Collaborative Research: GEM: Investigation of UT Dependence of Magnetic Storm Strength

合作研究：GEM：磁暴强度对 UT 依赖性的调查

• 批准号: 1102863
• 负责人: Michael Liemohn
• 金额: $ 12万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2015-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1102863&HistoricalAwards=false
• 关键词: Collaborative; Research; GEM; Investigation; UT

This is a three-year project to investigate a remarkable new finding, that the intensity of geomagnetic storms displays distinct universal time dependence, and that it varies in concert with middle latitude ionospheric plasma abundance during storms. Geomagnetic indices provide our most consistent measure of physical processes occurring in geospace since their creation over the last century. The strength of geomagnetic storms, most notably, is captured in the so-called Dst index, calculated from a set of four ground-based magnetometer measurements located strategically around the Globe. This project will utilize a newly derived, improved Dst index dataset to carry out a detailed examination of trends in the storm-time Dst with UT, season and solar cycle. Ionospheric plasma adds greatly to the pressure, pressure gradients, and currents in the magnetosphere, the last of which are measured on the ground to indicate magnetic storm strength. Ion outflow in the auroral zone, particularly in the dayside ?cusp? and nightside tail-reconnection region, provides most of this plasma. The abundance of ionospheric plasma at high latitudes has recently been shown to be a more complex process than previously thought, with a number of processes delivering plasma from middle to high latitudes in rapid fashion during periods of enhanced magnetic activity. A UT-dependent modulation of outflow during enhanced magnetic activity is one possible explanation for the observed variation in magnetic storm strength. The examination of how ionospheric ion outflow into the magnetosphere may vary during different storms and impact the UT dependence of the Dst index is the main overarching objective for this project. A parallel effort will examine whether the UT dependence in the observations is also reproduced by first-principles models of the coupled physical system. The project will use the suite of ionosphere-thermosphere-magnetosphere models that make up the University of Michigan Space Weather Modeling Framework.The project has impacts beyond the immediate benefits of improved scientific understanding. Students will participate in all aspects of the work, both at U. Michigan and Berkeley, results will be submitted to widely-read publications, and the team will work with the Center for Science Education at Berkeley to make the findings accessible to the network of teachers that it works with around the country on magnetometer data and magnetism. The importance of determining whether magnetic storms are indeed more powerful in the afternoon in the United States during summer can hardly be overstated, particularly in light of recent National Academy findings of the likely economic costs to the U.S.A. of a truly major geomagnetic storm.

这是一个为期三年的项目，目的是调查一个引人注目的新发现，即地磁风暴的强度表现出明显的全球时间依赖性，并且它与风暴期间中纬度电离层等离子体的丰度变化一致。地磁指数提供了自上个世纪创建以来地球空间中发生的物理过程的最一致的衡量标准。最值得注意的是，地磁风暴的强度被记录在所谓的DST指数中，该指数是根据一套位于地球周围具有战略意义的四个地面磁力计测量结果计算得出的。该项目将利用一个新派生的、改进的DST指数数据集，对风暴时间DST与UT、季节和太阳周期的趋势进行详细研究。电离层等离子体极大地增加了磁层中的压力、压力梯度和电流，其中最后一个是在地面上测量的，以指示磁暴强度。极光区的离子外流，特别是在日侧？尖端？而夜间的尾部重联区提供了大部分的等离子体。最近证明，高纬度地区电离层等离子体的丰富程度比以前认为的要复杂得多，在磁活动增强期间，一些过程以快速方式将等离子体从中纬度输送到高纬度地区。磁暴强度变化的一种可能解释是，在增强的磁活动期间，UT依赖于外流的调制。研究在不同风暴期间电离层离子流出到磁层的变化情况以及对DST指数的UT依赖性的影响是该项目的主要目标。一项平行的努力将检验观测中的UT依赖是否也被耦合物理系统的第一原理模型所复制。该项目将使用组成密歇根大学空间天气模型框架的一套电离层-热层-磁层模型。该项目的影响超出了提高科学理解的直接好处。密歇根大学和伯克利分校的学生将参与这项工作的所有方面，结果将提交给广泛阅读的出版物，该团队将与伯克利科学教育中心合作，将研究结果提供给全国各地与其合作的磁强计数据和磁学教师网络。确定夏季美国下午的磁暴是否真的更强都不为过，尤其是考虑到美国国家科学院最近发现，一场真正重大的地磁风暴可能会给美国带来经济损失。