Open AccessGravity wave exclusion circles in background flows modulated by the semidiurnal tide
Author(s) -
Lei Zhong,
A. H. Manson,
L. J. Sonmor,
C. E. Meek
Publication year - 1996
Publication title -
annales geophysicae (1988)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.522
H-Index - 93
eISSN - 1432-0576
pISSN - 0992-7689
DOI - 10.1007/s00585-996-0557-x
Subject(s) - gravity wave , phase (matter) , internal wave , phase velocity , geology , physics , doppler effect , ray tracing (physics) , atmosphere (unit) , gravitational wave , geophysics , mechanics , geodesy , optics , wave propagation , meteorology , astrophysics , quantum mechanics , astronomy
In this short paper the exclusion circles andvertical phase locities for gravity waves launched from the ground into atime-varying wind are studied using a ray-tracing technique. It is shown thatwaves with initial observed phase speeds that should place them within the localtemporally varying exclusion circle, are often Doppler shifted outside of thecircle. This, and the finite lifetime of some critical levels, allow waves tosurvive the critical layer and reach higher altitudes. Also, for slowerphase-speed waves, the temporally varying wind can shift the observed frequencyto negative values, so that the observed phase motions will be opposite (i.e.horizontally reversed and vertically upward), even though the energy stillpropagates upward. This effect can also cause the phase velocity to move insidethe local exclusion circle. Due to the directional filtering of wave sources bythe stratospheric wind, the percentage of such reverse-propagating waves willchange systematically with local time and height in our simplified but realisticmodel. These results are related to ground-based systems, optical and radar,which sample the wind field and gravity waves in the middle atmosphere