[P-EM03] Mesosphere-Thermosphere-Ionosphere Coupling in the Earth's Atmosphere

[PEM03-13] Relationship between ionospheric and atmospheric perturbations associated with typhoons

平林 慎一郎¹、*中田 裕之¹、鷹野 敏明¹、冨澤 一郎²、長尾 大道³ (1.千葉大学大学院工学研究科人工システム科学専攻、2.電気通信大学宇宙・電磁環境研究センター、3.東京大学地震研究所)

キーワード：Ionospheric perturbation, Atmospheric perturbation, Typhoon, HF Doppler, Microbarometer

It is known that ionospheric disturbances are caused by extreme weather conditions, such as tornadoes and typhoons. In this study, we have examined the relationship between ionospheric and atmospheric disturbances caused by typhoons, using HF doppler (HFD) and a microbarometer. HFD observation system used in this study is maintained by The University of Electro-Communications (UEC). The receiver is located at Sugadaira, Nagano Prefecture and the transmitters are located at Chofu Campus of UEC and Nagara, Chiba Prefecture. The microbarometer is also located at Sugadaira, Nagano Prefecture. In examining typhoons which came closer to Japan since 2004, we have found ionospheric perturbations associated with 8 typhoons. In almost events, the amplitude of the doppler shift is about several hertz, which is much less than the cases for earthquakes. By dynamic spectral analyses, it is found that spectral intensity of both of ionospheric and atmospheric perturbations at frequency from 5 mHz to 50 mHz were enhanced. These results imply that the effect of the typhoon to the ionosphere is quite smaller and that the atmospheric waves propagated to the ionosphere drive the ionospheric perturbations. In this study, as a typical example, the perturbations asssociated with Typhoon WIPHA (No.18 in 2013) at 30 mHz are examined in detail. This is because the wind direction in the transmitter (Chofu), the receiver (Sugadaira), and the middle point (Chofu) is quite stable (eastward) when Typhoon WIPHA was closest to Japan for several tens of hours. The temporal variation of the spectral intensity of ionospheric perturbation is almost the same as the wind speed at Sugadaira, where is the windward of Chofu. This result shows that the ionospheric perturbations associated with typhoons is affected by the atmospheric perturbations windwardly below the ionosphere.