F1

講演予稿:
　電離層F層のイオン流出と電子温度上昇はしばしばよい相関を持つことが 観測されている。また、このような現象の間に、レーダースペクトルの中に 卓越したイオン音波のラインが頻繁に観測されている。 これらのスペクトルを示すプラズマ振動の起源は、まだ明らかにされておらず またイオン流や電子温度上昇との関係も定かでない。 新しく建設されたスヴァールバル島の非干渉散乱レーダーから、 ビームによって発生されたラングミュア波の減衰によって引き起こされる イオン音波振動のモデルを提案する。

abstract:
　It has been observed with the EISCAT radars on the Scandinavian mainland, that events of high electron temperatures and upward ion flows in the upper F region are often well correlated. During such events one can also frequently witness the development of so-called naturally enhanced ion-acoustic lines in the radar spectra. The origin of these probably superthermal plasma fluctuations, which cause the unusual spectra, has not yet been clearly identified, neither has been their relation with the electron heating and ion flow. It is shown in this work, that very similar events, namely enhanced radar power after a period of increasing electron heating in the F region, can be seen also with the new ESR radar on the dayside. IS radars actually probe plasma fluctuation at slightly different wave lengths by varying cyclically the transmitter frequency. At ESR, during the superthermal enhancements, the power seems to vary significantly over the applied frequencies. This new observation favours a recently suggested model where ion-acoustic fluctuation are caused by the parametric decay of beam-generated Langmuir waves. The power of waves produced by this mechanism would depend strongly in their wave length. Other models for the generation ion-acoustic ``turbulence'' would rather predict a smooth, Kolmogorov-type k-spectrum.

キーワード:
イオン流出、非干渉散乱レーダー、イオン音波

Keywords:
ion-acoustic lines,ion flow,ESR radar