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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Rethinking the polar cap: Eccentric dipole structuring of ULF power at the highest corrected geomagnetic latitudes
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Rethinking the polar cap: Eccentric dipole structuring of ULF power at the highest corrected geomagnetic latitudes

机译：重新思考极极帽：在最高校正地磁纬度下ULF功率的偏心偶极结构

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The day-to-day evolution and statistical features of Pc3-Pc7 band ultralow frequency (ULF) power throughout the southern polar cap suggest that the corrected geomagnetic (CGM) coordinates do not adequately organize the observed hydromagnetic spatial structure. It is shown that that the local-time distribution of ULF power at sites along CGM latitudinal parallels exhibit fundamental differences and that the CGM latitude of a site in general is not indicative of the site’s projection into the magnetosphere. Thus, ULF characteristics observed at a single site in the polar cap cannot be freely generalized to other sites of similar CGM latitude but separated in magnetic local time, and the inadequacy of CGM coordinates in the polar cap has implications for conjugacy/mapping studies in general. In seeking alternative, observationally motivated systems of “polar cap latitudes,” it is found that eccentric dipole (ED) coordinates have several strengths in organizing the hydromagnetic spatial structure in the polar cap region. ED latitudes appear to better classify the local-time ULF power in both magnitude and morphology and better differentiate the “deep polar cap” (where the ULF power is largely UT dependent and nearly free of local-time structure) from the “peripheral polar cap” (where near-magnetic noon pulsations dominate at lower and lower frequencies as one increases in ED latitude). Eccentric local time is shown to better align the local-time profiles in the magnetic east component over several PcX bands but worsen in the magnetic north component. It is suggested that a hybrid ED-CGM coordinate system might capture the strengths of both CGM and ED coordinates. It is shown that the local-time morphology of median ULF power at high-latitude sites is dominantly driven by where they project into the magnetosphere, which is best quantified by their proximity to the low-altitude cusp on the dayside (which is not necessarily quantified by a site’s CGM latitude), and that variations in the local-time morphology at sites similar in ED latitude are due to both geographic local-time control (relative amplification or dampening by the diurnal variation in the local ionospheric conductivity) and geomagnetic coastal effects (enhanced power in a coastally mediated direction). Regardless of cause, it is emphasized that the application of CGM latitudes in the polar cap region is not entirely meaningful and likely should be dispensed with in favor of a scheme that is in better accord with the observed hydromagnetic spatial structure.
机译：在整个南极极地地区，Pc3-Pc7波段超低频（ULF）功率的日常演变和统计特征表明，校正后的地磁（CGM）坐标不能充分组织观察到的水磁空间结构。结果表明，沿CGM纬度平行线的站点的ULF功率的本地时间分布显示出根本差异，并且站点的CGM纬度通常并不表示该站点向磁层的投影。因此，在极地帽的单个位置观察到的ULF特性不能自由地推广到CGM纬度类似的其他位置，但在磁局部时间上是分开的，极地帽中CGM坐标的不足通常会影响共轭/映射研究。在寻找“极帽纬度”的替代性观测动力系统时，发现偏心偶极子（ED）坐标在组织极帽地区的水磁空间结构方面具有多种优势。 ED纬度似乎可以更好地在大小和形态上对本地时间ULF功率进行分类，并且可以更好地区分“深极帽”（其中ULF功率很大程度上取决于UT且几乎没有本地时间结构）与“外围极帽” ”（其中随着ED纬度的增加，近磁中午脉动在越来越低的频率上占主导地位）。偏心本地时间显示为在几个PcX波段上更好地对准了东部磁性成分中的本地时间剖面，但在北部磁性成分中却更差了。建议使用混合ED-CGM坐标系来捕获CGM和ED坐标的强度。结果表明，高纬度地点的中频ULF功率的本地时间形态主要由它们进入磁层的位置驱动，这可以通过它们与白天低海拔尖端的接近程度来最好地量化（不一定）由某地点的CGM纬度量化），而与ED纬度类似的地点的本地时间形态变化是由于地理本地时间控制（相对电离层电导率日变化引起的相对放大或衰减）和地磁沿海效果（沿海力量增强的力量）。无论出于何种原因，都应强调指出，在极地盖区应用CGM纬度并不完全有意义，应放弃使用CGM纬度，而应采用与实测水磁空间结构更好地匹配的方案。

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