Ground-based observation of MF auroral radio emissions in the polar cap and cusp regions

Recent ground-based observations have detected MF auroral radio emissions called MF burst and auroral roar. It is interpreted that origin of both emissions is upper hybrid waves generated in the ionosphere by auroral electrons. Some theoretical studies [e.g. Weatherwax et al., 2002] have proposed that MF burst which has a broad band spectrum is generated at an altitude of few hundred kilometers over a wide altitude range while auroral roar is excited in altitudes where a condition of fuh ~ nfce (n=2, 3) is met, which leads to its narrow band spectrum. The polarization spectrum observation at the Husafell observatory in Iceland, which started in 2005, revealed the polarization characteristics of 3fce roar and the relationship with energy of precipitating electrons [Sato et al., 2008]. However, occurrence rate is low because the observation site is located in the auroral zone. We install a new instrument for MF auroral radio emissions at Longyearbyen in Svalbard. The observation at Longyearbyen has several advantages: higher occurrence rate can be expected in the polar cap region, and simultaneous observations with EISCAT Svalbard Radar (ESR) and other ground-based observations can be easily obtained. The instrument consists of two types of observation systems. One is designed for the continuous observation of spectrum in a frequency range below 6 MHz. The other is designed to obtain waveform data in a frequency range below 4 MHz by an A/D converter with a sampling speed of 10MSPS. By using the wave form data, the arrival direction angle of a received radio wave can be estimated. In this presentation, we will introduce the purpose of the observation and the detail of the instrument, and report some initial results.