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

为了最终探测大气中的背景长周期声波，我们在本州中部10公里宽的大学森林中安装了一个气压计的交叉阵列，这些声波必须由与固体地球背景自由振荡相同的源不断激发。该阵列有28个微气压计，采用石英晶体谐振器技术，站间距约500米。对2002年3月至2003年11月的1秒连续采样记录进行了分析，得到了1 mHz ~ 0.5 Hz地震带3种地震波的一维频率-波数谱和二维频率-慢度谱。我们在随机平稳平面波的假设下测量了这些波的频散曲线。我们检测到的波浪是(1)背景内部重力波从西北频率从1到5 mHz的相速度约50米/秒,(2)背景声波从也 ... 更多西邻频率从0.01到0.1 Hz频率相关相速度约400 m / s, 0.1赫兹和1000 m / s在0.01赫兹,和(3)从东南microbaroms旅游频率从0.1到0.5赫兹的相速度约350 m / s。在相关频率范围内，内重力波(1)优于大气湍流的随机分量。在较高频率下，相干长度小于500米的随机分量占主导地位。背景声波(2)表现出明显的年变化特征，在冬季达到最大值。每年的变化和它们的入射方位角表明它们可能起源于山区。微气压(3)最有可能被附近沿海地区的常驻海浪激发。将这些声波的功率谱与同一大学森林中获得的地震谱进行了比较。它们的光谱形状相互相似，并随气候条件的变化而共同变化，表明微震和微震具有共同的起源。少

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