1987年9月23日日环食所产生的大气内重力波

在日食期间,月影以超声速移过地球大气而使局部大气冷却。Chimonas和Hines认为大气冷却的结果产生激波,诱发大气重力波。这时在电离层中可检测到TID而在地面上可检测到大气压力变化。虽然在电离层中这种重力波信号很弱,但仍可检测到。地面压力变化发生在日食附近地区,甚至离主食带相当远的地方也可以测到。本文报告了在中国首次直接观测日环食引起地面压力波的检测结果。1987年9月23日日环食期间,位于环食带的乌鲁木齐,太原,徐州,苏州及位于偏食带的北京和贵阳共六个次声观测站用电容式微气压计在我国首次探测到日环食产生的声重力波,其周期为10—60min,振幅为7—20Pa(峰-峰值)。动态谱分析的结果表明,各地的重力波周期都有连续的谱分布,其主周期为40min。此外,各地记录到出现时间不同而周期更长的波,对这些结果本文作了初步计论。     

山背波:对飞机的潜在威胁

山背波对飞机的潜在威胁现已毋庸置疑。为了提高在这方面作出更确切判断的能力并能进一步找出实践中可行的相应措施，首要的问题就是必须对山背波本身有足够的认识，而这正是当前国内文献中极为薄弱的环节。有鉴于此，本文系统地、较全面地介绍了山背波这种独特的次声波，对其发生机理和基本特征、以及作为其直接衍生物的相关云相和晴空湍流－－后者正是对飞机的主要潜在威胁所在－－作出简明扼要的评述。     

大气声学:关于现象、原理和应用的综述

作为声学主要分支之一的大气声学在国内迄今未能得到应有的重视，既无专著又无综述性文章介绍．有鉴于此，本文比较全面、系统而又简明扼要地阐述了该领域最重要的一些现象、原理和应用，并穿插揭示出从经典到现代的历史发展过程，使读者可以概括了解大气声学的对象、方法、基本原理和实际应用─—特别是有关涉及高层大气的各种类型次声波现象，以及它们日益成为一种重要的主、被动遥感手段的态势．     

REFLECTION AND REFRACTION OF PLANE SOUND WAVES IN MOVING STRATIFIED MEDIA

This paper deals with the fundamental problems concerning the propagation of plane soundwaves in moving stratified media.Starting from the wave equation in moving media,we haveaccomplished a systematic study of reflection and refraction of the waves at the interface between twomoving homogeneous media under the assumption that the Mach numbers of the motion are smallcompared with unity.The coefficients of reflection and transmission as well as the equation for thetotal reflection cone are obtained. Similar treatment is extended to a slowly varying stratified moving medium,and the W.K.B.solu-tion and the successive modifications to the sound field are worked out.Following the approachdeveloped by Gans,we have investigated the field within the total reflection zone where the geometricalacoustics is no longer valid,and obtained an appropriate solution which can be connected with thegeometrical acoustics solution at the boundaries of that zone.     

水下声道

苏联“少年技术家”杂志最近出版了一期问题专辑,向青年们提出了大量科学界尚未解决的“谜”。其中之一就是饶有兴味的所谓“水下声道”(Подводиыйэвуковойка     

RAY TRACING FOR INFRASONIC WAVES GENERATED BY TYPHOON

The propagation problem of infrasonic waves generated from typhoon has been treated by clas-sical ray theory methods.Starting from the fundamental equations of hydrodynamics includingthe influences due to horizontal winds and gravitational force,a set of three-dimensional ray equa-tions in rectangular coordinate system governing the infrasonic waves,the main frequency of whichis 0.2 Hz approximately,is obtained under the assumption of horizontal stratification. These equations have been integrated numerically on a microcomputer with association to asomewhat simplified model of realistic atmosphere to obtain the specific tracks of acoustic rays cor-responding to various projecting angles. The rays can be divided into three groups,corresponding to three sound channels in the atmosphere.Accordingly,a corresponding relationship between the angle of arrival and the"span"(i.e.,thehorizontal distance between two successive reflections of the same ray)of various rays has been ob-tained.This theoretical relations     

低层大气中可听声超额衰减的测量

声音在大气中的传播衰减是个很复杂的问题。除了声波本身的球面衰减和大气媒质对声音的吸收以外,还存在着由于大气不均匀性所造成的附加衰减。这种衰减主要由两方面引起:气象条件(温度和风随高度的分布)所导致的声传播路径的弯曲;大气湍流和其它不均匀性(如雾等)对声波的散射。球面衰减以外的衰减统称作“超额衰减”。由于牵涉的因素很多,关系也很复杂,所以它的理论估值非常困难,往往主要地依靠实地测量。     

CALCULATIONS FOR THE FIELD OF PLANE SOUND WAVES IN A REALISTIC ATMOSPHERE

The general theoretical results concerning the reflection and refraction of plane sound wavesin a moving stratified medium obtained in a previous work have been applied to calculate thesound field in a realistic atmosphere.Two distinct approaches,the analytic and the graphic method,have been suggested to estimate the sound field in a multi-layered atmosphere where the gradientsof both temperature and wind velocity are present. The analytic method gives series expressions for the WKB approximation of the field as wellas successive modifications to it.All these expressions may be used as a basis for obtaining specificresults by some further elementary calculations devoted to the profiles of the realistic atmospheremodel. The graphic method gives a clear illustration of the field in a specific example which can beregarded as a standard atmosphere.Both a approaches enable us to simplify considerably the cal-culations referring to the usual multi-layer approaches.     

运动分层介质中脉冲点声源的衍射场

本文研究了作定常无旋运动的分层介质中形成影区条件下一δ型脉冲点声源的衍射场.用混合积分变换将运动介质声学基本方程化为一非齐次线性二阶常微分方程,并将它的解展开成各阶简正波之迭加;运用Friedlander所发展的方法由Langer渐近解求出本征值和各本征函数的渐近表式;对于深入影区边界之内的观察点得到了波前附近场的渐近表式.根据这一表式讨论了场随时间的建立过程和随水平距离的衰减关系.这些关系强烈地依赖于边界条件以及声源和接收点是否位于界面上这一情况.     

日环食激发大气声重力波的研究

利用1987年9月23日日环食期间在中国多个测站获得的地面微压波、无线电探空及太阳辐射资料研究了日食激发声重力波的波源机制、波谱特征、地区差异,并与同时进行的电离层探测结果进行了比较。结果表明此次日环食过程中肯定有重力波发生,其周期与太阳直接辐射起伏经历的时间有明显的一致性。不同地方的日食重力波都来自太阳直接辐射变化直接产生的强迫振荡和各地大气层内的浮力振荡。前者的波动周期较长,振幅较大,直接与日食期间太阳辐射的起伏有关;后者的波动周期较短,振幅较小,与各地日食时局地大气层内的稳定度及湿度条件有关。研究中发现由日食引起的太阳直接辐射有两种与重力波激发有关的起伏过程,一种是初亏-复圆阶段的振荡,其周期与各地日食开始时间有关;一种是复圆后的振荡,其周期与各地食分值有关。这两种起伏周期与日食参数的相关系数都在0.99以上。本文在分析日食的太阳辐射和局地大气效应的基础上,提出了相应的声重力波发生的物理机制,并讨论了日食声重力波与同时发生的电离层振荡的关系。针对70年代以来国内外一直未能解决的日食是否激发大气声重力波的问题,本文得到一个简单而重要的结论:早上发生日食的地方有长周期宽频谱的大气声重力波产生,下午发生日食的地方则没有这种波出现。