Realistic and time-varying outer heliospheric modelling
Realistic and time-varying outer heliospheric modelling
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DOI：
10.1111/j.1365-2966.2011.19144.x
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发表时间：
2011-09
影响因子：
4.8
通讯作者：
H. Washimi;G. Zank;Q. Hu;Takashi Tanaka;K. Munakata;H. Shinagawa
中科院分区：
文献类型：
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作者：
H. Washimi;G. Zank;Q. Hu;Takashi Tanaka;K. Munakata;H. Shinagawa
我们开发了一个现实的和随时间变化的模型，同时满足旅行者1号（V1）和旅行者2号（V2）观察到的交叉时间和终止激波（TS）的位置进行三维（3D）磁流体动力学（MHD）模拟使用总变差递减（TVD）计划，其中包括中性粒子的影响。在每个模拟步骤中使用V2观测到的太阳风速度和密度的每日值，以便再现短期动力学效应。在进行动力学模拟之前，我们使用一组标准参数生成一个3D稳态解：星际质子密度假设为0.061 cc−1，星际中性氢密度假设为0.176 cc−1，星际介质相对于太阳的速度假设为26.3 km s−1，温度假设为6300 K。星际磁场强度为0.3 nT，取向与氢偏转平面内的流动方向倾斜。太阳风速度的各向异性也被考虑在内，在低纬度使用400 km s-1，在高纬度使用1.5倍。1 Au处的太阳风密度为3.55 cc−1，高/低太阳风速度区域的纬度角为80°，从稳态解开始，产生满足V1和V2交叉时间和位置的动态解。我们的模拟清楚地表明：（i）当太阳风高压脉冲与TS碰撞时，TS的位置增加;（ii）当太阳风高压脉冲与TS碰撞时，TS下游产生大幅度的磁声脉冲;（iii）日鞘中存在精细结构，对应于日顶附近的磁壁和等离子体片，以及薄的电流片;（iv）磁声脉冲在日鞘中的等离子体片处被反射，并且当反射脉冲与TS碰撞时，TS位置减小，以及（v）当TS粒子在V2处被观察时，V2和模拟TS位置之间的时变径向距离似乎与TS粒子强度分布一致。这最后一点，加上我们的MHD结果与一组标准的太阳风和本地星际介质（LISM）参数的压倒性的一致性，表明外日球层基本上是由MHD和中性星际气体过程控制的，尽管在我们的模拟中没有很好地再现V2观测到日鞘中的太阳风等离子体。
We develop a realistic and time-varying model that satisfies both the Voyager 1 (V1) and Voyager 2 (V2) observed crossing times and locations of the termination shock (TS) simultaneously by performing three-dimensional (3D) magnetohydrodynamic (MHD) simulations using a total variation diminishing (TVD) scheme that includes the effects of neutral particles. Daily values of solar-wind speed and density observed by V2 are used at every simulation step so that short-term dynamical effects are reproduced. Before performing the dynamic simulation, we generate a 3D stationary solution using a set of standard parameters: the interstellar proton density is assumed to be 0.061 cc−1, the interstellar neutral hydrogen density 0.176 cc−1, the interstellar medium speed relative to the Sun 26.3 km s−1 and a temperature of 6300 K. The interstellar magnetic field intensity is 0.3 nT and the orientation is oblique to the flow direction lying in the hydrogen deflection plane. The anisotropy of the solar-wind speed is also taken into account using 400 km s−1 at low latitudes and 1.5 times faster at high latitudes. A solar-wind density at 1 au of 3.55 cc−1 and a latitudinal angle separating the high/low solar-wind speed regions of 80° yield dynamic solutions, starting from the stationary solution, that satisfy the V1 and V2 crossing times and locations. Our simulations clearly show that (i) the TS position increases whenever a solar-wind high-ram-pressure pulse collides with the TS; (ii) a large-amplitude magneto-sonic pulse is generated downstream of the TS when a solar-wind high-ram-pressure pulse collides with the TS; (iii) fine structure in the heliosheath is present, corresponding to a magnetic wall and plasma sheet near the heliopause (HP), and a thin current sheet; (iv) the magneto-sonic pulse is reflected at the plasma sheet in the heliosheath, and the TS position decreases when the reflected pulse collides with the TS and (v) the time-varying radial distance between V2 and simulated TS positions appears to be consistent with the TS particle intensity profile during the period when the TS particles were observed at V2. This last point, together with the overwhelming consistency of our MHD results with a standard set of solar-wind and local interstellar medium (LISM) parameters, suggests that the outer heliosphere is controlled essentially by MHD and neutral interstellar gas processes, although V2 observations of solar-wind plasma in the heliosheath are not well reproduced in our simulations.