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arXiv 2007.02625astro-ph.SRphysics.space-ph
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近地高速太阳风流峰值速度与太阳源冕洞面积的关系

On the Dependency between the Peak Velocity of High-speed Solar Wind Streams near Earth and the Area of Their Solar Source Coronal Holes

Stefan J. Hofmeister, Astrid M. Veronig, Stefaan Poedts, Evangelia Samara, Jasmina Magdalenic

摘要:

研究了地球附近高速太阳风流的峰值速度与其太阳源区面积的关系,日冕洞,自20世纪70年代以来就已为人所知,但它在物理上仍然没有得到很好的理解。我们使用欧洲日光层预报信息资产(EUHFORIA)代码进行3D磁流体动力学(MHD)模拟,以表明这种经验关系在从太阳到地球的高速流传播阶段形成。为此,我们忽略了高速流的加速阶段,并将冕洞的面积投影到0.1天文单位的球体上。然后我们只改变冕洞的面积和纬度。在0.1天文单位的相应高速流的截面中的速度、温度和密度被设置为恒定的均匀值。最后,我们传播相关的高速流通过内日光层使用EUHFORIA代码。在地球上模拟的高速流峰值速度揭示了其源冕洞面积的线性依赖关系。该关系的斜率随着冕洞纬度的增加而减小,峰值速度在约730 km/s处饱和,与观测结果相似。这些发现意味着冕洞面积和高速流峰值速度之间的经验关系并不能描述高速流的加速阶段,而是高速流从太阳传播到地球的结果。

英文摘要:

The relationship between the peak velocities of high-speed solar wind streams near Earth and the areas of their solar source regions, i.e., coronal holes, has been known since the 1970s, but it is still physically not well understood. We perform 3D magnetohydrodynamic (MHD) simulations using the European Heliospheric Forecasting Information Asset (EUHFORIA) code to show that this empirical relationship forms during the propagation phase of high-speed streams from the Sun to Earth. For this purpose, we neglect the acceleration phase of high-speed streams, and project the areas of coronal holes to a sphere at 0.1 au. We then vary only the areas and latitudes of the coronal holes. The velocity, temperature, and density in the cross section of the corresponding highspeed streams at 0.1 au are set to constant, homogeneous values. Finally, we propagate the associated high-speed streams through the inner heliosphere using the EUHFORIA code. The simulated high-speed stream peak velocities at Earth reveal a linear dependence on the area of their source coronal holes. The slopes of the relationship decrease with increasing latitudes of the coronal holes, and the peak velocities saturate at a value of about 730 km/s, similar to the observations. These findings imply that the empirical relationship between the coronal hole areas and high-speed stream peak velocities does not describe the acceleration phase of high-speed streams, but is a result of the high-speed stream propagation from the Sun to Earth.

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