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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 10 | Copyright
Atmos. Chem. Phys., 17, 6455-6476, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 30 May 2017

Research article | 30 May 2017

Quasi-12 h inertia–gravity waves in the lower mesosphere observed by the PANSY radar at Syowa Station (39.6° E, 69.0° S)

Ryosuke Shibuya1, Kaoru Sato1, Masaki Tsutsumi2,3, Toru Sato4, Yoshihiro Tomikawa2,3, Koji Nishimura2,3, and Masashi Kohma1 Ryosuke Shibuya et al.
  • 1Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
  • 2National Institute of Polar Research, Tachikawa, Japan
  • 3The Graduate University for Advanced Studies (SOKENDAI), Tokyo, Japan
  • 4Department of Communications and Computer Engineering, Kyoto University, Kyoto, Japan

Abstract. The first observations made by a complete PANSY radar system (Program of the Antarctic Syowa MST/IS Radar) installed at Syowa Station (39.6°E, 69.0°S) were successfully performed from 16 to 24 March 2015. Over this period, quasi-half-day period (12h) disturbances in the lower mesosphere at heights of 70 to 80km were observed. Estimated vertical wavelengths, wave periods and vertical phase velocities of the disturbances were approximately 13.7km, 12.3h and −0.3ms−1, respectively. Under the working hypothesis that such disturbances are attributable to inertia–gravity waves, wave parameters are estimated using a hodograph analysis. The estimated horizontal wavelengths are longer than 1100km, and the wavenumber vectors tend to point northeastward or southwestward. Using the nonhydrostatic numerical model with a model top of 87km, quasi-12h disturbances in the mesosphere were successfully simulated. We show that quasi-12h disturbances are due to wave-like disturbances with horizontal wavelengths longer than 1400km and are not due to semidiurnal migrating tides. Wave parameters, such as horizontal wavelengths, vertical wavelengths and wave periods, simulated by the model agree well with those estimated by the PANSY radar observations under the abovementioned assumption. The parameters of the simulated waves are consistent with the dispersion relationship of the inertia–gravity wave. These results indicate that the quasi-12h disturbances observed by the PANSY radar are attributable to large-scale inertia–gravity waves. By examining a residual of the nonlinear balance equation, it is inferred that the inertia–gravity waves are likely generated by the spontaneous radiation mechanism of two different jet streams. One is the midlatitude tropospheric jet around the tropopause while the other is the polar night jet. Large vertical fluxes of zonal and meridional momentum associated with large-scale inertia–gravity waves are distributed across a slanted region from the midlatitude lower stratosphere to the polar mesosphere in the meridional cross section. Moreover, the vertical flux of the zonal momentum has a strong negative peak in the mesosphere, suggesting that some large-scale inertia–gravity waves originate in the upper stratosphere.

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The first observations made by a complete PANSY radar system (Program of the Antarctic Syowa MST/IS radar) installed at Syowa Station were successfully performed from 16 to 24 March 2015. Over this period, quasi-12 h period disturbances in the mesosphere at heights of 70 to 80 km were observed. Combining the observational data and numerical simulation outputs, we found that quasi-12 h disturbances are due to large-scale inertia–gravity waves, not to semi-diurnal migrating tides.
The first observations made by a complete PANSY radar system (Program of the Antarctic Syowa...