'Different flow regions exciting inertia-gravity waves in idealized
baroclinic life cycles'
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Riwal Plougonven
Laboratoire de Meteorologie Dynamique, ENS, IPSL, Paris, France.
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Chris Snyder
National Center for Atmospheric Research, Boulder, U.S.A.
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Previous numerical investigations of the excitation of gravity waves
in idealized baroclinic life cycles have emphasized the upper-level
jet, and in particular jet exit regions, as the dominant source.
Yet, two-dimensional simulations and observations have also indicated
that surface fronts were another likely important source.
We have used the mesoscale meteorological model WRF (Weather Research
and Forecast) to study this excitation of gravity waves in different
idealized baroclinic lifecycles and to bring these different threads
together.
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The excitation of the gravity waves is shown to be sensitive to the
type on nonlinear development of the baroclinic life cycle. Four
different wavepackets are identified, produced either by the
upper-level jet or the surface fronts. Some of these are comparable to
waves described in previous simulations, while others are
significantly different. These different wavepackets likely indicate
that there may be several possible generation mechanisms. 
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Regarding the characteristics of the excited waves, the analysis of
the waves excited in the lower stratosphere show that a
coarse-grained knowledge of the background flow and an understanding
of some simple propagation effects ('wave-capture') already allow
the prediction of the orientation and intrinsic frequency of the
excited waves.