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arXiv 1604.08528physics.space-ph
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斜行星际磁场的局部昼侧重联率

The local dayside reconnection rate for oblique interplanetary magnetic fields

Colin M. Komar, Paul A. Cassak

摘要:

在全球磁层模拟中,我们分析了不同行星际磁场(IMF)方向下昼侧磁层顶磁重联的局部特性。迄今为止,这是不实际的,因为它是难以定位的重联发生斜IMF,但新的技术使之成为可能。方法是识别磁分离器,即分离不同磁拓扑的四个区域的曲线,这些曲线映射了重联X线。平行于X线的电场是局部重联率。我们将结果与一个简单的局部二维非对称重联模型进行了比较。要做到这一点,我们发现等离子体参数,本地驱动重联在磁鞘和磁层中的平面垂直于X线在大量的点沿X线。全球磁流体动力学模拟是从三维块自适应,树太阳风Roe-type逆风计划(BATS-R-US)代码与统一的电阻率,虽然这里描述的技术是可扩展的任何全球磁层模拟模型。我们发现,预测的本地重连率规模以及与所有模拟的测量值,由于南向IMF几乎是准确的。然而,绝对的预测不同的一个未定的比例常数,其幅度增加的国际货币基金组织的时钟角度从南向北的变化。我们还显示了类似的缩放协议在模拟斜向南IMF和偶极子倾斜。目前的结果将是一个重要的组成部分,充分了解本地和全球性的白昼重联。

英文摘要:

We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X-line. The electric field parallel to the X-line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X-line at a large number of points along the X-line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the techniques described here are extensible to any global magnetospheric simulation model. We find that the predicted local reconnection rates scale well with the measured values for all simulations, being nearly exact for due southward IMF. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. We also show similar scaling agreement in a simulation with oblique southward IMF and a dipole tilt. The present results will be an important component of a full understanding of the local and global properties of dayside reconnection.

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