[1] 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.INDEX TERMS: 2704 Magnetospheric Physics: Auroral phenomena (2407); 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; 6964 Radio Science: Radio wave propagation; 6939 Radio Science: Magnetospheric physics; KEYWORDS: antennas, auroral phenomena, radio wave propagation, wave in plasma, auroral kilometric radiation Citation: Hanasz, J., M. Panchenko, H. de Feraudy, R. Schreiber, and M. M. Mogilevsky, Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes,

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We present results of intense auroral kilometric radiation (AKR) sources direction finding based on single‐spacecraft truek→ vector source location performed in the frame of Interball‐2 mission (POLRAD experiment on board Auroral Probe). With our swept frequency analyzer we are not able to work with single AKR bursts generated in small, elementary sources, but we improve our signal‐to‐noise (s/n) ratio and determine direction to the AKR source region averaging data over 10 consecutive 4 kHz frequency steps. Measurements of directions to the AKR sources confirm recent Mutel et al. () findings based on Cluster Very Long Baseline Interferometry (VLBI) data—AKR rays are mostly confined to the direction tangent to the auroral oval as measured in Mutel's tangent plane (TP) coordinates. In this paper we use additional coordinate system rotated with respect to TP coordinates in order to determine azimuths of AKR rays with respect to the auroral oval. We see cases of AKR propagation significantly deflected from the tangent plane. Additional information concerning geometry of auroral arc at the AKR source can help to distinguish between propagation along and propagation across the auroral cavity. Examples of instantaneous AKR visibility maps defined in this paper for both coordinate systems are shown and discussed. Using such map (valid for our spacecraft for relatively short observational periods of the order of 10 min), it is possible for known positions of the AKR sources in invariant latitude‐magnetic local time coordinates to visualize direction angles of AKR beams reaching the observer.

A spectral analysis at the second order (power spectrum) loses the phase information among the different Fourier components. To retain this information, the bispectrum (third order) and/or the bicoherence (normalized bispectrum) are calculated. Application to simulated data, shows the dependence of the bispectrum to amplitudes of involved waves and of the bicoherence to signal‐to‐noise ratio. Bicoherence technique is applied in the analysis of harmonics produced by an electronic receiver, as well as in the investigation of phase coherence between a ground‐transmitter signal, a natural ELF emission near the proton gyrofrequency, and the sidebands around the carrier. Strong arguments are provided that the sidebands are generated by a parametric interaction between the transmitter signal and the ELF emission.