A study of the dynamical characteristics of inertia–gravity waves in the Antarctic mesosphere combining the PANSY radar and a non-hydrostatic general circulation model

Ryosuke Shibuya, Kaoru Sato
2019 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> This study aims to examine the dynamical characteristics of gravity waves with relatively low frequency in the Antarctic mesosphere via the first long-term simulation using a high-top high-resolution non-hydrostatic general circulation model (NICAM). Successive runs lasting 7 days are performed using initial conditions from the MERRA reanalysis data with an overlap of 2 days between consecutive runs in the period from April to August in 2016. The data for the
more » ... data for the analyses were compiled from the last 5 days of each run. The simulated wind fields were closely compared to the MERRA reanalysis data and to the observational data collected by a complete PANSY (Program of the Antarctic Syowa MST/IS radar) radar system installed at Syowa Station (39.6<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;E, 69.0<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;S). It is shown that the NICAM mesospheric wind fields are realistic, even though the amplitudes of the wind disturbances appear to be larger than those from the radar observations.</p> <p>The power spectrum of the meridional wind fluctuations at a height of 70&amp;thinsp;km has an isolated and broad peak at frequencies slightly lower than the inertial frequency, <span class="inline-formula"><i>f</i></span>, for latitudes from 30 to 75<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;S, while another isolated peak is observed at frequencies of approximately 2<span class="inline-formula"><i>π</i>∕8</span>&amp;thinsp;h at latitudes from 78 to 90<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;S. The spectrum of the vertical fluxes of the zonal momentum also has an isolated peak at frequencies slightly lower than <span class="inline-formula"><i>f</i></span> at latitudes from 30 to 75<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;S at a height of 70&amp;thinsp;km. It is shown that these isolated peaks are primarily composed of gravity waves with horizontal wavelengths of more than 1000&amp;thinsp;km. The latitude–height structure of the momentum fluxes indicates that the isolated peaks at frequencies slightly lower than <span class="inline-formula"><i>f</i></span> originate from two branches of gravity wave propagation paths. It is thought that one branch originates from 75<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;S due to topographic gravity waves generated over the Antarctic Peninsula and its coast, while more than 80&amp;thinsp;% of the other branch originates from 45<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;S and includes contributions by non-orographic gravity waves. The existence of isolated peaks in the high-latitude region in the mesosphere is likely explained by the poleward propagation of quasi-inertia–gravity waves and by the accumulation of wave energies near the inertial frequency at each latitude.</p>
doi:10.5194/acp-19-3395-2019 fatcat:b6otxcv5efhuxpz5ke3oebjidq