Quasi‐steady drift paths in a model magnetosphere with AMIE electric field: Implications for ring current formation
Quasi‐steady drift paths in a model magnetosphere with AMIE electric field: Implications for ring current formation
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AMIE 电场模型磁层中的准稳态漂移路径：对环电流形成的影响
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发表时间：
2003
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影响因子：
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通讯作者：
L. Lyons
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作者：
Margaret W. Chen;M. Schulz;G. Lu;L. Lyons
[1]最近的测量表明，磁暴主要阶段的磁层对流电场在空间结构上比通常用于模拟风暴环流形成的电场复杂得多。为了研究这种更真实的风暴时电场对磁层带电粒子的输运效应，我们用一个简单的磁场模型解析地映射了电离层电动力学(AMIE)电势函数的同化模型，在1997-1998年的几个磁暴期间和2000年7月的极大磁暴期间。对于0到30 MeV/G(代表冷等离子体、环电流和辐射带离子和电子的赤道镜像)的第一不变值，我们计算了相应的恒定哈密顿量(动能加势能)的等高线。如果电场在时间上确实是恒定的，这些赤道等高线将构成漂移路径。因此，我们计算了相应粒子在特定时间后沿着这种准漂移路径漂移了多远，并将这些准漂移特性与从简单的对流电场半经验模型获得的特性进行了比较。我们发现风暴时赤道准漂移路径之间有相当大的变异性，反映了已知的Amie等位势的变异性。简化电场模型中赤道准漂移的模式(通过构造)是关于子午线对称的。在风暴的主要阶段，AMIE产生的赤道电场往往在夜间几个小时宽的MLT扇区最强。这种浓度的胺等电势为离子的快速传输(需要∼20-30分钟)提供了通道，第一不变值代表环电流布居的离子在黄昏时从夜侧中性线到低L值(∼3-4)，在那里形成了部分环电流。在2000年7月15日极大的“巴士底日”风暴期间(最小DST=−300nT)，从AMIE得到的漂移图样显示离子穿透到低至L∼2。这种环流离子的深度穿透有助于解释在风暴期间观察到的非常强的环流。准稳态漂移特性有助于我们预测更真实的电场模型对导致风暴环流形成的粒子漂移的影响。
[1] Recent measurements show that magnetospheric convection electric fields during the main phases of magnetic storms are much more complicated in spatial structure than the electric fields that have generally been used to model formation of the stormtime ring current. To investigate the transport effects of such more realistic stormtime electric fields on magnetospheric charged particles, we map the Assimilative Model of Ionospheric Electrodynamics (AMIE) electric potential functions analytically with a simple magnetic field model at selected times of interest during several magnetic storms from 1997–1998 and during the extremely large storm of July 2000. We calculated corresponding contours of constant Hamiltonian (kinetic plus potential energy) for first invariant values that range from 0 to 30 MeV/G (representative of equatorially mirroring cold plasma, ring current, and radiation-belt ions and electrons). These equatorial contours would constitute drift paths if the electric field were truly constant in time. We thus calculated how far along such quasi-drift paths the corresponding particles would have drifted after specific amounts of time, and we compare these quasi-drift characteristics with those obtained from a simple semiempirical model of the convection electric field. We find considerable variability among stormtime equatorial quasi-drift paths, reflecting the known variability of AMIE equipotentials. Patterns of equatorial quasi-drift in the simplified electric field model are (by construction) symmetric about the dawn-dusk meridian. During the main phases of storms, the equatorial electric field derived from AMIE tends to be strongest in an MLT sector several hours wide on the night side. This concentration of AMIE equipotentials provides a channel for rapid transport (requiring ∼20–30 min) for ions with first invariant values representative of the ring current population from the nightside neutral line to low L values (∼3–4) near dusk, where the partial ring current forms. During the extremely large “Bastille Day” storm of 15 July 2000 (minimum Dst = −300 nT) the drift patterns derived from AMIE show penetration of ions to as low as L ∼ 2. This deep penetration of ring current ions could help to account for the very strong ring current that was observed during this storm. The quasi-steady state drift properties help us anticipate the implications of a more realistic electric field model for the particle drifts that lead to the formation of the stormtime ring current.