion hole, resulting in a power gain increase greater than 100 dB. The gain curve is sharply peaked just above the R‐mode cutoff frequency, with an effective bandwidth ≤50 Hz, consistent with the observed bandwidth of striated AKR emission. Ion holes are observed in situ in the acceleration region moving upward with spatial scales and speeds consistent with the observed bandwidth and slopes of SAKR bursts. Hence we suggest that SAKR bursts are a remote sensor of ion holes and can be used to determine the frequency of occurrence, locations in the acceleration region, and lifetimes of these structures.