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The contribution of magnetospheric currents to ground magnetic perturbation during geomagnetic storms.

机译：地磁暴期间磁层电流对地面磁扰动的贡献。

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摘要

A geomagnetic storm is triggered in response to a disturbance in the solar wind. The earth's ring current gets energized during a geomagnetic storm, which leads to a decrease in the horizontal component of the geomagnetic field on the earth's surface. The Disturbance Storm Time (Dst) index, which is a measure of the intensity of the ring current, is calculated by taking the average of this decrease in the horizontal intensity across four low latitude magnetometer stations and removing the quiet time secular variations. The rate of decrease of the Dst index is an indicator of the deenergization of the ring current particles. But there are several issues with the Dst measurement as a proxy of the ring current energy. In particular, the percentage contribution of the tail current effect to the Dst index is still debated. In this work, an effort has been made to separate and quantify the possible contribution of the tail current to the Dst index. The relative contribution for a selected set of storms for which the interplanetary magnetic field turned northward abruptly after the peak in Dst was observed is estimated.;The WINDMI model of the nightside magnetosphere is used to investigate the contributions of ring current, magnetotail current, and magnetopause current on the observed two-phase decay of the Dst index. The role of different solar wind magnetosphere coupling functions on the Dst index calculated by the WINDMI model is also investigated. The performance of four other coupling functions in addition to the rectified vBs is evaluated. These coupling functions emphasize different physical mechanisms to explain the energy transfer into the magnetosphere due to solar wind velocity, dynamic pressure, magnetic field, and Mach number. One coupling function is due to Siscoe, another by Borovsky, and two by Newell. The results indicate that for a majority of cases, at most only vx, By, and Bz are needed to sufficiently account for the supply of energy to the ring current and geotail current components that contribute to the Dst index.;The capabilities of the WINDMI model to reliably determine the state of the global magnetosphere are improved by employing the the Magnetotail (MT) index as a measurement constraint during large geomagnetic storms. The MT index is used as a proxy for the strength of the magnetotail current in the magnetosphere. The inclusion of the MT index as an optimization constraint in turn increases our confidence that the ring current contribution to the Dst index calculated by the WINDMI model is correct during large geomagnetic storms. To improve the models prediction of AL index, we also modify the ionospheric conductivity and fit to two substorms.;The rate of reduction of convection in the magnetotail for some of these storms is numerically simulated by using inner magnetospheric models like the Fok Ring Current (FRC) and the Rice Convection Model along with the global BATSRUS model at the community coordinated modeling center. Model results are compared against magnetometer data by creating movie maps from several low-latitude magnetometer stations.;The results indicate the contribution from the tail current to the Dst is important. In addition, the reduction of the cross-tail current during substorm dipolarization is predicted by the measured isotropic boundary locations. Several well known phenomena are identified in the magnetometer movie maps.
机译：响应于太阳风的干扰而触发地磁风暴。在地磁风暴期间，地球的环形电流被激励，这导致地表上地磁场的水平分量减小。扰动风暴时间（Dst）指数是对环形电流强度的一种度量，它是通过取四个低纬度磁力计测站上水平强度下降的平均值并消除静默时间长期变化来计算的。 Dst指数的降低速率是环电流粒子断电的指标。但是，Dst测量作为环电流能量的替代存在一些问题。特别是，尾流效应对Dst指数的百分比贡献仍在争论中。在这项工作中，已做出努力来分离和量化尾电流对Dst指数的可能贡献。估计了观测到Dst峰值后行星际磁场突然向北偏向的一组选定风暴的相对贡献。;使用夜侧磁层的WINDMI模型研究环流，磁尾电流和磁层顶电流对Dst指数两相衰减的影响。还研究了不同的太阳风磁层耦合函数对WINDMI模型计算的Dst指数的作用。除了校正的vB之外，还评估了其他四个耦合功能的性能。这些耦合功能强调了不同的物理机制来解释由于太阳风速，动态压力，磁场和马赫数导致的能量转移到磁层。一种耦合功能归功于Siscoe，另一种归功于Borovsky，另外两项归功于Newell。结果表明，在大多数情况下，最多仅需要vx，By和Bz即可充分考虑向构成Dst指数的环流和地尾电流分量的能量供应。在大地磁暴期间，通过使用磁尾（MT）指数作为测量约束条件，改进了可靠确定全球磁层状态的模型。 MT指数用作磁层中磁尾电流强度的代表。将MT指数作为优化约束包括在内，反过来增加了我们的信心，即在大地磁风暴期间，由WINDMI模型计算出的环流对Dst指数的贡献是正确的。为了改善模型对AL指数的预测，我们还修改了电离层的电导率并适合于两次亚暴。;通过使用内部磁层模型（如霍克环流（ FRC）和莱斯对流模型以及全球BATSRUS模型在社区协调建模中心进行。通过从几个低纬度磁力计站点创建电影地图，将模型结果与磁力计数据进行比较。；结果表明，尾电流对Dst的贡献很重要。此外，通过测得的各向同性边界位置可以预测亚风暴双极化期间交叉尾电流的减少。在磁力计电影图中确定了几种众所周知的现象。

著录项

  • 作者

    Patra, Swadesh.;

  • 作者单位

    Utah State University.;

  • 授予单位 Utah State University.;
  • 学科 Engineering Electronics and Electrical.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 182 p.
  • 总页数 182
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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