Gravity Waves and The Study of LowerUpper atmosphere Coupling

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Gravity Waves and The Study of Lower/Upper
atmosphere Coupling
Han-Li Liu High Altitude Observatory National
Center for Atmospheric Research
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Upper atmospheric gravity wave TID

• The start of upper atmospheric gravity wave
  study Traveling Ionospheric Disturbance (TID)
  and (linear) gravity waves (Hines, 1960).

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Upper atmospheric gravity wave Wave breaking

• Gravity wave wave breaking and turbulence
  generation (Hodges, 1967).

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Mesospheric Circulation

• Anomalous mesospheric structures and need for
  dynamical forcing (Rayleigh friction) (Murgatroyd
  and Singleton, 1961 Leovy, 1964).

• Gravity wave impact on the mesospheric
  circulation (Holton, 1982, 1983).

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• Seasonal variability of mesospheric atomic oxygen
  is closely dependent on the seasonal variability
  of eddy diffusion induced by gravity wave
  breaking (Garcia and Solomon, 1985) O peak
  around equinox.

• Atomic oxygen distribution also closely dependent
  on the change of mesospheric circulation driven
  by the gravity wave (Liu and Roble, 2004) O
  depleted around equinox.

• Proximity of the characteristic times of
  diffusive and advective transport, which are the
  competive processes in this case, is the cause of
  the large variability and highlights the need for
  accurate gravity wave information.

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Change of Gravity Wave Forcing During SSW

• Filtering of gravity waves by wind gravity wave
  will be reflected or absorbed at critical layer.
• Eastward stratospheric jet under normal winter
  conditions dominant westward propagating gravity
  waves in the mesosphere.
• Jet reversal during SSW dominant direction of
  gravity wave in mesosphere also reverses.

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Variability/Uncertainty of GW Forcing
Liu and Roble, 2002
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Gravity Wave and Mesospheric Variability

• Interaction of gravity waves and planetary waves
  (Smith, 1997) and tides (Meyer, 1999).
• Mesosphere semi-annual oscillation (MSAO) is
  sensitive to convectively generated gravity waves
  (Sassi Garcia, 1997 Garcia Sassi, 1999
  Beres, 2005).
• How are the variability affected by gravity wave
  sources with spatial and temporal distributions?

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Carbone et al, 2002
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Some Issues Regarding GW Parameterization

• The GW source specification in most global models
  are necessity-based (to obtain mean middle/upper
  atmospheric structures that are climatologically
  OK).
• Spatial/temporal distribution usually not
  considered, and its impact on mesospheric
  dynamics not well understood.
• Difficult to estimate the variability and
  uncertainty. Lack means to constrain and justify
  the parameterization.

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How to Address These Issues

• Better understanding of the wave generation
  mechanisms related to various tropospheric
  processes and waves generated in realistic
  atmospheric flows (Smolarkievicz, Lane, Alexakis,
  Shapiro, Hsu, Pan, Sassi, Richter ).
• Spectral structures of wave sources (Cohn
  Brown, Sassi, Richter).
• Global distribution of gravity wave sources
  (Randel, Sassi, Richter).
• Quantification of gravity waves at various
  atmosphere layers (Wu, Randel).
• Gravity wave propagation and breaking processes
  (Smolarkievicz, Lane, Smith ).
• Get more people to work on it (Foster).
• Disclaimer These studies will help the study of
  upper atmospheric GW and GW parameterziations,
  but they are surely of interests and values in
  their own rights.

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Back to the Thermosphere/Ionosphereand Beyond

• Thermosphere compositional structure dependent on
  transport between the thermosphere and the
  mesosphere. Diffusive transport is critical in
  quantifying the transport (Smith).
• Ionospheric disturbances in E and F regions that
  are thought to have lower atmospheric origins
  (Wang).
• Gravity wave generation and properties in the
  Solar atmosphere (MacGregor).