Detection of background acoustic free oscillations and development of a theory of background free oscillations in the system of the solid Earth and the atmosphere

固体地球和大气系统中背景声自由振荡的探测和背景自由振荡理论的发展

• 批准号: 13304034
• 负责人: FUKAO Yoshio
• 金额: $ 32.95万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13304034/
• 关键词: Lone period infrasounds; Earth's background free oscillations; Observation of barometers; 地球自由振動; 気圧計; 観測システム; 気圧変動

In an eventual aim to detect background long period acoustic waves in the atmosphere that have to be excited incessantly by the same sources as for background free oscillations of the solid Earth, we installed a cross array of barometers in a 10 km--wide university forest in central Honshu. The array has 28 micro--barometers employing quartz crystal resonator technology with a station spacing of about 500 m. We analyzed 1-second continuous sampling records in a time period from March 2002 to November 2003 to obtain one--dimensional frequency--wavenumber spectra and two-dimensional frequency--slowness spectra to detect three kinds of waves in the seismic band from 1 mHz to 0.5 Hz. We measured the dispersion curves of these waves with an assumption of stochastic stationary plane waves. The waves we detected are (1)background internal gravity waves traveling from northwest at frequencies from 1 to 5 mHz with a phase velocity of about 50 m/s, (2)background acoustic waves traveling from nor … More thwest at frequencies from 0.01 to 0.1 Hz with a frequency-dependent phase velocity of about 400 m/s at 0.1 Hz and about 1000 m/s at 0.01 Hz, and (3)microbaroms traveling from southeast at frequencies from 0.1 to 0.5 Hz with a phase velocity of about 350 m/s. Internal gravity waves (1) dominate over the random component of atmospheric turbulence in the relevant frequency range. At higher frequencies the random component with coherent length shorter than 500m is dominant. Background acoustic waves (2) show clear annual variation with maxima in winter. The annual variation and their incident azimuths suggest their possible origins in mountain regions. Microbaroms (3) are most likely to be excited by standing ocean waves in nearby coastal regions. The power spectra of these acoustic waves were compared to the seismic spectra obtained in the same university forest. Their spectral shapes are mutually similar and change commonly with variable weather conditions, indicating that the microbaroms and microseisms have their common origins. Less

最终目标是探测大气中的背景长周期声波，这些声波必须由与固体地球的背景自由振荡相同的源不断激发，我们在 10 公里宽的大学森林中安装了气压计的十字阵列该阵列有 28 个采用石英晶体谐振器技术的微气压计，站间距约为 500 m。我们分析了 3 月份以来的一个时间段内的 1 秒连续采样记录。 2002年至2003年11月，获得一维频率波数谱和二维频率慢度谱，检测了1 mHz至0.5 Hz地震频带内的三种波，并测量了这些波的频散曲线。我们检测到的随机静止平面波的假设是 (1) 从西北方向传播的背景内部重力波，频率为 1 到 5 mHz，相速度约为50 m/s，(2)背景声波从正方向传播，频率为 0.01 至 0.1 Hz，与频率相关的相速度在 0.1 Hz 时约为 400 m/s，在 0.01 Hz 时约为 1000 m/s， (3)微气压从东南方向传播，频率为0.1至0.5 Hz，相速度约为350 m/s。在相关频率范围内，内部重力波 (1) 主导大气湍流的随机分量。在较高频率下，相干长度小于 500m 的随机分量占主导地位。背景声波 (2) 显示出明显的年度变化，在冬季达到最大值。年度变化及其入射方位角表明，微气压 (3) 可能起源于附近沿海地区的驻海波。将这些声波的功率谱与地震谱进行了比较。它们的光谱形状相互相似，并且随着天气条件的变化而变化，这表明微气压和微震有其共同的起源。

项目成果

Nawa, K.: "Sea level variation in seismic normal mode band observed with on-ice GPS and on-land SG at Syowa Station, Antarctica"Geophys.Res.Lett.. 30(7). 1402 (2003)

Nawa, K.：“在南极洲昭和站用冰上 GPS 和陆上 SG 观测到的地震正模带中的海平面变化”Geophys.Res.Lett.. 30(7)。

田平 誠: "大気の温度構造とインフラソニック波の長距離伝播"超音波TECHNO, 第3巻. 3・10. 23-27 (2001)

田平诚：“次声波的大气温度结构和长距离传播”《超声波技术》，第 3 卷，23-27（2001 年）。

Nawa, K.: "Sea level variation in seismic normal mode band at Syowa Station"Chikyuu. 25(6). 440-444 (2003)

Nawa, K.：“昭和站地震常模带的海平面变化”Chikyuu。

Fukao Y, Nishida K, Suda N, Nawa K, Kobayashi N: "A theory of the Earth's background free oscillations"JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH. 107・B9. 2203 (2002)

Fukao Y、Nishida K、Suda N、Nawa K、Kobayashi N：“地球背景自由振荡理论”地球物理研究杂志-固体地球 107・B9。

Nawa, K.: "Sea level variation in seismic normal mode band observed with on-ice GPS and on-land SG at Syowa Station, Antarctica"Geophys.Res.Lett. 30(7). 1402 (2003)

Nawa, K.：“在南极洲昭和站用冰上 GPS 和陆上 SG 观测到的地震正模带中的海平面变化”Geophys.Res.Lett。