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408 VOLUME 54J O U R N A L O F T H E A T M O S P H E R I C S C I E N C E S 1997 American Meteorological Society

Summary: 408 VOLUME 54J O U R N A L O F T H E A T M O S P H E R I C S C I E N C E S
1997 American Meteorological Society
A Model Study of Zonal Forcing in the Equatorial Stratosphere by
Convectively Induced Gravity Waves
Department of Atmospheric Sciences, University of Washington, Seattle, Washington
(Manuscript received 16 April 1996, in final form 16 July 1996)
A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated
by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the
equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations
with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases
a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background
wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for
waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward
propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly
scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping
are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the
zonal forcing is of order 5 m s 1
day 1


Source: Alexander, M. Joan - Colorado Research Associates Division, Northwest Research Associates, Inc.


Collections: Geosciences