Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm53a1448c&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM53A-1448
Physics
2407 Auroral Ionosphere (2704)
Scientific paper
It is well accepted that the source of auroral kilometric radiation (AKR) is an electron-cyclotron maser, situated within a density cavity in the auroral acceleration region. These cavities, field-aligned volumes largely depleted of low-energy electrons, are believed to have widths of order 100 km meridionally, but may extend for thousands of km longitudinally. Pritchett et al. (2002) has modelled the AKR generation within such a cavity, and found that the most likely route for the escape of the radiation is longitudinally. We present results from the Cluster Wideband Data (WBD) instrument supporting this. We use multi-spacecraft observations to determine, using direction-finding techniques, the location of many AKR sources, and at the same time, estimate the beaming pattern of the radiation emitted by them. We find a pattern that is consistent with radiation escaping from deep within a long, thin rectangular cavity. In addition to shedding light on the beaming pattern of AKR, this result also helps re-interpret the distribution of AKR source locations previously determined from Cluster WBD waveform data (Mutel et al., 2003). These locations are now seen to be only a subset of all sources on the auroral oval--specifically, those places for which a clear line-of-sight exists between all four Cluster spacecraft and the bottom of the long, thin density cavity described above. Mutel, R. L., et al. (2003), Locations of auroral kilometric radiation bursts inferred from multispacecraft wideband Cluster VLBI observations. 1: Description of techniques and initial results, J. Geophys. Res., 108(A11). Pritchett, P. L., et al. (2002), Generation and propagation of cyclotron maser emissions in the finite auroral kilometric radiation source cavity, J. Geophys. Res., 104(A12).
Christopher I. W.
Mutel Robert L.
Pickett Jolene S.
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