4～8级大风的次声波三维动态频谱测量研究

MEASUREMENT OF THREE-DIMENSIONAL DYNAMIC FREQUENCY SPECTRA OF INFRASONIC WAVES PRODUCED BY WINDS WITH 4-8 WIND SCALES

将三台次声接收器 ,以次声三点阵形式安装在北京昌平 ,测量到 2 0 0 0年 1～ 4月 12次 4级大风、10次 5级大风、5次 6级大风、3次 7级大风和 2次 8级大风的次声波P t曲线。用快速傅立叶变换得到它们的三维动态频谱。频谱分析结果表明 ,4～ 8级大风均能产生振幅较强、方向可测的次声波 ,它们有许多 5 ,8,10 ,12 ,15min左右的短周期成分 ,同时也有 30～ 6 5min的长周期成分 ,每隔一段时间就出现从短周期到长周期连成一片的现象 ,风力越大 ,连接出现得越频繁。大风的次声波三维动态频谱的强振幅平均值与风力级数的大小有关 ,前者随后者的增加而增大 。

Three infrasonic receivers arranged in a tripartite array were used to measure the frequency spectra of infrasonic waves of high winds in Changping County of Beijing. The infrasonic waves produced by high winds, including wind scale 4(twelve times), wind scale 5(ten times), wind scale 6(five times), wind scale 7(three times) and wind scale 8(two times) were observed from the January to April in 2000. The corresponding three dimensional dynamic frequency spectra were obtained using fast Fourier transformation. The spectrum analyses show that high winds with 4 8 wind scales can produce infrasonic waves with larger amplitude and a measurable direction. These waves possess three similar characteristics different from precursory infrasound of strong earthquakes. There are lots of short periods of 1 5(or 8, 10,12,15) minutes and some long periods of 30 65 minutes at the same time. In every third moment or so, the short periods could join the long periods together. The larger the wind power is, the more the joining frequency will be. The average of strong amplitudes of the three dimensional dynamic frequency spectra produced by winds is on the increase with the enhancement of the wind force. The experiential expressions could be applied to estimate the wind scale using the three dimensional dynamic spectra of infrasonic waves.