1天文单位黄道行星际磁场双峰分布的性质
On the nature of the in-ecliptic interplanetary magnetic field's two-humped distribution at 1AU
摘要：
研究发现，行星际磁场（IMF）的黄道内（以及径向）分量的分布形状随着日心距的变化而显著变化，这与经典的太阳风模型和行星际磁场（IMF）膨胀模型的对应性较差。例如，径向光球和源面磁场在黄道面内呈高斯分布，径向IMF分量在地球轨道上呈双峰分布，在3-4 AU处又呈高斯分布。这些差异导致在1 AU和观察的IMF行为的模拟之间缺乏对应性。我们的结果表明，IMF向空间的扩展比通常认为的要复杂得多，并且扇形结构不是黄道或径向IMF分量双峰形状的唯一来源。我们已经分析了来自不同航天器的数据，从0.29 AU到4 AU的距离，发现径向IMF分量分布的形状强烈依赖于日心距离和日纬度。“双峰IMF”效应在0.7-2天文单位的低日纬度处表现得最明显，但在3-4天文单位处完全消失。由于活跃的过程，如太阳耀斑和日冕物质抛射，IMF分布的观点也依赖于太阳活动周期。我们假设1天文单位处的黄内太阳风场受太阳活动区的影响较大，实际上是三峰分布：两峰对应于中高日纬度的IMF，第三峰对应于日磁赤道附近太阳场的理论预期分布。IMF零分量随离日距离的增加而消失，部分原因可能是太阳风中电流片处的磁重联。
英文摘要：
It was found out that the distribution's shape of the in-ecliptic (as well as radial) component of the interplanetary magnetic field (IMF) significantly changes with the heliocentric distance, which poorly corresponds to classical models of the solar wind and the interplanetary magnetic field (IMF) expansion. For example, distributions of the radial photospheric and the source surface's magnetic field in the ecliptic plane are Gaussian-like, the distribution of the radial IMF component at the Earth orbit demonstrates two-humped shape, and it becomes again Gaussian-like at 3-4 AU. These differences lead to lack of correspondence between simulations of the IMF behaviour at 1 AU and observations. Our results indicate that picture of the IMF expansion into space is more complicated than usually considered, and the sector structure is not the only source of the two-humped shape of the in-ecliptic or radial IMF component. We have analysed data from different spacecraft at the distances from 0.29 AU to 4 AU and found that the shape of the radial IMF component distribution strongly depends on a heliocentric distance and a heliolatitude. The "two-humped IMF" effect is most brightly expressed at low heliolatitudes at 0.7-2 AU, but it fully disappears at 3-4 AU. There is also dependence of the IMF distributions' view on a solar cycle due to active processes, such as solar flares and CMEs. We suppose that the in-ecliptic solar wind field at 1 AU is influenced by solar active regions in a high degree, and actually the distribution is the three-humped: two humps correspond to the IMF from the middle and high heliolatitudes and the third one is the theoretically expected distribution from the solar field nearby the heliomagnetic equator. Vanishing of the IMF zero-component with the distance from the Sun partially could be a result of a magnetic reconnection at the current sheets in the solar wind.
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