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@ARTICLE{Ern:895022,
      author       = {Ern, Manfred and Diallo, Mohamadou and Preusse, Peter and
                      Mlynczak, Martin G. and Schwartz, Michael J. and Wu, Qian
                      and Riese, Martin},
      title        = {{T}he semiannual oscillation ({SAO}) in the tropical middle
                      atmosphere and its gravity wave driving in reanalyses and
                      satellite observations},
      journal      = {Atmospheric chemistry and physics},
      volume       = {21},
      number       = {18},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2021-03535},
      pages        = {13763 - 13795},
      year         = {2021},
      abstract     = {Gravity waves play a significant role in driving the
                      semiannual oscillation (SAO) of the zonal wind in the
                      tropics. However, detailed knowledge of this forcing is
                      missing, and direct estimates from global observations of
                      gravity waves are sparse. For the period 2002–2018, we
                      investigate the SAO in four different reanalyses:
                      ERA-Interim, JRA-55, ERA-5, and MERRA-2. Comparison with the
                      SPARC zonal wind climatology and quasi-geostrophic winds
                      derived from Microwave Limb Sounder (MLS) and Sounding of
                      the Atmosphere using Broadband Emission Radiometry (SABER)
                      satellite observations show that the reanalyses reproduce
                      some basic features of the SAO. However, there are also
                      large differences, depending on the model setup.
                      Particularly, MERRA-2 seems to benefit from dedicated tuning
                      of the gravity wave drag parameterization and assimilation
                      of MLS observations. To study the interaction of gravity
                      waves with the background wind, absolute values of gravity
                      wave momentum fluxes and a proxy for absolute gravity wave
                      drag derived from SABER satellite observations are compared
                      with different wind data sets: the SPARC wind climatology;
                      data sets combining ERA-Interim at low altitudes and MLS or
                      SABER quasi-geostrophic winds at high altitudes; and data
                      sets that combine ERA-Interim, SABER quasi-geostrophic
                      winds, and direct wind observations by the TIMED Doppler
                      Interferometer (TIDI). In the lower and middle mesosphere
                      the SABER absolute gravity wave drag proxy correlates well
                      with positive vertical gradients of the background wind,
                      indicating that gravity waves contribute mainly to the
                      driving of the SAO eastward wind phases and their downward
                      propagation with time. At altitudes 75–85 km, the SABER
                      absolute gravity wave drag proxy correlates better with
                      absolute values of the background wind, suggesting a more
                      direct forcing of the SAO winds by gravity wave amplitude
                      saturation. Above about 80 km SABER gravity wave drag is
                      mainly governed by tides rather than by the SAO. The
                      reanalyses reproduce some basic features of the SAO gravity
                      wave driving: all reanalyses show stronger gravity wave
                      driving of the SAO eastward phase in the stratopause region.
                      For the higher-top models ERA-5 and MERRA-2, this is also
                      the case in the lower mesosphere. However, all reanalyses
                      are limited by model-inherent damping in the upper model
                      levels, leading to unrealistic features near the model top.
                      Our analysis of the SABER and reanalysis gravity wave drag
                      suggests that the magnitude of SAO gravity wave forcing is
                      often too weak in the free-running general circulation
                      models; therefore, a more realistic representation is
                      needed.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {2112 - Climate Feedbacks (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2112},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000697295500002},
      doi          = {10.5194/acp-21-13763-2021},
      url          = {https://juser.fz-juelich.de/record/895022},
}