Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms
Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms
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DOI：
10.1029/2004ja010798
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发表时间：
2005-03-15
影响因子：
2.8
通讯作者：
Sitnov, MI
中科院分区：
文献类型：
--
作者：
Tsyganenko, NA;Sitnov, MI
[1]这项工作建立在并扩展了我们以前的努力（Tsyganenko等人，2003年），利用1996 - 2000年37次重大事件期间获得的空间磁力计数据以及对太阳风和行星际磁场的同时观测，建立一个内磁层风暴时地磁场的动力学模型。该方法的本质是从数据中得出的时间变化的所有主要电流系统的远地磁场在整个风暴周期，使用一个简单的模型，其增长和衰减。外部磁场的每个主要来源（磁层顶、交叉尾电流片、轴对称和部分环电流以及Birkeland电流系统）都由一个单独的变量驱动，该变量计算为地球效应参数N-lambda V-beta B-s（gamma）的组合的时间积分，其中N、V和B-s分别是太阳风密度、速度和IMF向南分量的幅度。在这种方法中，我们假设每个源有其单独的弛豫时间尺度和剩余的安静时间的强度，其部分贡献的总场取决于整个历史的外部驱动的磁暴期间的磁层。此外，假设在具有异常强的外部驱动的特大风暴期间，主要场源的幅度饱和。模型场源的所有参数，包括它们的大小，几何特征，太阳风/IMF驱动函数，衰减时间尺度和饱和阈值，被视为自由变量，其值来自数据。作为一个独立的一致性检验，我们计算了预期的DST变化的基础上，在地球表面的模型输出，并将其与实际观测到的DST。尽管拟合中使用的航天器数据中有90%是在同步轨道及更远的轨道上获得的，而这些数据中只有3.7%来自距离2.5
[1] This work builds on and extends our previous effort (Tsyganenko et al., 2003) to develop a dynamical model of the storm-time geomagnetic field in the inner magnetosphere, using space magnetometer data taken during 37 major events in 1996-2000 and concurrent observations of the solar wind and interplanetary magnetic field (IMF). The essence of the approach is to derive from the data the temporal variation of all major current systems contributing to the distant geomagnetic field during the entire storm cycle, using a simple model of their growth and decay. Each principal source of the external magnetic field (magnetopause, cross-tail current sheet, axisymmetric and partial ring currents, and Birkeland current systems) is driven by a separate variable, calculated as a time integral of a combination of geoeffective parameters N-lambda V-beta B-s(gamma), where N, V, and B-s are the solar wind density, speed, and the magnitude of the southward component of the IMF, respectively. In this approach we assume that each source has its individual relaxation timescale and residual quiet-time strength, and its partial contribution to the total field depends on the entire history of the external driving of the magnetosphere during a storm. In addition, the magnitudes of the principal field sources were assumed to saturate during extremely large storms with abnormally strong external driving. All the parameters of the model field sources, including their magnitudes, geometrical characteristics, solar wind/IMF driving functions, decay timescales, and saturation thresholds, were treated as free variables, and their values were derived from the data. As an independent consistency test, we calculated the expected Dst variation on the basis of the model output at Earth's surface and compared it with the actual observed Dst. A good agreement (cumulative correlation coefficient R = 0.92) was found, in spite of the fact that similar to 90% of the spacecraft data used in the fitting were taken at synchronous orbit and beyond, while only 3.7% of those data came from distances 2.5