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

在一个最终的目标，以检测在大气中的背景长周期声波，必须不断地激发由相同的源作为背景自由振荡的固体地球，我们安装了一个十字阵列的气压计在10公里宽的大学森林在本州中部。该阵列有28个微型气压计，采用石英晶体谐振器技术，站间距约为500米。我们分析了2002年3月至2003年11月期间的1秒连续采样记录，获得一维频率-波数谱和二维频率-慢度谱，以检测1 mHz至0.5 Hz地震频带内的3种波。我们测量了这些波的色散曲线与随机平稳平面波的假设。我们探测到的波是：（1）来自西北方向的背景重力内波，频率为1 ~ 5 mHz，相速度约为50 m/s;（2）来自东北方向的背景声波，频率为1 ~ 5 mHz，相速度约为50 m/s; ...更多信息 在0.01至0.1 Hz的频率下的微气压，在0.1 Hz下具有约400 m/s的频率依赖性相速度，在0.01 Hz下具有约1000 m/s的频率依赖性相速度，以及（3）在0.1至0.5 Hz的频率下从东南方向行进的微气压，具有约350 m/s的相速度。重力内波（1）在相应的频率范围内占主导地位。在较高频率下，相干长度小于500 m的随机分量占主导地位。背景声波（2）表现出明显的年变化，冬季最大。年变化和入射方位角表明它们可能起源于山区。微气压（3）最有可能是由附近沿海地区的海洋驻波激发的。将这些声波的功率谱与在同一大学森林中获得的地震谱进行比较。它们的频谱形状是相互相似的，通常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。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