A global climatological model of extreme geomagnetic field fluctuations
A global climatological model of extreme geomagnetic field fluctuations
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DOI：
10.1051/swsc/2020008
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发表时间：
2020-02-18
影响因子：
3.3
通讯作者：
Thomson, Alan W. P.
中科院分区：
文献类型：
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作者：
Rogers, Neil C.;Wild, James A.;Thomson, Alan W. P.
本文提出了一个多参数的全球统计模型的极端水平地磁场波动（dB（H）/dt），这是一个有用的输入模型评估的地磁感应电流在地面基础设施的风险。将广义帕累托（GP）分布拟合至以下各项的1分钟测量值：|dB（H）/dt|根据125个磁力计（每个站点平均28年的数据）和重现期（RP）为5至500年的重现水平（RL）预测。分析函数的最大似然GP模型参数和导出的RL的配置文件作为一个功能的校正地磁纬度，λ。在GP形状参数和RL中均观察到尖锐的峰，|Lambda| = 53度在两个半球，表明一个尖锐的赤道极限的极光电喷流区域。在极尖的向阳面极向区域，RLs也强烈增加（|Lambda|> 75度），RP> 100年。我们描述了如何通过对以下事件的发生概率进行建模来进一步完善GP模型：|dB（H）/dt|超过第99.97百分位数作为一个月的函数，磁当地时间，和磁场波动的方向，分贝（H），并证明这些模式的发生密切配合已知的极光亚暴爆发，超低频Pc 5波活动，（风暴）突然开始的影响模式。随行星际磁场（IMF）方向的发生概率分布的变化揭示了驱动极端电离层电流性质的进一步细节。|dB（H）/dt|这些波动，如极尖位置的变化和罗素-麦弗隆效应解释的季节性变化。
This paper presents a multi-parameter global statistical model of extreme horizontal geomagnetic field fluctuations (dB(H)/dt), which are a useful input to models assessing the risk of geomagnetically induced currents in ground infrastructure. Generalised Pareto (GP) distributions were fitted to 1-min measurements of |dB(H)/dt| from 125 magnetometers (with an average of 28 years of data per site) and return levels (RL) predicted for return periods (RP) between 5 and 500 years. Analytical functions characterise the profiles of maximum-likelihood GP model parameters and the derived RLs as a function of corrected geomagnetic latitude, lambda. A sharp peak in both the GP shape parameter and the RLs is observed at |lambda| = 53 degrees in both hemispheres, indicating a sharp equatorward limit of the auroral electrojet region. RLs also increase strongly in the dayside region poleward of the polar cusp (|lambda| > 75 degrees) for RPs > 100 years. We describe how the GP model may be further refined by modelling the probability of occurrences of |dB(H)/dt| exceeding the 99.97th percentile as a function of month, magnetic local time, and the direction of the field fluctuation, dB(H), and demonstrate that these patterns of occurrence align closely to known patterns of auroral substorm onsets, ULF Pc5 wave activity, and (storm) sudden commencement impacts. Changes in the occurrence probability profiles with the interplanetary magnetic field (IMF) orientation reveal further details of the nature of the ionospheric currents driving extreme |dB(H)/dt| fluctuations, such as the changing location of the polar cusp and seasonal variations explained by the Russell-McPherron effect.