Experimental Studies of Convection in the Earth's Core

本提案要求为加州大学洛杉矶分校一个新的实验流体力学实验室的工作提供资金。该实验室将利用两种新的强大诊断技术，对地球外核的模拟对流进行高分辨率、定量的速度测量。研究结果将测试长期以来关于岩心流体对流特性的理论，并将提供近行星参数值下流动动力学的详细表征。第一个项目将使用最近开发的声学多普勒测速技术来研究对流液态金属，它具有与熔融外核相似的物理性质。结果将检验旋转磁对流的线性稳定性理论，这是现代发电机理论的基础。这种稳定性理论是由钱德拉塞卡在20世纪50年代建立的，目前只进行过一次达到渐近状态的实验研究。第二个项目将利用粒子图像测速（PIV）的光学技术，将其应用于一个旋转的对流水球壳，一个模拟外核动力学和几何形状的装置。PIV将首次提供流场（速度、涡度和螺旋度）的定量测量，这些被认为是地球发电机的基本组成部分，但从未通过实验手段进行过充分的测量。此外，实验设计将使PIV能够测量极地地区的对流，这一点尚未得到广泛研究，但现在看来是重要的。总之，这些最先进的声学和光学测速技术将为核心对流和地球动力学的数值和理论研究提供基准。它们还将生成迄今为止分辨率最高的实验对流数据，用于解释地球深处的地磁和地震观测。

AurnouEAR-0229791This proposal requests funding for work in a new experimental fluidmechanics laboratory at UCLA. The lab will utilize two, new powerfuldiagnostic techniques to provide high-resolution, quantitative velocitymeasurements of simulated convection in the Earth's outer core. Theresults will test long-held theories regarding the properties ofconvective flows in core fluids and will provide a detailedcharacterization of flow dynamics at nearly planetary parameter values.The first project will use the recently developed technique of acousticDoppler velocimetry to study convecting liquid metals, which havephysical properties similar to that of the molten outer core. Theresults will test the linear stability theory of rotatingmagnetoconvection, the foundation of modern dynamo theory. Establishedby Chandrasekhar in the 1950's, this stability theory has only undergonea single prior experimental investigation that reached the asymptoticregime. The second project will utilize the optical technique ofparticle image velocimetry (PIV), applying it to a rotating sphericalshell of convecting water, a set-up that mimics the dynamics and thegeometry of the outer core. PIV will provide, for the first time,quantitative measurements of the flow fields (velocity, vorticity andhelicity) that are believed to be essential components of the geodynamo,but have never been measured adequately by experimental means.Furthermore, the experimental design will enable PIV to measureconvection in the polar regions, which have not been studied extensivelybut now appear to be significant. Together, these state-of-the-artacoustic and optical velocimetry techniques will provide benchmarks fornumerical and theoretical studies of core convection and the geodynamo.They will also generate the highest resolution experimental convectiondata to date for interpreting geomagnetic and seismic observations ofthe deep Earth.