| Summary: | MF (Middle Frequency) radars have widely been used to measure wind velocity in mesosphere and lower thermosphere by detecting echoes from weakly ionized atmosphere based on correlation analysis techniques. These echoes are mostly obtained in the vertical direction because of their aspect sensitive nature. On the other hand, meteor echoes are another type of echoes coming back from large off-vertical angles, mostly above 80 km altitude. Because of the low radio frequency (2-3 MHz) employed the duration of MF radar meteor echoes is by two orders longer than that of VHF meteor echoes. Thus, meteor echoes can sometimes dominate received MF radar signals when the return from the ionized atmosphere is weak. At Syowa station (69S, 39E), Antarctic, these meteor echoes have routinely been used since 1999 to reinforce the correlation technique by providing meteor winds in the height region of 85-120 km. We have recently scrutinized and redeveloped the MF radar meteor measurement technique and found that wind velocity can be estimated with a time resolution as good as 10 min under preferable ionosphere conditions. Such a resolution is exceptionally high as meteor wind measurements. Horizontal structure of wind field can be further resolved with a spatial resolution of about 50 km within the radar illuminating area of 200 x 200 km. The application of the technique to gravity wave studies will be discussed.
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