Earth's dipole magnetic moment M is known to decrease by ∼9% over the past 150 years. It has been argued that the decrease in M makes the near‐Earth space environment different. We investigated how the change in M affects the development of an auroral substorm by increasing and decreasing M by a factor of 1.5 in global magnetohydrodynamics simulation. The ionospheric conductivity decreases with increasing M, in accordance with the aid of empirical relations. When we imposed the southward interplanetary magnetic field, an auroral substorm took place regardless of M, but its development depends largely on M. When M is lower, (1) the expansion onset takes place later, (2) the auroral electrojet develops slowly, and (3) the maximum auroral electrojet increases. The first two consequences are probably associated with the slow magnetospheric convection as manifested by the polar cap potential drop. The third consequence is associated with the nonlinear dependence of substorm‐associated field‐aligned currents (FACs) on the ionospheric conductivity. The maximum values of the westward auroral electrojet and the net FACs increase with decreasing M, whereas the incident magnetic energy into the magnetosphere decreases with decreasing M. This implies that the efficiency of the generation of the substorm‐associated FACs increases with decreasing M. It is also found that, for the lower M‐value, the auroral oval shifts equatorward during the growth phase and expands more equatorward and poleward during the expansion phase. Evolution of substorms depends largely on the value of Earth's dipole moment and the ionospheric conductivity.

中文翻译：

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极光亚暴如何取决于地球的偶极磁矩？

已知地球的偶极磁矩M在过去150年中下降了约9％。有人认为，M的减小使近地空间环境有所不同。我们研究如何在变化中号通过增加和减少会影响极光亚暴的发展中号为1.5，全球磁流体模拟的一个因素。根据经验关系，电离层电导率随M的增加而降低。当我们实行的南行星际磁场，极光亚暴发生，无论中号，但其发展在很大程度上取决于中号。当M较低，（1）扩张开始较晚，（2）极光电喷射缓慢发展，（3）最大极光电喷射增加。前两个后果可能与磁极层对流缓慢有关，这由极帽电位下降所表明。第三个结果与亚暴相关的场对准电流（FAC）对电离层电导率的非线性相关性有关。随着M的减小，向西极光电喷和净FAC的最大值增加，而进入磁层的磁能随M的减小而减小。这意味着与亚暴有关的FAC的生成效率随着M的降低而增加。还发现，对于较低的M值，极光椭圆在生长阶段向赤道移动，在扩展阶段向赤道和极向扩展。亚暴的演变很大程度上取决于地球的偶极矩和电离层电导率的值。