Rayleigh lidar observations of temperature for ~2--7 hours on 38 nights during the period of 18 January--5 March 1999 and for ~3 hours on 29 nights during 29 February--2 April 2000 in the altitude region of 27--60 km over Gadanki (13.5¿N, 85¿E) clearly show the dominance of the quasi-sinusoidal waves of periods in the range of ~6--13 hours in temperature in the tropical middle atmosphere. During 1999, the vertical wavelength of these waves ranges from 7.1 to 17 km with a mean value of 12.0 ¿ 2.4 km while during 2000 it ranges from 5.5 to 17 km with a mean value of 11.4 ¿ 3.5 km. The wave periods estimated from the observations during 1999 are generally greater than the observation period on each night and are estimated to be in the range of 6.5--13.1 hours with an average period of 9.7 ¿ 1.8 hours, which is significantly smaller than the inertial period of 53 hours. The amplitudes of these waves are in the range of 1 to 8 K. Such sinusoidal wave modes are clearly discernible in the temperature profiles for ~50% nights of observation. Another striking feature is that the quasi-sinusoidal structure is clearly observed in the equivalent day analysis also, indicating only small day-to-day variability in phase, a property that is characteristic of atmospheric tides.