Quasi-12 h Inertia-Gravity Waves in the Lower Mesosphere Observed by the PANSY Radar at Syowa Station (39.6 °E, 69.0 °S)

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 inertiagravity 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 wavelike 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. IntroductionGravity 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). Adiabatic heating and cooling associated with vertical flow branches of the circulation maintain the thermal structure, which is considerably different from the radiative equilibrium state. Gravity waves also play an essential role in driving the quasi-biennial oscillation (QBO) and semiannual oscillation in the equatorial stratosphere Haynes, 1998;Baldwin et al., 2003). In addition, it has been shown that gravity ...

Explicit Global Simulation of Gravity Waves in the Thermosphere

“…Liu et al., 2014; Watanabe & Miyahara, 2009). At this point we do not know what role GWs generated from the polar vortex due to spontaneous emission (Sato et al., 2012; Sato & Yoshiki, 2008; Shibuya et al., 2017; Triplett et al., 2017) play in the eastward GW drag around the winter polar mesopause.…”

“…That is, these are primary GWs generated by flow over orography, moist convection, and “spontaneous emission” from tropospheric jets and fronts (see reviews of Fritts & Alexander, 2003; Plougonven & Zhang, 2014). On the other hand, GWs can be generated in the stratosphere and lower mesosphere by the nonlinear dynamics of the polar vortex (e.g., Sato & Yoshiki, 2008; Sato et al., 2012; Shibuya et al., 2017; Triplett et al., 2017). Furthermore, secondary GW generation due to the intermittent body forces resulting from the dissipation of primary GWs is a predominant mechanism in the southern winter hemisphere over orography (Becker & Vadas, 2018; Vadas & Becker, 2018; Vadas et al., 2018).…”

Formation of a Mesospheric Inversion Layer and the Subsequent Elevated Stratopause Associated With the Major Stratospheric Sudden Warming in 2018/19

“…Using continuous mesospheric wind observation data over 50 days from a mesosphere-stratosphere-troposphere radar called the PANSY radar at Syowa Station (69.0°S, 39.6°E), where PANSY stands for Program of the Antarctic Syowa MST/IS radar, Sato et al (2017) showed that GW momentum fluxes are mainly associated with waves having long periods of several hours to a day at the southern high latitudes in summer. Using observational data from the PANSY radar, Shibuya et al (2017) and Shibuya and Sato (2019) showed the GWs having such long periods are dominant also in the winter mesosphere and their horizontal wavelengths are greater than 1,000 km and vertical wavelengths of about 14 km. Ern et al (2018) analyzed the satellite observation data and showed that dominant GWs in the middle atmosphere on average have horizontal wavelengths greater than 1,000 km and vertical wavelengths in excess of 10 km, although the observational filter problem remains.…”

Climatologies and long-term changes in mesospheric wind and wave measurements based on radar observations at high and mid latitudes

“…Examining the observed wind by decomposing it into its distinct spectral components has been performed by several studies in recent years (e.g., Eckermann et al, 2016;Hysell et al, 2017;Shibuya et al, 2017;Baumgarten et al, 2018). For this study, we use the approach of decomposing the wind according to Stober et al (2017) and Baumgarten and Stober (2019) by applying an adaptive spectral filter technique (ASF).…”