Abstract
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 (12 h) disturbances in the lower mesosphere at heights of 70 to 80 km were observed. Estimated vertical wavelengths, wave periods and vertical phase velocities of the disturbances were approximately 13.7 km, 12.3 h and −0.3 m s−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 1100 km, and the wavenumber vectors tend to point northeastward or southwestward. Using the nonhydrostatic numerical model with a model top of 87 km, quasi-12 h disturbances in the mesosphere were successfully simulated. We show that quasi-12 h disturbances are due to wave-like disturbances with horizontal wavelengths longer than 1400 km 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-12 h 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.
Highlights
Gravity waves are atmospheric waves with a restoring force of buoyancy that can transport momentum upward from the troposphere to the middle atmosphere (e.g., Fritts and Alexander, 2003)
The PANSY radar system is designed to observe three-dimensional winds at a high time resolution and vertical resolution along beam directions of t =∼ 1 min and z = 150 m in the troposphere and lower stratosphere, respectively, and of t =∼ 1 min and z = 600 m in the mesosphere
The first observation with a complete system of the PANSY radar were successfully performed for 16–24 March 2015
Summary
Gravity waves are atmospheric waves with a restoring force of buoyancy that can transport momentum upward from the troposphere to the middle atmosphere (e.g., Fritts and Alexander, 2003). Momentum deposition by gravity waves in the mesosphere is a major driving force for the summerto-winter pole material circulation in the mesosphere (e.g., Plumb, 2002). Gravity waves play an essential role in driving the quasi-biennial oscillation (QBO) and semiannual oscillation in the equatorial stratosphere (Sato and Dunkerton, 1997; Haynes, 1998; Baldwin et al, 2003). R. Shibuya et al.: Quasi-12 h inertia–gravity waves summer hemispheric low-latitude part of winter stratospheric circulation (Okamoto et al, 2011)
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