| Summary: | 1972-03-30 VLF hiss observed at Syowa Station may be divided into steady and impulsive types. The steady VLF hiss which appears in association with moderate geomagnetic activity and weak cosmic noise absorption (CNA) at 30 MHz, continues from ten to several tens of minutes and dominates in the lower frequency range (5-12kHz), usually occurring in the evening side of the nighttime. Near the magnetic midnight, an impulsive VLF hiss occurs almost synchronously with the auroral break-up always followed by sharp and large fluctuations of magnetic H-component and CNA. It falls sharply in short period before the maximum activity of the aurora and its frequency range extends more than 100 kHz. Through a polarimeter, VLF hiss is divided into right-handed polarized (R-) component and left-handed polarized (L-) component. The polarization record teaches us that VLF hiss is right-handed polarized. However, the ratio of R-component to L-component was smaller than we had expected. Supposed that VLF hiss comes down to the ground with nearly circular polarization and small angle of incidence, the polarization data seem to be explained by the simultaneous arrival of multiple rays uncorrelated. Displaying Lissajous' figures on a cathode ray tube, we investigated the polarization, incident angle and arriving direction of VLF hiss (hereafter the method is called as CRT method). The figures show that VLF hiss propagates downward with not so large an angle of incidence, roughly within the magnetic meridian plane. departmental bulletin paper
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