Characteristics of Ionospheric Flows Observed by Syowa East/South Radars During May 10-13, 1999

Nozomu NISHITANI and Tadahiko OGAWA
Nagoya University, Japan
Natsuo SATO, Hisao YAMIGISHI and Akira Sessai YUKIMATU
National Institute of Polar Research, Japan

Ionospheric convection during May 10-13, 1999 has been studied by using the HF radars, when the solar wind density is very low (up to <0.1 /cc). The echo regions observed by Syowa East/ South SuperDARN radars were located several degrees poleward of the averaged location. In contrast, the radars observed very high (>1000 m/s) plasma flows directed from the nightside toward the dayside. This high-speed flow was observed across the fields of view of Syowa East and Syowa south radars from 1530 to 2400 UT on May 11, when the solar wind density was close to minimum and the IMF was constantly northward. The comparison with the DMSP particle data shows that the westward flow regions were collocated with the auroral oval. The generation mechanism for this fast flow will be discussed.

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