Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes

Details Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003jgra..108.1408h&link_type=abstract

Journal of Geophysical Research, Volume 108, Issue A11, pp. SMP 14-1, CiteID 1408, DOI 10.1029/2002JA009579

Physics

17

Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Magnetopause, Cusp, And Boundary Layers, Radio Science: Radio Wave Propagation, Radio Science: Magnetospheric Physics

Scientific paper

Occurrence distributions of the auroral kilometric radiation (AKR) and its right-hand extraordinary (R-X) and left-hand ordinary (L-O) wave modes are determined from polarization measurements on Interball-2 (Auroral). The AKR is much less frequent on the dayside (20% of the observing time) than on the nightside (70%). A bulk of its occurrence extends from invariant latitude of 80 at afternoon hours of MLT to 60 at night hours. Like the nightside AKR, the dayside one is generated through the electron-cyclotron maser instability. This is concluded from domination of the R-X mode on the dayside similarly to the nightside. On the dayside the L-O mode of AKR is roughly three times more frequent (30% of the AKR time) than that on the nightside (10%). At afternoon hours the L-O occurs more frequently at lower invariant latitudes. This is explained by propagation of the L-O mode from nightside sources far beyond the ``horizon'' of the R-X mode. We find two classes of the circular polarization spectra: ``regular,'' with the dominating R-X mode observed in the upper part of the AKR frequency spectrum and the weak L-O mode in its lower part, and patchy ``irregular,'' with different polarizations interwoven randomly over the whole frequency range of AKR. For ``regular'' spectra the L-O/R-X power ratios are between 0.2 and 0.002. For the ``irregular'' ones they are between 1 and 0.01. The ``irregular'' spectra, reported for the first time, are interpreted as due to irregular refraction of the R-X rays on the plasma density fluctuations near the nightside sources. We show also evidence of another component of the AKR observed on the dayside, which arrives from directions of possible dayside sources likely related to the cusp or the low-latitude boundary layers.

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