Japanese sounding rocket "S-310-35" was launched from Andøya Rocket Range in Norway on December 13, 2004 during Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, in which the rocket-borne in-situ measurements and ground-based measurements were coordinated to conduct a comprehensive observation of the upper atmospheric response against the auroral energy input. The Fast Langmuir Probe (FLP) was installed on the sounding rocket to study thermal structure and energy balance of the plasma by measuring the electron temperature in the polar lower ionosphere. The FLP observations indicate that the electron temperatures were found to be remarkably high in an altitude range from 106 km to 114 km during the ascending phase of the rocket. The lowest part of this high temperature region might be affected by artificial electron beam which was generated by the N2 temperature instrument on the same rocket. On the other hand, a small increase of the electron temperature was observed at the altitude from 114 to 119 km in the descending phase. This is possibly the first time that both the temperature increase and density fluctuation that may be caused by the Farley-Buneman instability were detected by in-situ observation.
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