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GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L07104, doi:10.1029/2008GL033377, 2008

Cluster multispacecraft determination of AKR angular beaming

R. L. Mutel

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA


I. W. Christopher

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA


J. S. Pickett

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA


Abstract

Simultaneous observations of AKR emission using the four-spacecraft Cluster array were used to make the first direct measurements of the angular beaming patterns of individual bursts. By comparing the spacecraft locations and AKR burst locations, the angular beaming pattern was found to be narrowly confined to a plane containing the magnetic field vector at the source and tangent to a circle of constant latitude. Most rays paths are confined within 15° of this tangent plane, consistent with numerical simulations of AKR k-vector orientation at maximum growth rate. The emission is also strongly directed upward in the tangent plane, which we interpret as refraction of the rays as they leave the auroral cavity. The narrow beaming pattern implies that an observer located above the polar cap can detect AKR emission only from a small fraction of the auroral oval at a given location. This has important consequences for interpreting AKR visibility at a given location. It also helps re-interpret previously published Cluster VLBI studies of AKR source locations, which are now seen to be only a subset of all possible source locations. The observations are inconsistent with either filled or hollow cone beaming models.

Received 22 January 2008; accepted 4 March 2008; published 9 April 2008.

Keywords: auroral kilometric radiation; magnetospheric physics; radiative processes.

Index Terms: 2704 Magnetospheric Physics: Auroral phenomena (2407); 2730 Magnetospheric Physics: Magnetosphere: inner; 3285 Mathematical Geophysics: Wave propagation (0689, 2487, 4275, 4455, 6934); 0689 Electromagnetics: Wave propagation (2487, 3285, 4275, 4455, 6934); 4494 Nonlinear Geophysics: Instruments and techniques.

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Citation: Mutel, R. L., I. W. Christopher, and J. S. Pickett (2008), Cluster multispacecraft determination of AKR angular beaming, Geophys. Res. Lett., 35, L07104, doi:10.1029/2008GL033377.