. Institute and . Helsinki, The authors also wish to thank the Ministry of Education, Culture, Sports, Science and Techonology for supporting the Syowa HF radar systems and the 39th and 40th Japanese Antarctic Research Expeditions (JAREs) for carrying out the HF radar operations at Syowa. EEW is indebted to PPARC for a research studentship. This study is funded by a part of 'Ground Research for Space Utilization' promoted by NASDA and Japan Space Forum, KH is supported by the Grant in Aid for Scientific Research (A:11304029) from Japan Society for the Promotion of Science (JSPS)

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