Magnetotail origins of auroral Alfvénic power
Magnetotail origins of auroral Alfvénic power
复制标题
DOI：
10.1029/2012ja017680
复制
发表时间：
2012-09
影响因子：
--
通讯作者：
Binzheng Zhang;W. Lotko;O. Brambles;P. Damiano;M. Wiltberger;J. Lyon
中科院分区：
文献类型：
--
作者：
Binzheng Zhang;W. Lotko;O. Brambles;P. Damiano;M. Wiltberger;J. Lyon
利用太阳风 - 磁层 - 电离层相互作用的三维全球模拟，研究了中心等离子体片中阿尔芬坡印廷通量的产生及其在低空的极向分布。由太阳风和行星际磁场数据驱动的一次24小时事件模拟（2004年2月4 - 5日）重现了由“极地”卫星测量的阿尔芬坡印廷通量的全球形态，包括其晨昏不对称性。对照模拟表明，晨昏不对称性受电离层电导率的空间变化所调节。当电导率在空间上均匀时，这种不对称性消失。模拟的阿尔芬坡印廷通量是在磁尾由夜间重联产生的随时间变化的快速流产生的。模拟的快速流在午夜前扇区如观测到的那样更强烈；当电离层电导率在空间上均匀时，这种不对称性也会消失。对等离子体片源区（靠近xGSM≈ - 15RE）中波传播的分析表明，当快速流减速时，其一部分动能转化为中速和快速磁流体动力学波的电磁能。在源区波能主要是压缩性的，并且当它沿着磁力线向电离层传播时变得越来越具有阿尔芬性。
[1] The generation of Alfvenic Poynting flux in the central plasma sheet and its polar distribution at low altitude are studied using three dimensional global simulations of the solar wind-magnetosphere-ionosphere interaction. A 24-hour event simulation (4–5 Feb 2004) driven by solar wind and interplanetary magnetic field data reproduces the global morphology of Alfvenic Poynting flux measured by the Polar satellite, including its dawn-dusk asymmetry. Controlled simulations show that the dawn-dusk asymmetry is regulated by the spatial variation in ionospheric conductance. The asymmetry disappears when the conductance is taken to be spatially uniform. The simulated Alfvenic Poynting flux is generated in the magnetotail by time-variable, fast flows emerging from nightside reconnection. The simulated fast flows are more intense in the premidnight sector as observed; this asymmetry also disappears when the ionospheric conductance is spatially uniform. Analysis of the wave propagation in the plasma sheet source region, near xGSM ≈ −15 RE, shows that as the fast flow brakes, a portion of its kinetic energy is transformed into the electromagnetic energy of intermediate and fast magnetohydrodynamic waves. The wave power is dominantly compressional in the source region and becomes increasingly Alfvenic as it propagates along magnetic field lines toward the ionosphere.