Tuesday, 5 November 2002
Gravity wave forcing in the stratosphere: Observationalconstraints from UARS
Gravity wave forcing in the stratosphere slows the winter jet stream
winds, accelerates the onset of the summer westward winds, helps to
drive the global mean-meridional transport circulation, and helps to
drive the equatorial quasibiennial and semiannual oscillations in
zonal winds. The effect of gravity waves in these processes is
quantified using stratospheric wave forcing derived from UARS
observations. These effects are inadequately handled in global
circulation models without parameterizations of gravity wave effects
that require details about the gravity wave properties as input.
In this study, a simple linear model of gravity wave propagation and
dissipation is applied to observed wind and stability fields
to study the sensitivity of modeled gravity wave effects to the input
properties of the gravity wave spectrum. A wide parameter space
describing gravity wave properties at the tropopause is sampled, and
the stratospheric gravity wave forcing effects are correlated
with those derived from the observations. The comparison reveals
whether or not modeled gravity wave forcing effects can be used to
constrain the input wave properties at the tropopause as has been
attempted in numerous global model studies. In some cases, the
solutions are shown to be very non-unique so that the gravity wave
input properties cannot be easily derived in this way. In other
cases, the gravity wave effects constrain the input wave properties
much more effectively. The results suggest important latitudinal
variations in the properties of gravity waves that affect the stratosphere.
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