A Green's function for the excitation of torsional oscillations in the Earth's core
A Green's function for the excitation of torsional oscillations in the Earth's core
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DOI：
10.1029/2004jb003495
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发表时间：
2005-08-31
影响因子：
3.9
通讯作者：
Mound, JE
中科院分区：
文献类型：
--
作者：
Buffett, BA;Mound, JE
地球外核的对流激发流体的扭转振荡，这耦合到内核和地幔的刚体运动。扭转振荡被检测为磁场的时间变化，而地幔的运动被观察到的变化，在一天的长度。我们开发了一个模型的核心地幔系统的运动使用绿色函数的脉冲响应本地化源的激发。通过将绿色函数与适当的源函数进行卷积，获得了对在空间和时间上均分布的源的响应。绿色函数是通过对系统的简正模求和来构造的。我们推导出一个正交条件的正常模式，并使用它来确定系数的正常模式展开。的绿色的功能的例子是各种源位置。预测可以与观测进行比较，以提供对激发振荡的对流过程的见解。还可以恢复确定简正模周期的物理特性，包括外核内部的磁场结构和流体边界处的耦合性质。我们概述了一个战略，反演的意见，并确定潜在的困难，由于反问题的非唯一性。
Convection in the Earth's outer core excites torsional oscillations in the fluid, which couple to rigid-body motion of the inner core and mantle. The torsional oscillations are detected as time variations of the magnetic field, whereas the motion of the mantle is observed as changes in the length of day. We develop a model for the motion of the core-mantle system using a Green's function for the impulse response to a localized source of excitation. The response to a source which is distributed in both space and time is obtained by convolving the Green's function with the appropriate source function. The Green's function is constructed by summing the normal modes of the system. We derive an orthogonality condition for the normal modes and use it to determine the coefficients of the normal mode expansion. Examples of the Green's function are presented for a variety of source locations. The predictions may be compared with observations to provide insights into the convective processes that excite the oscillations. It may also be possible to recover the physical properties that determine the period of the normal modes, including the structure of the magnetic field inside the outer core and the nature of coupling at the fluid boundaries. We outline a strategy for inverting the observations and identify potential difficulties due to the nonuniqueness of the inverse problem.