Rayleigh lidar observations of quasi-sinusoidal waves in the tropical middle atmosphere

Abstract

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-sinusoidall 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. Copyright 2003 by the American Geophysical Union.