L. Vijayan et Ca. Reddy, RADIATIVE DAMPING OF EQUATORIAL WAVES IN THE MIDDLE ATMOSPHERE, Quarterly Journal of the Royal Meteorological Society, 120(519), 1994, pp. 1323-1343
Theoretical estimates are made of the radiative damping of various Kel
vin and Rossby-gravity (RG) wave modes in the 20-70 km region, for a p
eriod of 24 months (1979-80), using the observed monthly mean zonal-wa
ve profiles at 8.5-degrees-N latitude and realistic values of scale-de
pendent cooling coefficients. The net changes in wave amplitudes at va
rious height regions are calculated by combining the attenuation due t
o radiative cooling and the growth due to density decrease. The calcul
ated height variations of wave amplitudes explain quite well several f
eatures of the observed height structures of Kelvin waves. They also e
xplain the observed rapid decay of RG waves below about 35 km when the
ir period exceeds 3 days. The calculated momentum flux convergences of
various waves are used to estimate the mean-flow accelerations genera
ted by the damped waves. The Kelvin waves are found to be capable of g
enerating the accelerations needed to drive the westerly phase of the
quasi-biennial oscillation (QBO) and the semi-annual oscillation (SAO)
in the zonal wind. However, RG waves seem to be capable of driving th
e easterly phase of the QBO but not the SAO. The remarkable consistenc
y of our theoretical results and the observed patterns of wave amplitu
des and mean-flow accelerations demonstrate that radiative damping is
the dominant dissipative process for the equatorial waves in the 20-70
km region and our theoretical approach is capable of characterizing t
he equatorial wave behaviour and the associated flow accelerations wit
h a good quantitative accuracy.