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

Abstract

Abstract. This study aims to examine the dynamical characteristics of gravity waves\nwith relatively low frequency in the Antarctic mesosphere via the first\nlong-term simulation using a high-top high-resolution non-hydrostatic general\ncirculation model (NICAM). Successive runs lasting 7\xa0days are performed using\ninitial conditions from the MERRA reanalysis data with an overlap of 2\xa0days\nbetween consecutive runs in the period from April to August in 2016. The data\nfor the analyses were compiled from the last 5\xa0days of each run. The\nsimulated wind fields were closely compared to the MERRA reanalysis data and\nto the observational data collected by a complete PANSY (Program of the\nAntarctic Syowa MST/IS radar) radar system installed at Syowa Station\n(39.6 ∘ \u2009E, 69.0 ∘ \u2009S). It is shown that the NICAM mesospheric\nwind fields are realistic, even though the amplitudes of the wind\ndisturbances appear to be larger than those from the radar observations. The power spectrum of the meridional wind fluctuations at a height of 70\u2009km\nhas an isolated and broad peak at frequencies slightly lower than the\ninertial frequency, f , for latitudes from 30 to 75 ∘ \u2009S, while another isolated peak is observed at frequencies of approximately\n2 π∕8 \u2009h at latitudes from 78 to 90 ∘ \u2009S. The\nspectrum of the vertical fluxes of the zonal momentum also has an isolated\npeak at frequencies slightly lower than f at latitudes from 30 to 75 ∘ \u2009S at a height of 70\u2009km. It is shown that these isolated\npeaks are primarily composed of gravity waves with horizontal wavelengths of\nmore than 1000\u2009km. The latitude–height structure of the momentum fluxes\nindicates that the isolated peaks at frequencies slightly lower than f \noriginate from two branches of gravity wave propagation paths. It is thought\nthat one branch originates from 75 ∘ \u2009S due to topographic gravity\nwaves generated over the Antarctic Peninsula and its coast, while more than\n80\u2009% of the other branch originates from 45 ∘ \u2009S and includes\ncontributions by non-orographic gravity waves. The existence of isolated\npeaks in the high-latitude region in the mesosphere is likely explained by\nthe poleward propagation of quasi-inertia–gravity waves and by the\naccumulation of wave energies near the inertial frequency at each latitude.