[P-EM13] Coupling Processes in the Atmosphere-Ionosphere System

[PEM13-P12] Examination of meteor echos observed by HF Doppler sounding

*Hiroki Saito¹, Hiroyuki Nakata², Hiroyo Ohya², Keisuke Hosokawa³ (1.Graduate School of Science Engineering, Chiba University, 2.Graduate School of Engineering, Chiba University, 3.Department of Communication Engineering and Informatics, University of Electro-Communications)

It is known that ionospheric disturbances occur at an altitude of 80 to 120 km when meteors enter the Earth's atmosphere. The plasma associated with meteors enter is called a meteor trail and reflects radio waves in the HF and VHF bands due to its plasma density. Since, most of the meteor radio observations have been performed using VHF band radio waves. meteor radio waves were observed using radio waves in the HF band, in this study We have examined meteor echos observed by the HF Doppler sounding system. The transmission point at this system is the Chofu Campus of the University of Electro-Communications. We used Doppler data received at the Sugito, Kakioka, Orai, and Kashima stations when 8 MHz radio waves transmitted from the Chofu campus. The event examined in this study occured at 20: 30: 27 JST on October 25, 2014. The temporal variation of the signal intensity of the observed meteor echo similar to that of the overdense echo. The duration of the meteor echo was much longer than that obtained by VHF radar. This is because the duration of the echo is proportional to the square of the wavelength. Because the meteor echo in this event is categorized as the overdense echo, the Doppler shift is related to the speed of the radial diffusion of the meteor trail. However, the neutral wind also affected the Doppler shift. Therefore, the speed of radial diffusion of the meteor trail was estimated from the difference between the Doppler shift at the time of meteor occurrence and that at just after the occurrence. Then, we also estimated it using the relation equations from the previous statistical results (Fish and Barkey, 1998). As a result, the values almost coincided each other. In Oarai, however, the difference is longer than the other observation points since the Doppler shift stayed constant for long time as compared to the other points. This is because the meteor trail is deformed by the influence of neutral wind as time goes on.