Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 2. Response to solar wind power input and relationships with solar wind dynamic pressure and magnetospheric flux transport
Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 2. Response to solar wind power input and relationships with solar wind dynamic pressure and magnetospheric flux transport
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DOI：
10.1051/swsc/2020033
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发表时间：
2020-07-16
影响因子：
3.3
通讯作者：
Coxon, John C.
中科院分区：
文献类型：
--
作者：
Lockwood, Mike;McWilliams, Kathryn A.;Coxon, John C.
这是研究磁层半年、年度和世界时 (UT) 变化的系列论文中的第二篇。我们提出了各种经验结果的集合，可用于约束这些变化的理论和建模。对两年跨极电压数据的初步研究表明，磁层通量环流存在半年变化；然而，它的幅度不如地磁活动的幅度大，这与后者随跨极电压呈现非线性（二次）变化的情况一致。我们发现，在地磁活动 UT 变化持续最小期间，大约 2 到 10 UT 之间，观测到的跨极电压也持续下降，这可能部分是由夜侧交叉尾电流片中的重联电压下降引起的。我们使用 1995 年以来的行星际数据研究地磁活动对输入磁层的估计功率的响应，在此期间数据相对没有数据间隙。我们发现响应延迟随时间变化没有一致的变化，并且使用最佳滞后，我们表明 F 年频谱图的变化模式对于地磁活动和磁层功率输入非常相似，无论是平均值还是大事件的发生。 Russell-McPherron (R-M) 机制被证明是这种行为的核心驱动因素。然而，（R-M）对磁层功率输入的影响很小，并且地磁响应的半年变化存在非线性放大，使得IMFB（Y）分量的“有利”和“不利”极性之间输入磁层P（α）的功率非常小的不对称性产生极大放大的地磁响应。分析有力地表明，这种放大与太阳风动态压力及其在挤压近地尾部从而调节从太阳风提取的能量的存储和释放方面的作用有关。在本文中，我们表明，在 P(alpha) 与 theamindex 的拟合残差中发现了分点模式，并且 theamfit 残差中这些分点模式的幅度随太阳风动态压力线性增加。类似地，在这些拟合残差中也发现了 UT 变化，并且其幅度也随着太阳风动态压力而增加。
This is the second in a series of papers that investigate the semi-annual, annual and Universal Time (UT) variations in the magnetosphere. We present a varied collection of empirical results that can be used to constrain theories and modelling of these variations. An initial study of two years' data on transpolar voltage shows that there is a semi-annual variation in magnetospheric flux circulation; however, it is not as large in amplitude as that in geomagnetic activity, consistent with the latter showing a non-linear (quadratic) variation with transpolar voltage. We find that during the persistent minimum of theUTvariation in geomagnetic activity, between about 2 and 10 UT, there is also a persistent decrease in observed transpolar voltage, which may be, in part, caused by a decrease in reconnection voltage in the nightside cross-tail current sheet. We study the response of geomagnetic activity to estimated power input into the magnetosphere using interplanetary data from 1995 onwards, an interval for which the data are relatively free of data gaps. We find no consistent variation in the response delay with time-of-yearFand, using the optimum lag, we show that the patterns of variation inF-year spectrograms are very similar for geomagnetic activity and power input into the magnetosphere, both for average values and for the occurrence of large events. The Russell-McPherron (R-M) mechanism is shown to be the central driver of this behaviour. However, the (R-M) effect on power input into the magnetosphere is small and there is a non-linear amplification of the semi-annual variation in the geomagnetic response, such that a very small asymmetry in power input into the magnetosphereP(alpha)between the "favourable" and "unfavourable" polarities of the IMFB(Y)component generates a greatly amplified geomagnetic response. The analysis strongly indicates that this amplification is associated with solar wind dynamic pressure and its role in squeezing the near-Earth tail and so modulating the storage and release of energy extracted from the solar wind. In this paper, we show that the equinoctial pattern is found in the residuals of fits ofP(alpha)to theamindex and that the amplitude of these equinoctial patterns in theamfit residuals increases linearly with solar wind dynamic pressure. Similarly, theUTvariation inamis also found in these fit residuals and also increases in amplitude with solar wind dynamic pressure.