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Suppression of the dayside magnetopause surface modes

机译：抑制日间磁更年期表面模式

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Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (frequency about 1–2 mHz). However, the search for a ground signature of these modes has not provided encouraging results. The comparison of multi-instrument data from Svalbard with the latitudinal structure of Pc5-6 pulsations, recorded by magnetometers covering near-cusp latitudes, has shown that often the latitudinal maximum of pulsation power occurs about 2–3° deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). The OCB proxy was determined from SuperDARN radar data as the equatorward boundary of enhanced width of a return radio signal. The OCB-ULF correspondence is further examined by comparing the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the meridian scanning photometer. In most analyzed events, the “epicenter” of Pc5-6 power is at 1–2° lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or with oscillations of the last field line. A lack of ground response to these modes beneath the ionospheric projection of OCB seems puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the excitation efficiency. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of its eigenfrequency. A solution of this problem predicts a substantial deterioration of resonant properties of MHD resonator even under a relatively low level of back-ground fluctuations. This effect may explain why there is no ground response to magnetopause surface modes or oscillations of the last field line at the OCB latitude, but it can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure.
机译：建议将磁更震层表面本征模式作为Pc5-6频带（频率约1-2 mHz）中日间高纬度宽带脉动的潜在来源。但是，寻找这些模式的地面信号并没有提供令人鼓舞的结果。来自斯瓦尔巴群岛的多仪器数据与Pc5-6脉动的纬度结构的比较（由覆盖近尖端纬度的磁力计记录）表明，脉动功率的纬度最大值通常比磁层深约2-3°。日间开闭场线边界（OCB）。 OCB代理根据SuperDARN雷达数据确定为回程无线电信号增强宽度的赤道边界。通过将近午脉动功率的纬度分布与子午扫描光度计发出的极光红色发射的赤道边缘进行比较，进一步检查了OCB-ULF对应关系。在大多数分析过的事件中，Pc5-6功率的“中心点”比光学OCB代理低1-2度。因此，白天的Pc5-6脉动不能与绝经表面模式的地面图像或最后一条磁力线的振荡相关联。在OCB的电离层投影以下，这些模式缺乏地面响应似乎令人困惑。作为一种可能的解释，我们建议磁层顶区附近的外部磁层的高变化性可能会抑制激发效率。为了量化这个假设，我们考虑一个驱动场线谐振器，该谐振器由共轭电离层终止，其固有频率随机波动。该问题的解决方案预测，即使在相对较低水平的背景波动下，MHD谐振器的谐振特性也会大大降低。该效应可以解释为什么对OCB纬度的绝磁表面模式或最后一条磁场线的振荡没有地面响应，但是可以在较低的纬度上看到更规则和稳定的磁和等离子体结构。

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