- 作者: 董豹; 業公節
- 作者服務機構: Department of Electrical and Computer Engineering University of Illinois at Urban-Chanpaign; 高雄市國立中山大學電機工程學系
- 中文摘要: 本文探討了在非同溫大氣中聲重波的激發。激發的波源可以是時空熱能、物質的注射,或外來動力。為探討此問題,我們應用了格林函數,並以特征函數(eigen function)展開。若波源為局部的,問題的解可用空間階矩(spatial moments)的和指示,並只取幾個低階矩為近似值。在本文中我們求出最高四限階矩並發現高限階矩不但會影響波的振輻,且對波的相位亦有所改變。這個結果對今後實驗資料之分析提出謹慎的信號。我們更用重疊積分(superposition integral)將單色結果推廣至多色結果。因而發現所激發的彼可分為二類。一類為被迫振盪(forcedoscillation)。若波源為局部的,被迫振盪僅存在於波源附近一。第二類為自由振盪(free oscillation)“自由振盪波滿足無源的色散關係(dispersion relation)。可長距離的傳播,甚至傳到源在球面上的對踵點(antipode )。
- 英文摘要: In this paper we investigate the excitation of gravity wave modes in a radially stratified non-isothermal spherical atmosphere. The exciting source can be time-space heating, mass injection or anexternal force. The problem is formulated in terms of a Green's function using eigen function expansionas done previously by Weston (1961). For a localized source, we find it convenient to express the solutionas a sum of various spatial moments which are, in ascending order, total strength, bipolar moment,quadrupolar moment, etc. Making use of the addition theorem for noninteger degree Legendre functions,the solutions corresponding to the moments up to the fourth order have been obtained. It is found thatthe higher order moments of the source generally influence not only the wave amplitude but also its phase.This implies that, in general, the horizontal phase front is not necessarily orthogonal to the great circlelinking the ground projections of the source and the observer. This certainly complicates the interpretationof the experimental data. By using a superposition integral, the monochromatic solution is further extendedto the polychromatic case. It is found that a time dependent source can excite waves that are the sumof a forced oscillation and a free oscillation. If the source is localized, the forced oscillation will existappreciably only near the source region. On the other hand, the free oscillations given by a discrete spectrumthat satisfies a source-free dispersion relation can propagate a long distance away in response to the source.
- 中文關鍵字: excitation; atmospheric gravity wave modes; Green's function; spatial moments; spherical globe
- 英文關鍵字: --