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Ann. Geophys., 20, 1239-1246, 2002
www.ann-geophys.net/20/1239/2002/
© European Geosciences Union 2002
Climatological studies of the quasi 16-day oscillations in the mesosphere and lower thermosphere at Yamagawa (31.2° N, 130.6° E), Japan
S. P. Namboothiri, P. Kishore, and K. Igarashi
Communications Research Laboratory, Tokyo, Japan
Correspondence to: S. P. Namboothiri
(nambooth@crl.go.jp)
Abstract. The 16-day wave
climatology at Yamagawa (31.2° N, 130.6° E) is investigated by analyzing the
mesosphere and lower thermosphere (MLT) wind data collected with the recently
installed MF radar. We have utilized the continuous data gathered during the
five-year period 1996–2000. The wave climatology clearly shows some seasonal
variations. The period of late autumn-spring is marked with larger wave
activity, with the strongest waves being observed in the winter months. The
maximum amplitude observed at Yamagawa is about 20 m/s, which is comparatively
larger than the amplitudes observed at mid-latitude stations. The height
dependence of the 16-day wave suggests that the maximum amplitude is observed
at altitudes below 80 km. The summer months are characterized with much weaker
wave activity. The vertical wavelength appears to be larger in the winter
months and shorter in the summer months. The present analysis again confirms
that the 16-day wave is highly sensitive to the background mean winds. Eastward
motion of the background winds is a more favourable condition for the 16-day
wave penetration to the MLT heights. The wave features show some signs of
interannual variability. Overall, the observed features of the 16-day wave at
Yamagawa, which is located at the edge of the subtropical latitudes, show some
correspondence with the results reported for mid-latitude stations.
Key words. Meteorology and
atmospheric dynamics (climatology; thermospheric dynamics)
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