1998年11月17日狮子座流星雨的次声观测

采用三台ＣＳＨ－１型次声接收器,在北京昌平区布置了一个次声测量三点阵,并观测到１９９８年１１月１７日狮子座流星雨产生的次声波Ｐ－ｔ曲线和波速波向图,借助快速富立叶变换,分析Ｐ－ｔ曲线的波形得到次声的三维动态谱,频谱分析结果表明,（１）各流星产生的次声波大都很短暂,持续时间在１－５分钟内;（２）流星次声波的周期都在４０－４０８秒内,少数在１－４８０秒内;（３）在１１月１７日１９：２１－２０：４１期间     

强地震的前兆次声波研究

利用在北京昌平安装的次声三点阵,对强地震前兆次声波进行了5年的连续观测。统计分析结果表明:强震前约10天内常能测到振幅很强的前兆次声。其三维动态频谱的特点是,振幅由弱逐渐加强,达到极值后变弱;先为长周期波(10-20分),紧跟着短周期波(5-10分),然后又出现更长的周期波,最后长短周期波一起出现。提前时间与三点阵到震中距离之间没有明显的关系,与震级之间也没有明显的关系。     

汤加火山喷发所产生的次声波

2022年1月15日汤加火山发生了剧烈的喷发。在火山喷发后的8 h 39 min,距离火山喷发位置10151 km的昆明次声台阵记录到很强的次声波信号。次声波波列前几个周期平均为443 s,传播速度约为321 m/s,其波形幅度与频率随时间变化与核爆炸产生的次声波形相似。采用相关检测方法估计次声信号的方位角为119°。在持续监测中,还观测到了火山喷发产生的次声信号沿反方向绕地球到达的信号和沿正方向绕地球一周后再次到达的信号。      

雷雨次声波的三维动态频谱测量研究

采用三台电容式次声接收器，在北京昌平安装次声三点阵，并测量到2000年7-8月15次强雷阵雨的次声波P-t曲线及其三维动态频谱，频谱分析结果表明：（1）雷阵雨的次声波主要来自雷次声。（2）雷次声的频谱有三大特点：其一是听到雷声越响时，雷次声振幅越强；其二是特强振幅持续时间很长；其三是周期范围时而连续、时布分布在周期较长和较短端，形成谱图上一个个空洞。据此可区别与其它次声波。（3）初步探讨了雷次声的产生机理和传播特点。     

Subjective loudness and annoyance of filtered N-wave sonic booms.

The contribution of the "infrasonic" low-frequency content of sonic boom N waves to subjective loudness and annoyance has been investigated. An extended low-frequency response loudspeaker-driven simulation booth was employed, with computer-generated input test signals. For test N waves of 1 ms rise time and 150 ms duration, frequencies below 25 and 50 Hz, respectively, were cut off by digital filters simulating simple RC circuits. The filtered signal amplitude was adjusted versus the amplitude (48 Pa) of a reference unfiltered N wave (effective low-frequency cutoff approximately 0.1 Hz) until the two sounded equally loud (first experiment) or equally annoying (second experiment). The amplitude differences for equality were very slight: less than 0.6 dB at most. Surprisingly, while loss of the low frequencies slightly decreased the loudness, it slightly increased the annoyance.     

Responses of the Ionosphere to the Great Sumatra Earthquake and Volcanic Eruption of Pinatubo

A sudden ionospheric disturbance was detected by the Doppler shift sounding equipment at Beijing, about 25 min later after the outbreak of the Sumatra earthquake on 26 December 2004. This ionospheric disturbance appeared less than lOmin after the earthquake was first recorded at Beijing seismological station by the arrival of the seismic Rayleigh wave. The analysis shows that about 18rain is the time necessary for the seismic Rayleigh wave to propagate from the epicentre to Beijing and then about 5-10min for acoustic waves to propagate from the surface of the Beijing area to the altitude of the ionosphere. Also, a report was made as another example to show the ionospheric response of Doppler shift observation at Beijing area during the Mount Pinatubo eruption of 1991. These two examples show clear evidence of the lithosphere-atmosphere-ionosphere coupling. The former case is in the frequency domain of infrasonic waves of the Earth surface oscillation due to the Rayleigh waves caused by the earthquake, while the latter is in the acoustic-gravity wave category directly excited in the atmosphere by the mass and energy eruptions of Mount Pinatubo.     

大气中一种低频次声波观测研究

分析大气中存在的一种低频次声波。利用宽频带次声测量传感器阵列组成的广域分布网络,对此种次声波进行了近5年不间断的检测。对所测次声信号的观察统计发现,它与自然事件密切相关。对这种信号波形、频谱、时频图及相关性进行分析进一步发现,该波通常以一组或间歇性多组形式出现,频率主要在0.001~0.02 Hz之间、幅度一般可达50~200 Pa。在2008年3月20日新疆于田地震、2008年5月12日四川汶川地震以及2009年10月29日陕甘川三省交界处的地震前,均检测到了大幅值的低频次声波。本文的分析结论对研究大气次声波的多样性及其与自然现象的关系提供了新的参考,对地震信息探测具有一定的实际意义。      

Infrasonic waves generated from the volcano eruption in Tonga

The Hunga-Tonga-Hunga-Ha'apai volcano in Tonga erupted violently on January 15, 2022. After 8 hours and 39 minutes, an infrasound array in Kunming at a distance of 10151 km away from the volcano recorded a sequence of strong infrasonic waves. The average period of the first four infrasonic waves is 443 s with propagation speed of 321 m/s. The azimuth angle of this event has been estimated by applying the progressive multi-channel correlation(PMCC) method to process the received signals. During continuous monitoring, the infrasonic waves propagating along and opposite to the direction towards the Kunming array around the earth are recorded respectively.     

Disturbances of the upper atmosphere and ionosphere caused by acoustic-gravity wave sources in the lower atmosphere

The results of observations of acoustic-gravity waves in the troposphere and the ionosphere at middle latitudes during periods of passage of the solar terminator are presented. Tropospheric observations were performed using a lidar. The frequency characteristics of variations of the tropospheric parameters are determined based on observations of the intensity of the scattered lidar signal. The characteristics of variations of the total electron content (TEC) in the atmosphere are determined from data collected by GPS navigation satellites. An analysis of the observational data showed that the spectrum of variations of the atmospheric and ionospheric parameters is indicative of acoustic-gravity waves (AGW) propagating from the lower atmosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.     

Observations of Acoustic Gravity Waves during the Solar Eclipse of March 20, 2015 in Kaliningrad

Results of observations of atmospheric and ionospheric parameters during the solar eclipse of March 20, 2015 have been described. The observations have been conducted by lidar sensing in the lower atmosphere and analysis of the total electron content (TEC) in the ionosphere in Kaliningrad. Observations at the troposphere altitudes have been conducted using an atmospheric lidar. Ionospheric parameter TEC has been determined according to observations of navigation satellite signals. The spectral analysis of the monitored parameters during the solar eclipse has shown that, in the lower atmosphere and the ionosphere in a period range of 2–20 min, internal gravity waves (IGWs) and infrasonic waves are excited. During the main phase of the eclipse, the major contribution to variations in the parameters of the medium comes from infrasonic vibrations. Changes in the variations in the atmospheric and ionospheric parameters with IGW periods are observed only in the initial and final phases of the eclipse.     

Weak guided wave signal detection using period jump of Duffing system

A potential risk in ultrasonic guided wave testing is that weak echo signals from small defects may be submerged in noisy signals, which will cause missed detection. To overcome this shortcoming, a weak guided wave signal detection method based on period jump of the Duffing system is proposed in this paper. The critical state of the system period jump can be obtained by analyzing the bifurcation characteristics of the Duffing system with the variation of the driving force amplitude. A weak ultrasonic guided wave signal with the same frequency as the driving force is added to the driving force. This is equivalent to changing the driving force amplitude, which causes the period state to jump. Consequently, the weak guided wave signals can be identified based on the period jumps. The increase or decrease in the driving force amplitude due to the interference of the guided wave signal depends on the phase difference between the intercepted signal and the periodic driving force. The conditions for increasing and decreasing the driving force amplitude are out of phase with each other.They have an approximate phase difference of π within the same period. Two detection models for small-scale periodic states(SPS) and large-scale periodic states(LPS) are constructed, and the effectiveness of the models in identifying the guided wave signal is verified numerically and experimentally. The anti-noise interference capabilities of the two models are also compared.The results show that the SPS detection model provides unique results and a strong anti-noise ability, and effectively improves the sensitivity of small defect detection using ultrasonic guided waves.     

Large variations in NLS bi-soliton wave groups

The nonlinear Schrödinger (NLS) equation describes the spatial–temporal evolution of the complex amplitude of wave groups in beams and pulses in both second and third order nonlinear material. In this paper we investigate in detail the wave group that has the exact two-soliton solution as amplitude, and show that large variations in the amplitude appear to form a pattern that, at the peak interaction, resembles quite well the linear superposition. The complexity of the phenomenon is a combination of nonlinear effects and linear interference of the carrier waves: the characteristic parameter is the quotient of wave amplitude and frequency difference of the carrier waves, which is also proportional to the quotient of the modulation period of the carrier waves during interaction and the interaction period of the soliton envelopes.     

Collective bubble oscillations as a component of surf infrasound

Plunging surf is a known generator of infrasound, though the mechanisms have not been clearly identified. A model based on collective bubble oscillations created by demise of the initially entrained air pocket is examined. Computed spectra are compared to infrasound data from the island of Kauai during periods of medium, large, and extreme surf. Model results suggest that bubble oscillations generated by plunging waves are plausible generators of infrasound, and that dynamic bubble plume evolution on a temporal scale comparable to the breaking wave period may contribute to the broad spectral lobe of dominant infrasonic energy observed in measured data. Application of an inverse model has potential to characterize breaking wave size distributions, energy, and temporal changes in seafloor morphology based on remotely sensed infrasound.     

Experimental frequency spectra of ultrasound transmission through two-dimensional ensembles of trapped microbubbles

The frequency spectra of transmission coefficients for ultrasound passing through a sheet of gas-filled micropores have been measured using incident waves with amplitudes up to 2.4 x 10(4) Pa. It is found that as the amplitude of the incident wave is increased, the peak frequency of transmission loss through the two-dimensional trapped-bubble ensemble shifts to lower values by as much as 47%. The experiments indicate that the shifting is caused by the net displacements of air-water-membrane triple-phase lines and the air loss of the trapped bubble, which are due to the radiation force and microbubble production produced by the incident wave. Results of the experiments and possible theoretical explanations are discussed.     

Modeling the spectrum of infrasonic hydroacoustic radiation generated by the sea surface under storm conditions

Generation of infrasonic radiation into a water medium by sea surface waves is analyzed. The analysis is carried out for the situation in which the infrasound is generated by surface waves with frequencies close to those of dominant waves. The presence of two wave systems on the sea surface is assumed: swell and wind waves. It is shown that if the frequencies of spectral peaks of wind waves and swell diverge by 20%, the maximum value of the radiation spectrum decreases by approximately 40% (if the general directions of the two wave systems are oriented strictly towards each other). A deviation of the general directions of the two wave systems from the opposite direction by 45° leads to a decrease in the maximum value of the radiation spectrum by more than two times.     

Properties of two-variable expansions of scattering amplitude

Two types of invariant expansions of scattering amplitude based on group O(3, 1) that can be considered as generalizations of the partial wave analysis are studied. They are shown to be identical with the Fourier transform of the modified parital waves, the modification being given by integrating or differentiating the partial wave. We search for a simple physical use of expansion coefficients, the so-called Lorentz amplitudes, and find the connection between the poles of Lorentz amplitude and the high-energy behaviour of the partial wave; the relation between the Lorentz amplitude and the position of the Regge poles is precisely formulated.     

Stimulus dependencies of the gerbil brain-stem auditory-evoked response (BAER). I: Effects of click level, rate, and polarity

Three experiments evaluating the effects of various stimulus manipulations on the click-evoked gerbil brain-stem auditory-evoked response (BAER) are reported. In experiment 1, click polarity and level were covaried. With increasing click level, there is a parallel decrease in the latency of the first five BAER peaks (i-v) and an increase in BAER peak amplitudes. Mean wave i amplitude was greater for rarefaction than condensation clicks at high click levels; mean wave v amplitude was greater for condensation clicks at higher click levels. Experiment 2 covaried click rate and polarity. The latency of the BAER peaks increased with increasing click repetition rate. This rate-dependent latency increase was greater for the later BAER peaks, resulting in an increase in the i-v interval with increasing click rate. As rate increased, the amplitudes of waves i and v decreased monotonically, whereas the amplitudes of waves ii-iv were largely uninfluenced by click rate. As in experiment 1, mean wave i amplitude was greater for rarefaction clicks, whereas mean wave v amplitude was greater for condensation clicks. The magnitude of these polarity dependencies on waves i and v amplitude decreased with increasing click rate. Experiment 3 evaluated the effects of click polarity on BAERs to high-intensity (100 dB pSPL) clicks presented at a rate of 10 Hz. In eight of ten gerbils evaluated, wave i amplitude was greater to rarefaction clicks, and, in all ten animals, wave v amplitude was greater to condensation clicks. The effects of click level and rate on BAER peak amplitudes, latencies, and interwave intervals are reminiscent of stimulus dependencies reported for the human BAER. The effects of click polarity on the amplitudes of waves i and v of the gerbil BAER have also been reported for the human BAER.     

复Ginzburg-Landau方程中模螺旋波的稳定性研究

研究了复Ginzburg-Landau方程系统中模螺旋波与其他斑图在同一平面内的竞争行为,发现演化结果在系统参数平面内可分为四个主要区域:在I区和III区中,模螺旋波与相螺旋波相比稳定性较差,模螺旋波的空间被相螺旋波所入侵.在II区中,模螺旋波具有较强的稳定性,相螺旋波的空间被模螺旋波所入侵.在IV区内,由于时空混沌所导致的频率不稳定性,演化的结果较为复杂.我们通过对模螺旋波、相螺旋波以及时空混沌的频率分析,发现当模螺旋波的系统参数为α1=-1.34,β1=0.35时,较高频率的模螺旋波具有较好的稳定性,高频模螺旋波可以入侵低频斑图空间.竞争结果主要受系统变量实部的频率影响,频率分析所得到的理论结果与数值实验结果符合得非常好.     

Modulation instability of Stokes wave → freak wave

Formation of waves of large amplitude (freak waves, killer waves) at the surface of the ocean is studied numerically. We have observed that freak waves have the same ratio of the wave height to the wave length as limiting Stokes waves. When a freak wave reaches this limiting state, it breaks. The physical mechanism of freak wave formation is discussed.     

次声波在非均匀大气中的超视距传播特性研究

本文基于Nonlinear Progressive Equation (NPE方程)开展了对非均匀大气中次声波超视距传播特性的研究, 通过数值模拟实验对武汉上空四季次声波传播情况以及路径传输损耗进行了模拟, 获取了次声波在非均匀大气中的超视距传播特性. 计算结果表明, 非均匀大气的性质及其中存在的风对次声波传播有明显的影响, 平流层折射与风速和声波传播方向密切相关, 数值模拟结果表明, 当高斯声源主频为0.1 Hz时, 在不同的背景风场传播条件下, 存在着两个反射高度, 其中40 km 高度反射传输损耗约为25 dB, 110 km反射传输损耗约为50 dB. 关键词： 次声波 超视距传播 非均匀大气 平流层折射