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RADIAL EVOLUTION OF SOLAR WIND TURBULENCE DURING EARTH AND ULYSSES ALIGNMENT OF 2007 AUGUST

机译:2007年8月地球和湍流调整期间太阳风湍流的径向演变

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At the end of 2007 August, during the minimum of solar cycle 23, a lineup of Earth and Ulysses occurred, giving the opportunity to analyze, for the first time, the same plasma sample at different observation points, namely at 1 and 1.4 AU. In particular, it allowed us to study the radial evolution of solar wind turbulence typical of fast wind streams as proposed in a Coordinated Investigation Programme for the International Heliophysical Year. This paper describes both the macrostructure and the fluctuations at small scales of this event. We find that soon after detecting the same fast stream, the Advanced Composition Explorer (ACE) observed a change of magnetic polarity being the interplanetary current sheet located between the orbits of the two spacecraft. Moreover, we observe that the compression region formed in front of the fast stream detected at ACE's location evolves in a fast forward shock at Ulysses' orbit. On the other hand, small-scale analysis shows that turbulence is evolving. The presence of a shift of the frequency break separating the injection range from the inertial range toward lower frequencies while distance increases is a clear indication that nonlinear interactions are at work. Moreover, we observe that intermittency, as measured by the flatness factor, increases with distance. This study confirms previous analyses performed using Helios observations of the same fast wind streams at different heliocentric distances, allowing us to relax about the hypothesis of the stationarity of the source regions adopted in previous studies. Consequently, any difference noticed in the solar wind parameters would be ascribed to radial (time) evolution.
机译:在2007年8月底的最短太阳周期23期间,出现了地球和尤利西斯星系,这使人们有机会第一次在不同的观察点(即1和1.4 AU)分析同一血浆样品。特别是,它使我们能够研究国际太阳物理年协调调查计划中提出的典型快速风流的太阳风湍流的径向演化。本文描述了该事件的宏观结构和小范围的波动。我们发现,在检测到相同的快速流之后,高级成分浏览器(ACE)很快观察到了磁极性的变化,这是位于两个航天器轨道之间的行星际电流板。此外,我们观察到在ACE位置检测到的快速流前方形成的压缩区域在尤利西斯轨道处以快速向前震动的形式演化。另一方面,小规模分析表明湍流正在演变。频率中断的出现将注入范围从惯性范围向低频降低,而距离增加,这清楚地表明非线性相互作用正在起作用。此外,我们观察到,通过平坦度因子衡量的间歇性随着距离的增加而增加。这项研究证实了以前的分析,这些分析是使用Helios对不同风心距离下的相同快速风流的观测进行的,从而使我们可以放宽先前研究中采用的源区平稳性假说。因此,太阳风参数中发现的任何差异都将归因于径向(时间)演变。

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