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Mesospheric WindsIn late 1998, the USU dynasonde operation at the Bear Lake Observatory was configured to acquire IDI soundings and regular synoptic measurements were begun in February 1999. Imaging Doppler Interferometry (IDI) is a MF Radar technique employed for observing the structure and dynamics of the mesospheric wind field at heights from 60-115 km. Influenced by the direction of the prevailing wind, a clear seasonal variation is seen in the mesospheric echo numbers. The amplitude and direction of the meridional and zonal winds compare very closely with those derived by the CIRA'86 model for 40°N. The technique also provides a tool for monitoring the amplitude of the main tidal modes as well as for studying planetary waves with periods of several days. The IDI measurements have thus far revealed the presence of a rich variety of dynamics and structures in the mesosphere above the Bear Lake Observatory. Tidal periods of 8, 12, and 24 hour periods are clearly evident in the data throughout the entire dataset. Moreover, the signature of planetary waves with periods between 2-20 days are also a feature of the wave structures observed in the data. The super-posed epoch analysis of the zonal wind data suggests that the tidal modes are strongest between April and August and weakest during the equinox months. Recent validation of the IDI winds with those measured by a co-sited VHF meteor radar (SKiYMET) demonstrates that the IDI techniques is a viable method of measuring mesospheric winds (Fig. 6). The diurnal variation of IDI echo occurrence for 6 December demonstrates that abundant echoes are present during the night-time hours. |
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Mesospheric Echo Numbers
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