Transfer entropy and cumulant-based cost as measures of nonlinear causal relationships in space plasmas: applications to Dst
Transfer entropy and cumulant-based cost as measures of nonlinear causal relationships in space plasmas: applications to Dst
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DOI：
10.5194/angeo-36-945-2018
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发表时间：
2018-07-02
影响因子：
1.9
通讯作者：
Camporeale, Enrico
中科院分区：
文献类型：
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作者：
Johnson, Jay R.;Wing, Simon;Camporeale, Enrico
众所周知，磁层对太阳风的响应是非线性的。信息理论工具，如互信息，传递熵，和基于累积量的分析能够表征系统中的非线性。使用累积量为基础的成本，我们表明，非线性意义的D-ST峰在3-12小时滞后，可以归因于VBs，这也表现出类似的行为。然而，在滞后25，50和90小时的峰值的非线性意义可以归因于内部动态，这可能与环电流的松弛。这些峰在VBs的线性和非线性自显著性中不存在。我们的分析与互信息和转移熵表明，这两种方法可以建立有很强的相关性和转移的信息从V-SW到D-ST的时间尺度是一致的，从累积量为基础的分析。然而，互信息也表明，从D-st到V-sw的反向方向存在很强的相关性，这是违反直觉的。相反，转移熵表明，从D-st到V-sw没有或很少有信息转移，正如预期的那样，因为是太阳风驱动磁层，而不是相反。我们的案例研究表明，这些信息理论工具是非常有用的空间物理研究，因为这些工具可以发现非线性动力学，不能看到与传统的分析和模型，假设线性关系。
It is well known that the magnetospheric response to the solar wind is nonlinear. Information theoretical tools such as mutual information, transfer entropy, and cumulant-based analysis are able to characterize the nonlinearities in the system. Using cumulant-based cost, we show that nonlinear significance of D-st peaks at 3-12 h lags that can be attributed to VBs, which also exhibits similar behavior. However, the nonlinear significance that peaks at lags 25, 50, and 90 h can be attributed to internal dynamics, which may be related to the relaxation of the ring current. These peaks are absent in the linear and nonlinear self-significance of VBs. Our analysis with mutual information and transfer entropy shows that both methods can establish that there are strong correlations and transfer of information from V-sw to D-st at a timescale that is consistent with that obtained from the cumulant-based analysis. However, mutual information also shows that there is a strong correlation in the backward direction, from D-st to V-sw, which is counterintuitive. In contrast, transfer entropy shows that there is no or little transfer of information from D-st to V-sw, as expected because it is the solar wind that drives the magnetosphere, not the other way around. Our case study demonstrates that these information theoretical tools are quite useful for space physics studies because these tools can uncover nonlinear dynamics that cannot be seen with the traditional analyses and models that assume linear relationships.