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Ann. Geophys., 19, 1027-1038, 2001
www.ann-geophys.net/19/1027/2001/
© European Geosciences Union 2001
Mean winds observed with Indian MST radar over tropical mesosphere and comparison with various techniques
M. Venkat Ratnam1, D. Narayana Rao1, T. Narayana Rao1, S. Thulasiraman2, J. B. Nee2, S. Gurubaran3, and R. Rajaram3
1Department of Physics, S. V. University, Tirupati – 517 502, India
2Department of Physics, National Central University, Chung Li, 32054, Taiwan
3Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India
Abstract. Temporal variation of
mean winds between the 65 to 85 km height region from the data collected over
the course of approximately four years (1995–99), using the Indian MST radar
located at Gadanki (13.5° N, 79.2° E), India is presented in this paper.
Mesospheric mean winds and their seasonal variation in the horizontal and
vertical components are presented in detail. Westward flows during each of the
equinoxes and eastward flows during the solstices are observed in the zonal
component. The features of the semi-annual oscillation (SAO) and the
quasi-biennial oscillation (QBO) in the zonal component are noted. In the
meridional component, contours reveal a northward motion during the winter and
a southward motion during the summer. Large inter-annual variability is found
in the vertical component with magnitudes of the order of ± 2 ms-1
. The MST observed winds are also compared with the winds observed by the MF
radar located at Tirunelveli (8.7° N, 77.8° E), India, the High Resolution
Doppler Imager (HRDI) onboard the Upper Atmospheric Research Satellite (UARS),
and with the CIRA-86 model. A very good agreement is found between both the
ground-based instruments (MST radar and MF radar) in the zonal component and
there are few discrepancies in the meridional component. UARS/HRDI observed
winds usually have larger magnitudes than the ground-based mean winds.
Comparison of the MST derived winds with the CIRA-86 model in the zonal
component shows that during the spring equinox and the summer, the winds agree
fairly well, but there are a lot of discrepancies in the other seasons and the
observed winds with the MST radar are less in magnitude, though the direction
is same. The strengths and limitations in estimating reliable mesospheric mean
winds using the MST radar are also discussed.
Key words. Meteorology and
atmospheric dynamics (general circulation; middle atmosphere dynamics; waves
and tides)
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