Thanks to mapping missions, like Ørsted, CHAMP, and Swarm, we have gained a detailed understanding of the geomagnetic field. High‐resolution models like POMME, GRIMM, or CHAOS are able to describe the main parts of the Earth's magnetic field reliably. These models represent well contributions from the core and crustal fields. But their validity of describing magnetospheric field effects is limited to low activity periods (Kp ~ 0–2). Here, we study the differences between CHAMP magnetic observations and the predictions from CHAOS‐6‐x9, a recent version, outside this validity range. Systematic residuals appear at times of elevated activity. Mean amplitudes at the equator grow up to 12 nT around 20 hr magnetic local time for magnetic activity around Kp = 4.7. Negative residuals are obtained in the evening to midnight sector and positive ones in the morning. A seasonal dependence of the magnetospheric currents causes more negative deflections of the residuals in the winter than in the summer hemisphere. This hemispheric asymmetry cannot be accounted for by a degree 1 spherical harmonics function. A surprising observation is that the residuals show a clear longitude dependent pattern, which changes with local time. The analysis reveals that this feature can be interpreted as a Universal Time dependence of the residuals with a peak‐to‐peak amplitude of about 8 nT and a period of 12 hr at an activity level of Kp = 4.7. All these results call for a better parameterization of the magnetospheric current effects in a geomagnetic field model that is reliable at least up to moderate activity levels.

中文翻译：

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磁活动增强期间磁层电流引起的CHAOS-6地磁场模型的残差

得益于Ørsted，CHAMP和Swarm等制图任务，我们对地磁场有了详细的了解。诸如POMME，GRIMM或CHAOS之类的高分辨率模型能够可靠地描述地球磁场的主要部分。这些模型代表了核心和地壳领域的良好贡献。但是，它们描述磁层磁场效应的有效性仅限于低活动周期（Kp〜0–2）。在这里，我们研究了CHAMP磁观测值与CHAOS-6-x9（最新版本）的预测在此有效范围之外的差异。活动性升高时会出现系统残留。对于Kp = 4.7左右的磁性活动，在20个小时的磁性局部时间处，赤道的平均振幅增长到12 nT。负残差在晚上到午夜时段获得，正残差在早上获得。磁层电流的季节依赖性导致冬季的残差比夏季半球的负偏斜更大。这种半球不对称性不能通过1度球谐函数来解决。令人惊讶的观察是，残差显示出明显的经度相关模式，随当地时间而变化。分析表明，此特征可以解释为残差的通用时间依赖性，其活动水平为Kp = 4.7时，其峰峰值幅度约为8 nT，周期为12 hr。所有这些结果都要求在地磁场模型中更好地参数化磁层电流效应，至少在中等活动水平下该参数是可靠的。磁层电流的季节依赖性导致冬季的残差比夏季半球的负偏斜更大。这种半球不对称性不能通过1度球谐函数来解决。令人惊讶的观察是，残差显示出明显的经度相关模式，随当地时间而变化。分析表明，该特征可以解释为残差的通用时间依赖性，其活动水平为Kp = 4.7时，其峰峰值幅度约为8 nT，周期为12 hr。所有这些结果都要求在地磁场模型中更好地参数化磁层电流效应，至少在中等活动水平下该参数是可靠的。磁层电流的季节依赖性导致冬季的残差比夏季半球的负偏斜更大。这种半球不对称性不能通过1度球谐函数来解决。令人惊讶的观察是，残差显示出明显的经度相关模式，随当地时间而变化。分析表明，该特征可以解释为残差的通用时间依赖性，其活动水平为Kp = 4.7时，其峰峰值幅度约为8 nT，周期为12 hr。所有这些结果都要求在地磁场模型中更好地参数化磁层电流效应，至少在中等活动水平下该参数是可靠的。