Example of the Source Region of Auroral Kilometric Radiation (AKR)

(From Ergun et al. [1998b])

Electric field and density measurements in the above figure show AKR and its associated source region in the pre-midnight auroral oval (22.5 MLT) at an altitude of approximately 3500 km. Panel (a) shows the plasma density as determined from fits to the whistler-Langmuir dispersion curve (black line) and from the hot (>100 eV) electron density (red line). The agreement between the two density calculations within the source region (~18:58:56-18:59:02) indicates that little or no cold electrons are present in these density cavities. Panel (b) shows RMS amplitudes of AKR that exceed 100 mV/m. Such amplitudes are larger than previously measured by instruments on other spacecraft. Panel (c) shows how the range of AKR wave power extends below the electron cyclotron frequency, f_ce, to the relativistic cyclotron frequency, f_cr, determined from the hot electron temperature. In Panel (d), the high-frequency wave power is shown over a larger range of frequencies demonstrating that the AKR power lies close to the electron cyclotron frequency, f_ce, indicated by the white line. Perpendicular, low-frequency wave power with the proton cyclotron frequency indicated by a white line are shown in panel (e) .

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