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@ARTICLE{Chen:864926,
      author       = {Chen, Dan and Strube, Cornelia and Ern, Manfred and
                      Preusse, Peter and Riese, Martin},
      title        = {{G}lobal analysis for periodic variations in gravity wave
                      squared amplitudes and momentum fluxes in the middle
                      atmosphere},
      journal      = {Annales geophysicae},
      volume       = {37},
      number       = {4},
      issn         = {1432-0576},
      address      = {Katlenburg, Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2019-04529},
      pages        = {487 - 506},
      year         = {2019},
      abstract     = {Atmospheric gravity waves (GWs) are an important coupling
                      mechanism in the middle atmosphere. For instance, they
                      provide a large part of the driving of long-period
                      atmospheric oscillations such as the Quasi-Biennial
                      Oscillation (QBO) and the semiannual oscillation (SAO) and
                      are in turn modulated. They also induce the wind reversal in
                      the mesosphere–lower thermosphere region (MLT) and the
                      residual mean circulation at these altitudes. In this study,
                      the variations in monthly zonal mean gravity wave square
                      temperature amplitudes (GWSTAs) and, for the first time,
                      absolute gravity wave momentum flux (GWMF) on different
                      timescales such as the annual, semiannual, terannual and
                      quasi-biennial variations are investigated by spectrally
                      analyzing SABER observations from 2002 to 2015.
                      Latitude–altitude cross sections of spectral amplitudes
                      and phases of GWSTA and absolute GWMF in the stratosphere
                      and mesosphere are presented and physically interpreted. It
                      is shown that the time series of GWSTA and GWMF at a certain
                      altitude and latitude results from the complex interplay of
                      GW sources, propagation through and filtering in lower
                      altitudes, oblique propagation superposing GWs from
                      different source locations, and, finally, the modulation of
                      the GW spectrum by the winds at a considered altitude and
                      latitude. The strongest component is the annual variation,
                      dominated in the summer hemisphere by subtropical convective
                      sources and in the winter hemisphere by polar vortex
                      dynamics. At heights of the wind reversal, a 180∘ phase
                      shift also occurs, which is at different altitudes for GWSTA
                      and GWMF. In the intermediate latitudes a semiannual
                      variation (SAV) is found. Dedicated GW modeling is used to
                      investigate the nature of this SAV, which is a different
                      phenomenon from the tropical SAO also seen in the data. In
                      the tropics a stratospheric and a mesospheric QBO are found,
                      which are, as expected, in antiphase. Indication for a QBO
                      influence is also found at higher latitudes. In previous
                      studies a terannual variation (TAV) was identified. In the
                      current study we explain its origin. In particular the
                      observed patterns for the shorter periods, SAV and TAV, can
                      only be explained by poleward propagation of GWs from the
                      lower-stratosphere subtropics into the midlatitude and
                      high-latitude mesosphere. In this way, critical wind
                      filtering in the lowermost stratosphere is avoided and this
                      oblique propagation is hence likely an important factor for
                      MLT dynamics.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244)},
      pid          = {G:(DE-HGF)POF3-244},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000489073700003},
      doi          = {10.5194/angeo-37-487-2019},
      url          = {https://juser.fz-juelich.de/record/864926},
}