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@ARTICLE{Hindley:892721,
      author       = {Hindley, Neil P. and Wright, Corwin J. and Gadian, Alan M.
                      and Hoffmann, Lars and Hughes, John K. and Jackson, David R.
                      and King, John C. and Mitchell, Nicholas J. and
                      Moffat-Griffin, Tracy and Moss, Andrew C. and Vosper, Simon
                      B. and Ross, Andrew N.},
      title        = {{S}tratospheric gravity waves over the mountainous island
                      of {S}outh {G}eorgia: testing a high-resolution dynamical
                      model with 3-{D} satellite observations and radiosondes},
      journal      = {Atmospheric chemistry and physics},
      volume       = {21},
      number       = {10},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2021-02288},
      pages        = {7695 - 7722},
      year         = {2021},
      abstract     = {Atmospheric gravity waves (GWs) play an important role in
                      atmospheric dynamics but accurately representing them in
                      general circulation models (GCMs) is challenging. This is
                      especially true for orographic GWs generated by wind flow
                      over small mountainous islands in the Southern Ocean.
                      Currently, these islands lie in the “grey zone” of
                      global model resolution, where they are neither fully
                      resolved nor fully parameterised. It is expected that as
                      GCMs approach the spatial resolution of current
                      high-resolution local-area models, small-island GW sources
                      may be resolved without the need for parameterisations. But
                      how realistic are the resolved GWs in these high-resolution
                      simulations compared to observations? Here, we test a
                      high-resolution (1.5 km horizontal grid, 118 vertical
                      levels) local-area configuration of the Met Office Unified
                      Model over the mountainous island of South Georgia
                      (54∘ S, 36∘ W), running without GW
                      parameterisations. The island's orography is well resolved
                      in the model, and real-time boundary conditions are used for
                      two time periods during July 2013 and June–July 2015. We
                      compare simulated GWs in the model to coincident 3-D
                      satellite observations from the Atmospheric Infrared Sounder
                      (AIRS) on board Aqua. By carefully sampling the model using
                      the AIRS resolution and measurement footprints (denoted as
                      model sampled as AIRS hereafter), we present the first
                      like-for-like comparison of simulated and observed 3-D GW
                      amplitudes, wavelengths and directional GW momentum flux
                      (GWMF) over the island using a 3-D S-transform method. We
                      find that the timing, magnitude and direction of simulated
                      GWMF over South Georgia are in good general agreement with
                      observations, once the AIRS sampling and resolution are
                      applied to the model. Area-averaged zonal GWMF during these
                      2 months is westward at around 5.3 and 5.6 mPa in AIRS and
                      model sampled as AIRS datasets respectively, but values
                      directly over the island can exceed 50 mPa. However, up to
                      $35 \%$ of the total GWMF in AIRS is actually found upwind
                      of the island compared to only $17 \%$ in the model
                      sampled as AIRS, suggesting that non-orographic GWs observed
                      by AIRS may be underestimated in our model configuration.
                      Meridional GWMF results show a small northward bias
                      $(∼20 \%)$ in the model sampled as AIRS that may
                      correspond to a southward wind bias compared to coincident
                      radiosonde measurements. Finally, we present one example of
                      large-amplitude (T′≈15–20 K at 45 km altitude) GWs
                      at short horizontal wavelengths (λH≈30–40 km)
                      directly over the island in AIRS measurements that show
                      excellent agreement with the model sampled as AIRS. This
                      suggests that orographic GWs in the full-resolution model
                      with T′≈45 K and λH≈30–40 km can occur in
                      reality. Our study demonstrates that not only can
                      high-resolution local-area models simulate realistic
                      stratospheric GWs over small mountainous islands but the
                      application of satellite sampling and resolution to these
                      models can also be a highly effective method for their
                      validation.},
      cin          = {JSC},
      ddc          = {550},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {511 - Enabling Computational- $\&$ Data-Intensive Science
                      and Engineering (POF4-511)},
      pid          = {G:(DE-HGF)POF4-511},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000655294100001},
      doi          = {10.5194/acp-21-7695-2021},
      url          = {https://juser.fz-juelich.de/record/892721},
}