Seasonal and Interannual Variation of Mesospheric Gravity Waves Based on MF Radar Observations over 15 Years at Syowa Station in the Antarctic

Yasui, Ryosuke; Sato, K.; Tsutsumi, Masaki

doi:10.2151/sola.2016-010

Cited by 22 publications

(30 citation statements)

References 13 publications

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“…We found that the AOAs of the MF echoes were more widely distributed in winter than in summer, implying more isotropic (less specular) echoes in winter. Gravity wave activity over Syowa has been shown to maximize in winter (Dowdy et al 2007;Yasui et al 2016). According to Yasui et al (2016) the gravity wave activity in winter at an altitude of 75 km is three times as high as that in summer in the wave period of 20 min−24 h, suggesting more turbulence generation in winter.…”

Section: Discussionmentioning

confidence: 99%

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Tsutsumi

Sato

et al. 2017

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We investigated characteristics of mesosphere echoes over Syowa Station (69S) in the Antarctic, which were detected by the Program of the Antarctic Syowa Mesosphere, Stratosphere and Troposphere/Incoherent Scatter (PANSY) radar (47 MHz) and Medium Frequency (MF) radar (2.4 MHz). Winter echoes from the PANSY radar and low altitude MF echoes below approximately 70−75 km mostly coexisted, appearing during the daytime as well as for a few hours post sunset. Summer echoes in the lower height region were absent in both radar observations, suggesting a close relationship in the generation mechanisms of these two radar echoes. High correlation between local K-index and the occurrence of winter echoes suggested that electron density enhancement due to ionized particle precipitation was one of the triggers of echo generation. Angles of arrival of the MF echoes were more isotropic in winter. Because gravity wave activity is much higher in winter over Syowa, higher turbulence energy caused by gravity wave breaking may also be responsible for the generation of the winter echoes and their isotropic behavior. The horizontal wind velocities of the two systems were further compared and agreed well throughout the height region of 60−90 km.

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Section: Discussionmentioning

confidence: 99%

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Tsutsumi

Sato

et al. 2017

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“…The dominance of poleward propagation is consistent with results by Yasui et al . [] indicating that gravity waves in the summer mesosphere in the Antarctic may originate from tropical convection based on MF radar observations at Syowa Station over 15 years. A numerical experiment and theoretical consideration by Sato et al .…”

Section: Statistical Characteristics Of the Mean Wind And Wind Fluctumentioning

confidence: 99%

“…This feature suggests that gravity waves propagating eastward and poleward relative to the mean wind are dominant if they originate from the lower atmosphere and propagate energy upward. The dominance of poleward propagation is consistent with results by Yasui et al [2016] indicating that gravity waves in the summer mesosphere in the Antarctic may originate from tropical convection based on MF radar observations at Syowa Station over 15 years. A numerical experiment and theoretical consideration by Sato et al [1999] and Sato [2000] suggested the possibility of such lateral propagation of gravity waves over a long distance.…”

Section: 1002/2016jd025834mentioning

confidence: 99%

“…According to Yasui et al . [], who examined 15 year observations of horizontal winds by the MF radar at Syowa Station (69.00°S, 39.35°E), the relationship between wind variances associated with mesospheric gravity waves in the SH and a sudden stratospheric warming (SSW) in the NH is not statistically significant, at least not over Syowa Station. Therefore, while the existence of the interhemispheric coupling phenomenon is widely accepted, the mechanism coupling the stratosphere of one hemisphere to the mesosphere of the other hemisphere is still unclear.…”

Section: Introductionmentioning

confidence: 99%

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Frequency spectra and vertical profiles of wind fluctuations in the summer Antarctic mesosphere revealed by MST radar observations

et al. 2017

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Continuous observations of polar mesosphere summer echoes at heights from 81–93 km were performed using the first Mesosphere‐Stratosphere‐Troposphere/Incoherent Scatter radar in the Antarctic over the three summer periods of 2013/2014, 2014/2015, and 2015/2016. Power spectra of horizontal and vertical wind fluctuations, and momentum flux spectra in a wide‐frequency range from (8 min)−1 to (20 days) −1 were first estimated for the Antarctic summer mesosphere. The horizontal (vertical) wind power spectra obey a power law with an exponent of approximately −2 (−1) at frequencies higher than the inertial frequency of (13 h)−1 and have isolated peaks at about 1 day and a half day. In addition, an isolated peak of a quasi‐2 day period is observed in the horizontal wind spectra but is absent from the vertical wind spectra, which is consistent with the characteristics of a normal‐mode Rossby‐gravity wave. Zonal (meridional) momentum flux spectra are mainly positive (negative), and large fluxes are observed in a relatively low‐frequency range from (1 day)−1 to (1 h)−1. A case study was performed to investigate vertical profiles of momentum fluxes associated with gravity waves and time mean winds on and around 3 January 2015 when a minor stratospheric warming occurred in the Northern Hemisphere. A significant momentum flux convergence corresponding to an eastward acceleration of ~200 m s−1 d−1 was observed before the warming and became stronger after the warming when mean zonal wind weakened. The strong wave forcing roughly accorded with the Coriolis force of mean meridional winds.

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“…The signs of momentum flux suggest that gravity waves propagate from low-latitude regions on the assumption of upward propagation. Yasui et al (2016) also suggested that gravity waves in the summer mesosphere may originate from the tropical convections using the MF radar observation at Syowa Station. Sato et al (1999) indicated that such meridional propagation of the inertia-gravity waves from the low-latitude region and the critical-level filtering mechanism can explain the isolated energy peak near the inertia frequency (near a frequency of 12 h at Syowa Station).…”

Section: Discussionmentioning

confidence: 96%

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

et al. 2017

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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.

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Seasonal and Interannual Variation of Mesospheric Gravity Waves Based on MF Radar Observations over 15 Years at Syowa Station in the Antarctic

Cited by 22 publications

References 13 publications

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Frequency spectra and vertical profiles of wind fluctuations in the summer Antarctic mesosphere revealed by MST radar observations

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

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Seasonal and Interannual Variation of Mesospheric Gravity Waves Based on MF Radar Observations over 15 Years at Syowa Station in the Antarctic

Cited by 22 publications

References 13 publications

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Frequency spectra and vertical profiles of wind fluctuations in the summer Antarctic mesosphere revealed by MST radar observations

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

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