GEM: The Time Sequence of Substorms in GEM Campaigns: A Comparison of Individual Events to Statistical Averages

GEM：GEM 活动中亚暴的时间序列：单个事件与统计平均值的比较

• 批准号: 9502124
• 负责人: Robert McPherron
• 金额: $ 20.64万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-07-15 至 1999-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9502124&HistoricalAwards=false
• 关键词: GEM; Time; Sequence; Substorms; Campaigns

A magnetospheric substorms is the collection of processes by which energy is extracted from the solar wind and deposited in the magnetosphere, ionosphere and earth's atmosphere. Substorms have significant effects on the near-earth environment and affect many of man's systems. The represent a natural hazard to human activities that is becoming more important. Unfortunately, the cause of substorms, particularly of the most destructive phase, the expansion phase, is not known. For may years the most popular physical model explaining substorms has been the near-earth neutral line (NENL) model. This model has been remarkably successful in organizing numerous observations in the near-earth plasma sheet and successful predicted the existence and properties of the magnetotail plasmoid, a bubble of plasma and magnetic field that the earth releases to the solar wind during substorms. A number of new observations have not been incorporated in the NENL model, and it appears difficult to do so. It seems that the substorms expansion begins at local midnight very close to synchronous orbit (6.6 Re) and propagates outward into the tail. This expansion begins on closed, quasi-dipolar field lines at the inner edge of the cross-tail current sheet. Subsequently it moves tailward by disrupting the tail current, diverting it along magnetic field lines to the auroral ionosphere. A new model called the current disruption (CD) model is being developed to explain these observations. Some versions of this model predict dynamics of the tail plasma sheet and magnetic field that are diametrically opposite to the predictions of the NENL model, and the observations on which it is based. Such a fortunate circumstance should be easy to resolve. The model either agrees or disagrees with observations and we should be able to decide between them. It is proposed to re-examine the observations in the near-earth plasma sheet and place them on a firmer footing so that it will be pos sible to develop a reasonable physical model of the substorm expansion phase. To this end, data already at UCLA, and additional data from other investigators will be used to study the problems of frequency of occurrence and time delay of phenomena relative to substorms onset. Other ground indicators of substorm onset will be used including brightenings in satellite auroral images, midlatitude positive bays, Pi 2 pulsation bursts, maxima in inclination of synchronous magnetic field, and dispersionless plasma injection at synchronous orbit. Features to be examined include changes in magnetic field, particle fluxes, plasma pressure, plasma flow and temperature. Based on these results, the different models and their success in explaining the observations will be considered.

磁层亚暴是从太阳风中提取能量并沉积在磁层、电离层和地球大气层的过程的集合。亚暴对近地环境有重大影响，并影响到人类的许多系统。它们对人类活动构成的自然危害正变得越来越重要。不幸的是，亚暴的成因，特别是最具破坏性的阶段，即膨胀阶段，尚不清楚。近五年来，最流行的解释亚暴的物理模型是近地中性线（NENL）模型。该模型在组织近地等离子体层的大量观测方面取得了显著的成功，并成功地预测了磁尾等离子体的存在及其性质，磁尾等离子体是地球在亚风暴期间释放到太阳风中的等离子体和磁场气泡。许多新的观测结果没有被纳入NENL模型，而且似乎很难这样做。亚暴似乎在午夜时分开始膨胀，非常接近同步轨道（6.6 Re），并向外传播到彗尾。这种扩展开始于闭合的准偶极场线，位于交叉尾电流片的内缘。随后，它通过扰乱尾电流向尾部移动，将其沿着磁力线转移到极光电离层。目前正在开发一种新的模型，称为当前干扰（CD）模型来解释这些观察结果。该模型的某些版本预测了尾等离子体片和磁场的动力学，这与NENL模型的预测和它所基于的观测结果截然相反。这种幸运的情况应该很容易解决。模型与观测结果或一致或不一致，我们应该能够在两者之间做出决定。建议重新检查近地等离子体层的观测结果，并将它们置于一个更坚实的基础上，以便有可能建立一个合理的亚暴膨胀阶段的物理模型。为此，加州大学洛杉矶分校已有的数据以及其他研究者提供的额外数据将用于研究与亚暴发生有关的现象的发生频率和时间延迟问题。亚暴发生的其他地面指标还包括卫星极光图像的变亮、中纬度正凹、Pi 2脉动爆发、同步磁场倾角最大值以及同步轨道上的无色散等离子体注入。要检查的特征包括磁场、粒子通量、等离子体压力、等离子体流量和温度的变化。基于这些结果，将考虑不同的模型及其在解释观测结果方面的成功。