Studies of Terrestrial Gravity Using Superconducting Gravimeters

该项目由两个独立的研究组成，使用由超导重力仪网络（全球地球动力学项目，简称GGP）收集的高精度重力数据。第一个是比较GRACE（重力恢复和气候实验）卫星任务和欧洲7个地面GGP站目前提供的高精度月度重力场。尽管这两组数据在空间和时间分辨率上存在很大差异，但其智力上的优点是首次使用这两组数据集来确定中欧水文的时间变化。作者和他的同事们所做的研究表明，这两个数据集有一个共同的信号，似乎与预测的地面水分含量密切相关。将进一步探讨这种相关性，以确定信号来自何处以及地面站能够在多大程度上验证基于卫星的模型。由于两种观测技术的独立性，这是一项独特的研究。GRACE实验更广泛的影响在于，它将为各种各样的地球物理问题提供极其有用的数据，例如为全球水资源的长期规划准确评估大陆储水量。第二项研究将使用过去7年中所有GGP数据（20个站点）来搜索来自地球深处的几个信号，特别是Slichter三重信号。这种三重态是由地球内核（IC）在流体外核内的振荡产生的，当受到地震等能量源的激发时；分裂成三种模式主要来自地球自转。这种运动非常小——大约1毫米或更小，但原则上可以用GGP重力阵列探测到。该研究的智力价值在于发现了内外核边界处的密度跃变。这种跳跃对于评估地球磁场产生的能量学至关重要，即随着时间的推移，IC冻结的潜热可以产生多少能量。最近对ICB密度跳跃的估计在0.3和0.8 Mg - m-3之间变化，使用的方法是来自ICB和地球正常模态频率的地震体波的差分散射。该项目更广泛的影响是研究生教育，通过3年的学生支持。这项新研究将大大加强圣路易斯大学的研究生项目。

This project consists of two separate studies using high precision gravity data collected by the network of superconducting gravimeters (Global Geodynamics Project, or GGP). The first is a comparison between the high precision monthly gravity field that is now available from the GRACE (Gravity Recovery and Climate Experiment) satellite mission and the 7 ground-based GGP stations in Europe. The intellectual merit is in using for the first time both data sets, even though they differ considerably in spatial and temporal resolution, to identify the time variation of the hydrology over central Europe. Studies done by the author and his colleagues have demonstrated that both data sets have a common signal that appears to correlate well with the predicted moisture content of the ground. This correlation will be further explored to determine where the signal comes from and to what extent the ground stations are able to validate the satellite-based models. This is a unique study because of the independence of the two observational techniques. The broader impact of the GRACE experiment is that it will provide extremely useful data for a wide variety of geophysical problems such as the accurate assessment of continental water storage for long-term planning of global water resources.The second study will use all the GGP data (20 stations), over the last 7 years, to search for several signals from the Earth's deep interior, particularly the Slichter triplet. This triplet arises from the oscillations of the Earth's inner core (IC) within the fluid outer core, when excited by an energetic source such as an earthquake; the splitting into 3 modes comes primarily from Earth rotation. The motions are extremely small - about one mm or less, but in principle detectable using the GGP gravity array. The intellectual merit of the study is to find the density jump between the inner and outer cores at the boundary (ICB). This jump is crucial for assessing the energetics to the Earth's magnetic field generation, i.e. how much energy can come from the latent heat of freezing of the IC as it grows in time. Recent estimates of the ICB density jump have varied between 0.3 and 0.8 Mg m-3, using methods such as differential scattering of seismic body waves from the ICB and from the frequencies of the normal modes of the Earth. The broader impact of this project is in graduate education, through student support for 3 years. This new study will strengthen considerably the graduate student program at St. Louis University.