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Reflection and attenuation of equatorial waves in the stratosphere and mesosphere
Author(s) -
Reddy C. A.,
Vijayan Lekshmi
Publication year - 1989
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711549006
Subject(s) - amplitude , mesosphere , stratosphere , kelvin wave , gravity wave , reflection (computer programming) , attenuation , infragravity wave , physics , wavenumber , wavelength , atmospheric sciences , radiative transfer , wave propagation , geophysics , mechanical wave , meteorology , longitudinal wave , optics , computer science , programming language
Quantitative theoretical estimates are made of the reflection and radiative damping of the Kelvin and Rossby‐gravity (RG) waves propagating upward in the 20–90 km altitude region. An atmosphere with realistic temperature, wind and cooling rate coefficient values is approximated by a model of vertically stacked, thin, homogeneous layers. The amplitude reflection coefficients are shown for different wave periods (T) and zonal wavenumbers (kx). Combining the attenuation due to radiative cooling with the growth due to density decrease, the net changes of wave amplitudes with height in the 20–90 km region are shown for various wave modes. For Kelvin waves the reflected wave energy is generally less than 15% of the incident wave energy, but the reflected wave amplitude can be 20%‐30% of the incident wave amplitude for many modes, at 20 km height. In contrast, many RG wave modes suffer strong or total reflection at various heights if they are not severely damped at lower heights. Calculations for January and July wind conditions reveal a good deal of sensitivity of RG wave reflection to wind conditions. Radiative damping is found to be severe in the mesosphere for Kelvin waves with T ⩾ 6–8 days, depending on wind conditions; it is severe even in the lower stratosphere for RG waves with T > 4 days. Considerable changes in the damping rates and wave amplitudes at various heights take place from January to July owing to wind changes. Kelvin waves in the 2–8‐day period range and RG waves in the 1.5‐3‐day range can propagate into the upper mesosphere/lower thermosphere without large attenuation, depending upon wind conditions. It is shown that our theoretical results can explain several observed characteristics of equatorial waves in the stratosphere and mesosphere, including the recent results on wave disturbances in satellite‐measured temperatures. Further modelling studies based on our methodology can lead to a good physical insight and quantitative interpretations of the SAO‐ and the QBO‐generation processes.