Diapositive 1

1
Identification and separation of the sources of
inertia-gravity waves in the Andes Cordillera
region
Aymeric Spiga, Hector Teitelbaum, Vladimir
Zeitlin Laboratoire de Météorologie
Dynamique Ecole Normale Supérieure, Paris
France
B.1. Jet-Stream source
The IGW emission by the jet is associated with
the geostrophic adjustment happening in the
regions of the jet with large Lagrangian Rossby
numbers Plougonven et al., 2003
No convective source

• Submitted to Journal of Geophysical Research -
  Atmospheres
• Abstract
• By combining the ECMWF and NCEP-NCAR reanalyses,
  the satellite data, the radiosoundings data and
  the meso-scale WRF simulations in the Andes
  Cordillera region, we identify the cases where
  only one of the three major sources of
  inertia-gravity waves, i.e. upper tropospheric
  jet-stream, convection, or topography is in
  action, although all of them are potentially
  present in this particular zone.

FILTER
IGW
No mountain wave event
IGW
Radiosounding analysis reveals upward (resp.
downward) IGW propagating above (resp. below) the
jet maximum
Jet-stream maximum 11 km

• A.1. Inertio-Gravity Wave (IGW) Sources
• Upper-Tropospheric Jet-Stream (e.g. OSullivan
  and Dunkerton 1995 )
• Convection (e.g. Pfister et al. 1993 )
• Mountain Wave induced perturbation (e.g.
  Scavuzzo et al. 1998 )
• Lower-Tropospheric Fronts (e.g. Eckerman and
  Vincent 1993 )
• A.2. Goal of our study
• The above-mentioned major sources of the IGW
  emission often combine in nature so for
  quantication purposes it is desirable to find
  some clear manifestations of each of them
  separately and compare the characteristics of the
  emitted waves. We chose for this purpose the
  Andes Cordilera region where at least three of
  the main sources (jet-stream, mountains and
  convection) are acting in the recurrent way.
• A.3. Investigation techniques
• We combined different technical tools in order to
  identify and quantify the IGW emission events
  corresponding to each source.
• Data analysis
• Radiosoundings (University of Wyoming Database)
• Satellite imagery and analysis (NOAA/SPIDR,
  MeteoFrance/SATMOS)

B.2. Convective source
No jet-stream source
The IGW emission by the convective source is
consistent with the "obstacle" mechanism Vincent
Alexander, 2000), as it was accompanied by a
strong shear at higher altitudes (other
convective mechanisms are nevertheless not
excluded)
FILTER
IGW
Wavelet analysis 2 different IGW waves emitted
No mountain wave event
Convective cell top 13-14 km
Radiosounding analysis reveals upward IGW
propagating above the CC top. Situation in the
troposphere is less clear (prob. wave reflexion)
(WRF simulation)
B.3. Topographic source
The IGW emission due to topography is triggered
by the mountain wave activity (close to
breaking), and is linked to the relaxation of
this perturbed state towards the thermal wind
balance Scavuzzo et al., 1998
Radiosounding analysis (below) reveals wave
activity. WRF analysis (right) is in good
agreement with ERA40 large-scale diagnostic and
shows the details of the MW/IGW event
IGW
MW
FILTER
Mixing layer 15-17 km
NB No jet-stream source, No convective source
(figures not shown)
Conclusion Correspondance
spiga_at_lmd.jussieu.fr The comparison of the IGW
characteristics for each source shows that the
frequencies and the vertical wavelengths of the
waves are close, but the horizontal wavelengths
are quite different. A distinctive feature of the
IGW emission by the jet-stream is a clear
presence of both upward and downward propagating
waves, which is not the case of the topographic
source. The convective cell seems to be the only
source that generates two distinctly different
IGW events. It should be noted that the cases
we display in the present work are not
exceptional. The ones we chose are qualitatively
clear-cut, and most fully covered by the
available data, which allows their quantitative
analysis. The quality of radiosoundings is
lesser, or some information is missing in other
similar cases. The cases of combined action of
two of three sources were also found during this
study. The WRF simulations used to complete the
diagnostics of the IGW sources (and atmospheric
processes involved or not involved) and to
independently estimate the characteristics of the
emitted IGW, were, at the same time, good tests
of this meso-scale model. They showed good
performance of the WRF which captured
systematically the IGW. However, the quantitative
agreement, especially on the amplitude of the
emitted waves, was lacking.

• References
• Andrews, Holton, Leovy 1987 Academic Press New
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• Eckerman and Vincent 1993 J. Atmos. Sci., 50,
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• Fritts and Nastrom 1992 J. Atmos. Sci., 49,
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• Fritts and Alexander 2003 Rev. Geophys., 41,
  3-1
• Moldovan et al. 2002 Q. J. R. Meteorol. Soc.,
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• Plougonven et al. 2003 J. Geophys. Res., 108,
  4686-4704
• OSullivan and Dunkerton 1995 J. Atmos. Sci.,
  52, 3695-3716
• Pfister et al. 1993 J. Atmos. Sci., 50,
  1058-1075
• Scavuzzo et al. 1998 J. Geophys.Res., 103,
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• Vincent and Alexander 2000 J. Geophys. Res.,
  105, 17,971-17,982