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Earth Planets Space, Vol. 61 (No. 4), pp. 513-524, 2009

Radar observations of the diurnal tide in the tropical mesosphere-lower thermosphere region: Longitudinal variabilities

S. Gurubaran1, R. Rajaram1, T. Nakamura2, T. Tsuda2, D. Riggin3, and R. A. Vincent4

1Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli, India
2Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan
3Colorado Research Associates, Boulder, U.S.A.
4Department of Physics and Mathematical Physics, University of Adelaide, Australia

(Received October 15, 2007; Revised July 5, 2008; Accepted July 5, 2008; Online published May 14, 2009)

Abstract: Significant attention is being paid in recent times by several observational and modeling studies to quantify the spatial and temporal variabilities of diurnal tide in the mesosphere and lower thermosphere (MLT) region. These variabilities are ascribed to spatial and temporal variations in the tidal forcing or interactions between the propagating tides and background wind, planetary waves or gravity waves. The present work makes use of simultaneous ground-based radar wind observations of different durations from five equatorial/low latitude sites in the Indian, Indonesian and Pacific sectors: Tirunelveli (8.7°N, 77.8°E), Jakarta (6.4°S, 106.7°E), Pontianak (0.03°N, 109°; E), Kauai (22°N, 160°W) and Christmas Island (2°N, 157°W). This study delineates the longitudinal differences in the tidal characteristics in (i) interannual time scales over Tirunelveli and Kauai during 1993-2002, (ii) seasonal time scales over Christmas Island, Jakarta and Tirunelveli for the years 1993-1997 and (iii) shorter than seasonal time scales over Christmas Island, Pontianak and Tirunelveli during 1996-1997. An important observational feature noticed in this work is the differing behavior of the long-term tidal fields over Tirunelveli and Kauai. The monthly tidal amplitudes over Tirunelveli reveal a strong QBO signature whereas a similar, strong QBO signal could not be traced in the long-term observations from Kauai.
Key words: Mesosphere-lower thermosphere, middle atmospheric dynamics, atmospheric tides, MLT-QBO, mean winds and tides, tropical atmosphere.


Corresponding author E-mail: gurubara@iigs.iigm.res.in


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