The Cusp for High and Low Merging Rates
The Cusp for High and Low Merging Rates
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高合并率和低合并率的尖端
DOI：
10.1029/2007ja012353
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发表时间：
2007
影响因子：
--
通讯作者：
F. Rich
中科院分区：
文献类型：
--
作者：
P. Newell;S. Wing;F. Rich
[1]传统上区分向北和向南行星际磁场（IMF）条件的尖点是有缺陷的，因为许多（如果不是大多数）“向北”IMF尖点遭遇非常类似于向南IMF遭遇。部分出于这个原因，国际货币基金组织的“南向”风口比“北向”风口更经常受到审查。“最近，纽韦尔等人（2007年）表明，磁层顶合并率dΦMP/dt比Bz（或Bs）更好地预测了尖点纬度。在这里，我们调查在何种程度上高，低合并率条件更好地分离尖点遇到相互不同的类。事实上，高合并率尖瓣（dΦMP/dt > 2* dΦMP/dt的尖瓣）与低合并率尖瓣（dΦMP/dt < 0.5 * dΦMP/dt的尖瓣）在几个定量甚至定性方面存在差异。高能（几十千电子伏）离子，显然是磁层起源，不延伸到高合并率的尖点，但经常为低合并率。然而，离子的色散曲线，显然磁鞘起源，延伸到几个千电子伏的高合并率，但只有1-2千电子伏的低合并率。低合并率条件下，尖点的当地时间范围为2.33小时MLT，高合并率条件下为3.45小时MLT。所有高合并率尖点都显示出清晰的前向色散（随着纬度的增加能量下降），在该色散内具有低能离子截止。低合并率的尖点很少表现出正向色散，但大约一半或稍少，在尖点的极向边缘表现出反向色散（能量随着纬度的降低而下降）。低能离子截止在低合并率尖点主要只发生在反向分散。合并率高的病例出现“双”尖，有的在纬向分离非常明显，合并率低的病例则无。高合并率的情况下，通常也有一个“阴影”的电子只有降水的区域，大致极地雨的能量和强度，直接位于赤道的主要尖点。对于低合并率的条件下，该地区立即赤道的尖点（主磁鞘离子人口）包含离子以及电子，并形成边界层。
[1] The traditional distinction between the cusp for northward and southward interplanetary magnetic field (IMF) conditions is deficient in that many, if not most, “northward” IMF cusp encounters closely resemble southward IMF encounters. Partly for that reason, “southward” IMF cusps have been far more often examined than “northward. ” Recently, Newell et al. (2007) showed that the magnetopause merging rate, dΦMP/dt, much better predicts cusp latitude than does Bz (or Bs). Here, we investigate the extent to which high and low merging rate conditions better separates cusp encounters into mutually distinct classes. Indeed, high merging rate cusps (those with dΦMP/dt > 2* 〈dΦMP/dt〉) differ from low merging rate cusps (those with dΦMP/dt < 0.5〈dΦMP/dt〉) in several quantitative and even qualitative ways. High-energy (tens of keV) ions, apparently of magnetospheric origin, do not extend into the high merging rate cusp but frequently do for low merging rates. However, the dispersion curve for ions, apparently of magnetosheath origin, extends to several keV for high merging rates but only to 1–2 keV for low merging rates. The local time extent of the cusp is 2.33 hours MLT for low merging rate conditions and 3.45 hours MLT for high merging rate conditions. All high merging rate cusps show clear forward dispersion (declining energy with increasing latitude) with low-energy ion cutoffs within that dispersion. Low merging rates cusps rarely show forward dispersion, but about half, or slightly less, show reverse dispersion (declining energy with decreasing latitude) at the poleward edge of the cusp. Low-energy ion cutoffs in the low-merging rate cusp primarily occur only within that reverse dispersion. “Double” cusps, some with very clear latitudinal separation, occur in some high merging rate cases, but no low merging rate cases. The high merging rates cases also typically have a “shadow” region of electron-only precipitation at roughly polar rain energies and intensities, lying immediately equatorward of the main cusp. For low-merging rate conditions, the region immediately equatorward of the cusp (main magnetosheath ion population) contains ions as well as electrons, and forms a boundary layer.